Mamiko Hirose

Localization of symbiotic cyanobacteria in the colonial ascidian Trididemnum miniatum (Didemnidae, Ascidiacea).

Abstract 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.

Marine invertebrate diversity in the oceanic Ogasawara Islands: a molecular examination of zoanthids (Anthozoa: Hexacorallia) and their Symbiodinium (Dinophyceae)

The Ogasawara (Bonin) Islands are oceanic islands approximately 1000 km south of mainland Japan noted for their high levels of both terrestrial and marine endemicity. Despite their unique location, the marine fauna of many taxa remains relatively under-examined. In this study, we specifically investigated the diversity of shallow water zoanthids (Cnidaria: Anthozoa: Hexacorallia) and their symbiotic zooxanthellae (Symbiodinium spp.) of the Ogasawara Islands for the first time. Using in situ field examinations combined with DNA sequencing and phylogenetic analyses, our results show the presence of five zoanthid species in the Ogasawara Islands; Zoanthus sansibaricus, Z. kuroshio, Palythoa tuberculosa, P. mutuki, and one potentially undescribed species of Palythoa. While most collected specimens were in symbiosis with clade C Symbiodinium as seen in southern Japan and other Indo-Pacific locations, one specimen of Z. kuroshio was unexpectedly in symbiosis with clade A, and no Z. sansibaricus colonies contained specific C1z type zooxanthellae previously observed at other locations. Overall, the Ogasawara Islands showed a lower zooxanthellate zoanthid species diversity (n = 5) than the non-oceanic Okinawa Islands (n > 10), which are at roughly the same latitude. Instead, the islands’ relatively depauperate zoanthid/symbiont fauna more closely resembles that of the northern Izu Islands.

The first internal molecular phylogeny of the animal phylum Entoprocta (Kamptozoa).

This article provides the first molecular phylogenetic study of the enigmatic invertebrate phylum Entoprocta and was designed to resolve the internal phylogenetic relationships of the taxon. The study is based on partial and combined analyses of the mitochondrial gene cytochrome c oxidase subunit I (COI), as well as the nuclear ribosomal genes 28S rDNA and 18S rDNA. A short morphological character matrix was constructed to trace character evolution along the combined molecular phylogenetic tree. The combined analyses of all three genes strongly support the monophyly of the phylum Entoprocta and a sister group relationship of Entoprocta and Cycliophora, a result which is consistent with a number of previous morphological and molecular assessments. We find evidence for two separate lineages within the Entoprocta, one lineage leading to all recent colonial taxa, Coloniales, another representing the clade of solitary entoprocts, Solitaria. Our study suggests that Loxosomella is a paraphyletic assembly with regard to the genera Loxomitra, Loxosoma, and Loxocorone. The results imply that the ancestral entoproct was a solitary, marine organism with an epizoic life style. The groundplan of the entoproct adult stage probably included a bilobed centralized nervous system, and the larva was assumedly planktonic, with a gut and a ciliated creeping sole.

A new species of Zanclea (Cnidaria: Hydrozoa) associated with scleractinian corals from Okinawa, Japan

The new species of Zanclea sango sp. nov. is described from Okinawajima Island, Ryukyu Archipelago, south-western Japan. The new hydrozoan species is associated with at least three scleractinian corals ( Pavona divaricata, P. venosa and Psammocora contigua ). Zanclea sango sp. nov. is a polymorphic hydroid and the hydrorhiza grows between the coral skeleton and calicoblastic ectoderm. The hydrocaulus and hydrorhiza are surrounded by perisarc. Newly released medusae are almost spherical, with four perradial exumbrellar nematocyst pouches including stenoteles, and two long marginal tentacles with cnidophores containing macrobasic euryteles. Zanclea sango sp. nov. is allied to Zanclea gilii Boero et al. , 2000 and Zanclea margaritae Pantos & Bythell, 2010, but it is distinguished by its cnidome, the presence of a perisarc around hydrorhiza, and lower host-specificity. According to a hypothetical Zanclea phylogeny, the ancestral species of Zanclea had an opportunistic association with some benthic organisms, such as algae or bivalves, and its hydrorhiza was covered by a perisarc. Later, some species established specific associations with benthic animals, after which the hydrorhiza lost the perisarc and became directly covered with host tissue. Among Zanclea inhabiting corals, the present species, with multiple coral host species and a perisarc around the hydrorhiza, seems to retain more ancestral character states than Z. gilii and Z. margaritae , which have specific coral host species and no perisarc around the hydrorhiza.

DNA Barcoding in Photosymbiotic Species of Diplosoma (Ascidiacea: Didemnidae), with the Description of a New Species from the Southern Ryukyus, Japan

Partial sequences of the cytochrome c oxidase subunlt I (COI) gene were determined for six species of the genus Diplosoma (Ascidiacea, Didemnidae) to develop tools for species identification. Because each Diplosoma species has distinctly different COI haplotype(s), the gene sequence seems to be usable for species discrimination in this ascidian genus. The phylogenetic hypothesis supported by the COI data is congruent with the distribution of character states of the retractor muscle. In this paper, we describe a new Diplosoma species harboring symbiotic cyanophytes, found on Miyakojima Island, Ryukyu Archipelago, Japan. Diplosoma aggregatum sp. nov. forms mosaic-like aggregates of small colonies. Although the zooids of D. aggregatum are similar to those of D. virens, these species are differentiated by colony form and COI sequences.

