Orbiniella spinosa Blake, 2017, new species

Orbiniella spinosa new species

Figure 54 D–G

Material examined. Off Argentina, 38°46′S, 55°20′W, on drifting Macrocystis holdfasts, coll. J.M. Orensanz (holotype, USNM 1013688).

Description. A small species, holotype 2.1 mm long, 0.2 mm wide, for 22 setigerous segments. Body not divided into distinct regions; posterior parapodia not dorsally elevated; body cylindrical throughout, individual setigerous segments narrower than long, similar throughout, posterior most segments more flattened dorsoventrally. Setal changes mainly with neurosetae anterior to posterior. Branchiae entirely absent. Pygidium with two blunt lobes, without anal cirri (Fig. 54 D). Color in alcohol light tan.

Prostomium elongate, rounded on anterior margin (Fig. 54 D), eyespots absent; nuchal organs extending from posterior margin of prostomium, under first peristomial annulation. Peristomium about 1.3x as long as prostomium with two achaetous rings, each of same size, with lateral annulae not cutting across dorsum (Fig. 54 D).

Parapodia reduced to low mounds from which setae emerge; no postsetal lamellae. Setae consisting of crenulated capillaries and curved spines; furcate setae absent; no evidence of imbedded aciculae. Notosetae 2–3 crenulated capillaries throughout, with longest and narrowest capillaries in anterior half of body (Fig. 54 E); neurosetae shorter, generally thicker than notosetae numbering 2–3 in anterior setigers and 1–2 in far posterior setigers; anterior neurosetae spine-like capillaries (Fig. 54 F); posterior setigers with longer, thicker curved spines (Fig. 54 G); initially 1–2 curved spines with smooth shaft and narrow curved tip with short barbs on convex side; some far posterior spines with fine hirsute covering on apical end and curved tip (Fig. 54 G).

Etymology. The name spinosa is from the Latin, spina for thorn, and refers to the distinctive neuropodial spines that characterize the species.

Remarks. The holotype of Orbiniella spinosa n. sp. was originally identified as Falklandiella annulata, but a more careful study suggested that a separate species with more setal complexity was evident. The morphology of the thick, sharply curved neuropodial spines differs from other species of the genus (See Table 2).

Distribution. Off Argentina, found on drifting kelp (Macrocystis sp.).