Sea anemone species of the genus Actinostella live in tropical and subtropical shallow waters. They are characterized by having a marginal ruff harboring zooxanthellae that expands during the day and retracts at night, allowing the anemone to catch prey with the tentacles. Currently, 10 or 11 species are considered valid depending on the author; however, most species within the genus were described in the 1800s or in early 1900s and, thus, most descriptions are incomplete by modern standards. In addition, several species of Actinostella have reported wide geographical distributions. We evaluate the morphology of newly collected and type material to assess potential synonymies and geographical distributions; we perform phylogenetic analysis using five standard molecular rDNA markers for sea anemones to corroborate our morphological results and to investigate the phylogenetic relationships of Actinostella, other actinioideans, and those Actinostella species present in the eastern Pacific and western Atlantic tropical region. Based on morphological and cnida differences, we find six species of Actinostella valid. We redescribe A. bradleyi, A. californica, A. digitata, and A. flosculifera and synonymize A. californica pro parte (Pacific specimens with four cycles of mesenteries and p-mastigophores A in the marginal ruff) with A. bradleyi (found in the Panamanian and Mexican Pacific and the Gulf of California). We also find that A. ornata does not belong within Actinostella. We discuss the membership of Actinostella, including species of the genus Phyllactis, and synonymize Phyllactis with Actinostella. We propose that the combination of the presence of p-mastigophores A in the marginal ruff and the arrangement and fertility of mesenteries are diagnostic characteristics to differentiate species of Actinostella from the American coasts. Finally, our phylogenetic analyses based on rDNA markers differentiated between the western Atlantic and eastern Pacific species but lacked support and resolution to elucidate relationships within species in the eastern Pacific.
INTRODUCTION
Sea anemones are relatively simple soft-body marine invertebrates with few external diagnostic morphological characters to distinguish among taxa; most of these external characters, such as acrorhagi, vesicles, verrucae, tubercles, and marginal ruff are specialized outgrowths or modifications of the column or column margin (Stephenson, 1928). The marginal ruff, in particular, is a very distinct external character present in only a handful of actiniarians; it is an extension of the margin of the column that folds below the tentacles and lies above the substrate in which the anemone has burrowed. On its upper side, the thin-layered ruff exhibits frondlike papillae arranged radially in each exo- and endocoel; on the underside, the marginal ruff might bear verrucae and possibly host zooxanthellae.
Currently, there are two views on the number of genera of sea anemones with a marginal ruff. According to Fautin (2016), there are four genera bearing a marginal ruff (i.e., Onubactis López-González et al., 1995; Oulactis Milne Edwards and Haime, 1851; Phyllactis Milne Edwards and Haime, 1851; and Actinostella Duchassaing, 1850). However, Häussermann (2003) considered three genera following Carlgren (1949), who synonymized Phyllactis and Actinostella (but Carlgren incorrectly used Phyllactis as the senior synonym instead of Actinostella). Although some authors agreed with this synonymy (e.g., Corrêa, 1964; Schlenz and Belém, 1992; Ocaña and den Hartog, 2002; Häussermann, 2003), others (Gomes and Mayal, 1997; Melo and Amaral, 2005; Fautin, 2016) still consider Phyllactis and Actinostella different genera.
Among the few genera with a marginal ruff, Onubactis is the most recently described genus with a single species; Oulactis includes seven species, Phyllactis has four species, and Actinostella includes 10 species, resulting in a total of 22 species with a marginal ruff (Rodríguez et al., 2024). Onubactis and Oulactis are easily distinguishable from Actinostella: Onubactis has no verrucae nor zooxanthellae in the marginal ruff or column (López-González et al., 1995); Oulactis holds (or may hold) acrorhagi on the margin, bears no zooxanthellae, has no distinct fosse and has a diffuse endodermal marginal sphincter muscle (Häussermann, 2003). In contrast, Phyllactis closely resembles Actinostella, with similarities such as verrucae in the column, the presence of zooxanthellae, fosse, circumscribed endodermal marginal sphincter muscle, same number of mesenteries distally and proximally, and the lack of acrorhagi (Häussermann, 2003). In fact, original descriptions of both genera overlap and are not helpful to distinguish them.
Species of Actinostella are common and conspicuous in intertidal to shallow waters in the tropical and subtropical Pacific and Atlantic basins as well as the Red Sea. They are usually found in crevices or burrows in the sand, sometimes attached to rocks, often with debris attached to the column (Corrêa, 1964; Schlenz and Belém, 1992; Ocaña and den Hartog, 2002, Ocaña et al., 2007; Häussermann, 2003; González-Muñoz et al., 2012; Barragán et al., 2019; Durán-Fuentes et al., 2023). Accurate identification of species is critical to draw valid conclusions about the conservation and ecology of marine organisms, especially within the dynamic and climate-sensitive intertidal environment (Mace, 2004). However, most of the species within Actinostella were described in the 1800s or early 1900s and, thus, most descriptions are incomplete or ambiguous by contemporary standards in that they lack information about internal anatomy or images of cnidae, etc. Furthermore, all species currently in Actinostella were originally described within different genera (i.e., Asteractis Verrill, 1869; Cradactis McMurrich, 1893; Lophactis Verrill, 1869; Oulactis, and Phyllactis) creating a complex history of synonymies.
Of the 10 valid species of Actinostella according to Fautin (2016), three do not belong within the genus: Actinostella variabilis (Hargitt, 1911) was synonymized with Lebrunia coralligens (Wilson, 1890) by González-Muñoz et al. (2012), and A. excelsa (Wassilieff, 1908) and A. striata (Wassilieff, 1908) from Japan do not belong to Actinostella based on the original descriptions (Ocaña, 1994; Häussermann, 2003). From the seven putatively valid species left, A. bradleyi (Verrill, 1869) and A. ornata (Verrill, 1869) likewise have incomplete descriptions: only the holotype of each of these two is known from the Pacific coast of Panama and these sole specimens are undissected. The rest of the species in the genus are also not free of issues. For example, A. flosculifera (Le Sueur, 1817) has a wide distribution, including both sides of the Atlantic, and the type specimen of A. radiata (Duchassaing and Michelotti, 1860) is half-sectioned and only the proximal part can be analyzed.
At present, the genus Phyllactis has four valid species: P. cichoracea (Milne Edwards in Haeckel, 1876), P. conquilega (Duchassaing and Michelotti, 1860), P. formosa (Duchassaing, 1850), and P. praetexta (Couthouy in Dana, 1846) (Fautin, 2016). These species are distributed in the Caribbean Sea, with the exception of P. cichoracea, which is from the Red Sea. However, other authors consider only P. cichoracea as a distinct species within this genus, with the other three species currently assigned to Phyllactis considered synonymies of A. flosculifera (e.g., Schlenz and Belém, 1992; Ocaña and den Hartog, 2002; Häussermann, 2003); these later authors provide an alternative view to that from Fautin (2016), considering only the genus Actinostella to be valid, which includes 11 species.
Here, we examine type, museum, and newly collected material of five species attributed to the genus Actinostella: A. bradleyi, A. californica (McMurrich, 1893), A. digitata (McMurrich, 1893), A. flosculifera, and A. ornata. In addition, we reexamine the only available type specimen of any species within the genus Phyllactis, P. conquilega, to clarify the validity or synonymy of Phyllactis and Actinostella. Finally, we performed molecular phylogenetic analyses using rDNA to corroborate our morphological results and to investigate the phylogenetic relationships of members of Actinostella and other actinioideans.
