Immunohistochemical Localization of a GnRH-Like Peptide in the Nerve Ganglion of Three Classes of Crustaceans, the Tadpole Shrimp Triops longicaudatus (Branchiopoda), the Barnacle Balanus crenatus (Hexanauplia), and the Hermit Crab Pagurus filholi (Malacostraca).

In vertebrates, gonadotropin-releasing hormone (GnRH) regulates gonadal maturation by stimulating the synthesis and release of pituitary gonadotropins. GnRH has also been identified in invertebrates. Crustacea consists of several classes including Cephalocarida, Remipedia, Branchiopoda (e.g., tadpole shrimp), Hexanauplia (e.g., barnacle) and Malacostraca (e.g., shrimp, crab). In the malacostracan crustaceans, the presence of GnRH has been detected in several species, mainly by immunohistochemistry. In the present study, we examined whether a GnRH-like peptide exists in the brain and/or nerve ganglion of three classes of crustaceans, the tadpole shrimp Triops longicaudatus (Branchiopoda), the barnacle Balanus crenatus (Hexanauplia), and the hermit crab Pagurus filholi (Malacostraca), by immunohistochemistry using a rabbit polyclonal antibody raised against chicken GnRH-II (GnRH2). This antibody was found to recognize the giant freshwater prawn Macrobrachium rosenbergii GnRH (MroGnRH). In the tadpole shrimp, GnRH-like-immunoreactive (ir) cell bodies were located in the circumesophageal connective of the deuterocerebrum, and GnRH-like-ir fibers were detected also in the ventral nerve cord. In the barnacle, GnRH-like-ir cell bodies and fibers were located in the supraesophageal ganglion (brain), the subesophageal ganglion, and the circumesophageal connective. In the hermit crab, GnRH-like-ir cell bodies were detected in the anterior-most part of the supraesophageal ganglion and the subesophageal ganglion. GnRH-like-ir fibers were observed also in the thoracic ganglion and the eyestalk. These results suggest that a GnRH-like peptide exists widely in crustacean species.

Morphology of Cyprid Attachment Organs Compared Across Disparate Barnacle Taxa: Does It Relate to Habitat?

This study used morphometric analyses to compare the structure of the third antennular segment, also called the attachment organ, in cyprid larvae from cirripede species representing a diverse set of taxonomic groups. The aim was to investigate the degree of morphological variation in view of the diversity of habitats, settlement substrata, and modes of life found in the Cirripedia. In all cyprids the third segment features a flat surface (the attachment disc) covered with small cuticular villi thought to function in adhesion. The parameters analyzed were the angle of this disc relative to the long axis of the antennule, its shape (outline), the density of cuticular villi, and the type of cuticular structure encircling the disc. The 10 species studied came from most major groups of cirripedes, and comprised shallow-water forms inhabiting hard bottoms (Capitulum mitella, Pollicipes pollicipes, Semibalanus balanoides, Austrominius modestus, Megabalanus rosa), sublittoral forms (Verruca stroemia, Scalpellum scalpellum), epibiotic forms settling on live, soft tissues (Balanus spongicola, Savignium crenatum), and a parasite (Peltogaster paguri). Significant structural variation was found among the species, but due to limited taxon sampling it was unclear whether the differences relate to ecological factors or phylogenetic affiliation. The disc perimeter is guarded by either a series of long and thin cuticular fringes overreaching the rim of the disc (= a velum) or a few low, but very broad cuticular flaps (= a skirt). The presence of a velum (in all rocky-shore species) or a skirt (all other species) around the attachment disc was the only parameter that was clearly correlated with habitat. The shape of the third antennular segment varied from a symmetrical bell shape with a distally facing attachment disc having a circular disc outline, to segments that were elongated in side view, with a very tilted ventral disc surface having an elliptical disc outline. The bell shape may be most common in forms from rocky shores, but in our test of morphometric parameters only Scalpellum scalpellum (sublittoral), Savignium crenatum (epibiotic in corals), and Peltogaster paguri (parasitic) had shapes that differed significantly from the other species. The density of villi on the attachment disc varied significantly, but also showed no clear-cut correlation with substratum or habitat. Attachment organ structure is clearly the most variable feature in cirripede cyprids. To evaluate the degree to which attachment organ structure is correlated with habitat, settlement substratum, and mode of life, future studies should employ a more refined statistical analysis on an enlarged dataset, with much increased taxon sampling and a more multifaceted definition of ecological variables.

