Aplidium ruzickai, Sanamyan, Karen & Gleason, Daniel F., 2009

Sanamyan, Karen & Gleason, Daniel F., 2009, Ascidians of the genus Aplidium collected on shallow hard-bottom reefs of coastal Georgia (Atlantic coast of N America, U. S. A.), Zootaxa 2066, pp. 50-58 : 54-57

Aplidium ruzickai n. sp.

( Figures 5 , 6)

Material examined: Holotype: collected in 2004, 31°37.688' N, 80°34.662' W, specimen #192 ( KBPIG 1/ 1380). Paratypes: specimens #181 ( KBPIG 3/1382) and #182 ( KBPIG 4/1383) both collected at 31°24.305' N, 80°34.010' W; #197 ( KBPIG 2/1381) collected at 3137.688' N, 80°34.662' W.

Description. The colonies are thick, massive, sometimes rather irregular and are divided into large lobed cushions that are attached by a wide base. The largest examined specimen (a part cut from a larger colony) is about 6 cm in maximum dimension and 3.5 cm thick. The test is soft, gelatinous, transparent and free from sand on the surface and inside. The surface is characterized by round, raised, branched ridges separated by shallow depressions of double rows of zooids. The systems are large and not numerous and are formed by short and long, sometimes branched, double rows of zooids converging to a common cloacal opening. The limits of each system are discernible on the living specimens ( Figure 5 C), but are obscured in formalinpreserved material. In preserved colonies, the zooid free ridges of the test become more prominent and the systems appear as deep narrow grooves between these ridges. Zooids open inside these grooves so that the openings are not visible from the surface. The living specimens are either uniformly opaque milky-white ( Figure 5 C), or with whitish branched systems separated by translucent red ridges ( Figure 5 A); preserved specimens are colourless.

The zooids are long and narrow, not contracted. The thorax and abdomen together are about 6 mm long, and the posterior abdomen is 5–10 mm or sometimes longer. The branchial siphon is short and wide and has six rounded lobes. A small round sessile atrial opening is noticeably displaced downward along the dorsal side and is on the same level as the fifth or sixth row of stigmata. A simple short and blunt atrial languet arises from the upper rim of the atrial opening. The stigmata are in 19 (KBPIG 1/1380, 2/1381) or 17 or 18 (KBPIG 3/1382, 4/1383) rows of 11–15 per row. The oesophagus is long and the stomach, located half-way down the abdomen, has about 30 narrow and rather regular straight folds. The post-pyloric portion of the intestine is typical for the genus with the duodenum, posterior stomach and rectal valves discernible in some zooids. The anal opening is opposite the 14th or 15th row of stigmata. There is a slight constriction between the abdomen and posterior abdomen. Relatively large male follicles occupy either the entire or only the posterior part of the posterior abdomen and are in single or double series. A compact ovary consisting of one or two large ova and a number of smaller ones is either anterior to the testis and some distance from the gut loop ( Figure 6 A), or between the testis follicles in the middle part of the posterior abdomen.

Up to six or seven embryos and larvae are in a single series in the posterior half of the thorax. A trunk of the tailed larva is 0.75–0.9 mm long with the tail winding slightly more than halfway around it. It has three adhesive organs on long stalks alternating with short median ampullae with clusters of large epidermal vesicles branching off of them. A bunch of epidermal vesicles is also present on each side of the dorsal and ventral mid-lines. No ampullae are posterior to the dorsal and ventral adhesive organs.

Remarks. The most distinctive feature of the species is the combination of large numbers of stomach folds and large numbers of rows of stigmata. The genus currently contains about 235 valid species, of which only five have a combination of numerous (more than 20) stomach folds and numerous (more than 17) rows of stigmata. These include the Atlantic A. pellucidum (Leidy, 1855) , Pacific A. japonicum ( Tokioka, 1949) and A. propinquum ( Van Name, 1945) , Antarctic A. loricatum (Harant & Vernieres, 1938) , and, probably, Mediterranean A. gelatinosum ( Médioni, 1970) . All these species are separated from the present record geographically and differ from Aplidium ruzickai n. sp. in many features: A. pellucidum and A. propinquum have completely different sandy colonies, A. japonicum has a trifid atrial languet and the larva seems to be different ( Tokioka, 1949, Plate 1.), A. loricatum has ovoid dome-shaped colonies with a smooth surface and double rows of zooids converging to a few cloacal apertures on the upper surface. Aplidium gelatinosum is insufficiently described, but the number of stomach plications, while not specified, appears to be less than in the present species and the larva is different ( Médioni, 1970, Plate 6).

The present species is not related to any West Atlantic species of which only A. pellucidum (discussed above), A. constellatum ( Verrill, 1871) and A. exile (Van Name, 1902) may have more than 20 stomach folds (but still less than 30 in the present species). The colonies of A. constellatum are "ovate or more or less turbinate in form, attached by a narrow base" ( Van Name, 1945: 38), and it has only 10–13 rows of stigmata and different larva ( Monniot F, 1983). Aplidium exile has 12–14 rows of stigmata and much smaller, button shaped colonies. Aplidium bermudae (Van Name, 1902) may have up to 17 rows of stigmata but only 10–15 stomach folds and its colony is different.

The shape of the colony surface of Aplidium n. sp. is stable and characteristic but not unique and resembles A. cerebrum Monniot, 2001 , A. lenticulum Kott, 1992 , A. multiplicatum Sluiter, 1909 and some other species (see Kott, 1992, Plate 13f, 14e, Monniot and Monniot, 2001, Fig.112B). All these species have different zooids.

The species is named after Rob Ruzicka to aknowledge his contribution in establishing the collection of benthic invertebrates of Gray’s Reef National Marine Sanctuary housed in the Department of Biology at Georgia Southern University.

Figures

FIGURE 5. Aplidium ruzickai n. sp. A—specimen KBPIG 4 / 1383 (freshly collected); B—formalin preserved specimen; C—holotype KBPIG 1 / 1380 (underwater).