Odontosyllis marombibooral, San Martin & Hutchings, 2006

San Martin, G & Hutchings, PA, 2006, Eusyllinae (Polychaeta: Syllidae) from Australia with the Description of a New Genus and Fifteen New Species, Records of the Australian Museum 58, pp. 257-370 : 297-298

Odontosyllis marombibooral n.sp.

Figs 23A,B, 32A–C, 33A–F, 34A–E

Material examined. HOLOTYPE ( AM W28387) AUSTRALIA: WESTERN AUSTRALIA: Off jetty adjacent to Fisheries Hut, Beacon Is. 28°25.5'S 113°47'E, dead coral substrate, plate-like Acropora and Montipora spp. , 12 m, coll. P.A. Hutchings, 23 May 1994. PARATYPES: 1 on SEM stub ( AM W5496) Blow Holes, Quobba, 24°29'S 113°25'E, in sponge, 2 m, coll. N. Coleman, 20 Jun 1972; E side of Mangrove Is. 20°56'S 116°09'E, in dead coral, 1 m, coll. Aquinas College, 9 Jan 1968, 1 ( AM W194813).

Description. Body broad, robust anteriorly, tapered posteriorly, 25 mm long, 2 mm wide, with 93 chaetigers. Distinctly coloured ( Fig. 32A) with transverse black rows and other yellowish areas on preserved specimens; 2 kidneyshaped black spots on prostomium ( Fig. 32B); chaetigers 1, 4, 6, 9 darkly pigmented, subsequent segments, consisting of one darkly pigmented segment followed by unpigmented segment, this striped pattern continues to mid body, following segments with reduced pigmentation; each segment slightly biannulate with dorsum rugose. Prostomium almost circular, totally covered by occipital flap ( Figs 32A, 34A,B), with 4 eyes in rectangular pattern, antennae short and thick, shorter than prostomium, indistinctly wrinkled ( Fig. 32B,C), originating close to each other, all similar size, median antenna originating slightly posteriorly to lateral antennae, all antennae covered by occipital flap. Palps triangular, ventrally folded ( Fig. 32C). Peristomium dorsally reduced, covered by chaetiger 1 and occipital flap ( Fig. 32A), forming 2 lobes ventrally ( Fig. 32C). Occipital flap large ( Figs 32A–C, 34A,B) colourless. Tentacular and dorsal cirri similar, short, thick, slightly with elongate, slender blades, distally bidentate and short spines on margin; remaining chaetae with shorter and wider blades that progressively along body, become strongly bidentate, with short spines on margin ( Figs 33B,D, 34E, 23A,B). Anterior compound chaetae shorter and more slender than posterior ones, about 20 per parapodium, with dorsoventral gradation in length of blades within fascicle, 38 µm in length dorsally, 16 µm in length ventrally, those of posterior parapodia, numbering about 15 per parapodium, 46 µm in length dorsally, 26 µm in length ventrally. Dorsal and ventral simple chaetae not seen. Aciculae slender, distally broad, numerous on anterior parapodium, numbers decreasing posteriorly to 2–3 on posterior parapodia ( Fig. 33C). Pharynx about half of length of proventricle ( Fig. 33E), with 5 teeth and 2 lateral plates ( Fig. 33F). Proventricle long and wide, with about 56 muscle cell rows ( Fig. 33E).

Remarks. Odontosyllis marombibooral n.sp. differs from all other species of the genus in having a large occipital flap, which covers totally the prostomium and antennae, a distinctive colour pattern, bifid parapodia with distal ventral cirri, and short, pseudoarticulated dorsal cirri. No other species has this combination of characters. The most similar species is Odontosyllis picta ( Kinberg, 1865 described as Eurymedusa picta ), from New Zealand ( Ehlers, 1904) (also questionably reported for Australia), which also has a large occipital flap, but not as large as the one present in Odontosyllis marombibooral n.sp. Odontosyllis picta also has black transverse stripes, but they are arranged in a different pattern to those of Odontosyllis marombibooral , and the compound chaetae have all short blades, whereas Odontosyllis marombibooral , has two types of chaetae present. Odontosyllis rubrofasciata ( Pruvot, 1930) , from New Caledonia, (described as Atelesyllis rubrofasciata ), and O. rubrofasciata Grube, 1878 (a possible homonym), have strikingly similar colour patterns, short dorsal cirri, and compound chaetae that resemble those present in Odontosyllis marombibooral , but the occipital flap is much smaller and this character easily separates these three species. Fauvel, in the notes given after the description of Atelesyllis rubrofasciata considered that is a different species to O. rubrofasciata Grube, 1879 . Odontosyllis rubrofasciata ( Pruvot, 1930) has transverse stripes, but only from the midbody onwards, the prostomium has 4 lobes. The chaetae, although similar to those of O. marombibooral are slightly different, with long blades not as elongated and short blades with distal tooth not as curved as those present in O. marombibooral . In the description of Atelesyllis rubrofasciata ( Pruvot, 1930) , pharyngeal teeth are not mentioned as being present, although examining a range of species of Odontosyllis some individuals appear to lack these teeth. In all other characters, however, they are identical to specimens with teeth, suggesting they may lose these teeth and be able to regenerate them.

Habitat. Occurring in dead corals and sponges, from depths of 1– 12 m.

Distribution. Australia (Western Australia).

Etymology. The name of this species comes from two aboriginal words, marombi, meaning shield, and booral, meaning big, or large, in reference to the large occipital flap present.