Aplidium variabile ( Herdman, 1886 )

Maggioni, Tamara, Taverna, Anabela, Reyna, Paola B., Alurralde, Gastón, Rimondino, Clara & Tatián, Marcos, 2018, Deep-sea ascidians (Chordata, Tunicata) from the SW Atlantic: species richness with descriptions of two new species, Zootaxa 4526 (1), pp. 1-28 : 5

Aplidium variabile ( Herdman, 1886)

References: Amaroucium variabile Herdman 1886: 216 , pl. XXIX, fig. 7–12. Aplidium variabile Millar, 1960: 32 , fig. 2B; Monniot & Monniot 1983: 30 (synonymy); Sanamyan & Schories 2003: 92, fig. 1B, 2E–F; Lagger et al. 2009: 178, fig. 2C.

Material examined: one colony; net; -37.9942 lat. -55.2175 long. (station 1); 250 m; 10 August 2012.

The only colony found is small and irregular in shape, with half of its side slightly convex and the other half plane. It measures 1.8 cm long by one cm wide and 0.4 cm thick. The tunic is smooth and transparent. Zooids are orange when alive and dull yellow after fixation in formalin. They are arranged parallel to each other.

Zooids reach an average of 2.5 mm in length, with the post-abdomen comparatively shorter than most Polyclinidae (from 0.8 to 1.6 mm). However, this feature might be related to the state of sexual maturation of the present colony. The small atrial aperture is located at the level of the third, fourth or fifth row of stigmata. The atrial languet is simple, short and triangular.

There are ten to 12 thin longitudinal muscles on each side of the zooid. The thorax bears 12 rows of stigmata. Each half row contains from 12 to 16 stigmata.

The stomach has from 12 to 14 well-marked folds. The middle intestine forms a middle-sized posterior swelling. The border of the anus is smooth and it can end at the level of the ninth, tenth or eleventh row of stigmata.

All zooids showed scarcely developed gonads. No larvae were found.

Remarks. Aplidium variabile is a common eurybathic species collected from 20 down to 1097 m depth ( Herdman 1886). Its known range of distribution is Circum Sub-Antarctic, with the majority of its records around the Magellan Strait. This is the second record for the type locality (off Mar del Plata, Argentine Sea), since its discovery during the Challenger expedition.