Phalacrostemma maloga, Hutchings & Capa & Peart, 2012

Hutchings, Pat, Capa, María & Peart, Rachael, 2012, 3306, Zootaxa 3306, pp. 1-60 : 31-36

Phalacrostemma maloga n. sp.

Figures 6A, 18, 19, 20, Table 3

Material examined. HOLOTYPE: AM W27566*, New South Wales: Tasman Sea , off Newcastle, 33°30S 152°06'E, iv.1971, 548.6 m, in 2 pieces 10+-5+ mm in length, 2 mm in width, 15-4 chaetigers, attached to mollusc shell . PARATYPES: Tasman Sea , off Newcastle, 32°30'S 152°06'E, iv.1971, 548.6 m, 1, AM W27567 ; 457.2– 502.9 m, 6, AM W27568 * attached to mollusc shell; 33° 40' S 152° 45' E, 15 vi.1971, 6, AM W27569 ; 33° 30'S 152° 06' E, iv.1971, 1, AM W26681 (mounted for SEM).

Additional material examined. MV F78859 , Stn S 05/84 29 from Tasman Sea, eastern slope 70 km S of Gabo Island , Victoria (1 specimen) .

Description. Holotype with body stout, tapering to elongated abdomen, reddish brown with darker areas along noto- and neuropodia. Operculum completely divided into two free short lobes with distal end perpendicular to longitudinal axis ( Figs 18A, B, 19A–D). Operculum with outer row of 12 pairs of paleae, arranged spirally ( Fig. 18C); paleae yellow as simple spines with acute tips and compact thecae with margins straight and not expanding ( Figs 19E, 20B, C); inner row with two pairs of short spines, yellow and tapering tip ( Fig. 18C). Ten pairs of robust and tapering opercular papillae, peripheral to outer paleae ( Figs 18C, 19B, C), almost as long as outer paleae. Five pairs of flattened nuchal hooks, with limbation present on concave side ( Figs 18B, C, 19D, 20B). Medial organ present at dorsal junction of opercular lobes ( Fig. 18C, see Capa et al., 2012). Eyes not observed. Three pairs of simple tentacular filaments ( Fig. 19B). A pair of buccal flaps below tentacular filaments ( Fig. 19A). Palps shorter than length of operculum ( Fig. 19B). Segment 1 (chaetiger 1) with long and tapering neuropodial lobe ( Fig. 19A) and capillary neurochaetae ( Fig. 19B, C). Segment 2 (chaetiger 2) with two triangular lateral lobes connecting branchiae to neuropodia ( Figs 18B, 19C). Eight pairs of dorsal tapering branchiae present from chaetiger 2, not meeting mid-dorsally ( Fig. 18B), reducing in size posteriorly but present on posterior segments. Segments 3–6 (parathoracic) with two types of notochaetae inserted in transverse rows with two types of notochaetae; eight lanceolate and fine capillaries interspersed ( Fig. 20D, E). Segments 3–6 with two types of neurochaetae arranged transversely, four lanceolate and fine short capillaries interspersed ( Fig. 20F). Notopodial lanceolate much stouter than those in neuropodia ( Fig. 20D–F). Abdominal notopodia as erect expanded tori, with uncini decreasing in numbers posteriorly. Each uncinus with three vertical rows of teeth imbricated ( Fig. 20H). Neuropodia with long fine capillaries with compact thecae arranged in discrete fascicles in two tiers ( Fig. 20G). Cauda smooth and about one third length of abdomen ( Fig. 18A).

Variations. The paratypes including sexually mature females, vary from 7–18 mm in length (without cauda) none of which is complete, 2 mm in width with 12–22 chaetigers, 12–16 pairs of outer paleae, 2–3 pairs of inner paleae, 7–13 pairs of opercular papillae, and with 3–9 pairs of dorsal branchiae. All these variations could be size dependent. None of the material is well preserved and fragile.

Remarks. Phalacrostemma maloga n. sp., is characterised by a unique combination of: 12–16 pairs of outer paleae with straight edges and without expanded thecae, five pairs of nuchal spines, three pairs of tentacular filaments, buccal flaps present and with some abdominal uncini provided with three vertical rows of teeth. Other species without expanded thecae on the outer paleae (see Table 3) include P. setosa Treadwell, 1906 described from the Caribbean which has irregular edges and P. cidariophilum Marezeller, 1895 described from the Northern Adriatic Sea, which has straight edges but lacks tentacular filaments. The closest species geographically is P. tenue Lechapt & Kirtley, 1998 , described from deep water off New Caledonia but this has only two pairs of nuchal spines whereas P. maloga n. sp., has five pairs. Most species of this genus, which typically occur in deep waters (see Table 3), are poorly known. We suggest that the number of pairs of lateral lobes on segment 2, the presence of buccal flaps and the number of pairs of tentacular filaments are useful characters to distinguish between species. The dentition of the abdominal uncini, with three rows of teeth instead of the two rows typical of other sabellariids, may be a synapomorphy for the species. But it could have also been overlooked in other species of the genus and therefore needs further study.

Distribution. South-eastern Australia, type known only from type locality and from a single record from south of Gabo Island, off the coast of Victoria ..

Habitat. Continental shelf in depths of 457–548 m and attached to mollusc shells in soft sediment substrates forming small colonies.

Etymology. The specific name maloga is an Aboriginal word for deep water ( Endacott 1973) and refers to the habitat of this species.