Chaetozone acuminata Dean & Blake, 2007, sp. nov.

Chaetozone acuminata sp. nov.

Figure 1 (A–D).

Material examined. Golfo de Nicoya, Costa Rica. Holotype: Sta. 23, 9°48'35"N, 84°43'50"W, 35 m, mud, 11 Jul 1980, (USNM 80164A). Paratypes: same sample (11 USNM 80164B).

Comparative material examined. Golfo de Nicoya, Costa Rica. Sta. 23, 9°48'35"N, 84°43'50"W, 35 m, mud, 11 Jul 1980 (2 HKD).

A small (defined as having an average body length of less than 5.0 mm) species, holotype 9.2 mm long, 0.2 mm wide anteriorly, 0.3 mm wide across middle of body, for 52 setigers; a second complete paratype 6.9 mm long, 0.2 mm wide anteriorly, 0.3 mm wide across middle of body, for 44 setigers. Body long, narrow, cylindrical, with anterior region narrower than midbody region, with middle and posterior setigers somewhat moniliform, parapodial lobes low, inconspicuous, with spines of posterior setigers forming complete cinctures having narrow dorsal and ventral gaps. Pygidium truncate, anus dorsal with ventral rounded lip (Fig. 1 C). Color pale tan in alcohol.

Prostomium conical, pointed, partially concealed dorsally by overhanging peristomium, with pair of round, ciliated nuchal organs laterally (Fig. 1 A B). Peristomium with prominent dorsal extension above prostomium; three asetigerous annulations present, with first two annulations subequal in length, third annulation longer than first two. Dorsal tentacles emerging from posterior margin of third annulation; first branchiae on setiger 1, dorsal to notosetal bundle, similar in subsequent branchiae.

Anterior and midbody regions with 4–6 long, fimbriated, capillary notosetae; spines from setiger 28 in holotype (26–29 in other specimens) with single spine accompanied by three capillaries, subsequently with three spines and four capillaries grading to six spines and six capillaries of varying length in posterior body region (Fig. 1 D); neurosetae of anterior region 5–8 fimbriated, capillary setae, spines first present from setiger 26 in holotype (21-28 in other specimens) as single spine accompanied by three capillaries, then in next two setigers with four spines accompanied by two capillaries, posteriorly with row of six spines of varying length each accompanied by hair-like capillary, most dorsal capillary seta in neuropodia approximately 2× length of other setae in fascicle (Fig. 1 D). Spines long, narrow, unidentate in posterior region dorsalmost notosetal spine and ventralmost neurosetal spine may be bidentate.

Methyl green staining pattern. Prostomium and peristomium not staining; peristomium staining only slightly; remainder of body staining a uniform light green.

Habitat. Known only from mud, 35 m in the Golfo de Nicoya.

Remarks. Chaetozone acuminata sp. nov. is an unusual species of Chaetozone due to the elongate nature of the peristomium and the narrow anterior body region. The thin, elongate spines are somewhat similar to those of C. nicoyana sp. nov., Chaetozone commonalis Blake, 1996 and Chaetozone curvata Hartmann- Schröder, 1965 but the spines of these species have recurved tips, whereas, the spines of C. acuminata sp. nov. have blunt tips. The narrow pre-tentacular and anterior body region of C. acuminata sp. nov. is also different from the body forms of the other three species. Based upon the first occurrence of notopodial and neuropodial spines, C. acuminata sp. nov. is similar to Chaetozone christiei Chambers, 2000 but the body morphology is very different. The spines of C. christiei appear to be somewhat long and thin with a unidentate tip similar to those of C. acuminata sp. nov. although they are not well illustrated by Chambers (2000).

Etymology. The specific name is from the Latin acuminus, meaning sharply pointed and is in reference to the narrow, pointed anterior region of the body of this species.