Tharyx tumulosa, Magalhães, Wagner F. & Bailey-Brock, Julie H., 2013

Magalhães, Wagner F. & Bailey-Brock, Julie H., 2013, Bitentaculate Cirratulidae (Annelida: Polychaeta) from the northwestern Pacific Islands with description of nine new species, Zootaxa 3630 (1), pp. 80-116 : 107-109

Tharyx tumulosa sp. nov.

Figures 19 A–E, 20 A–F

Material examined. Holotype: Mamala Bay, Sand Island outfall, south shore of Oahu Island, Hawaii, Sta. D2, 21°16ʹ56.4ʺ N, 157°54ʹ35.8ʺ W, 53.3 m, Aug. 2009 (USNM 1195171). Paratypes: from the same location and date as holotype (2, USNM 1195172); Sta. E5R3, 21°16ʹ44.3ʺ N, 157°53ʹ50.0ʺ W, 82 m, Aug. 2009 (1, BPBM R3651); Mamala Bay, Barbers Point outfall, south shore of Oahu Island, Hawaii, Sta. HB7R4, 21°15ʹ49ʺ N, 158°03ʹ25.5ʺ W, 61 m, Mar. 2003 (5 on stub, USNM 1195174); Mamala Bay, Barbers Point outfall, south shore of Oahu Island, Hawaii, Sta. HB1R3, 21°17ʹ11.8ʺ N, 157°59ʹ31ʺ W, 61 m, Mar. 2002 (BPBM R3653); Mamala Bay, Barbers Point outfall, south shore of Oahu Island, Hawaii, Sta. HB1R5, 21°16ʹ51.0ʺ N, 157°59ʹ19.8ʺ W, 64.9 m, Jan. 2010 (3, USNM 1195173); Mamala Bay, south shore of Oahu Island, Sta. 40, 21°18ʹ0 0.8ʺ N, 158°01ʹ0 8.6ʺ W, 5.8 m, Jan. 2001 (1, BPBM R3652).

Description. Holotype 6.5 mm long, 0.1 mm wide with about 60 chaetigers. Paratypes 3.0–6.0 mm long, 0.1–0.2 wide for 28–48 chaetigers. Body slender and elongate, composed of slightly expanded thoracic region of 5–6 chaetigers, an abdominal region with weakly moniliform segments, and a posterior end narrowing toward the pygidium ( Figs 19 A, B, 20A). Pygidium simple rounded lobe with anal aperture placed dorsally ( Figs 19 B, 20D).

Prostomium elongate, as long as peristomium with pair of discrete postero-lateral nuchal organs as vertical slits; peristomium with three sub-equal annulations ( Figs 19 A, 20C). Dorsal tentacles originate from anterior border of chaetiger 1, anterior to the first branchiae, lateral to dorsal tentacles ( Figs 19 A, 20C); branchiae present only in anterior third of the body. Thoracic chaetigers with simple capillary chaetae only ( Fig. 20 B). Long natatorylike chaetae, with long and numerous fibrils along the edge, numbering 6–8 in abdominal segments. In far posterior chaetigers, long natatory-like capillaries replaced by 1–2 simple capillaries and 3–4 long and short, slightly curved, knob-shaped hooks with denticulate edge and sub-equal blunt teeth, not easily seen at 1000× magnification and usually at lateral edges of fascicles ( Figs 19 C, 20E, F).

MGSP. No distinct staining pattern; body stains equally a dark green, including the branchiae ( Fig. 19 D).

Remarks. This species is unique among Tharyx species due to the presence of natatory-like capillaries, weakly moniliform segments on abdominal region, and long and short modified chaetae on far posterior segments. The modified chaetae are entirely geniculated, not reported for other species, but this feature was only seen under SEM. Tharyx kirkegaardi Blake, 1991 has distinct serrations on the concave edge near the tip but also differs from T. tumulosa sp. nov., in having the peristomium uni- or biannulated (Blake 1991, 1996b; Table 4 ).

Etymology. The Latin tumulosa refers to the beadlike/mounded shape of the abdominal segments.

Biology/Ecology. Tharyx tumulosa sp. nov., was collected from the Sand Island and Barbers Point Wastewater Outfalls and in Mamala Bay, in fine to medium sand sediments at 5.8–82 m depths. Several mature females were found with the middle body segments filled up with eggs and enlarged dorsal vessels, which seems to be responsible for the beadlike shape of the abdominal segments ( Fig. 19 E).

Distribution. This species is only known from the south coast of Oahu Island, Hawaii, USA.

Figures

FIGURE 19. Tharyx tumulosa sp. nov. A, anterior end, dorsal view; B, posterior end with pygidium; C, posterior end knobshaped hook; D, MGSP showing homogenous staining pattern; E, dorsally inflated mid-body segments filled with eggs.

FIGURE 20. SEM of Tharyx tumulosa sp. nov. A, anterior and mid-body segments showing slightly inflated thoracic region and moniliform abdominal segments; B, back view of a thoracic capillary chaeta; C, anterior end, lateral view; D, posterior end with pygidium; E, knob-shaped hooks from very posterior chaetigers; F, detail of the knob-shaped hook showing the denticulate edge and sub-equals blunt distal teeth.