Materials and Methods
Morphological Study: The studied material was newly collected or gathered through loans from several museum collections: American Museum of Natural History (AMNH) in New York, National Museum of Natural History (USNM) in Washington DC, Museo Argentino de Ciencias Naturales Bernardino Rivadavia (MACN) in Buenos Aires, Museu de Zoologia da Universidade de São Paulo (MZUSP) in São Paulo, Yale Peabody Museum (YPM) in New Haven, CT, and Swedish Museum of Natural History (SMNH) in Stockholm, Sweden. During 2013–2016, 12 specimens of Actinostella bradleyi were collected, nine from Baja California Sur (Mexico) and three from the Pacific Ocean off Panama—with one specimen collected in the Azuero Peninsula, Los Santos Province, and two in the Pearl Islands, Gulf of Panama Province. Twenty-two specimens of A. californica were collected during 2013–2016, 20 specimens from Baja California Sur (Mexico) and two in the Pearl Islands, Gulf of Panama Province (Panama). A single specimen of A. digitata was collected in Chubut (Argentina) in 2010. Sixteen specimens of A. flosculifera were collected, 13 in Bocas del Toro (Panama) in 2016 and three in São Paulo (Brazil) in 2017. All newly collected specimens were collected by hand while snorkeling intertidally in Mexico, Panama, and Brazil, or through scuba diving in the subtidal in Mexico, Panama and Argentina (fig. 1). Freshly collected specimens were relaxed with menthol crystals, photographed alive, and subsequently fixed in 10% seawater formalin. Small pieces from the pedal disc of several specimens were fixed in 100% ethanol for molecular studies. Newly collected material for this study was deposited at the AMNH, MACN, MZUSP, and USNM. For locality details, see table 1.
Preserved specimens were examined whole and dissected. Histological sections 5–10 µm thick were made from different parts and were stained with Azocarmine triple stain (Humason, 1967). Small pieces of tissue were smeared on slides and examined using differential interference microscopy (DIC) at 1000× magnification to measure the cnidae. We scanned through the slides and haphazardly measured 20 capsules of each type (when possible) to generate a range: frequencies given are subjective impressions based on all the cnidae seen on the slides. Measurements of body region sizes and cnidae were made from preserved material.
Cnidae terminology follows Gusmão et al. (2018). We emphasize that we use a combination of classifications to better capture the underlying variation in cnidae morphology but do not imply any evolutionary relationship among these types of capsules. Finally, because of the complexity of several of the terminology issues discussed by Gusmão et al. (2018), we underscore that any comparison of nematocysts among taxa going forward should be based on images (drawings or photographs) in order to be considered reliable.
We have followed the taxonomic classification implemented in Rodríguez et al. (2014). Within each genus, taxa are discussed in alphabetical order. The list of synonymies we provide for each species is not exhaustive. We provide only references to the first citation of a species by a particular name. We include all references citing specimens under an incorrect species name because it is important to note incorrect species records.
Molecular Methodology: Genomic DNA was isolated from approximately 25 mg of tissue using the Qiagen DNeasy kit or the Qiagen Gentra Puregene Tissue Kit following the manufacture's protocol. Whole genomic DNA was amplified using published primers and the protocol detailed in Lauretta et al. (2014) for the mitochondrial genes 12S, 16S, and CO3, and the nuclear 18S and 28S. PCR products were cleaned using ExosapIT (Exonuclease I and FastAP thermosensitive alkaline phosphatase per manufacturer's specifications, except that shrimp alkaline phosphatase was replaced with FastAP). Cycle sequencing reactions used a total of 5 µL of cleaned PCR product, at a concentration of 25 ng of product for every 200 base pairs (bp) of marker length. Cycle sequencing products were cleaned using Centri-Sept columns (Princeton Separations; following the manufacturer's protocol) containing DNA-grade Sephadex (G-50 fine; GE Healthcare) and later sequenced using PCR amplification primers on an ABI 3730x at the in-house facilities of the AMNH. Forward and reverse sequences were assembled and edited in Geneious v.11.1.4 (Kearse et al., 2012) and blasted against the nucleotide database of GenBank to confirm that the obtained sequences corresponded to the target sequence/organism and not to their endosymbiotic algae. Sequences have been deposited in GenBank (see table S1 in the online supplement: https://doi.org/10.5531/sd.sp.62).
TABLE 1.
Material examined in this study. Catalogue number, locality, coordinates, depth and date of collection are provided. Abbreviations: AMNH, American Museum of Natural History; MACN, Museo Argentino de Ciencias Naturales Bernardino Rivadavia; MZUSP, Museu de Zoologia da Universidade de São Paulo; SMNH, Swedish Museum of Natural History; USNM, National Museum of Natural History; YPM, Yale Peaboy Museum; (*), data transcribed from museum label, but does not correspond with type locality.
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Newly generated rDNA sequences for each of the five markers were combined and analyzed with sequences from Gusmão and Rodríguez, 2021(see table S1). Sequences for each marker were separately aligned using MAFFT v.7.307 (Katoh and Standley, 2013) using the following settings: Strategy, L-INS-I; Scoring matrix for nucleotide sequences, 200PAM/k = 2; Gap open penalty, 1.53; Offset value, 0.05. Alignments for each marker were analyzed separately and as a concatenated dataset.
Phylogenetic Inference: For the rDNA dataset (12S, 16S, CO3, 18S, 28S) each gene region, the best model of nucleotide substitution was chosen using Akaike information criterion (AIC) on jModeltest2 (Guindon and Gascuel, 2003; Darriba et al., 2012) implemented on the CIPRES Portal (Miller et al., 2010). Maximum likelihood (ML) analyses were performed using RAxML-NG v0.6.0 (Kozlov et al., 2019) using the appropriate model of nucleotide substitution for each marker. We used the majority rule criterion to access clade support and allowed automatic haul(-autoMRE). An additional ML analysis was conducted on PhyML v.3.0 online ( http://www.atgc-montpellier.fr/phyml/) (Guindon et al., 2010), allowing automatic model selection using the AIC criterion (Lefort et al., 2017) and 1000 rounds of bootstrap for each marker separately and in combination. All analyses were run with gaps treated as missing data. The actiniarian Nematostella vectensis Stephenson, 1935, was used as an outgroup for the analyses. Phylogenetic trees were edited using FigTree v1.4.3 and Adobe Photoshop.
RESULTS
Taxonomic Account
Order Actiniaria Hertwig, 1882
Suborder Enthemonae Rodríguez and Daly, 2014, in Rodríguez et al., 2014
Superfamily Actinioidea Rafinesque, 1815
Family Actiniidae Rafinesque, 1815
Genus Actinostella Duchassaing, 1850
Asteractis Verrill, 1869.
Cradactis McMurrich, 1893.
Lophactis Verrill, 1869.
Metridium Dana, 1846.
Oulactis Milne Edwards and Haime, 1851.
Phyllactis Milne Edwards and Haime, 1851.
Diagnosis (after Häussermann, 2003; changes in boldface): Actiniidae with well-developed pedal disc and basilar muscles. Oral disc round; column more or less elongate, with verrucae distally. Wide marginal ruff or collar between verrucae and column margin, with series of small frondlike papillae (= vesicles) containing basitrichs and sometimes p-mastigophores A. Above vesicles a more or less distinct fosse. Generally 48 tentacles, but up to 96 in some species. No acrorhagi. All mesenteries might be perfect, hexamerously and regularly arranged. Same number of mesenteries proximally and distally. Endodermal marginal sphincter muscle strong to very weak, circumscribed. Longitudinal muscles of tentacles ectodermal. As a rule, two siphonoglyphs. Retractors typically strong, diffuse to restricted. Parietobasilar muscles well developed. Zooxanthellae present. Cnidom: spirocysts, basitrichs, basitrichs S, b-mastigophores, p-mastigophores A and p-mastigophores B1.
Type Species: Actinostella formosa Duchassaing, 1850.
Species Included: Actinostella bradleyi; A. correae Schlenz and Belém, 1992; A. californica; A. digitata; A. flosculifera; and A. cichoracea.
