Pelonaia quadrivena n. sp. a case of bipolarity in Ascidiacea Author Monniot, Françoise text Zootaxa 2011 2833 41 48 journal article 10.5281/zenodo.201828 f2668c4c-0ffc-4736-bbc0-c627820abd4e 1175-5326 201828 Pelonaia quadrivena n. sp. (Figures 1,2,3,4A) Material. REVOLTA 2010, Terre Adélie, Pointe Géologie, 66°6726 S–139°916817 E, 52m . ( MNHN PEL 2). Etymology. In latin: quadrivena = four veins. The single specimen, 6cm long and 3.5 cm in diameter, is egg-shaped and brown when alive ( Fig. 1 ). The body is erect above a solid base made of a mass of agglomerated sediment containing varied epibionts. Both siphons are apical, close together and slightly protruding. The surface of the thin tunic is bare with a pavement design made of criss-crossed ridges ( Fig. 1 ); this aspect is not due to contraction, the internal layer is smooth. The longitudinal and transverse muscular fibres are dense in a continuous layer making the body wall opaque. About 40 simple oral tentacles in 3 orders of size form an anterior ring. The peri-pharyngeal band, in a single rod, draws a wide dorsal indentation. The dorsal tubercle opens in a U-shaped slit. The dorsal lamina is a tall smooth-edged membrane ( Fig. 2A). The branchial sac ( Figs 2 A, 3A) occupies the whole internal volume of the body. It is made of a flat tissue loosely attached to the body wall by thin connections. About 95 rows of elongates stigmata have been counted which are generally crossed by parastigmatic vessels ( Fig.3 A). There are 4 thick longitudinal vessels on each side ( Fig. 2 A). Anteriorly, these longitudinal vessels join the peripharyngeal band and fused to it; posteriorly they reach independently the oesophagus entrance. The transverse vessels alternate in 3 orders of size ( Fig. 2 A). The digestive tract is not included into the body wall, but loosely attached to it by bridles ( Fig. 2 B). The oesophagus is narrow and long. The voluminous stomach is barrel-shaped ( Figs 2 A, 4A); its wall is internally plicated with 14 folds counted on its mesial side. No caecum is present. A particularly strong ligament attaches the ventral side of the stomach to the body wall ( Figs 2 A, 4A). The first part of the intestine is applied against the whole length of the stomach and then curves at the oesophagus level to follow the dorsal body line. The anus is fringed with round lobes. There is one U-shaped gonad on each side with the ventral branch shorter than the dorsal one ( Figs 2 A, 4A). The ovary is linear covered along its length by dense masses of round male vesicles. The sperm duct follows the ovary opening in a short tube close to the female papilla. The left gonad is partially located between the stomach and the body wall ( Fig. 4A ). Some endocarps are irregularly distributed on the body wall ( Figs 2 A, 4A).At the base of the atrial aperture the body wall bears a triangular line of ramified tentacles ( Figs. 3 B, 4A)). The internal lining of the atrial siphon also has tentacles, less and less ramified towards the rim of the aperture. FIGURE 1. Pelonaia quadrivena n. sp. Holotype photo taken on the deck and detail of the tunic surface. Scale bar = 2cm. FIGURE 2. Pelonaia quadrivena n. sp. A: branchial sac. B: body ventrally opened. FIGURE 3. Pelonaia quadrivena n. sp. A: branchial tissue between 2 longitudinal vessels. B. atrial tentacles. FIGURE 4. A: Pelonaia quadrivena n. sp. body ventrally opened. B: Pelonaia corrugata body ventrally opened. Scale bars A = 2cm; B = 1cm. Pelonaia quadrivena has numerous common characters with Pelonaia corrugata Goodsir & Forbes 1841 , the single species of the genus until now. The generic characters include: an elongate body, a branchial sac without folds, one hermaphrodite gonad on each side U-shaped and made of a central ovary edged with numerous male vesicles, a long stomach with longitudinal folds. In spite of its large size, Pelonaia quadrivena n. sp. was never collected during other cruises to Terre Adélie (CEAMARC expedition, Monniot et al. 2011 ) or previous surveys around other antarctic sectors (Ross Sea, Antarctic Peninsula, Weddell sea, Enderby Land). This species is likely to be endemic of the Pointe Geologie archipelago. The other ascidians of the REVOLTA program have all a peri-antarctic distribution and confirm the general opinion of a low percentage of sector endemism ( Primo & Vazquez 2009 )