Kaori Wakabayashi

Predation by the Phyllosoma Larva of Ibacus novemdentatus on Various Kinds of Venomous Jellyfish

The phyllosoma, a larva of spiny and slipper lobsters, has an exceptionally flat body and long appendages. It is known to associate with several species of cnidarian jellyfish, a behavior that is not rare in crustaceans. Indeed, phyllosomas clinging onto jellyfish have been observed both in the laboratory and in the natural environment. Wild phyllosomas have been found to contain jellyfish tissues in their hepatopancreas and feces, suggesting that the larvae utilize jellyfish as a food source; however, how they capture jellyfish and what species of jellyfish they prefer have rarely been investigated. The few previous studies conducted have suggested that phyllosomas have a high specificity for jellyfish (preying on only a few species); in contrast, the results of our study indicate that specificity is low. We show that phyllosomas prey on a variety of jellyfish species including deadly stinging types, on a variety of jellyfish developmental stages, and on various parts of the jellyfish body. When making contact with a jellyfish, phyllosomas first cling onto its exumbrella, feed on its tentacles or oral arms, and then consume the exumbrella. Phyllosomas may be capable of defending themselves against any types of nematocyst sting, and it is likely that they have evolved to utilize venomous jellyfish as a food in the open sea, where food may be scarce.

A new species of parasitic copepod, Sarcotretes umitakae sp. n. (Siphonostomatoida, Pennellidae), on the rattail (Actinopterygii, Macrouridae) from the East China Sea, Japan.

Abstract A new species of copepod, Sarcotretes umitakae sp. n., of the siphonostomatoid family Pennellidae is described based on female specimens from the rattail Coelorinchus jordani Smith and Pope (Actinopterygii: Gadiformes: Macrouridae) caught in the East China Sea. This species is characterized by exhibiting the following characters: the large proboscis projects strongly; the head bears paired lateral processes which are bulbous and taper into a slender horn; the twisting neck is significantly longer than the trunk; and the trunk bears an anterior constriction with a reduced abdomen.

Morphology and Gene Analysis of Hybrids Between Two Congeneric Sea Stars With Different Modes of Development

The sea star Astropecten scoparius has feeding bipinnarian larvae, whereas its congener Astropecten latespinosus has nonfeeding barrel-shaped larvae. To investigate evolutionary changes in the development of asteroids, we performed reciprocal crosses between these two species with different larval forms. In the cross between A. scoparius eggs and A. latespinosus sperm, embryos developed into bipinnaria-like larvae. The larvae exhibited either a functional digestive system (a maternal feature) or a nonfunctional digestive system with the tip of the archenteron not connected to the stomodeum (a paternal characteristic). However, in the reciprocal cross between A. latespinosus eggs and A. scoparius sperm, barrel-shaped larvae resembling those of A. latespinosus were produced, in addition to bipinnaria-like larvae, some with functional digestive systems and some with nonfunctional ones. Juveniles were produced from all types of crosses. 18S rDNA was used as a gene marker in cycle sequencing analysis to investigate the genetic features of these juveniles. The sequences of juveniles from bipinnaria-like larvae showed double-peak nucleotide signals, indicating a biparental genome. On the other hand, juveniles from barrel-shaped larvae from A. latespinosus eggs and A. scoparius sperm showed the same sequence as A. latespinosus juveniles. This suggests that bipinnaria-like larvae of both crosses are always hybrids, whereas barrel-shaped larvae develop parthenogenetically.

Choniomyzon inflatus n. sp. (Crustacea: Copepoda: Nicothoidae) associated with Ibacus novemdentatus (Crustacea: Decapoda: Scyllaridae) from Japanese waters

A new species of parasitic copepod, Choniomyzon inflatus n. sp., is described based on specimens collected from the external egg masses of the smooth fan lobster Ibacus novemdentatus Gibbes captured in the North Pacific Ocean off Ainan, Ehime Prefecture, western Japan. The new species differs from its congeners in having a globular to ovoid prosome, in bearing asymmetrically arranged denticles at a rounded apex of both the terminal segment of the antenna and the maxilliped, and in lacking serrate lobes on the basis of legs 1 and 2. The species is similar in size and shape to the host’s eggs, which may be interpreted as egg mimicry. The new species is the first member of Choniomyzon Pillai, 1962 from subtropical regions.

Embryonic development of the sea butterfly Desmopterus papilio (Gastropoda: Thecosomata)

Abstract The embryonic development of the thecosome Desmopterus papilio is described for the first time. The mature individual produced a round-shaped egg mass containing ca. 200 fertilised eggs. First cleavage was observed 15 min after the release of the egg mass. Embryos showed typical molluscan spiral cleavage: macromeres produced the first and second quartets of micromeres in clockwise and counterclockwise directions, respectively. A trochophore larva hatched from the egg capsule 28 h after the release of the egg mass. Thereafter, the larva secreted a primary shell at the posterior part, developing into the veliger stage. These findings may be useful for future work on postembryonic development, especially on the loss of the veliger shell, in the genus Desmopterus which is the only group of thecosome species without a shell in the adult stage.

Life-cycle of Choniomyzon inflatus Wakabayashi, Otake, Tanaka & Nagasawa, 2013 (Copepoda: Siphonostomatoida: Nicothoidae) with the morphological descriptions of the nauplius, copepodid and adult male.

Choniomyzon inflatus Wakabayashi, Otake, Tanaka & Nagasawa, 2013 (Copepoda: Siphonostomatoida: Nicothoidae), an associate of the scyllarid lobster Ibacus novemdentatus Gibbes, was found to pass through at least four developmental stages: nauplius, copepodid I (CI), copepodid II or later (CII+) and adult. Free-living nauplii were observed hatching from the ovisacs of adult females. CI was found on the body surface of both female and male hosts, whereas CII+ and adult were obtained from the female host’s egg masses. The life-cycle of this copepod is presumed to be as follows: (i) nauplius develops into CI in the water column; (ii) infective CI settles on body surface of host; (iii) CI moults into the following stage, changing its microhabitat from host’s body surface to egg masses; (iv) CII+ develops on egg masses of host until adult stage; and (v) adult female and male mate on the host’s egg masses.