Remarks: We amend the diagnosis to include species having up to 96 tentacles (i.e., Actinostella bradleyi) and use more specific terms for the description of structures (e.g., distally); in addition, we combine cnidae terminology that allows us to describe the diversity of mastigophore nematocysts. Based on the redescription of A. flosculifera from the east Atlantic by Ocaña (1994), Häussermann (2003) modified the diagnosis of Actinostella by Carlgren (1949) to acknowledge the possible presence of holotrichs in the column. However, the presence of holotrichs is not known within any other species of Actinostella and because we have noticed other inconsistencies in the description of the material studied by Ocaña (1994) (see observations below in species' descriptions and in Discussion), we prefer to not incorporate features in that material until this species has been reexamined.
Actinostella bradleyi (Verrill, 1869)
Figures 2–6, tables 1, 2
Asteractis bradleyi Verrill, 1869.
Phyllactis bradleyi (Verrill, 1869): Stephenson, 1922.
Non Phyllactis bradleyi (Verrill, 1869): Carlgren, 1951.
Actinostella bradleyi (Verrill, 1869): Häussermann, 2003.
Actinostella californica (McMurrich, 1893): Barragán et al., 2019 pro parte.
Differential Diagnosis: Actinostella with up to four cycles of mesenteries and 96 tentacles, all mesenteries, including directives, perfect and fertile. Marginal ruff and column with p-mastigophores A and basitrichs.
Examined Material: Actinostella bradleyi: AMNH_IZC 00361355, AMNH_IZC 00361356, AMNH_IZC 00361357, AMNH_IZC 00361358, USNM 1606849, USNM 1606850; Asteractis bradleyi Verrill, 1869 [= A. bradleyi]: YPM 1009 (holotype). Lophactis ornata Verrill, 1869 [= Telmatactis cf. panamensis (Verrill, 1869)]: YPM–2015 (holotype). YPM repository IZAR.001433: Frank Howe Bradley Correspondence; 1866–1867; Correspondence from F.H. Bradley to A.E. Verrill; all sent from his expedition to America Central (letters transcribed by E. Lazo-Wasem).
Description: External anatomy (figs. 2, 5): Well-developed pedal disc, to 23 mm diameter. Column elongate, to 55 mm height and 42 mm diameter, with 96 longitudinal rows of verrucae distally in each endo- and exocoel. Marginal ruff with rows of vesicles. Oral disc to 34 mm diameter. Fosse deep. Tentacles, to 96 in five cycles; simple, smooth, all similar length, to 18 mm. Mesenterial insertions visible in pedal disc.
Internal anatomy (figs. 3, 5): Same number of mesenteries distally and proximally. Forty-eight pairs of mesenteries hexamerously arranged in four cycles (6 + 6 + 12 + 24 = 48). All cycles perfect and fertile, including directives (fig. 3B). Two pairs of directives attached to two clearly distinct siphonoglyphs. Gonochoric, developed oocysts 0.06–0.15 mm in diameter (fig. 3F) in specimen collected in May 2013, developed spermatic cysts 0.09–0.23 mm in diameter (fig. 3E) in specimens collected in August, October, and November 2013. Retractor muscles strong, bandlike, and restricted. Parietobasilar muscles well developed (fig. 3G), with long free mesogleal lamella. Basilar muscles well developed, processes short and thin (fig. 3H). Endodermal marginal sphincter muscle circumscribed (fig. 3A, C). Longitudinal muscles of tentacles ectodermal (fig. 3D). Zooxanthellae present in tentacles and marginal ruff.
Color (fig. 2): Variable in live specimens. In specimens from Mexico, pedal disc and column pinkish or opaque orange; verrucae darker than column. Oral disc olive green with beige radial lines. Marginal ruff olive green with radial brown and beige stripes. Tentacles brownish or reddish with brown base and spots with a brown dot along the entire tentacle. Specimens from Panama, same pedal disc, column, and oral disc, but with brownish marginal ruff. Preserved material beige and marginal ruff lighter.
Cnidom (figs. 4, 6): Basitrichs, basitrichs S, b-mastigophores, p-mastigophores A, p-mastigophores B1, and spirocysts. Sizes and distribution in table 2.
Geographic and Bathymetric Distribution and Natural History: Actinostella bradleyi can be found in the Pacific Ocean in Mexico and Panama. Although Verrill (1869) did not specify the location of the type locality (i.e., Panama Reef) in the Pacific, we confirm the type locality of A. bradleyi in the Pacific side of Panama, off the coast of Panama City based on transcriptions of the original correspondence (archived record IZAR.001433) between Verrill and F.H. Bradley (collector). In Mexico, A. bradleyi can be found on the intertidal shore in Pichilingue Bay in the Gulf of California and in Conquista Agraria and Magdalena Bay on the Pacific side. In Panama, this species was collected in the Azuero Peninsula (Los Santos Province) and the Pearl Islands (Gulf of Panama Province) between 3–10 m. The specimens were found burrowed in sand attached to a buried rock or shell, or hidden in rock crevices, with the marginal ruff above the substratum. Actinostella bradleyi and A. californica live in sympatry, although in Mexico, A. californica is more common (and found at shallower depths) than its Pacific congener.
Remarks: Actinostella bradleyi differs from the five other species of the genus by the combination of the number of tentacles (up to 96), perfect mesenteries and distribution of fertile cycles of mesenteries (all four cycles), and the presence of p-mastigophores A in the marginal ruff and column (figs. 4, 6). Until the specimens analyzed by Ocaña (1994) from the Canary Islands are examined, A. bradleyi is the only species within the genus with up to five cycles of tentacles and four cycles of mesenteries. Although externally A. bradleyi closely resembles the only other species of the genus recorded from the eastern Pacific, A. californica, they can be easily distinguished in the field by the number of tentacles (to 96 in A. bradleyi and up to 48 in A. californica). However, both species live in sympatry and when specimens of A. bradleyi are not completely mature, as it is the case of the holotype of the species (YPM 1009), they can be confused with A. californica. Attributes of the cnidom can differentiate them. Barragán (2015) redescribed one sterile specimen with three cycles of mesenteries collected in Pichilingue Bay in the Gulf of California (Mexico) and considered it as A. californica based mainly on its distribution. Our detailed revision of this material here shows that this specimen is an immature specimen of A. bradleyi in which the fourth cycle of mesenteries is not yet developed.
Fautin (2016: 177) cited under the list of synonymies of Actinostella bradleyi the following: “Oulactis californica McMurrich, 1893 [Ref. 386], p. 196–197, 198, 206 (original description).” This synonymy is incorrect because those specimens correspond to the type material of the species A. californica. In addition, Fautin (2016) mentioned as valid names used for Oulactis californica McMurrich, 1893, both A. bradleyi and A. californica. In this study, we show that O. californica is a synonym of A. californica (McMurrich, 1893) and different from A. bradleyi (see remarks under A. californica).
FIG. 2.
External anatomy of Actinostella bradleyi (Verrill, 1869). A, Oral view of live semiexpanded specimen showing the marginal ruff; B, oral view of live and expanded specimen; C, lateral view of live semiexpanded specimen; notice rows of distal verrucae (v); D, lateral view of preserved specimen; E, detail of oral view of a semiexpanded preserved specimen; F, detail of the vesicles (ve) in the marginal ruff (f) of a preserved specimen. Abbreviations: f, marginal ruff; v, verrucae; ve, vesicles. Scale bars: A–F, 5 mm.
FIG. 3.
