Due to their curious phylogenetic position and anatomy, hagfishes have attracted the interest of zoologists, especially in the context of vertebrate evolution. Embryological information on these animals is now also needed in the field of evolutionary developmental biology (Evo-Devo), as it is expected to provide hints about the origin of vertebrate traits, whether the hagfishes are an in- or outgroup of vertebrates. This review summarizes the importance of hagfish embryology from a phylogenetic perspective, and the history of attempts to obtain hagfish eggs and embryos. Clearly, the main difficulty associated with these animals is their deep-sea habitat. To circumvent this problem, this review also discusses the future prospects for obtaining embryological material, both from the wild and in the laboratory.

The scincid lizard Plestiodon latiscutatus is found in the Izu Islands and Izu Peninsula of central Japan, whereas P. japonicus, a close relative, is found over the entire main island group of Japan, except the Izu Peninsula. The precise area of occupancy of these species was surveyed around the Izu Peninsula. Species identification was made through comparison of mitochondrial DNA partial sequences of specimens from the Izu Peninsula with those from the other regions, since morphological differences between these species have not yet been characterized. This study determined that these species are deeply diverged from each other in mitochondrial DNA sequence, and that the ranges of these species overlap only in a narrow zone. The results imply that gene flow between these species, if any, is restricted to a low level, without physical barriers. The boundary between the geographic ranges of these species was established as occurring along the lower Fuji River, Mt. Fuji, and the Sakawa River. This region is concordant with that of the old sea that is assumed to have separated the Izu Peninsula from other parts of the Japanese main island group until the middle Pleistocene. This pattern suggests that P. latiscutatus and P. japonicus were differentiated allopatrically before the connection of land areas of the Izu Peninsula and Honshu, the main island of Japan, and come into secondary contact through this connection. Thus, the species boundary is likely to have been maintained in situ, without physical barriers, since the secondary contact in the middle Pleistocene.

An ontogenetic series of 22 cleared and double-stained prenatal specimens was used to study the sequence of ossification of selected postcranial skeletal elements of Talpa europaea. Results were compared with nine other therian mammals, with Alligator, Chelydra, and Lacerta as outgroups. Using the event-pairing method, shifts in the onset of ossification in T. europaea, Sus, and Homo were identified. In T. europaea, the ossification of the cervical vertebrae starts before the metatarsals. In Homo and Sus, the tarsals ossify before the pubic bone. These shifts in the sequence of ossification are unique among the mammals examined, whereas many other changes, characterising monophyletic groups and/or evolving convergently, were also identified. Particular attention was given to some peculiar calcified elements of the hand in T. europaea, which were identified as accessory ‘sesamoid bones’, and do not display a chondrified precursor. They start to calcify before all others of the hand and later fuse. They appear in all fingers and function as reinforcement for the distal phalanges, most likely as an adaptation for burrowing. The development of the sesamoid bones was examined using histological sections and macerated adults.

Trididemnum miniatum is a colonial ascidian harboring the photosymbiotic prokaryote Prochloron sp. These bacterial cells are located in the tunic of the host animal. The present study revealed, by ultrastructural analysis, that the Prochloron cells were exclusively distributed and proliferated in the tunic. They were shown to be embedded in the tunic matrix and to have no direct contact with ascidian cells. Some tunic cells of the ascidians, however, did phagocytize and digest the symbiont. Round cell masses were sometimes found in the tunic and appeared to consist of disintegrating cyanobacterial cells. The thoracic epidermis of ascidian zooids was often digitated, and the epidermal cells extended microvilli into the tunic. Since there were no Prochloron cells in the alimentary tract of the ascidian zooids, the photosymbionts would not be considered part of the typical diet of the host ascidians. Thin layer chromatography showed that the symbionts possessed both chlorophyll a and b, while a 16S rRNA gene phylogeny supported the identification of the photosymbiont of T. miniatum as Prochloron sp.

A cDNA encoding transthyretin was cloned from the Pacific bluefin tuna (Thunnus orientalis). This cDNA contains a complete open reading frame encoding 151 amino acid residues. The deduced amino acid sequence is 81% and 55% identical to the gilthead seabream and common carp forms, respectively, and 33–39% to mammalian, reptilian, and amphibian forms. A 1.0-kb transcript was found in the the liver and ovary; the liver is the main source of this protein. Analysis of triiodo-L-thyronine (T₃) and L-thyroxine (T₄) binding demonstrated that both T₃ and T₄ bind to bluefin transthyretin. The binding activity of T₃ for bluefin transthyretin is higher than that of T₄. These results indicate that bluefin transthyretin acts as a transporter of thyroid hormones (THs) in the plasma, and plays an important role in the function of THs in target cells.

