Sigmodontomys aphrastus, the long-tailed rat, is an exceedingly rare rodent species from montane regions of Central and South America of which very little is known ecologically or systematically. It has been variously placed in the genera Oryzomys, Nectomys, and Sigmodontomys based on the five previously known specimens. Two new individuals were collected in northwestern Costa Rica's Cordillera de Tilarán. These new specimens and the other five known specimens are used to redescribe the species, detail measurements of external and cranial morphology, and compare S. aphrastus to similarly appearing sympatric species (Nephelomys albigularis and N. devius) and proposed closely related species (Sigmodontomys alfari, Mindomys hammondi, and Melanomys caliginosus). New ecological data is presented and the general knowledge of its natural history is summarized. The phylogenetic relatedness of S. aphrastus with purported sister taxa remains unresolved until combined molecular and morphological analyses are conducted.

Didemnum galacteum, a new species of ascidian from tropical west Atlantic, is described. The species comprises Brazilian specimens previously identified as Didemnum lutarium, as important differences were noticed between this and the new species. The species described herein has a milky white color, with colonies of moderate size and a tunic filled of small spicules. The zooids are small and present a divided testis.

Nihonotrypaea thermophila, new species, is described on the basis of 26 specimens from a hydrothermally influenced field off northeastern Taiwan at depths of 128–320 m. This is the first callianassid shrimp to be reported from deep-water hydrothermal vents, and available data seems to suggest that the new species is vent-endemic. The new species is assigned to Nihonotrypaea Manning & Tamaki, 1998, a genus including three previously described species inhabiting coastal mud or sand flat areas in Japan and its adjacent waters. The new species is unique in the genus in having the antennal peduncle distinctly longer than the antennular peduncle.

A new species of crangonid shrimp, Philocheras magnioculus, is described on the basis of a single female specimen from off the island of Panglao, southwest of Bohol, the Philippines. The presence of a sharp lateral tooth on the antennal scale links the new species to eight previously described species, but the structure of the rostrum, very large cornea, and poorly sculptured pleon immediately distinguish it from its relatives. The new species is the third Philocheras known from the Philippines.

Munidopsis sarissa, a new galatheid crustacean associated with gorgonian corals, is described from Taiwan at depths of about 1000 m. This new species is unique in the genus by having an extremely spinose carapace with elongated spearhead-like rostrum, fourth thoracic sternite much larger than following sternites, and very long and slender chelipeds possessing broad coxae which are clearly visible from the dorsal view of the animal.

Two species of the chaetognath family Spadellidae were recorded in a reef-related environment of the Mexican Caribbean; one of these spadellids represents a new species which is described and compared with its congeners. Spadella xcalakensis, new species differs from the other species of the genus by having a unique suite of taxonomically relevant structures such as the structure of the female genital opening, the shape of the seminal vesicles, the arrangement of the lateral and caudal fins with respect to the seminal vesicles, and the eye pigmentation. The nominal S. cephaloptera Busch was also recorded in the area; inconsistencies in the morphological descriptions related to this species worldwide suggest that it probably represents a species complex. These records set the southernmost distribution range for this genus in the Atlantic Ocean and the first record in Mexican waters. A dichotomous key for the identification of the currently known species of Spadella is included herein.

During examination of the holotype of Echiniscus tamus Mehlen, 1969 it became obvious the description did not match the specimen in a critical characteristic. The original description states the species has no dorsal leg spines (teeth on the dentated collar) of the fourth legs. Yet the holotype clearly has four large separate teeth on each collar. This article updates the description of Echiniscus tamus to reflect the characteristics visible on the holotype specimen. Additional detail is added to the description of the punctation of the cuticle. The original describer collaborated on this re-description.

Isohypsibius archangajensis Kaczmarek & Michalczyk, 2004 is reported as a newly recorded species from China. Diphascon (Adropion) linzhiensis, new species is similar to D. (Adropion) mauccii Dastych & McInnes, 1996, and D. (Adropion) tricuspidatum Binda & Pilato, 2000, but differs from them by the presence of microplacoid and septulum together, instead of only septulum present in D. (A.) mauccii and only microplacoid present in D. (A.) tricuspidatum. The absence of cuticular bars on the legs and the shorter claws distinguishes this new species from the Australian D. gordonense Pilato, Claxton & Horning, 1991.

Cyanonemertes elegans, new genus and species, is described as a member of the order Hoplonemertea, suborder Monostilifera. In general morphology, it appears to be most closely related to the genus Amphiporus (family Amphiporidae). The most important features justifying the new taxon are: 1) cephalic muscle layer with anteriorly divided longitudinal musculature, 2) diagonal muscles of non-fasciated, lattice type, 3) retractor muscles derived from the outer portion of the longitudinal musculature, 4) cephalic blood system with extra-cerebral vessels, 5) rhynchocoel extending almost to posterior end of body, 6) rhynchocoel wall bilayered, 7) neurochord cells absent, 8) rhynchodeum with an outer layer of longitudinal muscle, 9) central stylet-basis complex present, and 10) proboscis sheath with thick muscular plate.

Madracis auretenra, new species, is described for a common, shallow-water, zooxanthellate coral species found throughout the wider Caribbean. This new species is distinguished from other species of the genus by a thin branched, dendritic morphology and depth distribution of 1–60 m. Other characteristics include: non-living basal branch portions; a fairly smooth coenosteum; a distinct line of coenosteal spines centrally located between adjacent corallites; no visible secondary septa in corallites; and closely spaced corallites. Individuals of this taxon have been incorrectly referred to Madracis mirabilis (Duchassaing & Michelotti 1860), which is a deep-water species and which is synonymous with Madracis myriaster (Milne-Edwards & Haime 1849), in several publications subsequent to 1973. Herein, a brief explanation of the taxonomic confusion surrounding M. mirabilis and the undescribed species is provided along with a complete description of this new species of Madracis. Records of the new species are confirmed for Puerto Rico, Curaçao, Grenada, and Bermuda. Authors of many recent studies on “Madracis mirabilis sensu Wells” will need to reconsider and reconfirm the identities of their study organisms.

A new species of Nicella, N. toeplitzae, is described from specimens collected from the western Atlantic Ocean, including the northern and eastern Gulf of Mexico. It is distinguished from other closely related species of this genus in having prominent, conical tubercles on the double head sclerites that measure up to 17 µm in height. Among the species having rotund body wall rods, it is distinguished by having double heads with a relatively thick waist.

Assembling phylogenetic trees for groups of organisms with thousands of taxa is problematic because of the large amount of data and trees that must be generated and analyzed. Several attempts have been made to develop a better way to handle the problems of large trees. Meta-trees (Meta Supertrees) are suggested as a way to generate a phylogeny for groups where you have many different data sets of overlapping but not identical sets of taxa and without a common set of markers. Meta-trees graft phylogenies onto a fixed base tree and avoid the problems of missing or redundant data and misplaced taxa that plague other types of supertrees.