Pseudopotamilla platensis Hartman 1953, new combination

Pseudopotamilla platensis (Hartman, 1953), new combination

( Figs 25–27, 33 C)

Potamilla platensis Hartman, 1953: 53 –54, fig. 19a–f.

Potamilla reniformis.— Rullier & Amoreux 1979: 191.

Potamilla (Pseudopotamilla) reniformis.— Augener 1931: 311.

Material examined. ARGENTINA, UANL 8104: Mar del Plata, Playa Grande, 38°01’30”S, 57°31’41”W, rocky intertidal, February 1965, coll. J.M. Orensanz, 1 specimen; UANL 8105: Campaña R/V Almirante Saldanha, Sta. 2287, shelf off Mar del Plata, 38°05’S, 56°43.5’W, 67 m depth, 16 November 1969, 1 specimen; UANL 8107: Campaña SAO II, Golfo de San Matías, St. 125, 41°42’S, 64°52’W, 70 m depth, 3 May 1971, 1 specimen. URUGUAY, UANL 8108: R/ V Walther Herwig 15, St. 234, 35°14’S, 52°28’W, 200 m depth, 12 June 1966, 2 specimens; UANL 8109: Campaña Akademik Knipovich, St. 1054, 35°56.5’S, 54°15.7’W, 58–65 m depth, 1967, coll. V.N. Semenova & V. Scarabino, 1 specimen; UANL 8110: St. 1059, 35°25.9’S, 53°27.9’W, 80– 72 m depth, 1967, coll. V.N. Semenova & V. Scarabino, 1 specimen.

Redescription. Trunk length 12–16 mm, width 2 mm. Branchial crown length 10 mm, with 14 pairs of radioles. Eight–12 thoracic and 48–62 abdominal segments. Radiolar flanges and palmate membrane absent. Long pinnules arranged in two alternating rows, decreasing in length distally; radiole tips short, as long as space of two pinnules (Fig. 26 A). Compound eyes located proximally in dorsal radioles, except for dorsal-most pair; unequal in size within same radiole: radiole 2 (2–3 eyes), radiole 3 (2–3 eyes) (Fig. 25 H, I). Branchial lobes short, with dorsal and ventral flanges: dorsal pair triangular (Fig. 25 A, C, E), ventral pair rounded (Fig. 25 D). Collar with dorsal margins fused to faecal groove; mid-dorsal collar margins long, triangular extending to base of radioles and covering one-half of branchial lobe dorsal flanges (Fig. 25 A–C); dorso-lateral v-shaped incisions. Anterior peristomial ring partially exposed dorsally (Fig. 25 B). Ventral lappets even, divided mid-ventrally by a depth incision (1/2 of the collar length). Dorsal lips triangular, erect, with radiolar appendages (Fig. 26 B); ventral lips short, broadly triangular. Ventral sacs present. Ventral shield of chaetiger 1 entire, rectangular with anterior margin rounded (Fig. 25 D). Chaetiger 1 notochaetae in two rows, broadly-hooded. Other thoracic shields rectangular but divided transversely (Fig. 24 D, F). Second thoracic segment with pair of large, whitish glandular areas dorsolaterally (Fig. 25 A, C, G). Thoracic neuropodial tori separated from ventral shields by broad gap (Fig. 25 D). Superior notochaetae elongate narrowly-hooded; inferior thoracic chaetae paleate, arranged in two rows, with long and pointed mucro (Fig. 27 A). Thoracic neuropodia with avicular uncini with several rows of small and similarlysized teeth above main fang; breast well developed (Fig. 27 B), handles long, three times the length of main fang. Companion chaetae with asymmetrical membranes and long handles, slightly longer than uncini handles (Fig. 27 B, C). Abdominal neurochaetae elongate broadly-hooded (Fig. 27 D). Notopodia with uncini with several rows of teeth above main fang along two thirds of its length, breast well developed, handles short (Fig. 27 E). Posterior abdomen narrow (Fig. 26 D, E). Pygidium bilobed, eyes absent (Fig. 26 D, E). Internal layer of tube translucent, chitinous; external surface covered by sand grains.

Type locality. North Argentina (37°15’S, 56°8’W), 100 m depth.

Remarks. In this study, Potamilla platensis is shown to belong to Pseudopotamilla, as it has unpaired compound eyes in dorsal radioles and flanges on bases of branchial lobes.

Pseudopotamilla reniformis (Bruguière, 1789) was reported by Augener (1931) as Potamilla (Pseudopotamilla) reniformis, from near Golfo de San Matías (42°17’S, 62°20’W), and Rullier & Amoureux (1979) reported Potamilla reniformis collected from 18–132 m depth at platforms off Brazil, Uruguay and Argentina. In this study, we consider records by Augener (1931) as belonging to P. platensis because tubes, eye distribution and collar described by that author agree with those present in P. platensis. According to João Nogueira, pers. com. (Universidade de São Paulo), records by Rullier & Amoureux (1979) from Brazil cannot be assigned to P. platensis.

For comparative purposes, we used images of Pseudopotamilla reniformis from the White Sea, kindly shared by Glafira Kolbasova (Moscow State University) from adult forms, not exhibiting regeneration. The most distinctive features between P. platensis and P. reniformis is the presence of two large, dorsal glandular areas on chaetiger 2 (absent in P. reniformis); presence of 2–3 eyes only on radioles 2 and 3 (1–2 eyes on radioles 2 to +8 radioles in P. reniformis); mid-dorsal collar margins triangular and long (rounded and short in P. reniformis); and ventral lappets of collar even, divided by a depth incision (rounded, divided by a short incision in P. reniformis) (Table 4).

Since its original description, there are no new records of Pseudopotamilla platensis, although Obenat et al. (2001) recorded? Potamilla sp. cf. P. platensis in an ecological survey about 11–12 m depth, in aggregations of Phyllochaetopterus socialis Claparède, 1869, near the Rio de la Plata mouth (35°23′– 35°31′S; 55°36′W - 55°48′W).

Differences between P. polyopthalma and P. platensis are the following: mid-dorsal collar margins are short, distally rounded in P. polyopthalma (long, triangular in P. platensis); dorso-lateral glandular shields in chaetiger 2 absent in P. polyopthalma (two glandular rectangular areas dorsally in P. platensis); 1–3 eyes present in dorsal and lateral radioles (radioles 2–6) in P. polyopthalma (2–3 eyes in dorsal radioles 2–3 in P. platensis) (Table 4).