Aplidium fuegiense Cunningham 1871

Aplidium fuegiense (Cunningham, 1871)

Fig. 4 A–C

References and synonymy: Amaroucium fuegiense Van Name (1945) p. 43; Aplidium fuegiense Monniot (1970) p. 325; Monniot & Monniot (1983) p. 16.

Localities: 2S, 7S, 8S.

Colonies of this species are cushion-like, measuring up to 10 cm in diameter and 4 cm in height. The colour in our specimens is brownish. The zooids form wide, meandering fields separated by narrow tunic stretches without zooids. The tunic is soft but consistent, particularly the outermost layer. The relaxed zooids measure over 20 mm in length (the thorax reaches ca. 5 mm, and the abdomen ca. 4 mm).

The oral siphon is six-lobed, and the atrial aperture is relatively wide, reaching from the second to the fifth row of stigmata. It is surmounted by a short languet that can be simple or, more often, have two, three, or more points. There are between 12 and 15 rows of stigmata (mostly 13–14), with over 20 stigmata per half-row, and 15–16 fine longitudinal muscles run longitudinally through each side of the thorax. The abdomen presents a folded stomach, usually with five folds plus the typhlosole. There is a posterior stomach and an elongated mid-intestine in vertical position in well relaxed zooids. The posterior intestine ends in a bi-lobed anus just at the posterior rim of the atrial aperture. Most zooids have well-developed gonads consisting of several reddish oocytes and white male testes occupying most of the post-abdomen. The space between the posterior intestinal loop and the ovary is filled by a folded and twisted spermduct. In a few zooids, undifferentiated embryos (up to four), of reddish colour, were seen in the posterior part of the peribranchial cavity.

Remarks. this species is widely distributed in Antarctic and subantarctic waters. Most descriptions of the species report wide morphological variation, perhaps encompassing a group of ill-defined species. We did not observe the small orange-reddish bodies in the surface layer of test reported in other descriptions (Millar 1960, 1970, Sanamyan & Schories 2003), which may be regressing bodies. The convoluted spermduct between the ovary and the digestive system (Millar 1960, Monniot 1970, Monniot & Monniot 1983) may be a good diagnostic character.