Early development of zooxanthella-containing eggs of the corals Porites cylindrica and Montipora digitata: The endodermal localization of zooxanthellae.

Abstract We studied the early development of zooxanthellae-containing eggs of the scleractinian corals Porites cylindrica and Montipora digitata to elucidate how zooxanthellae become localized to the endoderm of planulae during the course of development. In both species, zooxanthellae were distributed evenly in the oocytes and delivered almost equally to the blastomeres during cleavage. In P. cylindrica, gastrulation occurred via delamination or ingression, and blastomeres containing zooxanthellae dropped into the blastocoel during gastrulation. Thus, zooxanthellae were restricted to the endodermal cells at the gastrula or early planula stage in P. cylindrica. In M. digitata, gastrulation occurred by a combination of invagination and epiboly to form a somewhat concave gastrula. Zooxanthellae were present in both endodermal and ectodermal cells of early planulae, but they disappeared from the ectoderm as the planulae matured. In our previous study on two species of Pocillopora, we found that zooxanthellae were localized in eggs as well as in embryos, and that blastomeres containing zooxanthellae later dropped into the blastocoel to become restricted to the endoderm (Hirose et al., 2000). The timing and mechanism of zooxanthella localization and types of gastrulation differed among species belonging to the three genera. These results suggest that zooxanthella localization in the embryos reflects the timing of the determination of presumptive endoderm cells and/or specificity of zooxanthellae toward presumptive endoderm cells.

Timing of Spawning and Early Development of Palythoa tuberculosa (Anthozoa, Zoantharia, Sphenopidae) in Okinawa, Japan

The spawning behavior and early embryogenesis of Palythoa tuberculosa (Anthozoa, Zoantharia) were observed in August 2009 off Okinawa Island, Japan. P. tuberculosa released zygotes just after high tide around new moon nights. The mean diameter of zygotes was 365.6 ± s.d.14.8 μm, and zygotes did not contain any symbiotic algae (zooxanthellae). About 2 h after spawning, the first cleavage furrow appeared on one side of the zygotes, although it was uncertain when eggs were fertilized. After second cleavage, the arrangement of blastomeres was pseudospherical. At 9 h after spawning, the embryo became a concave-convex dish shape, then gastrulation occurred and the blastopore was formed. Seven-day old larvae were ellipsoid and about 700 μm long, with an open mouth at one end. Two weeks after spawning, the larvae developed a longitudinal band of long cilia (= ventral ciliate band) that is characteristic of zoanthella larvae. In P. tuberculosa, larvae show a non-radial body plan and then metamorphose to almost-radial (in outward appearance) polyps after settlement. These results may support a hypothesis that a common ancestor of Cnidaria had a bilateral body plan that has been secondarily lost in some extant cnidarians.

Two New Species of Photosymbiotic Ascidians of the Genus Diplosoma from the Ryukyu Archipelago, with Partial Sequences of the COI Gene

Two new species of Diplosoma are described from coral reefs in the Ryukyu Archipelago, Japan: D. watanabei sp. nov. and D. gumavirens sp. nov. Colonies of both species are green due to algal symbionts of Prochloron, which are distributed in the common cloacal cavity. Both species are characterized by the point of emergence of the retractor muscle and a unique combination of stigma numbers among the four rows of the branchial sac. There are three adhesive papillae in the embryos of D. watanabei, as in most ascidian embryos and larvae, whereas the pre-hatching embryos of D. gumavirens sp. nov. posses 12–16 adhesive papillae. Partial sequences of the cytochrome c oxidase subunit I (COI) gene discriminated the new species from each other and from congeners.

A New Genus and Two New Species of Peltogastridae (Crustacea: Cirripedia: Rhizocephala) Parasitizing Hermit Crabs from Okinawa Island (Ryukyu Archipelago, Japan), and their DNA-barcodes

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.

First records of didemnid ascidians harbouring Prochloron from Caribbean Panama: genetic relationships between Caribbean and Pacific photosymbionts and host ascidians

Two didemnid ascidians associating with cyanobacterial symbionts (Prochloron spp.) were firstly recorded from Caribbean Panama: Lissoclinum verrilli, which facultatively harboured Prochloron cells on the colony surface, and Diplosoma simile, which obligately harboured algal cells in the peribranchial and common cloacal cavities within the colonies. While L. verrilli sensu stricto has been exclusively recorded from the Bermudas and Caribbean islands, D. simile is widely distributed in tropical Indo-Pacific regions including oceanic islands such as Hawaii. Partial COI sequences of D. simile from the Caribbean were identical to those from the West Pacific, suggesting a high larval-dispersal ability and broad range of environmental tolerance. Molecular phylogenetics of the symbionts, based on 16S rRNA gene sequences, revealed that both ascidian species were associated with Prochloron, while a Synechocystis sp. sequence was also obtained for L. verrilli. In addition, L. verrilli and D. simile harboured different phylotypes within the Prochloron lineage that included symbionts from various hosts and various Pacific sites. Our results indicate that multiple phylotypes of Prochloron exist in Caribbean Panama and that considering the abundance and the number of host species in the Pacific, Prochloron and D. simile may have come from tropical Indo-West Pacific.