Aplidium stellatum ( Verrill, 1871 )

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 : 52-54

Aplidium stellatum ( Verrill, 1871)

( Figures 3 , 4 A,B)

Amouroucium stellatum Verrill, 1871: 291 .

Amaroucium stellatum: Van Name, 1945: 34 (and synonymy)

Material examined: collected in 2004, 31°36.056' N, 80°47.431' W, specimen #240 ( KBPIG 1/1233); 24.05.2005, 31°23.815' N, 80°53.462' W, specimen #1 ( KBPIG 2/1243).

Previous records: The species has already been recorded from Georgia and is widely distributed from Massachusetts to the Gulf of Florida ( Van Name 1945).

Description. Several fragments up to about 5 cm in their largest dimension were examined. Underwater photographs show robust colonies that are large and thick (up to about 20 cm in width and length) that are attached to hard substratum by a wide basal surface ( Figure 2 A). Colonies are irregularly lobed and folded; the test is firm and hard to the touch. Zooids are in regularly spaced circular, oval, or sometimes slightly elongated systems and open into the base of the test depressions. The depressions on living specimens are bright red and contrast with the white or pinkish test that separates them. In preservative the test is pinkish and zooids (especially their thoraxes) still retain their bright red colour even after three years of storage in formalin.

Most zooids are contracted, the thorax and abdomen together are 3–5 mm long, and the posterior abdomen may reach 10 mm. The branchial siphon has six short rounded lobes. A short atrial languet extends from the upper rim of the atrial aperture and has a simple blunt tip. About 15 thin longitudinal muscles are on each side of the thorax. The branchial sac has 14 (one colony) or 12 (another colony) rows of stigmata of about 15 stigmata per half row. The abdomen is relatively short; in the rare zooid that is more or less expanded, it is shorter than the thorax. The barrel shaped stomach has nine or ten well marked folds which may be regular and undivided, or occasionally broken ( Figure 4 A). In many zooids the posterior abdomen is filled with numerous closely packed testis follicles distributed along the whole of its length. A few large ova are in the middle part of the posterior abdomen.

Up to five larvae are in the atrial cavity of many zooids. The trunk of tailed larvae is 1–1.1 mm. Larvae have three adhesive organs and four thick median ampullae, the latter are not always well developed. Epidermal vesicles are in four bunches, one on each side of the dorsal and ventral mid-lines behind the adhesive organs ( Figure 4 B).

Remarks. The colony shape and colour, and the hardness of the test allow easy identification of this species and confusion with other Aplidium species in the region is hardly possible.

Aplidium peruvianum Sanamyan & Schories, 2004 described from Peru has almost identical colonies and similar zooids. It has slightly smaller larvae with anterior bunches of epidermal vesicles which are not present in the examined specimens of A. stellatum . Synonymy between Pacific and Atlantic species is unlikely.

Figures

FIGURE 3. Aplidium stellatum. A—underwater; B—formalin preserved colony.