On the morphology of antennular sensory and attachment organs in cypris larvae of the deep-sea vent/seep barnacles, Ashinkailepas and Neoverruca.

Barnacle cypris larvae show high morphological variation in the organs used in search of and attaching to a substratum. This variation may represent adaptation to the habitat of the species. Here, we studied SEM level morphologies of cypris antennular sensory and attachment organs in a deep-sea vent endemic species (Neoverruca sp.) and a vent/seep inhabiting species (Ashinkailepas seepiophila). We compare them with three species from other environments. The antennular morphologies of Neoverruca sp. and A. seepiophila were similar, which is consistent with recent molecular studies showing a close relationship of the two species. The setation pattern of the antennules was very conservative among species from various environments. In contrast, striking differences were observed in the structure of the attachment organ (the third antennular segment). Neoverruca sp. and A. seepiophila had no velum or a skirt surrounding the attachment disc on the third segment, while other cirripede cyprids almost always have either of these structures. In addition, both cyprids of A. seepiophila and Neoverruca sp. had the attachment disc angled toward the substratum, whereas it faces distally in cyprids from hard bottom inhabiting barnacles. We suggest that both velum/skirt and the angle of the attachment disc play an important role, when the antennules are contacting the substratum during surface exploration. Differences in attachment organ structures may be highly adaptive, enabling cirripede species to enter new habitats during evolution.

Biochemical and immunohistochemical analyses of GnRH-like peptides in the nerve ganglion of the chiton, Acanthopleura japonica.

We examined whether a gonadotropin-releasing hormone (GnRH)-like peptide is present in the nerve ganglion of the chiton Acanthopleura japonica (Mollusca, Polyplacophora) using reverse-phase high performance liquid chromatography (rpHPLC) combined with time-resolved fluoroimmunoas-say (TR-FIA) analysis, and immunohistochemistry. An extract of the chiton head region showed a similar retention time to that of synthetic lamprey GnRH-II on rpHPLC combined with TR-FIA analysis using a rabbit polyclonal antibody raised against chicken GnRH-II (aCII6). Cell bodies immunostained with LRH13 (a mouse monoclonal antibody raised against the common amino acid sequence of vertebrate GnRH) were detected in the cerebrobuccal ring (CBR). Cell bodies immunostained with aCII6 were not only observed in the CBR but also in the lateral nerve cord (LCo). Fibers immunostained with LRH13 and aCII6 were widely distributed throughout the central nervous system in the CBR, subradular ganglion (SubRG), pedal nerve cord (PCo), pedal commissure (P/PCom), lateropedal commissure (L/PCom), and from the LCo to the suprarectal commissure (SupRecCom). The cell bodies and fibers immunostained with these two antisera were distinguishable by dual-label immunohistochemistry. These results suggest that multiple GnRH-like peptides are present in the nerve ganglion of the chiton Acanthopleura japonica.

Possible role of a taurine transporter in the deep-sea mussel Bathymodiolus septemdierum in adaptation to hydrothermal vents.

Various invertebrates inhabiting hydrothermal vents possess sulfur-oxidizing bacteria in their tissues; however, the mechanisms by which toxic sulfides are delivered to these endosymbionts remain unknown. Recently, detoxification of sulfides using thiotaurine, a sulfur-containing amino acid, has been suggested. In this study, we propose the involvement of a taurine transporter in sulfide detoxification in the deep-sea mussel Bathymodiolus septemdierum by demonstrating: (i) the abundance of its mRNA in the gill; (ii) its activity under a wide range of salinities; (iii) its low Michaelis constant value in taurine transportation; and (iv) its affinity for thiotaurine and the thiotaurine precursor, hypotaurine.