Aplidium peruvianum Sanamyan & Schories, 2004

Turon, Xavier, Cañete, Juan I., Sellanes, Javier, Rocha, Rosana M. & López-Legentil, Susanna, 2016, Ascidian fauna (Tunicata, Ascidiacea) of subantarctic and temperate regions of Chile, Zootaxa 4093 (2), pp. 151-180 : 160

Aplidium peruvianum Sanamyan & Schories, 2004

Figs. 5 , 10 A

References and synonymy: Aplidium peruvianum Sanamyan & Schories (2004) p. 193.

Localities: 1N, 6N.

The colonies form thick encrusting sheets, reaching tens of cm in the largest dimension and up to 2 cm in thickness. Several colours have been found, the commonest being beige-brownish. However, whitish, yellowish and reddish colonies are also observed. In all cases the colony organisation consists of circular zooid systems with one common cloacal aperture placed in depressions of the colony surfaces and separated by elevated ridges of tunic. Sometimes the systems are elongated with more than one aperture. The tunic is strong and consistent. In reddish colonies the colour is intense in the zooid systems (with pigment concentrated in the thoraces) and fades in the ridges in-between.

The zooids reach 11 mm in length; the thorax measures up to 2.5 mm and the abdomen up to 2 mm. The thorax has a six-lobed oral siphon, and a narrow atrial opening facing the first two stigmata rows. There is an undivided atrial languet in the anterior rim of the aperture. When the zooids are contracted, minute denticulations are visible in the posterior part of the atrial aperture. There are from 11 to 14 stigmata rows (most often 12–13), with 15–20 slits per half-row. At each side of the branchial sac there are 14–16 fine longitudinal muscular bands.

The abdomen has a stomach with many ridges (up to 18–20). They are difficult to count as they are often interrupted, sometimes even substituted by irregular protuberances more or less aligned (particularly so on the side facing the intestine). There is a post-stomach and a mid-intestine in oblique or horizontal position at the lower end of the gut loop. The posterior intestine opens in a bi-lobed anus at the level of the fifth or sixth posterior-most stigmata row.

Some zooids have well-developed gonads, with oocytes adjacent to the digestive loop and male follicles filling the post-abdomen. There are also embryos in incubation in the atrial cavity, up to 6 of them more or less in a row. In red colonies, the oocytes and immature embryos are red in colour. Fully developed larvae are elongated, up to 1 mm in trunk length, and bear three adhesive papillae. There are four clusters of small vesicles. Two between the papillae, one dorsal and one ventral. The vesicles of each cluster seem to arise from a common stem.

Remarks. the species was described from Peru (hence its name) in 2004, and was later reported from the Coquimbo area in Chile (Sanamyan et al. 2010). This is the third finding of this species, which is well characterised by the colony aspect, stomach and larval morphology.

Figures

FIGURE 5. Aplidium peruvianum. A, colony; B, thorax; C, stomach; D, larva. Scale bars: A, 2 cm, B, 0.5 mm, C, 0.2 mm, D, 0.2 mm.

FIGURE 10. Polyzoa iosune. A, image of a colony carpeting the substrate and overgrowing Aplidium peruvianum (whitish masses) exposed at low tide; B, close-up of the apical part of the zooids; C, mantle of two zooids, vision of the right side (left of the image) and ventral vision (right of the image); D, dissected zooid; E, same zooid without branchial sac; F, G, details of the branchial sac; H, close-up of hermaphrodite gonads from the right side of the zooid (endostyle is towards the upper-left of the image); I, larva. Images D – H are of stained material. Scale bars: A, 5 cm, B, C, 5 mm, D, E, 2 mm, F, 1 mm, G, 0.2 mm, H, 1 mm, I, 0.2 mm.