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Lissoclinum punctatum is a colonial ascidian that harbors the symbiotic prokaryotic alga Prochloron in its tunic and in the peribranchial and common cloacal cavities. Most symbiotic cells in the tunic are intracellular (tunic phycocytes), while those in the cavities are extracellular. We found that neither gametes nor embryos brooded in the tunic were associated with photosymbionts. We determined that algal cells attach to posterior parts of the trunk of hatching larvae swimming in the common cloacal cavity. No symbiont cells were found intracellularly in larval tissues. Thus, extracellular Prochloron cells in the cloacal cavities were transferred to the larvae, but intracellular photosymbionts in the tunic were not. The intracellular symbiosis must be reestablished in each generation after larval settlement. [ABSTRACT FROM AUTHOR]

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 end e unique combination of stigma numbers among the four rows of the branchial sac. There are three adhesive pepillae 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. [ABSTRACT FROM AUTHOR]

Lissoclinum timorense is a colonial ascidian that harbors the prokaryotic alga Prochloron. The algal photosymbionts adhere to the lamellae of the tunic on the posterior half of the trunk of larvae, which aggregate in the common cloacal cavity of the mother colony. Bead-adhesion tests demonstrated that the lamellae are adhesive, whereas the anterior half of the larval trunk is not. The anterior half is covered with a thin layer of outer tunic, which probably prevents Prochloron cells from attaching and interfering with sensory receptors and adhesive organs. The larval structures and the mode of algal transmission between generations are very similar to those of the Prochloronharboring ascidian Didemnum molle. Molecular phylogenetic analyses have suggested that photosymbiosis was independently established in each genus, and thus the apparent similarity in the larvae probably resulted from convergence. The distribution pattern of photosymbionts is probably more determinative of algal transmission than phylogenetic constraints. [ABSTRACT FROM AUTHOR]

A new solitary entoproct, Loxosomella plakorticola sp. nov., was found on a sponge, Plakortis sp., on a coral reef slope on the western coast of Okinawa Island, Ryukyu Archipelago, Japan. This species has a medium-sized body (up to about 1.2 mm), slender proportion (the stalk is 0.83-1.76 times longer than the calyx), a slug-like foot with a foot gland and foot groove, and 14 to 18 tentacles. Small black pigment granules are visible only in the living stage in the calyx, stalk, and buds. This is the first report of a commensal loxosomatid from the Ryukyu Archipelago and the second species inhabiting sponges reported from Japan. Detailed morphological observations indicate that this species attaches to sponges by narrowing the foot groove; the sponge surface is pinched in the deepest part of the groove, which is free of the cuticle layer but covered by microvilli of epidermal cells. The accessory cells lining the foot groove have long been believed to be gland cells, but they are not gland cells in ultrastructure, at least in this species. [ABSTRACT FROM AUTHOR]

Didemnum molle is a colonial ascidian that harbors the prokaryotic photosymbiont Prochloron in its cloacal cavity. Colonies occur over a relatively wide bathymetric range (approximately 0-30 m), and colony color is widely variable, partly depending on depth. Colonies in shallow sites are bright white, with densely distributed spicules, and often with brown or dark gray pigmentation, while colonies in deeper sites are less pigmented, with sparsely distributed spicules. Didemnum molle colonies contain mycosporine-like amino acids (MAAs) as UV-absorbing substances. These include mycosporine-glycine, shinorine, and porphyra-334. Among colonies from 5-, 10-, 15-, and 20-m depths, the concentration of total MAAs was significantly high at 10 m and low at 20 m. Colonies at 10 m need to maintain low spicule densities to have enough photosynthetically active radiation (PAR) to maintain the photosymbionts, and they probably concentrate MAAs to block UV radiation without attenuating PAR. Because high levels of PAR cause photoinhibition of photosynthesis, spicules and pigment cells would be more effective for photoprotection in shallow water. Colonies of D. molle may adjust the light conditions for photosymbionts by combining MAAs, spicules, and pigment cells in varying amounts. [ABSTRACT FROM AUTHOR]