Internal anatomy of Actinostella bradleyi (Verrill, 1869). A, longitudinal section of the distal column showing distal verrucae (v), vesicles (ve) in the marginal ruff, marginal sphincter muscle (s), and the fosse; B, cross section at the actinopharynx level showing four cycles of mesenteries; numbers between pairs of mesenteries indicate the corresponding cycle; C, detail of the endodermal marginal sphincter muscle; D, cross section of a tentacle showing the ectodermal longitudinal muscles; E, detail of developing spermatic cysts (sc); F, detail of developing oocytes (o); G, detail of a cross section showing the retractor (r) and parietobasilar (p) muscles; H, cross section of proximal end showing the basilar muscles (b). Abbreviations: b, basilar muscles; ep, epidermis; ga, gastrodermis; me, mesoglea; o, oocytes; p, parietobasilar muscle; r, retractor muscle; s, sphincter; sc, spermatic cysts; t, tentacle; v, verrucae; ve, vesicles. Scale bars: A, B, G, H, 0.5 mm; C–F, 0.1 mm.
FIG. 4.
Cnidae of Actinostella bradleyi (Verrill, 1869). A, C, E, H, I, K, L, M, basitrichs; B, spirocysts; F, N, basitrichs S; D, G, J, P, p-mastigophore A; O, b-mastigophore; Q, p-mastigophore B1.
FIG. 5.
External and internal anatomy of the holotype of Asteractis bradleyi Verrill, 1869 (YPM-1009) (= Actinostella bradleyi). A, lateral view of holotype, showing the marginal ruff; B, oral view of holotype; C, detail of the pedal disc of holotype; D, longitudinal section of the distal column showing distal verrucae (v), vesicles (ve) in the marginal ruff, marginal sphincter muscle (s), and the fosse; E, detail of the endodermal marginal sphincter muscle; F, detail of the verrucae in the distal column; G, cross section at the actinopharynx level showing the directive mesenteries, retractor muscle (r), and siphonoglyphs (si); H, detail of a pair of mesenteries of the third cycle showing the parietobasilar muscle (p); I, longitudinal section of proximal end showing basilar muscles (b). Abbreviations: b, basilar muscle; f, marginal ruff; p, parietobasilar muscle; r, retractor muscle; s, sphincter; si, siphonoglyphs; v, verrucae; ve, vesicle. Scale bars: A–C, 5 mm; D–I, 0.5 mm.
FIG. 6.
Cnidae of holotype of Actinostella bradleyi (Verrill, 1869) (YPM-1009). A, C, E, H, I, K, L, M, basitrichs; B, spirocysts; F, N, basitrichs S; D, G, J, P, p-mastigophore A; O, b-mastigophore.
TABLE 2.
Size ranges and distribution of cnidae of Actinostella bradleyi (Verrill, 1869). N, Total number of capsules measured; M, Ratio of number of specimens in which each cnidae was found to number of specimens examined; F, Frequency, +++ = very common, ++ = common, + = rather common, --- = sporadic; SD, standard deviation; NF, not found. Sizes in micrometers. Letters in parenthesis correspond to images in figures 4 and 6.
Actinostella californica (McMurrich, 1893)
Figures 7–9, tables 1, 3
Oulactis californica McMurrich, 1893.
Non Asteractis concinnata (Drayon in Dana, 1846): Pax 1912.
Phyllactis californica (McMurrich, 1893): Stephenson, 1922.
(?)Phyllactis bradleyi (Verrill, 1869): Carlgren, 1951.
(?)Phyllactis concinnata (Drayon in Dana, 1846): Carlgren, 1951.
Actinostella californica (McMurrich, 1893): Häussermann, 2003.
Actinostella californica (McMurrich, 1893): pro parte Barragán, 2015; Barragán, 2019; Barragán et al., 2019.
Differential Diagnosis: Actinostella with three cycles of mesenteries, first and second perfect, third imperfect. All mesenteries fertile including directives. Column and marginal ruff only with basitrichs and no p-mastigophores A.
Examined Material: Actinostella californica: AMNH_IZC 00361339, AMNH_IZC 00361340, AMNH_IZC 00361341, AMNH_IZC 00361342, AMNH_IZC 00361343, AMNH_ IZC 00361344, AMNH_IZC 00361345, AMNH_IZC 00361346, AMNH_IZC 00361347, AMNH_IZC 00361348, AMNH_IZC 00361349, AMNH_IZC 00361350, AMNH_IZC 00361351, AMNH_IZC 00361352, AMNH_IZC 00361353, AMNH_IZC 00361354; USNM 1606851; USNM 17812 (syntype). See table 1 for material details.
Description: External anatomy (fig. 7): Well-developed pedal disc, to 25 mm diameter. Column elongate, to 65 mm height and 52 mm diameter, with 48 longitudinal rows of verrucae distally in each endo- and exocoel. Marginal ruff with rows of vesicles. Oral disc, to 38 mm diameter. Fosse deep. Tentacles, 48, arranged in four cycles; simple, smooth, all of similar length, to 16 mm. Mesenterial insertions visible in pedal disc and column.
Internal anatomy (fig. 8): Same number of mesenteries distally and proximally. Twenty-four pairs of mesenteries hexamerously arranged in three cycles (6 + 6 + 12 = 24). First and second cycles perfect, third imperfect (fig. 8B). All mesenteries fertile including directives (fig. 8B). Two pairs of directives attached to two clearly distinct siphonoglyphs. Gonochoric, developed oocysts 0.08–0.18 mm in diameter (fig. 8E) in specimens collected in May and November 2013, and March 2016. Retractor muscles strong, diffuse to restricted; variability within studied specimens. Parietobasilar muscles well developed, with short free mesogleal lamella in juveniles, longer in adults (fig. 8F). Basilar muscles well developed, processes short and thin (fig. 8G). Endodermal marginal sphincter muscle weakly circumscribed (fig. 8A, C). Longitudinal muscles of tentacles ectodermal (fig. 8D). Zooxanthellae present in tentacles and marginal ruff.
Color (fig. 7): Variable in live specimens. Specimens with pedal disc and column pinkish, beige, or opaque orange; verrucae darker than column. Oral disc olive green with white radial lines. Marginal ruff olive green with lighter stripes and a brown ring closer to the mouth. Mouth light pink. Tentacles translucent greenish, brownish, or reddish, with white bases; white spots with brown dots along entire tentacles. Preserved material beige, oral disc and marginal ruff lighter.
Cnidom (fig. 9); Basitrichs, basitrichs S, b-mastigophores, p-mastigophores A, p-mastigophores B1 and spirocysts. Sizes and distribution in table 3.
Geographic and Bathymetric Distribution and Natural History: Actinostella californica can be found in the Pacific Ocean from Mexico to Panama (McMurrich, 1893; Carlgren, 1951). Although Carlgren (1951) cited A. bradleyi (= A. californica pro parte in this study) in the Pearl Islands (Panama) he did not examine specimens from this locality, but he was referring to Verrill's original description of A. bradleyi. Häussermann (2003) and Fautin (2016) considered the citation of Asteractis concinnata from Peru by Pax (1912) to correspond to A. californica; however, Pax (1912) described his Peruvian specimens having 4–5 cycles of tentacles and without zooxanthellae, and thus we consider those specimens to be Oulactis concinnata. In Mexico, A. californica can be found in the Pacific side (west of Baja Peninsula) in Magdalena Bay, and in the Gulf of California it can be found in La Paz Bay and Concepcion Bay. In addition, this species was collected in Panama in the Pearl Islands. The specimens were found burrowed in sand, attached to a rock or shell, buried, or hidden in rock crevices with the marginal ruff above the substratum. They are often found in the intertidal to up to 12 meters in La Paz Bay (Gulf of California; see Barragán et al., 2019).
Remarks: Actinostella californica is distinguished from congeners by the combination of having three cycles of fertile mesenteries, first and second cycles perfect, and only basitrichs in the marginal ruff and column (table 6). It was initially described by McMurrich (1893) as Oulactis californica without any mention of the cnidom (a common practice in those days). Later, Carlgren (1951) redescribed Phyllactis bradleyi and P. concinnata (Drayton in Dana, 1846; current valid name: Oulactis concinnata) based on specimens from the Gulf of California, emphasizing they might need to be revised. Carlgren (1951) mentioned only the number of mesenteries (24) without describing their arrangement for the two specimens of P. bradleyi from the Gulf of California. The presence of only three cycles of mesenteries and the brief description of the cnidom suggest the two specimens might be A. californica. However, we cannot state confidently that the specimens of P. bradleyi from the Gulf of California redescribed by Carlgren (1951) are synonyms of A. californica because p-mastigophores A are easily overlooked unless surveying thoroughly; thus, we report this citation with a question mark (see synonymy list).
