Sphaerodoropsis biserialis Berkeley and Berkeley 1944

Sphaerodoropsis biserialis (Berkeley and Berkeley, 1944)

(Figure 5)

Sphaerodorum biserialis Berkeley and Berkeley, 1944: 3, figs. 1–3.

Sphaerodoridium biseralis Hartman, 1968: 601. Imajima, 1969: 154 –155, figs. 3a–d. Sphaerodoropsis biserialis Fauchald, 1974: 272, fig. 3.17.

Material examined. 1 Paratype USNM 32862. Western Canadian Arctic region. Dease Strait, 69ºN, 106º25’W.

Description. Paratype 3 mm long, with 24 chaetigers. Body shape circular in section, ventrally flattened. Prostomium with two lateral slender antennae and one median conical and short. Eyes not present. Long papillae on anterior margin of prostomium. Segment 1 cirri digitiform, similar in length to lateral antennae. Papillae covering completely dorsum and ventral side of the body distributed in several irregular transversal rows per segment.

Four sessile and pear-shaped macrotubercles on the dorsum of each segment. First chaetiger with two only macrotubercles, subsequent chaetigers with four. Conical parapodia with wrinkled surface. Anterior parapodial lobes digitiform and slender, 1/3 of parapodia length. Prechaetal lobes and ventral cirri present; dorsal cirri and postchaetal lobes absent. Ventral cirri conical, slightly longer than parapodia but not exceeding length of prechaetal lobes. Several papillae on each face of parapodia, 3 located distally over dorsal edge of parapodia. Compound falcigers, apparently divided in two different groups, division difficult to ascertain under light microscope; 15–25 chaetae with clear dorsoventral gradation in length (36 µm dorsally, 15.5 µm ventrally in midbody parapodia) (Fig. 5 A). Hooked blades unidentate (under light microscope), with thick and curved distal tooth, short spinulation on blade edge (Fig. 5 A). One straight acicula per parapodium. Pygidium small, rounded with two spherical anal cirri, similar in shape to macrotubercles. Cylindrical proventricle visible as dark structure, visible through three segments, muscle cell-rows not possible to distinguish.

Remarks. The compound chaetae of S. biserialis were described by Berkeley & Berkeley (1944) as without spinulation. After studying them under high magnification, spinulation is present as short spines on each blade's edge. While similar overall to S. anae n. sp., there are clear differences between the two species as outlined in the Remarks section above.