Aplidium constellatum (Verrill, 1871)

Fortaleza, Maria Tarciana Vieira & Lotufo, Tito Monteiro Da Cruz, 2018, Polyclinidae (Ascidiacea: Aplousobranchia) from the Gulf of Mexico, collected during the “ Hourglass ” cruises (1965 - 1967), Zootaxa 4422 (4), pp. 519-536 : 524-525

Aplidium constellatum (Verrill, 1871)

(Figuras 6, 7)

Amaroucium constellatum Verrill, 1871a: 359 .

Aplidium constellatum Monniot, 1983: 414 (and synonymy). Examined material: collected in 15/11/1967, 26°24’N, 083°43’W, 73.2 m, specimen # EJ-67-354.

Description: The colony is formed by two lobules with rounded borders, 1.9 cm and 4.9 cm high, stemming from a broad base with some sediment included. Tunic cream colored with a soft gelatinous consistency. Colony surface sediment free and very irregular with undistinguished zooids systems.

Zooids slender and contracted with average length of 7.30 mm (length range–thorax plus abdomen = 1.54–2.24 mm; post-abdomen = 3.8 4–6.60 mm). Branchial siphon between 0.13–0.16 mm and six rounded lobes. Atrial opening located between the third and fourth rows of stigmata, slightly rounded and relatively broad when compared with species of the same genus. Atrial languet is simple and very short, up to 0.21 mm long. Around 20 muscular bundles, longitudinal and parallel, reaching the post-abdomen. Pharynx with 13 to 14 stigmata rows. It was not possible to observe the number of stigmata on each side. Very short esophagus. Stomach strongly flattened in the anterior and posterior ends, with 22 to 25 longitudinal continuous or interrupted folds. The stomach and esophagus size together is equal to almost half the length of the abdomen. Posterior stomach present. Anal opening located between the height of the eight and tenth stigmata rows. Abdomen and post-abdomen without a constriction between them. Gonads were well developed in the zooids, and testicular follicles could occupy nearly all postabdomen. Ovary located near the intestinal loop, composed of oocytes with different sizes. The posterior portion of the thorax may hold up to two embryos. Larvae up to 0.64 mm in length and a tail wound less than halfway around the trunk, three adhesive papillae with long and thin peduncles, without conspicuous ampullae, and few epidermal vesicles distributed in the anterior portion of the trunk.

Remarks. The original description of Aplidium constellatum is fairly succinct; however, later descriptions included the presence of 10 to 13 rows of stigmata ( Van Name, 1945; Monniot, 1983). Some of the zooids in the Gulf of Mexico material had 14 stigmata rows, but we do not believe this discrepancy is within the expected range. The number of folds in the stomach described here coincided with those observed by Van Name (1945). In contrast, Monniot (1983) observed only 15 to 20 longitudinal folds in the stomach, pointing to a larger variation of this feature for this species.