We agree with Haüssermann (2003) that Carlgren's (1951) redescription of seven specimens from the Gulf of California as Phyllactis concinnata actually corresponds to specimens of Actinostella californica. Like Haüssermann (2003), we think that Oulactis concinnata and A. californica (both previously described as Phyllactis) are clearly different species, with O. concinnata having many more tentacles and mesenteries (up to 400 tentacles), often acrorhagi and fighting tentacles (and thus holotrichs) but no zooxanthellae, whereas A. californica has only up to 48 tentacles and zooxanthellae, but lacks acrorhagi (see Haüssermann, 2003). The only attribute from Carlgren's (1951) treatment that does not fit A. californica is the presence of three perfect cycles of mesenteries: in the type material from McMurrich (1893) and the other 22 specimens we studied, the third cycle of mesenteries is imperfect. We observed in the studied specimens longitudinal lines of tissue (corresponding to the third cycle of mesenteries) attached to the actinopharynx side distally, which might be interpreted as broken perfect mesenteries; it is highly unlikely that this artifact occurred in every single specimen examined, and most feasible that Carlgren's (1951) observation might have been an artifact of observing the mesenteries distally. Consequently, we consider the third cycle in A. californica as imperfect. Alternatively, the specimens from the Gulf of California revised by Carlgren (1951) might have been juveniles of A. bradleyi with only three cycles of mesenteries developed (similar to the holotype of the species). Although the absence of p-mastigophores A in the marginal ruff and column suggests they were specimens of A. californica, we still consider this attribution an open question because it is also possible that Carlgren (1951) might have overlooked this cnida: we therefore reflect this in the synonymy list.
FIG. 7.
External anatomy of Actinostella californica (McMurrich, 1893). A, Oral view of live semiexpanded specimen; B, lateral view of live specimen; notice row of distal verrucae (v); C, oral view of live semiexpanded specimen showing the marginal ruff (f); D, lateral view of preserved syntype USNM 1776; E, oral view of preserved syntype USNM 1776 showing the vesicles (ve). Abbreviations: f, marginal ruff; v, verrucae; ve, vesicles. Images in A and B courtesy of V. Häussermann. Scale bars: A–D, 5 mm.
FIG. 8.
Internal anatomy of Actinostella californica (McMurrich, 1893). A, longitudinal section of the distal column showing distal verrucae (v), vesicles (ve) in the marginal ruff, marginal sphincter muscle (s), and the fosse; B, cross section at the actinopharynx level showing cycles of mesenteries and siphonoglyphs (si); numbers between pairs of mesenteries indicate the corresponding cycle; C, detail of the endodermal marginal sphincter muscle; D, cross section of a tentacle showing the ectodermal longitudinal muscles; E, detail of developing oocytes (o); F, detail of a cross section showing the retractor (r) and parietobasilar (p) muscles; G, cross section of proximal end showing the basilar muscles (r). Abbreviations: b, basilar muscles; ep, epidermis; ga, gastrodermis; me, mesoglea; o, oocytes; p, parietobasilar muscle; r, retractor muscle; s, sphincter; si, siphonoglyph; t, tentacle; v, verrucae; ve, vesicles. Scale bars: A, B, F, 0.5 mm; C–E, G, 0.1 mm.
FIG. 9.
Cnidae of Actinostella californica (McMurrich, 1893). A, C, D, F, G, I, J, K, basitrichs; B, spirocysts; E, L, basitrichs S; H, N, p-mastigophore A; M, b-mastigophore; O, p-mastigophore B1.
TABLE 3.
Size ranges and distribution of cnidae of Actinostella californica (McMurrich, 1893). Data in parenthesis of Phyllactis concinnata (Drayton) from Carlgren (1951). N, Total number of capsules measured; M, Ratio of number of specimens in which each cnidae was found to number of specimens examined; F, Frequency, +++ = very common, ++ = common, + = rather common, --- = sporadic; SD, standard deviation; ND, no data; NF, not found. Sizes in micrometers. Letters in parenthesis after categories correspond to images in figure 9. (*) Category named as basitrichs by Carlgren (1951).
Actinostella digitata (McMurrich, 1893)
Figures 10–12, tables 1, 4
Cradactis digitata McMurrich, 1893.
Phyllactis digitata (McMurrich, 1893): Carlgren, 1949.
Actinostella digitata (McMurrich, 1893): Häussermann, 2003.
Differential Diagnosis: Actinostella with three cycles of mesenteries, all perfect and fertile, including directives. Marginal ruff with p-mastigophores A and basitrichs; column only with basitrichs.
Examined Material: Actinostella digitata: MACN-In 43521; Cradactis digitata: USNM 17776 (syntypes). See table 1 for material details.
Description: External anatomy (fig. 10): Well-developed pedal disc, to 35 mm diameter. Column elongate, to 70 mm height and 30 mm diameter, with 48 longitudinal rows of verrucae distally in each endo- and exocoel. Marginal ruff with rows of vesicles. Oral disc to 17 mm diameter. Fosse deep. Tentacles, 48, arranged in four cycles; simple, smooth, all of similar length, to 12 mm, with terminal pore. Mesenterial insertions not visible in pedal disc or column.
Internal anatomy (fig. 11): Same number of mesenteries distally and proximally. Twenty-four pairs of mesenteries hexamerously arranged in three cycles (6 + 6 +12 = 24). All cycles perfect. All mesenteries fertile including directives. Two pairs of directives attached to two clearly distinct siphonoglyphs (fig. 11B). Gonochoric, developed spermatic cysts to 0.15 mm in diameter (fig. 11E) in specimen collected in February 2010. Retractor muscles strong, bandlike, restricted. Parietobasilar muscles well developed, with short, free mesogleal lamella (fig. 11F). Basilar muscles poorly developed, processes short and thin (fig. 11G). Endodermal marginal sphincter muscle strong, circumscribed with thin central lamella of mesoglea (fig. 11A). Longitudinal muscles of tentacles ectodermal (fig. 11D). Zooxanthellae present in tentacles and marginal ruff.
Color (fig. 10): Newly collected specimen from Chubut (Argentina) with beige pedal disc with irregular bright orange spots. Column orange over a beige base color, with verrucae darker orange. Oral disc beige with darker radial lines. Marginal ruff same color as column with beige vesicles. Tentacles translucent brownish, with darker longitudinal lines. Preserved material beige, oral disc and marginal ruff lighter.
Cnidom (fig. 12): Basitrichs, b-mastigophores, p-mastigophores A, p-mastigophores B1, and spirocysts. Sizes and distribution in table 4.
Geographic and Bathymetric Distribution and Natural History: Actinostella digitata can be found in the southern Atlantic Ocean off the coast of Argentina (McMurrich, 1893). This is the second record of the species, and it was collected in Paraná Beach, Chubut, southward to the type locality (La Plata River) in Argentina. The single specimen from Paraná Beach was found attached to a rolling stone with only the oral disc above the substratum. Despite working in the area for several years, this was the first and only time the collectors noticed this species. It can be found from 5 to 10 meters (Paraná Beach).
