Aphelochaeta saipanensis sp. nov.

Figures 5 A–E, 6 A–F

Material examined. Saipan, Mariana Islands. Holotype: Tanapag reef flats, 15°14ʹ12.40ʺ N, 145°44ʹ36.33ʺ E, Dec. 2006, coll. D. Bybee (USNM 1195150). Paratypes: same locality, date and collector as holotype (4, USNM 1195151; 2 on stub, USNM 1195152; 5, BPBM R3642; 20 incomplete specimens, BPBM R3643). Additional material: same locality, date and collector as type series (21).

Description. Holotype 4.2 mm long, 0.2 mm wide in thoracic and abdominal segments for 67 chaetigers. Paratypes 3–6.0 mm long, 0.1–0.2 mm wide, for about 60–84 chaetigers. Body divided into three regions: thoracic region slightly expanded, rounded dorsally and flattened ventrally (sometimes with a shallow ventral groove), with 8–10 more or less crowded chaetigers; abdominal region with narrow segments, wider than long, never moniliform (Fig. 6 C); posterior end with 15 expanded crowded chaetigers with a shallow ventral groove only (Fig. 6 D). Pygidium with a ventral lip and anal aperture placed dorsally (Figs 5 C, 6D).

Prostomium conical, rounded anteriorly, without eyes and with a pair of postero-lateral nuchal organs, as vertical slits (Figs 5 A, B, 6A, B); peristomium elongate, with 3–4 annulations, first and second sub-equal and third elongate, almost as long as the two first combined; second annulation sometimes seen as two (Figs 5 A, B, 6A, B). Dorsal tentacles arising anterior to chaetiger 1 (Fig. 6 A); first pair of branchia postero-lateral to dorsal tentacles on chaetiger 1 (Fig. 6 A), continuing until posterior end.

Chaetae all capillaries with thick, dark gold base of about 1/4 of the capillary length (Figs 5 E; 6E); fibrils not visible in light microscopy. Thoracic chaetigers with 10–12 capillary chaetae per fascicle (Fig. 6 E, F) reducing to 4–6 posteriorly in abdomen.

MGSP. Third peristomial annulation densely stained, transverse ventral bands present on posterior margin of thoracic segments.

Remarks. See Remarks for Aphelochaeta arizonae sp. nov., and Table 2. This new species has distinct capillary chaetae that are basally thick and brown in color, readily seen under light microscope (Fig. 5 E).

Etymology. This species is named after the type locality Saipan in the Mariana Islands. Biology/Ecology. Several specimens found regenerating anterior and posterior ends.

Distribution. Only known from Saipan, Mariana Islands, northwestern Pacific Ocean.