Aplidium hourglassum, Fortaleza & Lotufo, 2018

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 : 526-527

Aplidium hourglassum sp. n.

( Figures 8, 9 )

Etymology: Species name refers to the “Hourglass” cruises.

Examined material: Holotype: collected in 7/6/1966, 27°37’N, 084°13’W, 73.2 m, specimen #EJ-66-222.

Description: Colony of irregular format, measuring 1.8 cm x 0.4 cm, attached to the substrate by the whole basal portion. Colony surface smooth and without incrustations. Small amounts of foreign material in the matrix and base of the colony. Tunic soft, transparent and yellowish, zooids with a darker brownish coloration. Zooids not organized in systems. Presence of copepods in the tunic matrix.

The zooids may vary between 1.50–2.24 mm in length depending on the contraction state (length range–thorax and abdomen = 1.12–1.44 mm; post-abdomen = 0.32–0.80 mm). Branchial siphon very short, measuring 0.08–0.12 mm and exhibiting six rounded lobes. Atrial opening short and smooth edged, located beside the second stigmata row. Atrial languet simple and very small, maximum length of 0.20 mm. Muscles are strong, with 10 to 15 longitudinal bundles in each side of the body running in parallel along the zooid. Pharynx with 10 rows of stigmata. The number of stigmata per row could not be counted. Esophagus short. Stomach slightly squared and flattened in the anterior and posterior ends, with 25 to 30 well-defined continuous longitudinal folds. The size of the esophagus and stomach together are equal to slightly more than half of the abdomen length. Posterior stomach discernible in some zooids. Anal opening located beside the fifth row of stigmata. Abdomen and post-abdomen not separated by a constriction. Gonads developed in some zooids; however, in most zooids, gonads are poorly developed, around 15 testicular follicles organized in a double row together with six yellow ovules.

Up to three embryos and/or larvae in a single series in the posterior thorax region. Larvae up to 1.04 mm long, 11 to 16 adhesive papillae with long and thin peduncles, ampullae absent, several small epidermal vesicles distributed over the whole larva; tail wound halfway around the trunk.

Remarks. Aplidium hourglassum is distinguished by the combination of a small number of rows of stigmata, a large number of stomach folds, and numerous adhesive papillae in the large larvae. The genus Aplidium is fairly diverse, comprising about 280 valid species (WoRMS, accessed 26 September 2017). According to Kott’s review, only A. triggsense ( Kott, 1963) and A. multipapillatum ( Millar, 1975) have an uncommon number of adhesive papillae in the larvae ( Kott, 1992). The Aplidium multipapillatum , common in the China Sea, has only four to six papillae, which is much lower than the number found in A. hourglassum . ( Millar, 1975). In contrast, the larvae from A. triggsense , a common species in the waters of western Australia and New Caledonia, have seven to fourteen adhesive papillae, but are considerably smaller, measuring only 0.60 mm, and a zooid with just 15 to 16 longitudinal folds in the stomach ( Kott, 1963; Kott, 1992). Hence, both differ from A. hourglassum , which has larvae up to 1.04 mm long, 14–16 adhesive papillae, and 25–30 stomach folds. After Kott’s review in 1992, no other species with this number of papillae was described for this genus.

Figures

FIGURE 9. Aplidium hourglassum sp. n. A—zooid; B and C—larvae. Scale: A = 1 mm; B and C = 0,1 mm.