Chaetozone dossena, 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 : 317

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Chaetozone dossena

new species

Chaetozone dossena new species

Figures 9–10 View FIGURE 9 View FIGURE 10

Material examined. Caribbean Sea, Venezuela, Bahía de Mochima, off Cumaná , Sucre State, 22 June 1971, coll. Rex Edwards, low water, 6–10 m in calcareous mud, holotype ( USNM 49932 View Materials ) .

Description. Holotype complete with about 95 setigers, posterior segments twisted, 10.5 mm long, 0.65 mm wide across anterior segments, 0.8 mm across largest middle body segments, narrowing in far posterior segments. Anterior 30 segments narrow, dorsoventrally flattened, about 8–10 times wider than long, with dorsum smooth, rounded; venter with distinct groove from about setiger 10–12 continuing through posterior segments; ventral groove narrowing, developing mid-ventral ridge or row of mounds at mid-point where left and right sides of parapodia merge. Anterior parapodia with well-developed lateral shoulders below elevated and rounded dorsum ( Figs. 9A View FIGURE 9 ; 10A View FIGURE 10 ). Middle body segments narrower, then becoming larger, more rounded than anterior setigers, but with individual segments still narrow, about 6–8 times wider than long. Color in alcohol light tan, with few weak pigment speckles on ventral lip of mouth and mid-ventral surface of first setiger ( Fig. 9B View FIGURE 9 ). A distinctive dorsal blood vessel and heart body apparent in anterior setigers ( Fig. 10A View FIGURE 10 ).

Pre-setiger region short, about as wide as long ( Figs. 9 View FIGURE 9 A–B; 10A). Prostomium elongate, triangular, tapering to narrow, rounded, slightly pointed tip ( Fig. 9A View FIGURE 9 ); eyespots absent; nuchal organs inconspicuous narrow lateral slits. Peristomium with two rings, first short dorsally ( Fig. 9A View FIGURE 9 ), ventrally larger, forming upper lip of mouth ( Fig. 9B View FIGURE 9 ); second ring large, inflated, producing rounded dorsal crest ( Fig. 9A View FIGURE 9 ), ventrally forming lower lip of mouth ( Fig. 9B View FIGURE 9 ). Dorsal tentacles widely separated, arising from posterior margin of peristomium ( Fig. 9A View FIGURE 9 ). First pair of branchiae arising from anterior margin of setiger 1, lateral and posterior to dorsal tentacles; second pair of branchiae on posterior margin of setiger 1, dorsal to notosetae ( Fig. 9A View FIGURE 9 ), thus with two pairs of branchiae on setiger 1.

Anterior setigers with long, basally thickened capillaries numbering 10–12 in both noto- and neuropodia. Notopodial acicular spines first present from setiger 26–27, numbering 1–2 at first, increasing to 3–4 in middle body segments with number of capillaries decreasing to a number equivalent to spines. Neuroacicular spines from setiger 17, replacing several unusually broad, flattened capillaries ( Fig. 9D View FIGURE 9 ); spines numbering 1–2 initially ( Fig. 10B View FIGURE 10 ), then increasing to 3–4 in middle body segments ( Fig. 10C View FIGURE 10 ), accompanied by an equal number of thin capillaries. In posterior setigers, parapodia becoming elevated, forming full cinctured segments with long spines and companion capillaries ( Figs. 9C View FIGURE 9 ; 10D View FIGURE 10 ). Cinctures with spines of left and right sides not merging dorsally, leaving gap with low mid-dorsal groove ( Fig. 9C View FIGURE 9 ). Cinctured spines numbering 7–9 in notopodia and 6–8 in neuropodia, thus with 13–17 spines on each side. Spines of anterior noto- and neuropodia short, thickened, barely emerging from podial lobes ( Figs. 9 View FIGURE 9 E–F; 10B–C); posterior spines in cinctured segments long, curved, tapering to rounded tip ( Figs. 9G View FIGURE 9 , 10D View FIGURE 10 ).

Pygidial segment with anal opening surrounded by three short dorsal cirri and two somewhat longer ventral cirri ( Fig. 9C View FIGURE 9 ).

Methyl Green stain. No stain retained.

Remarks. Chaetozone dossena n. sp. is a distinctive species. The short pre-setiger region with the bulbous and expanded peristomium with a dorsal crest together with the long, tapering prostomium is unique within known species of the genus. In addition, the short, thick, noto- and neuropodial acicular spines transition to long sigmoid spines in the posterior cinctures. The unusually large capillaries with broad, flattened blades in anterior noto- and neuropodia are also distinct. The first pair of branchiae are interpreted as arising from the anterior edge of setiger 1 resulting in two pairs of branchiae on the first setiger.

Etymology. The epithet, dossena , is from the Latin dossenus for clown or jester, and refers to the pre-setiger region of this worm, which resembles the hat of a jester.

Distribution. Venezuela, known only from shallow subtidal sediments in the Bahía de Mochima.