Leitoscoloplos phyllobranchus, 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 : 35

Leitoscoloplos phyllobranchus new species

Figure 16

Haploscoloplos minutus: Hartman 1978: 156 (in part, Glacier Sta. 68-Palmer II). Not Hartman 1953.

Material examined. Antarctic Peninsula, Anvers Island, Arthur Harbor, Hero Inlet, Glacier Sta. 68- Palmer II, 17 Mar 1968, 64.77°S, 64.07°W, 40 m, holotype ( USNM 61943 ).

Description. Holotype complete, broken into three parts, totaling 20 mm long and 1.2 mm wide for 56 setigerous segments. Color in alcohol: light tan. Thoracic region slightly flattened dorsoventrally; abdominal region cylindrical; middle abdominal segments moniliform.

Prostomium reduced, short, triangular, wider than long, weakly pointed anteriorly, smoothly rounded on anterior margin, recessed into large peristomial segment; nuchal organs not observed; no eyespots ( Fig.16 A). Peristomium superficially divided into one large and one small achaetous ring; distinct from setiger 1.

Thorax with eight setigers, all similar. Notopodia with thin, cirriform postsetal lobes throughout body ( Fig.16 C–D); thoracic neuropodia simple, with elliptical postsetal lobes ( Fig.16 C); neuropodia of middle and posterior segments dorsoventrally swollen, forming weakly developed ventral flange, surmounted by short, triangular postsetal lobe ( Fig.16 E).

All thoracic setae arranged in irregular fascicles of 25–30 crenulated capillaries ( Fig.16 C). Abdominal neurosetae including 2–3 simple, non-crenulated capillaries and 2–3 imbedded aciculae. Abdominal notosetae including 3–5 long, crenulated capillaries and 1–2 furcate setae; furcate setae with three thin needles connected to blunted subequal tynes by a thin membrane ( Fig.16 F).

Branchiae from setiger 17; small, stubby at first ( Fig.16 D), increasing in size over subsequent setigers, becoming greatly enlarged; middle and posterior setigers with enlarged, flattened, membranous branchiae with thick inner and outer gland-like supportive structures and thin membranous blade with venation ( Fig.16 E).

Pygidium with two lobes lacking cirri ( Fig.16 B).

Etymology. The epithet, phyllobranchus , is derived from the Greek phyllon for leaf; branchos for gill. The name is suggested by the thin membranous appearance of the branchiae.

Remarks. Leitoscoloplos phyllobranchus n. sp. is a unique species in the form of the thin, membranous branchiae that start from setiger 17.

Distribution. Antarctic Peninsula, 40 m.

Figures

FIGURE 16. Leitoscoloplos phyllobranchus n. sp. Holotype (USNM 61943). A, anterior end, dorsal view; B, posterior end, dorsal view; C, thoracic parapodium, anterior view; D, anterior abdominal parapodium, anterior view; E, posterior abdominal parapodium; F, furcate seta.