Rhynchospio cf. foliosa Imajima, 1991

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 : 583-584

Rhynchospio cf. foliosa Imajima, 1991

( Fig. 1 )

Rhynchospio foliosa Imajima, 1991: 14 –17, figs 6, 7.

Material. USA, Oregon, Newport, sea water pump of the Hatfield Marine Science Center, 44.6223°N, 124.0433°W, coll. J.W. Chapman, 20 Oct 2010, MIMB 28 104 (2).

Synopsis. Up to 22 mm long, 1 mm wide for 90 chaetigers. Prostomium with two conical pointed fronto-lateral horns. Caruncle low and indistinct, decreasing in height and ending at posterior margin of chaetiger 1. Occipital antenna absent. Two pairs of dark red eyes arranged trapezoidally, comprising one pair of small median eyes and one pair of slightly larger lateral eyes situated anteriorly and set wider apart. Nuchal organs metameric, one pair of metamers on posterior half of each chaetiger ending on about chaetiger 25. Chaetiger 1 with capillaries and postchaetal lamellae in both rami; notopodial capillaries directed upwards, about 1.5 times as long as those on succeeding chaetigers. Notopodia with only capillary chaetae throughout body. Sabre chaetae in neuropodia as gradual transformation of inferior capillaries on chaetigers 25–30; chaetae with narrow limbation and granulation on distal part of shaft. Hooks in neuropodia from chaetigers 17–18, with only outer hood, tridentate, with two small upper teeth arranged in line above main fang; shaft slightly curved, with weak constriction in upper part. Branchiae from chaetiger 2 onwards, large, broad and foliaceous on anterior chaetigers, gradually becoming narrower and smaller on posterior chaetigers, flattened, with surfaces oriented parallel to body axis, free from notopodial lamellae. Pygidium with one pair of ventral cirri and up to 15 pairs of thinner and longer dorsal cirri; ventral cirri with dark pigment diffused in basal part; dorsal cirri transparent. Simultaneous hermaphrodites with sperm in chaetigers 13–34 and oocytes from chaetiger 36 onwards. Oogenesis intraovarian; vitellogenesis occurring when oocytes growing attached to segmental blood vessels. Vitellogenic oocytes subspherical, up to about 50 µm in diameter, with honey-combed envelope without vesicles. Developed coelomic oocytes oval, up to 75x 125 µm in diameter, with germinal vesicle about 40 µm and single nucleolus 12 µm in diameter; envelope about 6 µm thick, with external honey-combed surface and 20–30 vesicles (cortical alveoli) each 6–7 µm in diameter associated with inner surface ( Fig. 1 A, B). Spermatids joined in tetrads; spermatozoa ect-aquasperm with conical acrosome about 1.5 µm long and 1 µm in diameter, ovoid nucleus 2 µm long and 1.5 µm in diameter, a few spherical mitochondria, and a long flagellum; acrosome with transparent central part and a small dark spherical structure in anterior part ( Fig. 1 C, D).

Remarks. Rhynchospio foliosa was originally described by Imajima (1991) from a single complete individual (18 mm long, about 1 mm wide for 79 chaetigers, with sabre chaetae in neuropodia from chaetiger 15 and hooks from chaetiger 17) from Usujiri Bay, Hokkaido Is., Japan. The species has never been redescribed or reported from outside of the type locality. Individuals from Oregon match the description of R. foliosa in most diagnostic features but differ in having up to 32 pygidial cirri instead of 18. This difference may be due to ontogenetic or individual variability which remain unknown in this species, but such variability has been documented in other similar spionids (Radashevsky 2012).

No Rhynchospio with numerous pygidial cirri and broad and foliaceous branchiae similar to those from the Hatfield Marine Science Center, Newport, Oregon has been reported from the Pacific coast of North America. Whether the worms from Newport belong to a rare new species native in Oregon or result from an introduction of R. foliosa from Japan or elsewhere, remains uncertain. Herein, we therefore tentatively refer to them as R. cf. foliosa .

Figures

FIGURE 1. Gamete morphology of Rhynchospio cf. foliosa (fixed material). A, B, developed coelomic oocytes. A, external honey-combed surface of oocyte thick envelope. B, optical section of an oocyte, showing 20 – 30 vesicles (cortical alveoli, ve) associated with inner surface, germinal vesicle (gv) and single nucleolus (nl). C, D, spermatozoa, showing conical acrosome (ac) with a small dark spherical structure in anterior part and a transparent central part, ovoid nucleus (nu), a few spherical mitochondria, and a long flagellum. Scale bars: A – C = 10 µm; D = 5 µm.