Dodecaceria dibranchiata, 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 : 332-335

Dodecaceria dibranchiata new species

Figures 18–19

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Material examined. Caribbean Sea, Carib 1, R/V Alpha Helix , Panama, Golfo De San Blas, Playita Point, Sta. ND-26, 09°32.8ʹN, 78°59.5ʹW, 30 June 1977, dredged in sand, and coral rubble, 30–50 cm, holotype ( USNM 1557520 ) , 26 paratypes + fragments ( USNM 1557521 ) .— off Peninsula Valiente, between Crawl Cay and Canal del Tirge, outside Laguna Chiriqui, Sta. ND-30, 09°12.8ʹN, 82°02.7ʹW, 08 July 1977, dredged along mangrove bank, between Isla Popa and Cayo Ferro , 1–2 m, 2 specimens ( USNM 1557522 ) ; Sta. ND-31, 09°12.8ʹN, 82°02.7ʹW, 08 July 1977, dredged in grass and sand around Deer Island, NE tip of Isla Popa , specimens removed from coral rock, 4 m, 12 specimens + fragments ( USNM 1557523 ) .

Description. Holotype complete, 6.2 mm long for 45 setigers, 0.25 mm across anterior segments, expanded to width of 0.6 mm across middle segments, tapering to a width of 0.25 mm across posterior segments. Complete paratype (USNM 1557521) 5.5 mm long with 40 setigers. Anterior segments about 3.2 times wider than long ( Figs. 18A ; 19A ), middle segments larger, about as wide as long, then tapering posteriorly to narrow crowded segments about eight times wider than long ( Fig. 19 A–B). Body generally cylindrical throughout with posterior region becoming dorsoventrally flattened ( Fig. 19B ). Some anterior segments biannulate; annuli generally not apparent in middle and posterior segments. Color in alcohol tan to dark brown, some segments with transverse rows of brown to black pigment spots, flecks of pigment along most of body, providing some specimens with darkened areas on some segments. A distinct heart body observed in mid-body segments; intestinal tract obvious along entire body ( Fig. 19 A–B).

Prostomium conical, with broadly rounded anterior margin ( Fig. 18A ); eyespots absent; nuchal organs longitudinal lateral slits indistinctly separated from peristomium. Peristomium smooth, elongate, annular rings absent, with little or no evidence of lateral grooves ( Fig. 18A ); with low rounded dorsal crest present; separate achaetous segment at posterior margin absent, but weak groove separates peristomium from setiger 1 ( Fig. 18A ). A pair of thick tentacles arise laterally at posterior-lateral margin of peristomium, these with distinct groove and with numerous transverse folds along length ( Figs. 18A ; 19A ). Branchiae two pairs: first pair arising from posterior margin of peristomium, dorsal to tentacles; second pair of branchiae arising from setiger 1, dorsal to notosetae ( Figs. 18A ; 19A ). Each branchia thick, with folds or grooves along length; both branchiae of same length or monomorphic.

Parapodia poorly developed in anterior setigers with setae arising directly from body wall or from notch. Anterior setigers with long, narrow capillaries with fine serrations along one edge ( Fig. 18B ). Heavy hooked setae from setigers 9–12 in notopodia (9 in holotype) and 8–11 in neuropodia (8 in holotype). Capillaries 3–4 in anterior setigers, then reduced to 1–2 after hooks appear; capillaries absent from about setiger 12–14, resuming from about setiger 20–25 (20 in holotype). Holotype and most paratypes with one notopodial hook initially, then increasing to no more than three hooks in middle segments, reduced to 1–2 hooks in posterior segments. Neuropodia with one hook initially, increasing to four per fascicle in middle segments, then reduced to 1–2 in posterior segments. All hooks spoon shaped, but with notopodial hooks slenderer, less curved, and with either a reduced or absent subapi- cal boss ( Figs. 18 C–D; 19C). Neuropodial hooks thicker, more robust, with distinct spoon shape and with enlarged subapical boss ( Figs. 18 E–F; 19D–G).

Pygidium a broad terminal lobe ventral to anal opening ( Fig. 19B ).

Methyl Green stain. No pattern, stain not retained.

Remarks. Dodecaceria dibranchiata n. sp. is most similar to D. laddi Hartman, 1954 that also exhibits two pairs of branchiae and is from the Marshall Islands in coral reefs, D. gallardoi with three pairs of branchiae from Chile ( Carrasco 1977), and D. diceria with 1–2 pair of branchiae from shelf depths off Florida ( Hartman 1951). Of these three species, D. laddi and D. gallardoi differ from D. dibranchiata n. sp. in having a distinct achaetous segment between the peristomium and setiger 1 from which the first branchiae arise ( Hartman 1954; Carrasco 1977), whereas D. dibranchiata n. sp. lacks such an achaetous segment and the first pair of branchiae arise directly from the posterior margin of the peristomium. In addition, D. gallardoi has two of three branchial pairs anterior to setiger 1. Instead of typical spoon-shaped hooks with a subterminal boss as seen in D. dibranchiata n. sp., D. gallardoi has hooks with a prominent subterminal row of transverse ribs.

Dodecaceria diceria , like D. dibranchiata n. sp., is described as lacking a distinct achaetous segment between the peristomium and setiger 1 and with the first pair of branchiae arising from the posterior margin of the peristomium. The species was originally described and illustrated as having only a single pair of branchiae; however, Hartman (1951) did note that some specimens had a second short pair on setiger 1. Both pairs of branchiae on D. dibranchiata n. sp. are of equivalent length, but the species differs from D. diceria most importantly in the nature of the modified hooks. In D. diceria the hooks have a distinctly serrated frontal margin instead of being spoon-shaped as in D. dibranchiata n. sp. Further, D. diceria is an offshore shelf species that according to Hartman (1951) occurs in shells of living gastropods. D. diceria has also been reported, but not characterized, from benthic samples from the North Sea in depths greater than 100 m ( Gibson 1996). In contrast, D. dibranchiata n. sp. is an intertidal to shallow subtidal (4 m) species that bores into coralline rock.

Etymology. The epithet is from the Greek, di, for two or double, and branchos, for gill, and represents the presence of two pair of branchiae in most specimens of this species.

Biology & habitat. A few non-type specimens from Sta. ND-31 (USNM 1557523) were ovigerous, with hundreds of oocytes in the coelom. The largest eggs were ovoid in shape, 45 x 60 µm, with a large germinal vesicle. Only minimal evidence of regeneration of anterior or posterior segments was found on 3– 4 paratypes from Sta. ND-26 (USNM 1557521).

Some paratypes from Sta. ND-26 were found in burrows in small pieces of coral rock still with the sample residue. The worms were removed by pressing the point of a steel dissecting needle into the rock. This resulted in the burrows splitting open and allowing the worms to be recovered intact. Individual worms were nearly always in a U-shape with the anterior and posterior ends side by side, indicating that at the time of preservation both the mouth and anus were extended from the same burrow opening.

Distribution. Panama, low water, 0–4 m, in burrows in coral rock.

Figures

FIGURE 18. Dodecaceria dibranchiata n. sp. Holotype (USNM 1557520): A, anterior end, dorsal view; B, capillary notoseta from anterior setiger; C–D, notopodial hooks from a middle body setiger; E–F, neuropodial hooks from a middle body setiger.

FIGURE 19. Dodecaceria dibranchiata n. sp. Holotype (USNM 1557520):A, anterior and middle body segments, right lateral view; B, posterior end, dorsolateral view; C, notopodial hook from a middle body setiger; D–G, neuropodial hooks from middle body setigers.