Perkinsiana assimilis ( McIntosh, 1885 )

Tovar-Hernández, María Ana, León-González, Jesús Ángel De & Bybee, David R., 2017, Sabellid worms from the Patagonian Shelf and Humboldt Current System (Annelida, Sabellidae): Phyllis Knight-Jones’ and José María Orensanz’s collections, Zootaxa 4283 (1), pp. 1-64 : 39-43

Perkinsiana assimilis ( McIntosh, 1885) , redescription

( Figs 19–21 , 33 B)

Sabella assimilis McIntosh, 1885: 488 –489, pl. 29A, figs 23–25.

Perkinsiana assimilis .— Knight-Jones 1983: 280 –281, fig. 16A–K.

Material examined. ARGENTINA, R/ V Walther Herwig, UANL 8077 : Sta. 231, 35°14’S, 52°21’W, 200 m depth, 12 June 1966, 20 specimens ; UANL 8078: Sta. 383, 40°22’S, 59°02’W, 90 m depth, 19 July 1966, 1 specimen; UANL 8079: Sta. 391, 38°53’S, 55°22’W, 400 m depth, 21 July 1966, 10 specimens; UANL 8080: Sta. 392, 38°49’S, 55°14’W, 500 m depth, on gastropod shells, 21 July 1966, 8 specimens; UANL 8081: Sta. 389, 38°56’S, 55°31’W, 200 m depth, 21 July 1966, 4 specimens; UANL 8082: Sta. 399, 37°51’S, 55°10’W, 250 m depth, 22 July 1966, 26 specimens; UANL 8083: Sta. 400, 37°23’S, 54°48’W, 200 m depth, 23 July 1966, 6 specimens; UANL 8084: Sta. 415, 35°51’S, 52°53’W, 270 m depth, 25 July 1966, 2 specimens. Campaña Almirante Saldanha , UANL 8085 : 2286, 38°05’S, 55°48’W, 95 m depth, 16 November 1969, 1 specimen . Campaña SAO II, UANL 8086 : Golfo de San Matías, St. 111, 41°08’S, 64°53’W, 111 m depth, 30 April 1971, 2 specimens .

Redescription. Trunk length 34–60 mm; width 2–4 mm. Branchial crown length 9–16 mm, with 16–26 pairs of radioles. Four to five pairs of ventrally involute radioles. Thorax with 4–8 segments. Abdomen with 52–120 segments. Palmate membrane and radiolar flanges absent ( Fig. 20 A, D, E). Longest pinnules at mid-radioles. Radioles with long tips, as long as equivalent space of 15 pinnules ( Fig. 20 C). Dorsal lips triangular ( Fig. 20 B, F, G), erect, with distinct radiolar appendages and very narrow lateral lamella, 2–3 dorsal pinnular appendages united by thin membrane. Ventral lips broadly rounded ( Fig. 20 B), with 1–2 ventral pinnular appendages. Parallel lamellae present; ventral sacs visible above collar ventral lappets ( Fig. 19 E). Dorsal collar margins not fused to faecal groove ( Fig. 19 A, D, F). Anterior peristomial ring even all around, dorsally exposed ( Fig. 19 A, D, F). Ventral lappets of collar distally rounded, not overlapping ( Fig. 19 B, E). Lateral collar margins oblique, higher ventrally, covering junction between anterior peristomial ring and branchial lobes ( Fig. 19 C). Ventral shield of chaetiger 1 divided transversely: anterior part thin, subdivided mid-ventrally in two triangular areas; posterior part wide, rectangular with anterior margin convex ( Fig. 19 B, E). Chaetiger 1 with narrowly hooded notochaetae.

Thoracic ventral shields trapezoidal ( Fig. 19 B). Thoracic neuropodial tori of equal length, contacting ventral shields ( Fig. 19 B, C). Superior thoracic notochaetae narrowly hooded ( Fig. 21 A), hood one-half width of shaft. Inferior thoracic notochaetae paleate ( Fig. 21 C), symmetrical, hood as wide as shaft, short mucro. Thoracic uncini with 7–8 rows of teeth of equal size above main fang, occupying one-half length of main fang, hood absent, breast well developed, handles 2.5 times longer than main fang ( Fig. 21 B). Companion chaetae with teardrop-shaped membranes, asymmetrical ( Fig. 21 E). Abdominal neurochaetae elongate, narrowly hooded; hood one-half width of shaft, slightly curved at base of hooded area, Type C ( Fig. 21 D). Abdominal uncini with dentition similar as in thorax (7–8 teeth covering half the main fang), but with handles as long as 1.5 length of main fang ( Fig. 21 F). Pygidium triangular, eyes absent ( Fig. 19 G); anus ventral. Tubes translucent green, rigid, distally covered with gravel and proximally with sponges ( Fig. 19 D, E).

Type locality. Near Buenos Aires ( Argentina) at 1100 m depth.

Remarks. Perkinsiana assimilis is herein reported from 90–500 m depth, on the Uruguayan and Argentine shelf. Perkinsiana assimilis is distinctive due to the absence of a palmate membrane (present in P. magalhaensis ) and radiolar flanges (present in P. antarctica and P. magalhaensis ), as well as the presence of long radiolar tips (very short in P. antarctica ) ( Table 3).

Among the species of Perkinsiana distributed in South America, only P. corcovandensis and P. pusilla have Type A abdominal chaetae, whereas in P. antarctica , P. assimilis , P. magalhaensis and P. minuta they are Type C ( Table 3). In P. antarctica the ventral shield of the chaetiger 1 is entire and rectangular. In P. magalhaensis it is divided transversely in two parts, the anterior one slightly narrower than posterior. Sometimes the shield is also divided mid-ventrally, forming four square areas.

Two specimens (UANL 8078) were found with regenerating branchial crowns, and one regenerating posterior abdominal segments. Regeneration was also reported among type material by Knight-Jones (1983).

Figures

FIGURE 19. Perkinsiana assimilis (McIntosh, 1885). A) Anterior thoracic segments, dorsal view, B) same, ventral view, C) same, lateral view, D) anterior peristomial ring, dorsal view, E) Collar, ventral view, F) anterior peristomial ring and faecal groove, G) posterior end, H) entire body. Scale bars: A, B, D 3 mm, C 2.5 mm, E, F 1.5 mm, G 2 mm, H 5 mm. Abbreviations: apr anterior peristomial ring, fg faecal groove, vs ventral sacs, vsc ventral shield of chaetiger 1. Specimen: A – H UANL 8078.

FIGURE 20. Perkinsiana assimilis (McIntosh, 1885). A) Radioles, B) inner view of right branchial lobe, C) radiolar tip, D) radioles, E) outer view of right branchial lobe, F, G) dorsal lip. Arrows in B, E – G point to dorsal lip. Scale bars: A, C, D 0. 4 mm, B, E – G 1.5 mm. Abbreviations: d dorsum, vl ventral lip, v ventrum. Specimen: A – G UANL 8078.

FIGURE 21. Perkinsiana assimilis (McIntosh, 1885). A) Thoracic noto- and neurochaetae, B) thoracic uncini, C) thoracic paleate notochaetae, D) abdominal neurochaetae, E) companion chaetae, F) abdominal uncini. Scale bars: A, D 100 µm, B, F 30 µm, C 20 µm, E 10 µm. Specimen: A – F UANL 8078.

FIGURE 33. Distribution of some sabellid species in South America. A) Perkinsiana antarctica (Kinberg, 1867), B) Perkinsiana assimilis (McIntosh, 1885), C) Pseudopotamilla platensis (Hartman, 1953) (circles) and P. knightjonesae sp. nov., (star denotes type locality).