Caulleriella quadrata Blake & Dean 2019, new species

Caulleriella quadrata new species

Figure 8

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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°59.5′W, 30 June 1977, dredged across sand, grass and rubble at beach, 5 m, holotype (USNM 1557509).

Description. Holotype incomplete, 2.0 mm long, 0.4 mm wide across anterior setigers, 0.3 across available posterior setigers; with 50 setigerous segments. Body robust, thick and wide anteriorly, tapering posteriorly. Segments rectangular in cross section with noto- and neuropodia located at each of four corners on each segment with lateral longitudinal grooves separating noto- and neuropodia and deep ventral groove separating neuropodia; grooves continuing along entire body. Dorsum weakly rounded, slightly elevated above notopodia across anterior setigers; narrow mid-dorsal groove in middle segments. Color in alcohol opaque white.

Pre-setiger region elongate, triangular, slightly longer than wide. Prostomium triangular, tapering to pointed apex (Fig. 8A); nuchal organs pigmented, oval when seen on posterior lateral margin (Fig. 8B) and when observed dorsally (Fig. 8A), may be mistaken for eyespots. Peristomium with four peristomial rings, variously developed, best seen dorsally (Fig. 8A); first three rings not extending across dorsum; posterior-most ring narrow, nearly continuous across dorsum, possibly an achaetous segment, although branchial scars absent (Fig. 8 A–B). Low dorsal crest over second and third rings, best seen in lateral view (Fig. 8B). Peristomium extending weakly over dorsum of setiger 1 (Fig. 8B). Dorsal tentacles on posterior margin of last peristomial ring. First pair of branchiae on setiger 1, dorsal to notosetae; subsequent branchiae in similar position, present for about 40 setigers (Fig 8A).

Parapodia narrow and crowded along entire body (Fig. 8 A–B); individual noto- and neuropodia narrow but swollen, with narrow ridge from which setae arise. Notosetae all capillaries in anterior setigers, 8–10 per fascicle, with thin fringe of fibrils along one edge (Fig. 8C); notopodial hooks from setiger 22–23, numbering 1–2 at first, up to three in posterior segments; hooks accompanied by 2–3 capillaries; notopodial hooks unidentate, with shaft curving to bluntly rounded tip (Fig. 8D). Neuropodia with 4–5 capillaries anteriorly; bidentate hooks from setiger 15; hooks numbering 2–3 at first, increasing to 5–6 in middle segments, then 4–5 in posterior segments; hooks accompanied by 4–5 capillaries initially, then reduced to 2–3 in middle segments and 1–2 posteriorly. Neuropodial hooks with curved shaft tapering to pointed main fang surmounted by closely adhering apical tooth (Fig. 8E).

Far posterior segments and pygidium unknown.

Methyl Green stain. No pattern, MG de-stains rapidly.

Remarks. Caulleriella quadrata n. sp. is distinctive when viewed superficially because the widely separated noto- and neuropodia result in a prominent lateral groove that extends on both sides along the entire body. In addition, there is a deep ventral channel that, in combination with the lateral channels, produces a body that is rectangular in cross-section with the parapodia at the four corners of the rectangle. The species also has distinctive thick unidentate notopodial hooks that have a rounded, blunt tip. No other American species of Caulleriella has unidentate notopodial hooks in combination with bidentate neuropodial hooks. Two Antarctic species, C. antarcticae Hartman, 1978 and C. kacyae Blake, 2018, have unidentate notopodial hooks, but these are deep-water species with long thread-like bodies that lack lateral and ventral grooves, and the notopodial hooks are slender, not thick.

Etymology. The epithet is from the Latin, quadratus, for four-cornered or square, referring to the widely separated noto- and neuropodia, that in cross-section appear at each of four corners of individual segments.

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