Remarks: Actinostella digitata is distinguished by the combination of having three cycles of perfect and fertile mesenteries and only small basitrichs in the column; it shares having p-mastigophores A and basitrichs in the marginal ruff with A. flosculifera and A. bradleyi. It was originally described by McMurrich (1893) as Cradactis digitata. We analyzed the type specimens and one newly collected specimen from Paraná Beach (in Chubut, Argentina), southward of the type locality in La Plata River (Argentina). In the type specimens, the perfect second cycle was hard to discern because of the state of preservation; Carlgren (1934) had analyzed the same specimens and suggested that the three cycles might be perfect, a characteristic we confirmed in the newly collected specimen, which clearly has the three cycles perfect and fertile, including directives.
FIG. 10.
External anatomy of Actinostella digitata (McMurrich, 1893). A, lateral view of live semiexpanded specimen; B, lateral view of preserved specimen; C, detail of vesicles (ve) in the marginal ruff; D, lateral view of preserved syntype (USNM 1776); E, lateral view of preserved syntype (USNM 1776) showing rows of verrucae (v) in distal column; F, oral view of preserved syntype (USNM 1776) showing the marginal ruff (f). Abbreviations: f, marginal ruff; v, verrucae; ve, vesicles. Scale bars: A, B, D, 10 mm; E, F, 5 mm; C, 0.1 mm.
FIG. 11.
Internal anatomy of Actinostella digitata (McMurrich, 1893). A, longitudinal section of the distal column showing distal vesicles (ve) in the marginal ruff, marginal sphincter muscle (s), and the fosse; B, cross section proximal to the actinopharynx level showing cycles of mesenteries, and the siphonoglyph (si); numbers between pairs of mesenteries indicate the corresponding cycle; C, detail of verrucae (v) in distal column; D, cross section of a tentacle showing ectodermal longitudinal muscles; E, detail of developing spermatic cysts (sc); F, detail of a cross section showing the retractor (r) and parietobasilar (p) muscles; G, cross section of proximal end showing weak basilar muscles (b). Abbreviations: b, basilar muscles; ep, epidermis; ga, gastrodermis; me, mesoglea; sc, spermatic cysts; p, parietobasilar muscle; r, retractor muscle; s, sphincter; si, siphonoglyph; t, tentacle; v, verrucae; ve, vesicles. Scale bars: A, F, 5mm; B–E, G, 1 mm.
FIG. 12.
Cnidae of Actinostella digitata (McMurrich, 1893). A, B, D, F, G, H, J, K, basitrichs; C, spirocysts; L, basitrichs S; E, I, N, p-mastigophore A; M, b-mastigophore; O, p-mastigophore B1. Capsules depicted in K and O were found only in type specimens.
TABLE 4.
Size ranges and distribution of cnidae of Actinostella digitata (McMurrich, 1893). Data in parenthesis from Carlgren (1934). N, Total number of capsules measured; M, Ratio of number of specimens in which each cnidae was found to number of specimens examined; F, Frequency, +++ = very common, ++ = common, + = rather common, --- = sporadic; SD, standard deviation, ND, no data; NF, not found. Sizes in micrometers. Letters in parenthesis correspond to images in figure 12.
Actinostella flosculifera (Le Sueur, 1817)
Figures 13–14, tables 1, 5
Actinia flosculifera Le Sueur, 1817.
Oulactis flosculifera [no author]: Milne Edwards, 1857.
Oulactis flosculifera (Lesueur): Milne Edwards, 1857.
Oulactis flosculifera (Le Sueur, 1817): Duchassaing and Michelotti, 1860.
Actinostella formosa Duchassaing, 1850.
Asteractis formosa (Duchassaing, 1850): Verrill, 1899.
Oulactis formosa Duchassaing and Michelotti, 1860.
Asteractis flosculifera (Le Sueur, 1817): Verrill, 1899.
Cradactis fasciculata (McMurrich, 1889): Haddon, 1898.
Evactis flosculifera (Le Sueur, 1817): Andres, 1883.
Oulactis fasciculata McMurrich, 1889.
Oulactis foliosa Andres, 1883.
Actinactis [sic] flosculifera: Verrill, 1900.
Actinostella flosculifera (Le Sueur, 1817): McMurrich, 1905.
Phyllactis flosculifera (Le Sueur, 1817): Stephenson, 1922.
Oulactis conquilega Duchassaing and Michelotti, 1860.
Actinostella conchilega (Duchassaing and Michelotti, 1860): McMurrich, 1905.
Asteractis conquilega (Duchassaing and Michelotti, 1860): Verrill, 1899.
Phyllactis conchilega (Duchassaing and Michelotti, 1860): Stephenson, 1922.
Phyllactis conquilega (Duchassaing and Michelotti, 1860): Carlgren, 1949.
Phyllactis conquilegia [sic] (Duchassaing and Michelotti, 1860): Voss et al., 1969.
Metridium prætextum Couthouy in Dana, 1846.
Asteractis, n. sp.: Duerden, 1897.
Asteractis expansa Duerden in McMurrich, 1898.
Oulactis radiata Duchassaing and Michelotti, 1860.
Lophactis radiata (Duchassaing and Michelotti, 1860): Andres, 1883.
Actinostella radiata (Duchassaing and Michelotti, 1860): McMurrich, 1905.
Phyllactis radiata (Duchassaing and Michelotti, 1860): Stephenson, 1922.
Differential Diagnosis: Actinostella with three cycles of mesenteries, first and second perfect, third imperfect; all fertile, including directives. Marginal ruff and column with p-mastigophores A and basitrichs.
Examined Material: Actinostella flosculifera: AMNH Cat.Cnidaria 587, AMNH Cat. Cnidaria 694, AMNH Cat.Cnidaria 741, AMNH Cat.Cnidaria 1283, AMNH Cat.Cnidaria 1324, AMNH Cat.Cnidaria 1330, AMNH Cat.Cnidaria 1352, AMNH Cat.Cnidaria 3585, AMNH Cat.Cnidaria 5308, USNM 1606852, USNM 1606853, USNM 1606854, USNM 1606855, USNM 1606856, USNM 1606857, USNM 1606858, USNM 1606859, USNM 1606860, USNM 1606861, USNM 1606862, USNM 1606863; MZUSP 8405; Phyllactis conquilega [= A. flosculifera]: SMNH-1170 (holotype). See table 1 for material details.
Description. External anatomy (fig. 13): Well-developed pedal disc, to 29 mm diameter. Column, to 65 mm height and 38 mm diameter, with 48 longitudinal rows of verrucae distally in each endo- and exocoel. Marginal ruff with rows of vesicles. Oral disc, to 34 mm diameter. Fosse deep. Tentacles, 48, arranged in four cycles; simple, smooth, all of similar length, to 13 mm. Mesenterial insertions visible in oral disc, column, and pedal disc.
Internal anatomy (fig. 13): Same number of mesenteries distally and proximally. Twenty-four pairs of mesenteries hexamerously arranged in three cycles (6 + 6 + 12 = 24). First and second cycles perfect. All mesenteries fertile, including directives. Two pairs of directives attached to two clearly distinct siphonoglyphs. Gonochoric, developed oocysts 0.18–0.29 mm in diameter in specimens collected in May 2010, June 1966, and November 1899. Retractor muscles restricted and strong. Parietobasilar muscles well developed, with free mesogleal lamella. Basilar muscles well developed, processes short and thin. Endodermal marginal sphincter muscle weakly circumscribed, without central mesogleal lamella (fig. 13F–I). Longitudinal muscles of tentacles ectodermal. Zooxanthellae present in tentacles and marginal ruff.
Color (fig. 13): Variable in live specimens. Specimens from Panama with pedal disc and column pinkish, beige, or opaque orange; verrucae darker than column. Oral disc brownish with white radial lines. Marginal ruff white, green, or brown, with lighter stripes and a brownish ring near the mouth. Mouth light brownish. Tentacles translucent white, brownish, or reddish with lighter spots and dots along the entire aboral side of tentacles. Preserved material beige, oral disc, and marginal ruff lighter.
