Leodamas hyphalos, 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 : 73-76

Leodamas hyphalos new species

Figures 33–34

Scoloplos (Leodamas) spp. Hartman 1967: 108 (in part).

Material examined. Drake Passage, Eltanin Sta. 4-112, 20 Jul 1962, 56.03°S, 61.93° W, 4008 m, 13 paratypes (USNM 56456); Sta. 4-126, 29 Jul 1962, 57.20°S, 62.75°W, 3733–3806 m, holotype (USNM 1013904); and 13 paratypes (USNM 56457); Sta. 4-155, 17 Aug 62, 56.52°S, 63.25°W 3927 m, 7 paratypes (USNM 56458); R/V Polarstern, ANDEEP I, Sta. PS-61/043-2, 3958 m (1, SEM, JAB); PS-61/046-3, 2888 m (1, SEM, JAB).

Description. Majority of specimens small, incomplete; holotype 5.5 mm long and 0.7 mm wide for 29 setigers; largest paratype 9.0 mm long and 0.6 mm wide for 34 setigers. A single, much larger incomplete specimen from ANDEEP I Sta. PS-61 046-3 broken into two parts with 82 setigers, measuring 36 mm long and 3 mm wide across thorax. Color in alcohol: light brown.

Thoracic region with 16–18 setigers, inflated in first 3–4 setigers ( Fig. 33 B), subsequent thoracic setigers depressed; transition to abdominal region gradual, with last three thoracic setigers having fewer setae ( Fig. 33 C). Intersegmental annulations first present from setigers 8–9; these weakly developed, never prominent ( Fig. 33 A). Branchiae from setiger 6 ( Figs. 33 A, 34A); thoracic and anterior abdominal branchiae basally inflated ( Figs. 33 A, 34A), subsequent abdominal branchiae expanded ( Fig. 33 J); branchiae absent from far posterior setigers.

Prostomium triangular in outline, pointed on anterior margin ( Figs. 33 A, 34A); eyespots absent; nuchal organs in SEM as transverse slits at border of prostomium and peristomium ( Fig 34 A); proboscis divided into 3–4 lobes ( Fig. 34 A). Peristomium with one short achaetous ring ( Figs. 33 A, 34A).

Thoracic notopodia with minute postsetal lamellae on setigers 1–2, barely seen in SEM ( Fig. 33 A), becoming larger more visible from setiger 3 ( Fig. 33 A), short at first, then elongating, becoming unusually long, fingerlike structures ( Figs. 33 A–C, 34A), continuing through abdominal region. Thoracic neuropodia with setae arising from elongated thickened lobes ( Figs. 33 C, 34B); postsetal lamellae from setiger 5–11, attached to posterior border of upper one-third of setal lobe ( Figs. 33 C, 34B); each lobe short triangular at first, then elongating in transitional region to form fingerlike lamella; a single subpodial lobe from setiger 14–15, continuing through anterior abdominal segments ( Fig. 33 C); absent from middle and posterior abdominal segments ( Fig. 33 J). Abdominal neuropodia elongated, with short ventral cirrus ( Fig. 33 J).

Thoracic notopodia with fascicles of numerous crenulated capillaries and a single furcate seta; abdominal notopodia with three thin crenulated capillaries, two flail setae ( Fig. 33 I) and 2–3 furcate setae ( Figs. 33 G, 34E); furcate setae thin, delicate, easily broken, with unequal tynes connected by thin webbing composed of fine needles and shaft with faint annulations ( Fig. 33 G); with SEM, furcate setae with 9–10 needles on each side with lateral ones merging with tynes; each tyne with minute apical opening ( Fig. 34 E). Flail setae with thick, non-crenulated shaft bearing thin, crenulated tips ( Fig. 33 I). Thoracic neuropodia with dense fascicles of blunt-tipped uncini arranged in four rows ( Fig. 33 B–C); uncini of anterior row typically continuing ventrally below rows 2 and 3, then merging with row 4 forming a U-shape ( Fig. 33 D); in some neuropodia, rows 2 and three also joined ventrally; uncini of anterior row sharply curved, with 3–5 transverse ridges ( Fig. 33 E), with SEM ridges appearing irregular, angular ( Fig. 34 C); uncini of posterior row not as sharply bent, with 9–10 transverse ridges ( Fig. 33 F); 2–3 long crenulated capillaries present in superior position of last row of uncini ( Fig. 33 B–C, 34B). Abdominal neurosetae including 1–2 simple, blunt-tipped acicula ( Figs. 33 H, 34D) and 2–3 thin, simple capillaries ( Fig. 33 J).

Etymology. hyphalos: Greek for submerged, in the deep.

Remarks. Of the six species of Leodamas encountered in this study, L. hyphalos n. sp. is the only one to bear flail setae in the abdominal notopodia. Leodamas hyphalos n. sp. is closest in morphology to L. marginatus in the nature and arrangement of the neuropodial uncini; both species have a few superior capillary setae dorsal to the posterior row of uncini. The thoracic neuropodial uncini of L. marginatus are arranged in three long vertical rows and with a short fourth row that continues ventral to the first three; in contrast, there are four long rows of uncini in L. hyphalos n. sp. with the first and last often merged ventrally and forming a U-shape. Although the majority of specimens were small, the much larger specimen from Sta. PS-61 046-3 from lower slope depths of 2888 m was similar to L. marginatus in size. The smaller specimens of L. hyphalos n. sp. all occurred at abyssal depths greater than 3600 m, suggesting that the species may be size limited in the deeper parts of its habitat, possibly due to limited or patchy organic input to the abyssal sediments. The close similarity of L. hyphalos n. sp. to L. marginatus suggests that it may be a lower slope and abyssal sibling of the widely distributed and common shelf and upper slope species.

Distribution. Known only from the Drake Passage between South America and the Antarctic Peninsula; 2888–4008 m.

Figures

FIGURE 33. Leodamas hyphalos n. sp. (Holotype USNM 1013904). A, anterior end, dorsal view; B, anterior end, left lateral view; C, posterior thoracic region in left lateral view showing transition to abdominal segments; D,. diagram of middle thoracic neuropodium showing arrangement of uncini (not to scale); E – F, thoracic neuropodial uncini; G, furcate seta; H, abdominal neuropodial acicula; I, abdominal notopodial flail seta; J, abdominal parapodium, posterior view.

FIGURE 34. Leodamas hyphalos n. sp. (ANDEEP I, Sta. PS- 61 / 046 - 3, SEMs, JAB) A, anterior end, dorsal view; B, two thoracic neuropodia in anterior view; C, thoracic neuropodial uncini, detail; D, abdominal parapodium, anterior view; E, furcate seta, arrow denotes opening in tip of tyne.