Kirkegaardia playita, 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 : 324-326

Kirkegaardia playita new species

Figures 14

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Material examined. Caribbean Sea, Carib 1, R/V Alpha Helix , Panama, Playita Point , south of tip of San Blas Peninsula, Sta. ND-24-1000, 9°32.8′N, 78°59.′W, 30 June 1977, dredged across sand, grass and rubble at beach, 5 m, holotype ( USNM 1557527 ) and 3 paratypes ( USNM 1557528 ) .

Description. Holotype mostly complete with 42 setigers, 5.2 mm long, 0.3 mm across enlarged anterior or thoracic segments, 0.23 mm across mid-body segments; all paratypes incomplete, of similar proportional size as holotype, but with fewer segments. Entire thoracic region distinctly swollen dorsally and ventrally, with crowded segments each about 10 times wider than long ( Fig. 14 A–B); segmental grooves weakly evident dorsally, inconspicuous ventrally. Middle segments narrower, not crowded, about three times as wide as long ( Fig. 14A ); far posterior segments as wide as long; no segments oval or moniliform in shape. Body generally cylindrical throughout, with no dorsal or ventral grooves evident. Color in alcohol light tan, with no pigment apparent.

Pre-setiger region elongate, smooth, about 1.4 times as long as wide. Prostomium short, conical tapering to rounded apex ( Fig. 14 A–B); eyespots absent; nuchal organs narrow lateral slits at posterior margin. Peristomium with relatively smooth surface, with two lateral grooves producing 1–2 weak annular rings anteriorly; rest of peristomium merging indistinctly with thoracic segments ( Fig. 14 A–B); dorsal tentacles widely spaced, arising anterior to setiger 1 ( Fig. 14B ); first pair of branchiae lateral to dorsal tentacles; second pair of branchiae on setiger 1, dorsal to notosetae; subsequent branchiae in similar location ( Fig. 14 A–B). Branchiae or stub apparent on thoracic segments and following mid-body segments.

Parapodia of anterior segments swollen, producing weak shoulders ( Fig. 14B ); podia reduced to small lobes from which setae emerge; middle and posterior segments with small, inconspicuous podial lobes. Holotype with 5–6 capillary notosetae in thoracic and anterior abdominal segments; neurosetae numbering 4–5 in similar segments. Capillaries of anterior setigers all with smooth margins as viewed in light microscopy (1500 x). Notosetae from about setiger 14–15 of holotype with distinct fibrils along one edge, with some long, thick, probably merged fibrils appearing as pointed barbs ( Fig. 14C ); from about setiger 20, notosetae with a row of low, blunt denticles along one edge ( Fig. 14D ). Neurosetae of holotype all smooth capillaries anteriorly, transitioning to denticulate capillaries by setiger 20–22; denticles more prominent in neurosetae ( Fig. 14E ) than notosetae ( Fig. 14D ).

Methyl Green stain. No pattern, body stains uniformly and de-stains rapidly.

Remarks. Kirkegaardia playita n. sp. is unique in having the entire thoracic region enlarged and swollen and smooth dorsal and ventral thoracic surfaces where the individual segmental morphology is largely obscured. In addition, the pre-setiger region is elongate and smooth, with only 1–2 weak lateral grooves posterior to the prostomium.

Kirkegaardia panamaensis n. sp. also has an expanded thoracic region but only the venter is noticeably swollen rather than both the dorsal and ventral surfaces being swollen as in K. playita n. sp. In addition, the peristomium of K. panamaensis n. sp. is not elongate, but short, about as long as wide, and with three more-or-less prominent annular rings instead of an elongate peristomium with 1–2 anterior weakly developed lateral grooves. Additionally, the serrations on the setae of K. panamaensis n. sp. more closely resemble short, sharp teeth rather than the rounded, blunt denticles of K. playita n. sp.

The mud ball worms, Kirkegaardia luticastella ( Jumars, 1975) and K. jumarsi Blake, 2016 , also have enlarged and swollen thoracic regions, but these species have other modifications of the body including moniliform segments allowing them to live in spiral burrows within mud balls ( Blake 2016). Nevertheless, the enlarged and swollen anterior body segments suggest such species use these body segments to assist hydrostatically in producing cracks in sediment as part of their burrowing activities ( Jumars et al. 2015).

The unusual structure of serrated notosetae having thickened fibrils or barbs in segments anterior to the more typical denticulate noto- and neurosetae of mid-body and posterior segments of Kirkegaardia playita n. sp. suggest perhaps a transitional stage in the development of the denticulate setae.

Etymology. The epithet is derived from Playita Point, the locality in Panama where the specimens of this species were collected. In Spanish, playita is a diminutive of playa, a beach; playita is thus a small beach.

Distribution. Panama, shallow subtidal, 5 m, in sand, grass and rubble.

Figures

FIGURE 14. Kirkegaardia playita n. sp. Holotype (USNM 1557527):A, anterior end, right lateral view; B, anterior end, dorsal view; C, anterior notopodial capillary; D, posterior notopodial capillary; E, posterior neuropodial capillary.