Polyzoa opuntia Lesson, 1830

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 : 171-172

Polyzoa opuntia Lesson, 1830

Fig. 12

References and synonymy: Polyzoa opuntia Lesson (1830b) p. 437; Van Name (1945) p. 236; Kott (1969) p. 100; Monniot (1970) p. 344; Polyzoa reticulata Van Name (1945) p. 237; Kott (1969) p. 102.

Localities: 1S, 2S, 4S, 7S, 8S, 9S.

This colonial species is very abundant on the artificial substrates surveyed in the Punta Arenas zone. Typically, it forms stalked colonies up to 20 cm in length and of different shapes, the larger ones being normally elongated and flattened, the smaller cylindrical or simply conical. The colour in general is reddish, although a yellow form has also been found in Cabo Negro docks (locality 7S). In the colonies the zooids are united forming a compact mass where the zooids are encased. Convex protuberances with siphons mark the different zooids from the outside. However, the species can also form investing colonies with zooids clustered closely together, or with zooids completely separated linked only by stolons.

Each cylindrical zooid can measure up to 10 mm in length, with the siphons at the apical end and, in the case of compact colonies, one or two stolons at the basal end entering the common tunic. Internally there are ca. 25 welldeveloped simple tentacles with intervening smaller ones. The aperture of the neural gland is an oblique slit. The branchial sac has 8 longitudinal vessels on each side and up to ten stigmata per mesh. The digestive forms a simple loop without secondary curvature. The stomach is folded, with a curved pyloric caecum. At the level of the caecum a strand of tissue connects the stomach with the intestine, bridging the primary loop. There is a row of hermaphrodite gonads at both sides of the endostyle (10–12 on the right, 6–8 on the left). The gonads are elongated, with a basal testis and some oocytes on top. There is a terminal female opening and a subterminal male papilla forming a slender tube. The right row of gonads curves anteriorly and dorsally in the posterior part of the body. Small endocarps are scattered at both sides of the mantle.

Remarks. the variability of colonial shapes, from clearly separated zooids to compact stalked colonies, is a characteristic of this species. The stolonial form with separate zooids has been known as Polyzoa reticulata (Herdman, 1886) , but it was later revealed to be the same species (Monniot & Monniot 1978, 1983). It is abundant in the Magellan region and the South Georgia Islands (Monniot & Monniot 1983).

Figures

FIGURE 12. Polyzoa opuntia. A, colonies; B, zooid dissected without branchial sac (stained), inset shows magnification of gonads and endocarps on the left side. Scale bars: A, 2 cm, B, 1 cm.