Leitoscoloplos plataensis, Blake, James A., 2017

Blake, James A., 2017, Polychaeta Orbiniidae from Antarctica, the Southern Ocean, the Abyssal Pacific Ocean, and off South America, Zootaxa 4218 (1), pp. 1-145 : 26-28

Leitoscoloplos plataensis new species

Figures 9 F, 10

Material examined. Uruguay, off the mouth of the Rio de la Plata, IBM Sta. N- 242, 63 m (2, USNM 1013639 ) ; Sta. N- 260, 144 m (1, USNM 1013638); Sta. N-1073, 115– 117 m (3, USNM 1013637); Sta. 1074, 35°29′S, 53°01′W, 112 m, holotype and 2 paratypes (USNM 1013633–4); Sta. N- 1075, 68 m (1, USNM 1013636). — Argentina, IBM Sta. N-1059, 35°25.9′S, 53°27.9′W, 72–80 m, 14 paratypes ( USNM 1013635 ) ; Golfo San Matías , SAO-1, Sta. 51, 41°08.30′S, 65°06.30′W, intertidal in gravel, coll. IBM (1, USNM 1013640 ) .

Description. A small species, holotype complete, approximately 13–14 mm long (posterior end coiled) and 0.8 mm wide for about 100 setigers. Color in alcohol: brown. Thoracic region with first 4–5 setigers weakly inflated, not depressed, with 9–10 setigers, similar in width to anterior abdominal segments ( Figs. 9 E, 10A).

Prostomium short, conical, pointed, and narrow ( Figs. 9 F, 10A); two nuchal slits sometimes apparent in dorsolateral locations ( Fig. 9 F); without eyespots. Peristomium a single triangular-shaped achaetous ring, narrower, but longer than setiger 1; with prostomium forming triangular “head.”

Thoracic parapodia all similar, inconspicuous, with elongated postsetal lobes, with notopodia short, triangular in shape ( Fig. 10 B); neuropodia with low basal cushion from which digitiform postsetal lobe emerges; postsetal lamellae short, narrow at first, becoming longer and thicker in last thoracic setigers. Abdominal notopodia with thin, narrow, fingerlike postsetal lobes; abdominal neuropodial lobes elongate, thickened apically with distinct ventral cirrus; subpodial flange small but distinct, continuous with neuropodial lobe ( Fig. 10 C–D).

Branchiae from setiger 13–16, short, triangular at first ( Fig. 10 A, C), then increasing in length posteriorly ( Fig. 10 D); branchiae asymmetrical, with large protruding lateral lobe ( Fig. 10 C–D).

Thoracic setae crenulated capillaries in dense fascicles with two rows of 20–25 setae per fascicle, arising from broad cushion ( Fig. 10 B); setae of first row shorter and thinner than those of second row. Abdominal notosetae including 8–9 capillaries and 0–2 furcate setae; furcate setae with unequal tynes connected by row of fine needles; both tynes with rounded tips, shaft with ribbed crenulations ( Fig. 10 E). Abdominal neurosetae including 2–3 long, smooth or weakly crenulated capillaries and 1–2 short, protruding, curved, blunt-tipped aciculae ( Fig. 10 C).

Pygidium a smooth, enlarged ring, lacking cirri.

Etymology. This species is named for its proximity to the Rio de la Plata.

Remarks. Leitoscoloplos plataensis n. sp. is closely related to L. kerguelensis in having 9–10 thoracic setigers and branchiae from setigers 13–16. Leitoscoloplos plataensis n. sp. differs in having the abdominal branchiae with a large protruding lateral lobe, ventral cirri on the abdominal neuropodia, and a different shape to the prostomium and peristomium. Further, furcate setae are rarely found in both the thoracic and abdominal notopodia of L. plataensis n. sp. but are commonly in the notopodia of L. kerguelensis .

Distribution. Known only from off Uruguay and Argentina, intertidal to 144 m in coarse sediments.

Figures

FIGURE 9. Leitoscoloplos kerguelensis (McIntosh, 1885). Antarctic Peninsula, Arthur Harbor (USNM 69381). A, anterior end, right lateral view; B, thoracic setae, arrow denotes a thin capillary seta of first row; C, abdominal parapodium, anterior view; D, posterior end and pygidium, dorsal view; E, furcate seta, arrows denote opening on tip of tynes. — F, Leitoscoloplos plataensis n. sp., off Argentina, paratype (USNM 1013635). E. anterior end in right lateral view.

FIGURE 10. Leitoscoloplos platensis n. sp. Holotype (USNM 1013633). A, anterior end, dorsal view; B, thoracic parapodium, anterior view; C, anterior abdominal parapodium, anterior view; D, posterior abdominal parapodium, anterior view; E, furcate seta.