Perkinsiana antarctica Kinberg 1867

Perkinsiana antarctica (Kinberg, 1867), redescription

( Figs 17, 18, 33 A)

Laonome antarctica Kinberg, 1867: 354.— Johansson 1922.

Perkinsiana antarctica.— Knight-Jones 1983: 277 –279, fig. 14.— Giangrande & Gambi 1997: 268, figs 1–2.— Rios et al. 2007: 94.— Bremec et al. 2000: 195.— Tovar-Hernández et al. 2012: 59 –60.

Material examined. ARGENTINA, UANL 8075: Puerto de Ushuaia, Tierra del Fuego, 54°48’S, 68°17’W, 2 m depth, dock fouling, 19 September 2005, coll. E. Schwindt, 5 specimens. CHILE, UANL 8076: Bahía Laredo, Magellan Straits, 2 m depth, 17 October 1994, 4 specimens, donated by A. Giangrande from those reported in Giangrande & Gambi (1997).

Redescription. Trunk length 10–14 mm; width 2–3 mm. Branchial crown length 4–9 mm, with 12–15 pairs of radioles. Five–8 thoracic and 27–48 abdominal segments. Radioles with irregular brown bands in pinnules (Fig. 17 G) along entire radiole length; radioles lacking pigmentation. Palmate membrane absent. Radioles with narrow flanges along entire lengths (Fig. 17 H). Longest pinnules at mid-radioles. Radioles with short tips, as long as equivalent space of one pinnule (Fig. 17 H). Dorsal lips subulate (Fig. 17 F), as long as 1/4 branchial crown length or length of seven thoracic segments, erect, with distinct radiolar appendage and very narrow lateral lamellae, 2–3 dorsal pinnular appendages. Ventral lips broadly rounded (Fig. 17 F) without ventral pinnular appendages. Parallel lamellae present. Ventral sacs visible above collar ventral lappets (Fig. 17 D, E). Dorsal collar margins not fused to faecal groove (Fig. 17 B). Anterior peristomial ring even dorsally, exposed (Fig. 17 B). Ventral collar lappets distally rounded, not overlapping when specimens are contracted (Fig. 17 D) or slightly overlapping when specimens were preserved inside tubes (Fig. 17 E). Lateral collar margins oblique, slightly higher ventrally, not covering junction between anterior peristomial ring and branchial lobes (Fig. 17 C). Ventral shield of chaetiger 1 divided transversely, anterior part thin, posterior shield wider. Chaetiger 1 with narrowly hooded notochaetae. Thoracic ventral shields rectangular (Fig. 17 D, E). Thoracic neuropodial tori of equal length on all segments, contacting ventral shields (Fig. 17 A, D, E). Superior thoracic notochaetae narrowly hooded, hood one-half width of shaft (Fig. 18 A, C). Inferior thoracic notochaetae paleate, symmetrical, hood same width as shaft, with short mucro (Fig. 17 A, B). Thoracic neuropodial uncini with several rows of teeth of equal size above main fang, occupying half of main fang length, hood absent, breast well developed, handles 2.5 times length of main fang (Fig. 18 E). Companion chaetae with teardrop-shaped membranes, symmetrical (Fig. 18 E). Abdominal neurochaetae elongate, narrowly hooded, hood one-half width of shaft, slightly curved at base of hooded area (type C according to Tovar-Hernández et al. 2012) (Fig. 18 D). Abdominal uncini with dentition similar to those from thorax but with shorter handles, as long as main fang (Fig. 18 F). Pygidium bilobed. Two groups of small pygidial eyes located dorsally, 8–14 eyes in each group. Anus ventral. Tubes not preserved.

Type locality. Bahía Laredo, Punta Arenas, Strait of Magellan (Chile).

Remarks. Perkinsiana antarctica was considered the most common sabellid in Antarctic and subantarctic waters (Pixell 1913; Benham 1927; Hartman 1953, 1966). It was poorly described and no illustrations were provided by Kinberg (1867) but records from Antarctic and subantarctic areas are extensive (Giangrande & Gambi 1997 and references therein). The revision by Giangrande & Gambi (1997) includes the designation of a neotype from Punta Arenas (Chile) and their study revealed that this species has often been confused with other taxa as P. milae Giangrande & Gambi and P. borsibrunoi Giangrande & Gambi and that P. antarctica probably has a distribution restricted to sub-Antarctic areas.

Tovar-Hernández et al. (2012) defined abdominal chaetae type A, present in P. antarctica (Kinberg, 1867), based on an illustration by Giangrande & Gambi (1997: fig. 2A). However, based on the re-examination of Giangrande & Gambi specimens from Bahia Laredo, abdominal chaetae are different from those illustrated in Giangrande & Gambi (1997). In the present study, these chaetae are described as elongate, narrowly hooded and slightly curved at the base of the hooded area (Type C). The hood is one-half width of the shaft, being different from type A. Type C chaetae are present also in P. assimilis, P. magalhaensis and P. minuta (Treadwell, 1941) (Table 3).

Perkinsiana antarctica and P. magalhaensis are distributed along the Magellan Strait. These species differ in the following: P. antarctica has short radiolar tips (long in P. magalhaensis, equivalent space of 8–10 pinnules) (Table 3); lateral collar margins not covering junction between anterior peristomial ring and branchial lobes (covered in P. magalhaensis); ventral shield of chaetiger 1 divided transversely (sometimes forming four square areas in P. magalhaensis); hoods of superior thoracic notochaetae one-half width of shaft (1/ 4 in P. magalhaensis); paleate chaetae with hoods as wide as shafts (hoods narrower than shaft width in P. magalhaensis); and thoracic uncini with handles as long as 2.5 times the length of the main fang (3 times in P. magalhaensis).

Comparisons between P. antarctica and other species of Perkinsiana distributed in Antarctic waters are the following: in P. decorata (Rullier, 1973), P. milae Giangrande & Gambi, 1997 and P. borsibrunoi Giangrande & Gambi, 1997 the anterior peristomial ring is exposed dorsal and laterally (only exposed dorsally in P. antarctica and covered in P. corcovadensis (Hartmann-Schröder, 1965)); whereas P. pusilla (Johansson, 1922) has ventral lappets very long and triangular (short and rounded in P. antarctica).

Jeldes (1962) reported Perkinsiana antarctica (as Potamilla) for Puerto Madryn and Puerto San Julián; as well as Schejter & Bremec (2007) and Bremec et al. (2000, 2001) for the Argentine shelf. As figures or descriptions were not provided in any of these ecological surveys, it is possible that those records belong to P. assimilis, a common species in these areas.

Embryos were not found among examined specimens and only two mature females were found, with oocytes distributed in abdomen. Presence of pygidial eyes is common among species of this genus, although one examined specimen lacked eyes. Regeneration was observed in two specimens: formation of new segments between old ones; a short thorax composed of five segments only and radioles regenerating.