Orbinia orensanzi, 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 : 86-89

Orbinia orensanzi new species

Figures 40–41

Material examined. Argentina, intertidal, sand beaches, coll., J. M. Orensanz: Golfo San Matías, Las Grutas, 14 Jan 1973, 4 paratypes ( USNM 1013910 ) ; Golfo Nuevo, Golfo San José, San Ramon , 17 Nov 1975, holotype and 2 p aratypes ( USNM 1013908–9 ) ; 17 Feb 1975, 2 paratypes (USNM 1013911).

Description. All specimens posteriorly incomplete; holotype from San Ramon 10 mm long, 1 mm wide for 60 setigerous segments; paratypes from Las Grutas larger, up to 30 mm long, 1.2 mm wide for 95 setigerous segments. Body depressed in thoracic region; abdominal segments cylindrical. Thorax with 17–24 setigerous segments, with largest specimens having more thoracic setigers; at least 1–2 segments transitional. Color in alcohol: light brown, with white-colored sub-neuropodial abdominal flanges.

Prostomium conical, acutely pointed on anterior margin ( Fig. 40 A); no eyespots; nuchal organs not observed. Peristomium reduced, fused to setiger 1; proboscis with 3–4 lobes.

Thoracic setigers all similar. Thoracic notopodia with postsetal lobes from setiger 4–5, lobes short at first, becoming cirriform in middle and posterior thoracic segments ( Fig. 40 A, C–D), continuing on following abdominal setigers ( Fig. 40 E–F). Largest specimens with distinct interramal cirrus in posterior thoracic setigers, first present from about setiger 18–19 ( Fig. 40 D); interramal cirrus absent in abdominal segments. Thoracic neuropodia reduced to low thickened ridge from which setae emerge ( Fig. 40 B–C); postsetal lobes present from medial posterior edge of setiger 3–4, short at first, becoming larger, triangular-shaped cirri by setiger 10–11 ( Fig. 40 C); last 1–4 thoracic setigers with two postsetal lobes and 1–9 subpodial lobes on each side, forming distinct ventral fringe ( Fig. 40 B, D) continuing through 3–7 abdominal setigers ( Fig. 40 B); all subpodial lobes cirriform, expanded basally; numbers of segments with subpodial lobes dependent upon size, larger specimens with more. Abdominal parapodia elevated dorsally on large fleshy parapodial cushion ( Fig. 40 E); neuropodia bilobed with inner lobe or dorsal cirrus shorter; outer lobe or ventral cirrus longer ( Fig. 40 E–F); fleshy subpodial flanges present, with medial notch ( Fig. 40 E–F).

Thoracic notosetae all crenulated capillaries ( Fig. 41 D); abdominal notosetae including crenulated capillaries ( Fig. 40 L) and furcate setae ( Fig. 40 J); furcate setae with bifid-tipped unequal tynes connected by thin webbing composed of very fine needles ( Fig. 40 J), with SEM individual needles tapering to fine tip, tips of tynes flattened, with distinct opening ( Fig. 41 E); shaft smooth, transverse rows of barbs not apparent. Thoracic neurosetae with 4– 5 more or less vertical rows of uncini ( Figs. 40 B, 41A–B); with companion crenulated capillaries in superior position of last row ( Figs. 40 B–D, 41A–B), some posterior thoracic setigers with a few additional capillaries in middle of neuropodium ( Figs. 40 D, 41B); uncini of setigers 1–4 thinner, more delicate than those on following thoracic setigers, where thick, heavy uncini in superior locations grade ventrally to thinner ones ( Figs. 40 B–C, 41A); thickest uncini with blunted tip, curved convex side flattened, then grading into 3–4 prominent transverse ribs on convex curvature, rest of shaft smooth; ribs most prominent on anteriormost uncini ( Figs. 40 G–H, 41A–C), thin uncini smooth or with transverse ribs weakly developed ( Fig. 40 I). Abdominal neurosetae include 3–4 flail setae ( Fig. 40 K), a thin, imbedded acicula, and an occasional delicate, smooth capillary seta; flail setae with thickened shaft bearing delicate ribs and very thin, smooth, terminal extension piece ( Fig. 40 K).

Branchiae from setiger 13–18, each elongated, expanded basally ( Figs. 40 C, E–F).

Etymology. This species is named for the late Dr. José M. (Lobo) Orensanz, who generously allowed me to study his collections of Orbiniidae from Argentina and Uruguay, and who made significant contributions to the study of the polychaetes of Argentina and the Southern Ocean.

Remarks. Orbinia orensanzi n. sp. belongs to a small group of species having branchiae from segments posterior to setigers 5–6, including O. hartmanae Day, 1977 from eastern Australia, O. riseri ( Pettibone, 1957) from eastern North America and O. johnsoni ( Moore, 1909) from western North America. Of these, only O. riseri and O. orensanzi n. sp. have interramal cirri. In O. riseri , the interramal cirrus is present in abdominal parapodia, whereas in O. orensanzi n. sp. they are present only in thoracic parapodia. A distinct ventral cirrus, present in O. riseri , is lacking in O. orensanzi n. sp. Thoracic neuropodial uncini are all smooth in O. hartmanae , ribbed and smooth in O. orensanzi n. sp., and ribbed with hoods in O. riseri and O. johnsoni .

Distribution. Argentina, intertidal in sand beaches.

Figures

FIGURE 40. Orbinia orensanzi n. sp. Paratype (USNM 1013910). A, anterior end, dorsal view; B, posterior thoracic and anterior abdominal setigers in left lateral view showing setal and podial transition; C, anterior thoracic neuropodial parapodium, anterior view; D, posterior thoracic parapodium, anterior view; E, anterior abdominal parapodium, posterior view; F, posterior abdominal parapodium, posterior view; G – H, thick thoracic neuropodial uncini with ribs; I, thin, smooth thoracic neuropodial uncinus; J, furcate seta; K, abdominal neuropodial flail seta; L, abdominal capillary notoseta, inset not to scale.

FIGURE 41. Orbinia orensanzi n. sp. Paratype (USNM 1013910). A, middle thoracic neuropodium showing arrangement of four rows of uncini and companion capillaries; B, posterior thoracic neuropodium in anterior view; C, detail of individual thick thoracic neuropodial uncini; D, thoracic notopodial capillaries; E, furcate setae, arrows denote opening in tips of tynes.