Cnidom (fig. 14): Basitrichs, basitrichs S, b-mastigophores, p-mastigophores A, p-mastigophores B1, and spirocysts. Sizes and distribution in table 5.
Geographic and Bathymetric Distribution and Natural History: Actinostella flosculifera is distributed along the entire Caribbean Sea (from Bermuda to the Lesser Antilles), Gulf of Mexico, Colombia, and the South Atlantic off the coast of Brazil (see Schlenz and Belém, 1992; González-Muñoz et al., 2012, 2013; Durán-Fuentes et al., 2022; 2023). The species has been also reported in the east Atlantic in the Cameroon, Canary Islands, Cape Verde Island, and Senegal (Ocaña and den Hartog, 2002; Ocaña et al., 2015) and the Gulf of Guinea (Wirtz, 2003), but these records need to be checked to confirm species-level identification. Individuals in Bermuda have been described as viviparous (Cairns and den Hartog, 1986).
Remarks: Actinostella flosculifera is distinguished by the combination of having three cycles of fertile mesenteries in which only the first and second cycles are perfect and p-mastigophores A in the marginal ruff and column. All members of Actinostella except for A. bradleyi are known to have up to three cycles of mesenteries. Nevertheless, Ocaña (1994) described specimens from the Canary Islands (east Atlantic) as A. flosculifera with four or five cycles of mesenteries and four cycles of tentacles. Because having more cycles of mesenteries than cycles of tentacles is not a common condition in Actiniaria (Stephenson, 1928), we suspect this might be a mistake and consider it as such until the specimens are reexamined.
Actinostella flosculifera was formerly clearly distinguished within the genus by lacking an endodermal marginal sphincter muscle and bearing only two fertile (first and second) cycles of mesenteries (McMurrich, 1905; González-Muñoz et al., 2012). However, after we reexamined the material (AMNH Cat.Cnidaria 5308) analyzed by González-Muñoz et al. (2012) and examined an additional 19 museum and 13 newly collected specimens from Panama (Atlantic side) (see table 1), an endodermal marginal sphincter muscle and gametogenic tissue in the third cycle were observed in all fertile specimens. Our observations of an endodermal marginal sphincter present in this species agree with those of Corrêa (1964), Schlenz and Belém (1992), and Ocaña (1994).
Corrêa (1964) did not report the presence of p-mastigophores A in the marginal ruff or the column of the material of A. flosculifera she studied. However, because capsules of p-mastigophores A in the ruff and in the column are not very abundant in specimens of A. flosculifera (and easy to miss unless looking for them specifically) and because we found this category of capsules in our examination of different specimens across the Caribbean and on those from Brazil (see tables 1, 5), we think Corrêa (1964) just overlooked this category of cnidae. Although this species has been redescribed a few times (e.g., Corrêa, 1964; Ocaña, 1994; González-Muñoz et al., 2012; Durán-Fuentes et al., 2022), the amount of revised material examined here allowed us to clarify the presence of an endodermal marginal sphincter muscle, all mesenteries fertile, p-mastigophores A in the marginal ruff and column, and S-shape basitrichs in column.
FIG. 13.
External and internal anatomy of Actinostella flosculifera (Le Sueur, 1817). A, lateral view of living relaxed specimen in aquarium, B, lateral view of semirelaxed live specimen; notice rows of distal verrucae (v); C-E, oral view of specimens in the field, burrowed with only marginal ruff above the substratum; F, longitudinal section of the distal column showing the position of the endodermal marginal sphincter muscle (s); G, H, detail of variability of the endodermal marginal sphincter muscle in two specimens. Abbreviations: f, marginal ruff; od, oral disc; s, sphincter; v, verrucae; ve, vesicle. Image in A courtesy of V. Häussermann. Scale bars: A, B, 5 mm; C, D, E, 10 mm; F, 1 mm; G, H, 0.5 mm.
FIG. 14.
Cnidae of Actinostella flosculifera (Le Sueur, 1817). A, C, E, H, I, K, L, M, basitrichs; B, spirocysts; F, N, basitrichs S; D, G, J, P, p-mastigophore A; O, b-mastigophore; Q, p-mastigophore B1.
Phylogenetic Analyses
We could amplify sequences only for a single specimen of Actinostella bradleyi. All ML analyses of the rDNA dataset recovered a monophyletic Actinostella within the superfamily Actinioidea with high support (fig. 15). Members of Actinostella were recovered either sister to a clade formed by Anthopleura biscayensis (Fisher, 1874) + Aulactinia marplatensis (Zamponi, 1977) sister to Actinostephanus Kwietniewski, 1897, or as sister to a clade formed by A. biscayensis + Au. marplatensis and Actinostephanus sister to a clade of several species symbiotic with clownfish e.g., Heteractis crispa (Hemprich and Ehrenberg in Ehrenberg, 1834), H. aurora (Quoy and Gaimard, 1833), etc.
Within the Actinostella clade, we consistently recovered two main clades with low support (64% and 59%, respectively): one corresponding to specimens of A. flosculifera from the Panamanian Caribbean Sea and the Gulf of Mexico (i.e., from the Atlantic Ocean) and a second clade with species of Actinostella from the Pacific Ocean, namely, A. californica + A. bradleyi. The single specimen of A. bradleyi sequenced (from the Panamanian Pacific) grouped with specimens of A. californica from Panama and the Gulf of California but without much support.
DISCUSSION
East Pacific and West Atlantic Actinostella Species
The genus Actinostella is characterized externally by having a marginal ruff covered by rows of vesicles, a column with rows of verrucae from middle to the distal column, and a more or less distinct fosse; internally, it is characterized by bearing an endodermal and somewhat circumscribed marginal sphincter muscle, and three to four cycles of mesenteries (e.g., Corrêa, 1964; Häussermann, 2003; González-Muñoz et al., 2012). Traditionally, species of Actinostella were distinguished by the number of tentacles, cycles, and fertility of mesenteries, slight differences in the ramification of the marginal ruff, presence and/or shape of endodermal marginal sphincter, and geographic distribution. However, not all descriptions mention all these characters (e.g., Verrill, 1869; see table 6); most species within the genus have similar numbers of tentacles and mesenteries, and at least two (A. bradleyi and A. californica) live in sympatry.
Corrêa (1964), in her exhaustive research on Actinostella flosculifera (named Phyllactis flosculifera following Carlgren, 1949), analyzed many specimens from the Caribbean Sea, type locality of all species of Phyllactis except P. cichoracea (which is from the Red Sea) and of several of the species of Actinostella. She synonymized all the material studied with A. flosculifera, arguing that they inhabited close localities and that the original descriptions did not mention relevant differences to separate them (Corrêa, 1964). Similarly, here we revised several specimens collected from different localities along the Caribbean Sea (e.g., Puerto Rico, Jamaica, Bermuda, Virgin Islands, Cuba, etc.; see table 1) identified as different species (e.g., Asteractis expansa, Phyllactis flosculifera, etc.) and found no differences in morphology or cnidae among them. We revised the holotype of P. conquilega (SMNH-1170, from the Virgin Islands); although only the distal part of the specimen is available, we were able to check the cnidae of the column, tentacles, and marginal ruff. All the specimens examined had the p-mastigophores A in marginal ruff and column, three cycles of mesenteries (only the first and second perfect) diagnostic characters of A. flosculifera, and therefore we agree with Corrêa (1964) that P. conquilega, P. formosa, P. praetexta, and A. radiata should be synonymized with A. flosculifera. Thus, we consider Phyllactis to have only one valid species, P. cichoracea. However, as the type specimen is not available for examination, and the original description of P. cichoracea by Milne Edwards in Haeckel (1876) fits within the diagnosis of Actinostella, we consider this species valid within Actinostella until new material from the type locality (Red Sea) is examined.
