Chaetozone novagracilis, Blake, 2022

Blake, James A., 2022, New species and records of Caulleriella, Chaetocirratulus and Chaetozone (Annelida, Cirratulidae) from continental shelf and slope depths of the Western North Atlantic Ocean, Zootaxa 5113 (1), pp. 1-89 : 54-57

Chaetozone novagracilis new species

Figures 27–28

urn:lsid:zoobank.org:act:D490E4E7-35ED-468F-A132-B9DD9D3446F2

Chaetozone setosa: Blake et al. 1987 : C-2 (in part). Not Malmgren 1867.

Material examined. (2 specimens) Off Charleston, South Carolina, US South Atlantic ACSAR Program, coll. J.A. Blake, Chief Scientist. Sta. 14A: Cruise SA-5, Rep. 2, 20 Sep 1985, 32°23.26′N, 77°165.29′W, 605 m, holotype ( USNM 1661373 ); Rep. 3, 20 Sep 1985, 32°22.22′N, 77°15.31′W, 605 m, 1 paratype ( USNM 1661374 ) .

Description. An elongate, relatively narrow-bodied species with width consistent through middle segments, then tapering slightly posteriorly. Holotype complete, but partially broken in two places posteriorly; with 77 setigers, 9.25 mm long, and 0.54 mm wide across anterior setigers ( Figs. 27A–B , 28A–B ). Paratype similar but with posterior setigers damaged, stretched, and terminal end missing. Body cylindrical in cross section, with dorsal and ventral surfaces weakly rounded; elevated.. