Search

A new rhizocephalan species, Peltogaster unigibba n. sp., is described from the host hermit crab, Pagurixus boninensis (Melin, 1939), from the Bonin Islands, Japan. Of the16 known species of Peltogaster now currently recognised, P. unigibba n. sp., and P. contorta Boschma, 1958 share a left lobe that projects beyond the mantle aperture. The two species can be distinguished from one another by the position of the opening of the mantle aperture. The new species most closely resembles P. naushonensis Reinhard, 1946 in its internal structure, but clearly differs in the relative length of the colleteric glands. Peltogaster unigibba n. sp. represents the first record of a rhizocephalan from the oceanic Bonin Islands, and the second record of a rhizocephalan from an oceanic island in the northern hemisphere.

Peltogasterella sensuru n. sp. infests Pagurixus hermit crabs inhabiting rocky shores off Okinawa Island (Ryukyu Archipelago, Japan). This species is clearly distinguishable from Peltogasterella gracilis (Boschma, 1927): the stalk emerges from the middle part of the externa in the present species and P. sulcata (Lilljeborg, 1859), while the stalk in P. gracilis emerges from the posterior end of the externae. The new species differs from P. sulcata based on the morphology of the mantle aperture. Peltogasterella sensuru n. sp. repeatedly produces single brood externae that have not been previously observed in species belonging to the suborder Kentrogonida Delage, 1884. We also determined partial sequences of the COI gene and 16S rRNA gene of the new species for use as molecular markers for species identification.

A new genus and two new species of Peltogastridae, Peltogaster postica sp. nov. and Ommatogaster nana gen. et sp. nov., are described from Okinawa Island, Ryukyu Islands, southwestern Japan. The two new rhizocephalans were found to be parasitic on the estuarine hermit crabs, Pagurus minutus Hess, 1865 and Diogenes leptocerus Forest, 1956, respectively. Peltogaster postica sp. nov. is allied to P. curvata Kossmann, 1874, P. paguri Rathke, 1842 , and P. reticulata Shiino, 1943 , but is distinguished by its relative length and internal and external structures of the mature externa. Ommatogaster gen. nov. is established for the present new species O. nana based on the morphologies of the visceral mass of the externa and the presence of a nauplius eye in the larvae. Partial COI sequences were obtained from the two new species and one known species, Dipterosaccus indicus Van Kampen and Boschma, 1925, to test the possible usefulness of the sequences as tags for species identification.

The order Amphipoda is one of the largest orders in the Crustacea, many species of which are involved in symbiotic relations with other animals. Despite the considerable diversity of the Amphipoda both in number of species and ecology, polychaete-commensalism has been poorly known and described from few species. In particular, there has been little discussion of the evolutionary origins of polychaete-commensalism relationships. Amphipods in the family Leucothoidae are known as commensal inhabitants of filter-feeding invertebrates, where they utilize the feeding current produced by their hosts. Leucothoids are typically found from three types of filter-feeding hosts: sponges, ascidians, and bivalve molluscs. Relatively little is known about leucothoids that associate with other types of hosts. An undescribed species of the genus Leucothoe associated with burrows of terebellid polychaetes from Japan has been found. We herein describe this species as Leucothoe vermicola sp. nov., providing COI mtDNA and 18S rDNA sequences for DNA barcoding. This is the first record of a symbiotic association between Leucothoidae and Terebellidae. We also provide a hypothesis of the phylogenetic position of L. vermicola sp. nov. and evolution of the polychaete-commensalism in this species. The polychaete-commensalism in the present new species may have resulted from the entry of generalist species into polychaete hosts, rather than from host-conversion from a specialist species. [ABSTRACT FROM AUTHOR]

Descriptions of the diversity of sexual systems in animal taxa such as the thoracican barnacles are needed to study the evolution of sexual systems. Androdioecious systems (coexistence of hermaphrodites and males) are particularly important due to their possible role as evolutionary intermediates in transitions between hermaphroditism and dioecy. In this study, we used histology to examine the sexual system of the crab-epizoic barnacle Octolasmis unguisiformis to determine if dwarf males were present or not; a previous study reported the existence of conspecific-attached individuals, but did not investigate their sexuality. All conspecific-attached individuals were dwarf males, irrespective of their attachment site. However, crab-attached individuals never acted as dwarf males even if they were small and lived together with large individuals. The result emphasizes the importance of attachment to conspecifics, but not to specific sites on conspecifics, in the evolution of dwarf males. Other individuals were hermaphroditic, indicating androdioecy in this species. However, their functional sexuality (that is, whether they actually do act as males) requires further study. The presence of dwarf males in this species supports theoretical predictions that small group size, short-lived habitats, or spatial limitation favor the evolution of dwarf males. [ABSTRACT FROM AUTHOR]

Minami-Daito is an oceanic island located about 360 km east of Okinawa Island (a continental island), Ryukyu Archipelago, Japan. This is the first report of a peltogastrid rhizocephalan from an oceanic island in the northern hemisphere. The present specimen was identified as Dipterosaccus indicus based on the diagnostic characters of its external and internal morphology. Molecular analyses based on the partial sequence of the COI gene were consistent with the morphological identification. The number of species reported from oceanic islands may be limited by the lack of diversity in the structure and condition of their coastline, as well as the dispersal abilities of peltogastrids and their hosts. [ABSTRACT FROM PUBLISHER]