Tunic Cell Morphology and Classification in Botryllid Ascidians(Morphology)

The morphology of tunic cells was investigated in ten botryllid ascidians, six Botryllus and four Botrylloides species, by means of light and electron microscopy. Three types of tunic cells were described, I.e. amoeboid, vacuo-granular and large granule tunic cells. Amoeboid tunic cells were irregularly shaped, and had many pseudopodia. They were found in the all species studied here. Vacuo-granular tunic cell had many vacuoles which contained round granules, and was found in four Botryllus and four Botrylloides species. The diameters of the granules varied amond species (ca. 1.4-0.8 ^m). Large granule tunic cells were peculiar to Botryllus scalaris, and each of them contained a single large granule with lamellate substructure. Some tunic cells showed intermediate characteristics of amoeboid and vacuo-granular tunic cells. It seems that amoeboid tunic cells probably differentiate into vacuo-granular tunic cells in the tunic. There are thread-like bacteria in the tunic, and they often dangle around vacuo-granular tunic cells. There may be some interactions between tunic cells and the bacteria

Algivore or phototroph?: Plakobranchus ocellatus (Gastropoda) continuously acquires kleptoplasts and nutrition from multiple algal species in nature

The sea slug Plakobranchus ocellatus (Sacoglossa, Gastropoda) retains photosynthetically active chloroplasts from ingested algae (functional kleptoplasts) in the epithelial cells of its digestive gland for up to 10 months. While its feeding behavior has not been observed in natural habitats, two hypotheses have been proposed: 1) adult P. ocellatus uses kleptoplasts to obtain photosynthates and nutritionally behaves as a photoautotroph without replenishing the kleptoplasts; or 2) it behaves as a mixotroph (photoautotroph and herbivorous consumer) and replenishes kleptoplasts continually or periodically. To address the question of which hypothesis is more likely, we examined the source algae for kleptoplasts and temporal changes in kleptoplast composition and nutritional contribution. By characterizing the temporal diversity of P. ocellatus kleptoplasts using rbcL sequences, we found that P. ocellatus harvests kleptoplasts from at least 8 different siphonous green algal species, that kleptoplasts from more than one species are present in each individual sea slug, and that the kleptoplast composition differs temporally. These results suggest that wild P. ocellatus often feed on multiple species of siphonous algae from which they continually obtain fresh chloroplasts. By estimating the trophic position of wild and starved P. ocellatus using the stable nitrogen isotopic composition of amino acids, we showed that despite the abundance of kleptoplasts, their photosynthates do not contribute greatly to the nutrition of wild P. ocellatus, but that kleptoplast photosynthates form a significant source of nutrition for starved sea slugs. The herbivorous nature of wild P. ocellatus is consistent with insights from molecular analyses indicating that kleptoplasts are frequently replenished from ingested algae, leading to the conclusion that natural populations of P. ocellatus do not rely on photosynthesis but mainly on the digestion of ingested algae

Photosymbiotic Ascidians from Nakanoshima Island and Takarajima Island (the Tokara Islands, Ryukyu Archipelago, Japan) with Remarks on the Status of Diplosoma midori (Tokioka, 1954)*

We studied the fauna of photosymbiotic ascidians in the shallow reef shore of the Tokara Islands. We collected Lissoclinum bistratum, L. punctatum, Trididemnum clinides, T. cyclops, T. sp. (cf. T. paraclinides), Diplosoma ooru, D. simile, D. simileguwa, D. virens, D. sp. A, and D. sp. B (cf. D. multipapillatum) from four sites off Nakanoshima Island and one site off Takarajima Island. Diplosoma midori (Tokioka, 1954) is a photosymbiotic ascidian that was originally described from Nakanoshima Island and Takarajima Island. Although there is argument as to the taxonomical status of this species, the conditions of the syntype specimens were inadequate for examining detailed features for identification. Based on the topotype specimens from Takarajima Island, we concluded that D. midori should be regarded as an invalid species, and is a junior synonym of D. simile or D. virens

A New Sponge-Inhabiting Loxosomella (Entoprocta: Loxosomatidae) from Okinawa Island, Japan, with Special Focus on Foot Structure

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

Differences in Associated Crustacean Fauna and Seasonality of Sexual Reproduction between Two Color Morphs of the Photosymbiotic Ascidian Didemnum molle (Ascidiacea: Didemnidae).

v. ill. 23 cm.QuarterlyPhotosymbiotic ascidians inhabiting subtropical waters tend to have gonads in spring and summer, whereas those in tropical waters are usually sexually mature year-round. We studied the seasonality of sexual reproduction in two populations of the photosymbiotic ascidian Didemnum molle (Herdman, 1886), sampling monthly for 12 months. Although the two populations were located only about 20 km apart, their color morphs were exclusively distributed: colonies of one population were always dark gray; those of the other population were mostly brown. The seasonality of sexual reproduction differed greatly between the populations (and thus between the color morphs). Sexual reproduction was limited to summer in the population with dark gray colonies, whereas the population with brown colonies possessed embryos with tails almost yearround. Moreover, the resident crustacean fauna in the colonies also differed between the populations. The microenvironment in each habitat may have caused these differences, but there may also be some physiological differences between the color morphs that affect the seasonality of sexual reproduction and the resident crustacean fauna

FIGURE 2 in Pattern of stigma numbers as a taxonomic character in some didemnid ascidians (Aplousobranchia: Didemnidae)

FIGURE 2. Component ratio of stigma patterns in the five morphotypes of Didemnum molle. Black indicates the eight stigma patterns found in all morphotypes; gray indicates the patterns shared in two to four morphotypes; white indicates the patterns unique to one morphotype.Published as part of <i>Nagaya, Kazuhiko & Hirose, Euichi, 2013, Pattern of stigma numbers as a taxonomic character in some didemnid ascidians (Aplousobranchia: Didemnidae), pp. 87-93 in Zootaxa 3608 (1)</i> on page 90, DOI: 10.11646/zootaxa.3608.1.7, <a href="http://zenodo.org/record/10096963">http://zenodo.org/record/10096963</a&gt