Molgula pyriformis Herdman, 1881

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 : 22-23

Molgula pyriformis Herdman, 1881

References: Molgula pyriformis Herdman 1881: 236 ; Herdman 1882: 79: pl. 6, fig. 1–3; Monniot & Monniot 1976: 652–655, fig. 11–12; Monniot & Monniot 1983: 101 (part).

not Molgula malvinensis Ärnbäck-Christie-Linde, 1938: 5, pl. 1, fig. 1–3; Millar, 1960: 132, fig. 57; Kott, 1969: 149 (part); Millar, 1970: 140; Monniot & Monniot, 1983: 101.

Material examined: Seven individuals; net; -37.9951 lat. -54.6975 long. (station 7); 852 m; 11 August 2012 — Two individuals; trawl; -37.9876 lat. -54.6906 long. (station 8); 854 m; 11 August 2012 —Four individuals; trawl; - 37.9651 lat. -54.5320 long. (station 10); 1144 m; 11 August 2012 —Two individuals; net; -38.0164 lat. -54.5054 long. (station 9); 1006 m; 11 August 2012 ( Figures 13 A–B).

Individuals are spherical, olive-shaped. The mean size of the specimens was 1.2 cm long by 1.5 cm wide, and the oral and atrial apertures were separated approximately 0.9 cm from each other. The tunic is completely embedded with rests of sand and fragments of algae and sea shells. Thin and evenly distributed hair-like processes also cover the totality of the body. Once all the external material is removed, the tunic appears delicate and transparent. The oral and atrial apertures have six pointed lobes. There is a short oral velum that may be smooth or bear small papillae. Seven two-sized oral tentacles of the third order are placed in a single circle alternately with numerous minute ones. One of the bigger tentacles is situated exactly in the mid-dorsal line. The slightly undulated pre-pharyngeal band lies away from the tentacular circle. It forms a deep V that surrounds the dorsal tubercle and part of the neural ganglion. The dorsal tubercle is “funnel-shaped” ( Herdman 1881). The broad dorsal lamina has smooth margins and extends until the entrance of the esophagus. The musculature is composed of a series of strong longitudinal fibers that radiate from both apertures and extend until the mid-ventral side of the body (from 24 to 27 per aperture), two dorsal muscular bands that enclose the neural complex, thin and densely packed circular muscles, and a series of short latero-dorsal fascicles unevenly distributed. The branchial sac bears seven folds on the right side and six on the left. The stigmata are long and curved, forming spirals at the top of the infundibula. The number of infundibula per fold ranges from seven to nine and may be single or double. The branchial formula on the right side of one of the biggest specimens is:

E-0- 5 -0- 7 -0- 9 -0- 10 -0- 11 -0- 9 -0- 8 -0-DL

The short esophagus connects with a stomach completely covered with liver lobes. The intestine is long. The primary intestinal loop forms an open curve, while the secondary loop forms a semicircle that runs adjacent to the stomach. The border of the anus is smooth. There are two elongated S-shaped gonads on each side of the body. The pear-shaped testes are distributed on the margins, while the ova reside in the center. They extend until the distal bend of the primary intestinal loop, never superpassing it ( Figs 13 A–B). The oviducts are thick and long, extending almost until the atrial aperture. The vas deferens, on the contrary, is short. There is a narrow atrial velum whose margins are smooth.

Remarks. Molgula pyriformis resembles the closely related species Molgula malvinensis Ärnbäck-Christie- Linde, 1938 and Molgula occidentalis Traustedt, 1883 . According to Millar (1960), the main characteristics that separate them rely on the structure of the gonads, the shape of the intestinal loop and the dorsal tubercle opening. On the distinction between M. malvinensis and M. pyriformis, Monniot & Monniot (1976) agreed, claiming that the fundamental difference was found on the structure of the gonads (with M. malvinensis presenting more male follicles on each gonad). However, on the revision of the species ( Monniot & Monniot 1983), the authors proposed instead the synonymy of M. malvinensis with M. pyriformis . Subsequent sampling in the SW Atlantic enabled us to reject the latter proposition and support the decision of maintaining both as separate species. Taverna (2013) found six individuals which were identified as M. malvinensis in an area close to its type location ( Malvinas / Falkland Islands) and in a similar depth range (65–128 m). Additionally, all of our specimens present the characters mentioned by Millar (1960) as belonging to M. pyriformis . Our specimens were also found in an area close to the type locality of the latter (off Buenos Aires) and in a similar depth range (100–1097 m). In this way, we believe that the range of distribution of M. pyriformis is restricted to the north of the Argentine Sea, while the range of distribution of M. malvinensis extends from the south of the Argentine Sea to the north of the South Orkney Islands. Thus, the only specimen found in the Southern Ocean classified as M. pyriformis by Monniot & Monniot, 1983, might belong to M. malvinensis .

Figures

FIGURE 13. Molgula pyriformis Herdman, 1881. A: right gonad; B: left gonad.