The developing indirect flight muscles of pharate moths are characterized by a rhythmic discharge of a long bout of flight-pattern-like muscle potentials in the absence of contractions. The electrical activity of the dorsal longitudinal flight muscles (DLMs) in the silkmoth, Bombyx mori, was discernible as a cluster of many series of muscle potentials that last for several minutes on day 4 of the pupal period. The duration of the active phases and the period of rhythmic activity gradually increased to a peak value on day 7 or 8 and then declined until the end of the pupal period. Mean duration of the active phases (±SD) and the mean period of the rhythmic activity (±SD) at the peak were 38.7±8.7 min and 74.5±7.3 min, respectively. The rhythmic electrical activity of immature DLMs was closely coordinated with the rhythmic (bursting) activity of a population of neurosecretory cells that are known to produce pheromone-biosynthesis activating neuropeptide (PBAN) and its related peptides, which belong to the multifunctional peptide family, pyrokinin/PBAN. The DLMs always became active a few minutes after the neurosecretory cells, and the timing of onset of these two activities appeared to be strictly regulated by a neural mechanism. The implication of the coordinated activity for development and maturation of imaginal tissues, including the flight motor system, and possible functions of the neuropeptides in this development are discussed.

Ultradian rhythmic firing activity (period of 40–90 min) of a population of neurosecretory cells (NSCs) producing FXPRLamide peptides in the subesophageal ganglion (SG) of the silkmoth, Bombyx mori, is closely coordinated with periodically occurring electrical activity of developing flight muscles (FMs) during metamorphosis. To examine neuronal mechanisms and pathways that mediate the coordination of the NSC and flight motor systems, the ventral nerve cord (VNC) or circum-esophageal connectives were transected. Transection of the VNC between the SG and thoracic ganglia greatly shortened the period of activity rhythm of the FMs (5–15 min) with no effect on the rhythmicity of NSCs. Bilateral transsection of the circumesophageal connectives between the brain and SG abolished the rhythmic activity of NSCs, thereby suggesting that the coordination of the two systems may be mediated by a common oscillatory mechanism in the brain. Further, bisection of the brain in the midline failed to abolish the ultradian rhythmicity of FMs. Thus, each brain hemisphere may have an ultradian oscillator that activates the NSC system in the SG, and modulates the short-period oscillation of the flight motor system located in the thoracic ganglia.

An immunocytochemical study using an FXPRLamide antiserum revealed three clusters of neurosecretory cells along the midline of the subesophageal ganglion of the mealworm beetle, Tenebrio obscurus. Firing activity of five pairs of neurosecretory cells in the mandibular and maxillary clusters was recorded from an axonal tract of the cells throughout the entire pupal period. The population of neurosecretory cells became active during the middle and late pupal periods, and they usually discharged clusters of action potentials at an interval of 30–90 min. The ultradian activity rhythm of the cells in T. obscurus was related to a periodic discharge of electrical activity in developing flight muscles, as has been observed in the homologous cells in the silkmoth, Bombyx mori. Furthermore, the rhythmic activity of the neurosecretory cells in the mealworm was closely synchronized with periodically occurring rhythmic abdominal movements that caused extracardiac hemocoelic pulsations, which facilitate hemolymph circulation and exchange of respiratory gases. The results suggest that the secretory products of the neurosecretory cells may activate and/or orchestrate physiological mechanisms supporting morphogenesis during metamorphosis.

A new tree frog of the genus Rhacophorus is described on the basis of specimens collected from Kalasin and Roi Et Provinces, eastern Thailand. It can be distinguished from all other congeners by the combination of: moderate body size (about 38 mm in males and 44 mm in females); brownish dorsum with irregular, dark marking; third finger webbed broadly to base of disk or less on outer side, and fourth finger to distal subarticular tubercle or base of disk; and no dermal appendage on snout, vent, or heel. It is currently known only around the type locality, where habitats suitable for anurans are limited.

Umazuracola elongatus n. gen., n. sp., is described based on specimens collected from the body surface of the black scraper, Thamnaconus modestus (Günther), taken from the Seto Inland Sea in western Japan. The new species belongs to a new family of the copepod order Poecilostomatoida. It is characterised by the reduction of the maxilliped and leg 1 in females and modification in both sexes of legs 2, 3, and 4 into robust attachment organs, with heavy, denticulate outer spines. Although the antenna, mandible, maxillule, and maxilla of U. elongatus resemble those of species of the “bomolochiform complex”, a cladistic analysis revealed that phylogenetically this species is embedded in a different clade containing the polychaete-parasitizing families Entobiidae Ho, 1984 and Nereicolidae Claus, 1875.