Kirkegaardia filiformis, Blake & Dean, 2019

Blake, James A. & Dean, Harlan K., 2019, New Species of Cirratulidae (Annelida, Polychaeta) from the Caribbean Sea, Zootaxa 4671 (3), pp. 301-338 : 320-322

Kirkegaardia filiformis new species

Figure 11

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Material examined. Caribbean Sea, Carib 1, R/V Alpha Helix , Aruba, western coast, 500 m off Oranjestad , Sta. ND-16-500, 12°30.3ʹN, 70°02.7ʹW, 26 June 1977, dredged, 30 m, holotype ( USNM 1557524 ) .— Belize, near mouth of channel to Southern Lagoon , Sta. PD-69-500, 17°13.2ʹN, 88°16.5ʹW, 17 July 1977, subtidal, pipe dredge from anchored vessel, depth 25 m, 8 paratypes ( USNM 1557525 ) .

Description. Holotype incomplete with about 40 setigers, 6.7 mm long, 0.36 mm wide across setiger 6; largest paratype (USNM 1557525) complete with 38 setigers, 6.2 mm long, 0.2 mm across thorax. Thoracic region ten setigers long in holotype, fewer in paratypes; segments about four times as wide as long in anterior segments with weakly developed parapodial shoulders only slightly elevated, dorsal surface weakly convex with narrow dorsal ridge over first four setigers ( Fig. 11A ). Middle body segments approximately as long as wide, not moniliform, with parapodial lobes greatly reduced and setae emerging directly from body wall. Body round in cross section throughout. Color in alcohol white.

Pre-setiger region twice as long as wide ( Fig. 11A ). Prostomium triangular, tip rounded, eyespots absent; nuchal organs lateral bulges on holotype, not observed on paratypes. Triannulate peristomium 1.4 times as long as wide, similar in width to anterior setigers; dorsal crest present ( Fig. 11A ). Dorsal tentacles at posterior margin of peristomium; first pair of branchiae arise dorsal to notosetae on setiger 1 ( Fig 11A ), branchiae similarly located in subsequent setigers.

Thoracic parapodia reduced ridges; thoracic notopodia of holotype with 10–12 capillary setae on first 15 setigers, reduced to 7–9 capillaries by setigers 20–22; setiger 35 and posteriormost segments with about 7 capillaries; smaller paratypes with fewer setae. Capillaries include both long, thin smooth capillaries and thicker setae from setiger 12, these with a finely denticulated edge bearing numerous pointed teeth ( Fig. 11D ). Thickened denticulated capillaries and a few simple, longer, natatory-like capillaries in a few mid-body segments. Anterior neuropodia with 5–8 denticulated capillaries, reduced to 5–6 at about setiger 35. All neuropodial capillaries thicker and shorter than notosetae and denticulated edge with more prominent teeth with a rounded edge ( Fig. 11C ). Certain views of denticulated neurosetae suggest up to three rows of denticles may occur; details beyond resolution with light microscopy.

Last segment on paratype tapering to narrow pygidium bearing terminal rounded lobe ( Fig. 11B ).

Methyl Green stain. No pattern; middle segments retain diffuse stain longest after differentiation.A few groups of cells retain stain along body, but not consistent.

Remarks. Among the known species of Kirkegaardia , K. filiformis n. sp. is most similar to K. acunai Dean & Blake, 2009 from off Pacific Costa Rica, K. fragilis Blake, 2016 from abyssal depths in the Pacific Ocean, and K. kladara Blake, 2016 from slope depths off North Carolina, USA. Each of these species has the first branchiae occurring singly on setiger 1 together with denticulated setae in both noto- and neuropodia. Of these, the two latter species have moniliform abdominal segments and an expanded posterior end with crowded segments instead of no moniliform segments and no expanded posterior segments.

Kirkegaardia filiformis n. sp. is, therefore, most similar to K. acunai , the Costa Rican species. The two species differ in that there are four peristomial rings in K. acunai instead of three and MG stain produces ventral bands on anterior segments of K. acunai , instead of no stain retained at all in K. filiformi s n. sp. In addition, in K. acunai den- ticulated setae begin in notopodial setigers 24–32 and neuropodial setigers 22–33; in K. filiformis n. sp. denticulated notosetae begin on setiger 12 and denticulated neurosetae are present from setiger 1.

Etymology. The epithet filiformis , is from the Latin, filum, for thread, and refers to the thin, thread-like body of this species.

Distribution. Caribbean Sea, Aruba and Belize, dredged from 25– 30 m.

Figures

FIGURE 11. Kirkegaardia filiformis n. sp. A, anterior end, dorsal view; B, posterior end, left lateral view; C, denticulated neuropodial capillary, inset not to scale; D, denticulated notopodial capillary, inset not to scale. A, C–D, holotype (USNM 1557524); B, paratype (USNM 1557525).