Rhynchospio darwini Radashevsky, 2015

Radashevsky, Vasily I., Pankova, Victoria V. & Nuzhdin, Sergey V., 2016, Molecular analysis of six Rhynchospio Hartman, 1936 species (Annelida: Spionidae) with comments on the evolution of brooding within the group, Zootaxa 4127 (3), pp. 579-590 : 582

Rhynchospio darwini Radashevsky, 2015

Rhynchospio darwini Radashevsky, 2015: 684 –686, figs 33, 34.

Material. Australia, Northern Territory, Timor Sea, Beagle Gulf, Fannie Bay, Darwin, Bullocky Point, 12.4356°S, 130.8323°E, intertidal, muddy sand, coll. V.I. Radashevsky, 3 Sep 2013, NTM W025648 (holotype), MIMB 28105 (paratype).

Synopsis. Up to 5 mm long, 0.3 mm wide for 60 chaetigers. Prostomium with two conical fronto-lateral horns, extending posteriorly to end of chaetiger 1 as a low, indistinct caruncle. Occipital antenna absent. Two pairs of small red eyes arranged trapezoidally. Nuchal organs metameric; first pair of metamers on chaetiger 1 as curved ciliary bands on either side of low caruncle; successive metamers as one pair of ciliary bands on posterior half of each chaetiger ending on at least chaetiger 15. Chaetiger 1 with long capillaries and small postchaetal lamellae in both rami. Notopodia with only capillary chaetae throughout body. Sabre chaetae in neuropodia from chaetigers 11–12. Hooks in neuropodia from chaetigers 11–12, with only outer hood, tridentate, with two small upper teeth arranged in line above main fang; shaft slightly curved, without constriction in upper part. Branchiae from chaetiger 2 through most of body, flattened, with surfaces oriented parallel to body axis, free from notopodial postchaetal lamellae. Pygidium with one pair of ventral cirri and two pairs of thinner and slightly longer dorsal cirri. Simultaneous hermaphrodites with sperm in chaetigers 11–14 and oocytes from chaetiger 15 to chaetigers 25–30. Oocytes subspherical, with thin and smooth envelope less than 1 µm thick, without vesicles. Spermatozoa with long and thin nucleus.

Remarks. Two Rhynchospio species were originally described from Australia by Blake and Kudenov (1978), R. australiana from Western Australia, and R. glycera from New South Wales. Both species were described based on single individuals, never re-described and not reported from other localities. Gamete morphology and reproductive biology are not known for both.

Adults of R. darwini from Northern Territory, Australia, appear very similar to those of R. nhatrangi from Nhatrang Bay, Vietnam (see Radashevsky 2007a). Worms from these two localities have prostomia, pygidia and gametes of similar shape, and sabre chaetae, nuchal organs and branchiae of similar morphology and arrangement. They differ, however, in that mature individuals of R. nhatrangi have falcate unidentate hooks in neuropodia of chaetigers 11–14, and tridentate hooks from chaetiger 15 onwards, whereas mature individuals of R. darwini have only tridentate hooks in neuropodia from chaetigers 11–12.