Leodamas cirratus ( Ehlers, 1897 )

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 : 68-71

Leodamas cirratus ( Ehlers, 1897)

Figures 29 D–H; 30

Aricia cirrata Ehlers, 1897: 94 –95, pl. 6, figs. 148–149.

Aricia ohlini Ehlers, 1900: 217 –218; 1901: 167–169, pl. 21, figs. 9–13. New synonymy. Scoloplos (Scoloplos) cirratus: Mesnil & Caullery 1898: 142 .

Scoloplos (Leodamas) cirratus: Hartman 1953: 38 ; 1957: 290; 1966: 11, pl. 2. Scoloplos (Leodamas) ohlini: Rozbaczylo 1985: 132 .

Material examined. Argentina, offshore, 190 km E Puerto San Julien, Santa Cruz, about 280 km NW of Falkland Islands, 49°35′S 64°43′W, 127 m, holotype of Arica cirrata ( ZMH V1224); R/V Vema Sta . V-17-86, SE of Camarones , 225–227 m , 11 Jun 1961 (4, LACM-AHF Poly 5034); R/V Vema Sta. V-18-12, continental slope E of Deseado , 424–428 m (2, LACM-AHF Poly 5030). — Argentina, nearshore, IBM Sta. Mej- 12, 24 m (1, JAB); IBM Sta. H- 17, 16 m (1, USNM 1013659 ) ; IBM Sta. N-1055, 92– 96 m (1, SEM stub, USNM 1013663); San Antonio Oeste, Marejada Norte (1, USNM 1013661 ); Golfo San Matías, Piedra Coloradas , Feb 1972, coll. Escofet and J.M. Orensanz (2, USNM 1013660); IBM Sta. Mej-12 (1, USNM 1013662).— Falkland Islands, Port William, 3 Sep 1902, Swedish Antarctic Expedition 1901–1903, Sta. 52, 51°40'S ; 57°44'W, 17 m, in sand (1, SMNH 3106 ); Port Stanley , 9 Apr 1927, coll. W.S. Schmidt (1, USNM 24341).— Chile, Straits of Magellan , Eltanin Sta. 7-967, 81 m (1, USNM 56465 ) . — Tribune Bank , 52°38′S, 70°00′W, 46 m, sand and gravel, coll. E. Nordenskold, holotype of Aricia ohlini ( SMNH 551 ) . — South Orkney Islands, Eltanin Sta. 12-1079, 593– 598 m (1, USNM 56467 ) .

Description. Holotype (ZMH V1224) incomplete, 24 mm long, 1.5 mm wide for 73 setigers; thoracic region narrow, with 27 setigers, flattened at first, becoming more rounded in abdominal region. Falkland Islands specimen (SMNH 3106) incomplete, about 17 mm long and 1.5 mm wide for 54 setigers; thoracic region narrowing anteriorly, slightly depressed, with 32 setigers, last four setigers increasingly smaller, with fewer uncini. Tribune Bank specimen (SMNH 551) also incomplete, 17 mm long and 1.5 mm wide for 47 setigers; thoracic region with 21 setigers. Color in alcohol: brown.

Prostomium triangular in outline, tapering anteriorly, but not acutely pointed; without eyespots; multi-lobed proboscis present ( Fig. 30 A); paired nuchal organs present dorsolaterally at border with peristomium ( Fig. 29 D, inset). Peristomium with one well-developed achaetous ring distinctly separated from prostomium and first setiger ( Figs. 29 D, 30A).

Notopodial postsetal lobes from setiger 1, short, fingerlike at first, then increasing in length, becoming cirriform by setigers 4–5 ( Figs. 29 D, 30B), continuing through abdominal segments.

Thoracic neuropodia with setae arising from elongate thickened lobe; with short, conical postsetal lobe first present from middle of neuropodium from about setiger 25 or last 3–7 thoracic setigers ( Fig. 30 B); with short, cirriform subpodial lobe resembling ventral cirrus first present from last 2–6 thoracic setigers, continuing posteriorly through 18–20 abdominal setigers ( Fig. 30 B–C). Abdominal neuropodia with thickened elongated lobes bearing short cirriform postsetal lobe ( Fig. 30 C).