Actinostella correae (Schlenz and Belém, 1992) is not revised here, its original description is comprehensive, and this species can be easily distinguished from the others within Actinostella because it is a hermaphrodite and only the first cycle of mesenteries (including the directives) is fertile. Although Schlenz and Belém (1992) described the third cycle of mesenteries of A. correae as microcnemes, because microcnemes are defined as lacking retractor muscles and gametogenic tissue (Carlgren, 1949) and Schlenz and Belém (1992) described the third cycle of A. correae as having retractor muscles, we consider those mesenteries imperfect (i.e., not reaching the actinopharynx) mesenteries rather than microcnemes.
TABLE 5.
Size ranges and distribution of cnidae of Actinostella flosculifera (Le Sueur, 1817). N, Total number of capsules measured; M, Ratio of number of specimens in which each cnidae was found to number of specimens examined; F, Frequency, +++ = very common, ++ = common, + = rather common, --- = sporadic; SD, standard deviation, ND. Sizes in micrometers. Letters in parenthesis correspond to images in figure 14.
TABLE 6.
Differential diagnostic characters of Actinostella species from American coasts.
After the reexamination and dissection of the only known specimen of Lophactis ornata (= Actinostella ornata), a species from the Pacific side of Panama (Pearl Islands), we found that it shows diagnostic characteristics of the genus Telmatactis Gravier, 1916 (i.e., tentacles with rounded tips, column with periderm but without protuberances, mesogleal marginal sphincter muscle, and p-mastigophores B2a; see fig. 16, table 7). Because the only species of Telmatactis reported for the tropical eastern Pacific is T. panamensis (Verrill, 1869), L. ornata is most probably a junior synonym of this species.
Our revision of the type material of Actinostella bradleyi, A. californica, A. digitata, A. ornata, Phyllactis conquilega, and additional material of A. flosculifera (type material of this species is not available) highlights the need to reevaluate the diagnostic characteristics for Actinostella. We consider that the traditional characters used to differentiate species of Actinostella must be complemented with the distribution of the cnidae. Therefore, (1) the number of cycles, (2) the fertility of the mesenteries, and (3) the distribution of cnidae (in particular those cnidae capsules in the marginal ruff and the column) are the diagnostic characters to distinguish the current species of Actinostella (table 6). We do not consider the presence of an endodermal marginal sphincter as diagnostic for species within Actinostella because all its species have a more or less circumscribed sphincter muscle; we also found that differences in the ramifications of the marginal ruff are hard to assess (especially in old, preserved material), and thus not useful or reliable to distinguish within species of Actinostella.
FIG. 16.
External and internal anatomy and cnidae of Lophactis ornata Verrill, 1869 (YPM 2105) (= Telmatactis cf. panamensis). A, lateral view of preserved specimen; B, oral view of preserved specimen; notice the capitulum (c); C, proximal view of preserved specimen; D, longitudinal section of the distal column showing mesogleal marginal sphincter muscle (s); E, detail of the muscle fibers within the mesoglea; F–H, basitrichs; I, p-mastigophores B1. Scale bars: A–D, 5 mm; E, 1 mm.
TABLE 7.
Size ranges and distribution of cnidae of Lophactis ornata Verrill, 1869 [=Telmatactis panamensis]. N, Total number of capsules measured; M, Ratio of number of specimens in which each cnidae was found to number of specimens examined; F, Frequency, +++ = very common, ++ = common, + = rather common, --- = sporadic; ND, no data. Sizes in micrometers. Letters in parenthesis correspond to images in figure 16. Data sources: 1Fautin et al. (2007); 2Carlgren (1951).
Phylogenetic Relationships of and within Actinostella
Our dataset of standard rDNA markers used for anemones (12S, 16S, CO3, 18S, 28S) recovered a monophyletic Actinostella not closely related to other genera with marginal ruff included in our analysis (i.e., Oulactis) with high support. Thus, our molecular results suggest that the marginal ruff has evolved independently at least twice (in Actinostella and Oulactis) based on the present subset of sampled actiniarians.
Similar to the pattern recovered for other members of Actinioidea (see Daly et al., 2017), our dataset split the species of Actinostella according to geography (i.e., Atlantic species separated from Pacific species) although with low support (fig. 15). Despite the anatomy of A. flosculifera and A. californica being very similar (see table 6), our molecular results do not support a finding of these two species as siblings (fig. 15). These results render the use of anatomy to identify and assess phylogenetic relationships of species within this genus unreliable; similarities in anatomy might reflect morphological convergence as it has been found multiple times within Actiniaria (e.g., Rodríguez et al., 2012, 2014; Daly et al., 2017). Because A. flosculifera and A. californica are distributed on each side of the Panama Isthmus, one potential evolutionary scenario to explain anatomical similarities despite the recovered genetic divergence between the two species (besides morphological convergence) is that the species divergence might have predated the closure of the isthmus; a similar pattern has been suggested and discussed for cerianthids (Stampar et al., 2012). However, the low support recovered, together with the fact that we could get molecular data for only one specimen of A. bradleyi, render the phylogenetic relationships within Actinostella and the associated hypothesis on their diversification uncertain until more specimens and genomic approaches are used.
ACKNOWLEDGMENTS
Andrés Averbuj and Soledad Zabala (CENPAT-CONICET, Argentina) are thanked for collecting the specimen of Actinostella digitata. We thank Ricardo González-Muñoz (Instituto de Investigaciones Marinas y Costeras [CONICET-UNMdP, Argentina]) for the material of A. flosculifera from the Mexican Caribbean. Staff and colleagues at the Smithsonian Tropical Research Institute (STRI, Panama) are thanked for their assistance during fieldwork. We thank colleagues at Fauna Arrecifal (UABCS, Mexico): Alejandro López, Adair A.G. Coria, Ramiro Arcos-Aguilar, and Zvi Hoffman; and MAYA group (UABCS, Mexico): Giovanni Garza, Diego Gutiérrez, Carlos Paredes, Perla Aragón, and Baruch Salas for their assistance and collecting specimens of Actinostella bradleyi and A. californica from the Mexican Pacific. Eric A. Lazo-Wasem (YPM), Lourdes Rojas (YPM), Stephen Cairns (USNM), William Moser (USNM), Emily Dock Åkerman (SMNH), and Lily Berniker (AMNH) are thanked for their help with loans and accession of specimens. We thank Verena Häussermann (Universidad de San Sebastián, Chile) for her assistance in fieldwork and taking photographs of several specimens. Discussions with Eric A. Lazo-Wasem and Luis Chasqui (INVEMAR, Colombia) greatly helped with the current location of the type locality of A. bradleyi. We extend our gratitude to Nautilus Dive Tech, a diving company for their commitment to environmental conservation and their invaluable assistance throughout our fieldwork. We extend our sincere appreciation to BlueNation, a diving company for their dedication to preserving the environment and their unwavering support during our fieldwork.
Y.B. was supported by a master's degree fellowship from the Consejo Nacional de Ciencia y Tecnología of Mexico (CONACYT) and by an AMNH Collection Study Grant and the Lerner-Gray Grant for Marine Research, also through the AMNH. This work was supported in part by NSF DEB-1456196, DEB-1457581 grants to E.R., and NSF DEB-1456674 grant to R. Collin (STRI). L.C.G. received a grant of Research Internship for the use of scientific resources at the Center for Marine Biology of the Universidade São Paulo (CEBIMar/USP, Brazil). This work was supported in part by SEMARNAT-CONACYT 2004-01-445 [“Biogeography and molecular systematics of sea fans and soft corals (Cnidaria: Octocorallia) in Mexico's Pacific and Gulf of California”] and CONABIO JF190/2013 [“Inventory of sessile marine life in the Pacific Islands of Baja California Sur”], UABCSSCRIPPS-CBMC [“Ecological Monitoring Project-ProMonitor”] grants to C.S. Partial support for this work was provided by Argentinean PIP-0253 and PICT-2504 grants and a CONICET (Argentina) grant to D.L.
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