Leodamas cochleatus ( Ehlers, 1900 )

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 : 71-73

Leodamas cochleatus ( Ehlers, 1900) . New Status

Figures 31–32

Aricia cochleata Ehlers, 1900:217 ; 1901: 166–167, pl. 21, figs. 14–21.

Material examined. Chile, Straits of Magellan, Tribune Bank, 52°38′S, 70°00′W, 46 m, sand and gravel, coll. E. Nordenskold, holotype of Aricia cochleata ( SMNH 549 ).—Off Argentina, E of Mar del Plata, R /V Vema Station, V-17 -101, 450– 454 m, 19 Jun 1961 (5, LACM-AHF Poly 5043; 3, LACM-AHF Poly 5045).

Description. Holotype (SMNH 549) incomplete, 32 mm long, 2 mm wide for 110 setigers, color in alcohol pale yellow. Argentinean specimens all incomplete, smaller, 8–10 mm long, 0.8–1 mm wide, with 24–30 setigers (LACM-AHF Poly 5043); juveniles also present, one mostly complete, 4.5 mm long, 0.3 mm wide, with 40 setigers (LACM-AHF Poly 5045), color in alcohol tan. Body of all specimens flattened dorsally throughout, rounded ventrally, more so in the abdominal segments; body widest in thoracic segments, tapering posteriorly.

Prostomium triangular in outline, tapering anteriorly to narrow, blunt tip ( Fig 31 A); without eyespots; paired nuchal organs narrow slits, dorsolateral at border with peristomium. Peristomium with one achaetous ring only vaguely separated from prostomium, but well separated from first setiger ( Fig. 31 A).

Holotype with 29 setigers in thoracic region; smaller Argentinean specimens with 10–11 thoracic setigers. Notopodial postsetal lobes from setiger 1, fingerlike in shape, well developed from the first, increasing in size over thoracic region ( Fig. 31 A), continuing through abdominal segments. Thoracic neuropodia elongate thickened lobes, with no postsetal lobe or lamella present; thoracic uncini arranged in three elongate rows, with the first appearing to curve ventrally forming a fourth row behind the third, similar to that of L. marginatus and L. cirratus . Abdominal neuropodia thickened elongated lobes, with short ventral cirrus on apex of neuropodium and prominent cirriform subpodial lobe at base of neuropodium ( Fig. 31 B) present from first present abdominal setigers, continuing posteriorly through on all abdominal segments.

Thoracic notosetae including fascicles of crenulated capillaries; abdominal notosetae including capillaries, 1–2 straight spines with narrow pointed tips ( Fig. 32 F), and 1–3 furcate setae ( Figs. 31 I, 32H); furcate setae each with unequal tynes bearing fine needles; shaft smooth ( Figs. 31 I, 32H). Thoracic neuropodia with uncini arranged in three long vertical rows and one short posterior row, similar to L. marginatus and L. cirratus ; without accompanying capillaries; uncini of anteriormost 2–3 setigers with straight shaft bearing weakly developed transverse ribs and with a rounded narrowing apex; with elongate narrow groove on one side ( Figs. 31 C–E, 32A– C); subsequent setigers with shaft of uncini developing prominent transverse ribs or rows of blunt barbs; with tip of uncini becoming expanded, curved, blunt, with subapical pocket or notch on concave side ( Figs. 31 F–H, 32D–E). Abdominal neurosetae including capillaries and 1–2 acicular spines with tip narrowing to curved blunt tip ( Fig. 32 G).

Branchiae from setiger 6, each broad, basally tapering to prolonged, narrow apical extension ( Fig. 31 A–B). Pygidium unknown.

Remarks. Aricia cochleata and A. ohlini were both briefly described but not illustrated by Ehlers (1900) from the same locality in the Strait of Magellan and subsequently fully described and illustrated in Ehlers (1901). Augener (1926) synonymized A. cochleata with A. ohlini based on collections from New Zealand. He did not examine the original collections and provided little justification for the synonymy. Hartman (1957, 1966), Rozbaczylo (1985) and others, however, recognized and perpetuated this synonymy with little or no discussion despite there being clear differences between the two species in Ehlers’ (1901) published descriptions and illustrations. Further, if these two species were synonyms, then A. cochleata would have to be the valid name, having been described first in the same paper by Ehlers (1900). Both species names were referred to Scoloplos (Leodamas) by Hartman (1957) and are clearly species of Leodamas as defined in the present paper. Despite the assumption of synonymy, an inspection of the descriptions of these two species suggests that they are different. This was verified by examining the type specimens and additional collections. In the present paper, Leodamas ohlini becomes a synonym of L. cirratus and L. cochleatus is redescribed and resurrected as a distinct and valid species.

The main difference between Leodamas cirratus (with L. ohlini as a synonym) and L. cochleatus is with the nature of the thoracic neuropodial uncini. In L. cirratus , these uncini are relatively simple, straight-shafted with a weakly developed subapical notch or groove; in SEM weakly developed transverse ridges were observed. In contrast, the thoracic neuropodial uncini of L. cochleatus exhibit a distinct change in structure from those of the anteriormost 2–3 setigers where uncini have a relatively smooth, straight shaft bearing weakly developed transverse ridges and a narrow, rounded apex and an elongate narrow groove on one side. These uncini are replaced in middle and posterior thoracic neuropodia by spines with distinct transverse ribs or rows of blunt barbs on the shaft and with the tip of the uncini becoming expanded, curved, blunt, and bearing a subapical pocket or notch on the concave side. These differences with the thoracic uncini between L. cochleatus and L. cirratus (as L ohlini ) were clearly described and illustrated by Ehlers (1901); L. cirratus is most closely related to L. marginatus (see above). Additional features of L. cochleatus not seen in L. cirratus are with the presence of abdominal spines (aciculae) in the neuropodia and uniquely, in the notopodia ( Fig. 31 B). The neuropodial spines number 1–2 and are weakly curved and blunt-tipped apically ( Fig. 32 F–G). The notopodial spines number 1–2 and are straight and also bluntly tipped ( Fig. 31 B).

Leodamas hamatus recently described from off Costa Rica by Dean & Blake (2015), is another species where the neuropodial uncini change morphologically from anterior to posterior thoracic setigers. However, in contrast to L. cochleatus , the posterior neuropodial spines of L. hamatus develop a prominent, thickened hood-like structure on the convex side of the curved spines. In addition, the abdominal neuropodial uncini of L. hamatus are large, heavy and curve to a pointed tip instead of being of being narrow and blunt-tipped.

Distribution. Offshore Argentina, to 454 m; Chile, Straits of Magellan; 46 m.

Figures

FIGURE 31. Leodamas cochleatus (Ehlers, 1900). Argentinean specimens (AHF Poly 5043). A, Anterior end dorsal view; B, abdominal parapodium, anterior view; C – E, anterior thoracic neuropodial uncini from setiger 2; F – H, posterior thoracic neuropodial uncini from setiger 8; I, furcate seta.

FIGURE 32. Leodamas cochleatus (Ehlers, 1900). Phase Contrast images from Argentinean specimens (AHF Poly 5043): A – B, anterior thoracic uncini from setiger 2; C, detail of anterior thoracic uncinus showing longitudinal notch; D – E, posterior thoracic uncini from setiger 8 showing expanded apex and notch; F, abdominal notopodial spine; G, abdominal neuropodium with spine and capillaries; H, abdominal notosetae including capillaries, spines (broken) and furcate seta.