Thoracic and abdominal notosetae including fascicles of crenulated capillaries and 3–4 short, furcate setae; furcate setae with unequal tynes, connected by thin webbing composed of very fine needles and with smooth shaft ( Fig. 30 D); with SEM fine needles between tynes numbering 7–8 on a side, merging with tynes; each tyne with expanded apex, narrowing to bluntly pointed tip, but with narrow, elongate opening on inner border of tyne ( Fig. 29 H); shaft with transverse rows of minute barbs ( Fig. 29 H). Thoracic neuropodial uncini arranged in three long vertical rows and one short posterior row, similar to S. marginatus ( Fig. 29 D–E), without accompanying capillaries; uncini blunt tipped, with weakly developed subapical notch or groove and with smooth shaft ( Fig. 30 E– F); with SEM subapical groove, elongate, flattened extending about one-third distance to point of emergence from neuropodium, rest of shaft with weakly developed transverse ribs ( Fig. 29 E–F); abdominal neurosetae including capillaries and an acicular spine sometimes with thin hyaline hood ( Fig. 30 G), sheath not apparent in SEM ( Fig. 29 G).

Branchiae from setiger 6 ( Figs. 29 D, 30A), each broad, basally tapering to prolonged, nipple-like extension; with lateral cilia visible ( Fig. 30 B–C). Branchial bases of some abdominal segments connected with low ciliated crest.

Pygidium of specimen from USNM 1013660 with anus directed posteriorly, surrounded by dorsal pair of thick lobes and four pairs of lateral cirri; dorsal most pair longest, weakly moniliform, one with bifurcate tip, other with single tapering tip; two middle pair short, stubby, sometimes one missing; ventral most pair short, narrow, tapering to pointed tip.

Remarks. The holotype was collected at a depth of ca. 125 m offshore SW Argentina and approximately 280 km NW of the Falkland Islands. The type specimen agreed very well with Ehlers’ (1887) original account both with size, number of segments, and morphology. The Falkland Islands specimen was examined by Hartman (1953:38) who found it agreed with Ehlers (1897) original account; my examination of this specimen confirms this identification. Ehlers’ holotype is 24 mm long for 73 segments with 27 thoracic segments; the largest specimens in the new collections are 17 mm long for 54 segments with 32 thoracic segments. The type specimen of Aricia ohlini from the Straits of Magellan also agrees well with Leodamas cirratus .

Leodamas cirratus closely resembles L marginatus and L. cochleatus in the arrangement and form of the thoracic neuropodial uncini, which are arranged into four vertical rows and have grooves on one side of the tip and transverse ridges or rows of minute barbs along the shaft seen best in SEM. In L. cirratus , the uncini are not accompanied by capillaries, whereas superior capillaries are sometimes present in L. marginatus . Leodamas cirratus has a single subpodial lobe or ventral cirrus from posterior thoracic and some abdominal segments; this lobe is lacking on L. marginatus . The prostomium of L. cirratus is more acutely pointed and the anterior thoracic region is less distinctly tapered than in L. marginatus . Further, the thoracic region of L. cirratus is more dorsoventrally flattened than in L. marginatus . Differences with L. cochleatus include the presence of thoracic neuropodial uncini with a broad, heavily notched apex and with distinct transverse ridges on the shafts. Additionally, L. cochleatus has abdominal notopodial acicular spines in addition to neuropodial (see below).

The presence of moniliform pygidial cirri appears to be unusual among orbiniids, but these have not been well studied.

Distribution. Off the SE coast of Argentina, shallow subtidal to 225–428 m; Falkland Islands 17–127 m; Straits of Magellan, 45–80 m; South Orkney Islands, 593– 598 m.

Figures

FIGURE 29. Leodamas marginatus (Ehlers, 1897) (ANDEEP I, Sta. PS- 61 / 045 - 1), A – C. A, Anterior end, right lateral view; B, detail of branchia; C, thoracic neuropodial uncini. — Leodamas cirratus (Ehlers, 1897) (USNM 1013660), D – H. D, anterior end, left lateral view [inset of nuchal organ, not to scale]; E, thoracic neuropodium; F, thoracic neuropodial uncini; G, abdominal neuropodium; H, furcate seta, arrow denotes opening in tip of tyne.

FIGURE 30. Leodamas cirratus (Ehlers, 1897) (USNM 1013659). A, anterior end, dorsal view; B, thoracic parapodium from setiger 26, anterior view; C, abdominal parapodium, from setiger 43, anterior view; D, furcate seta; E – F, thoracic neuropodial uncini; G, abdominal neuropodial acicula.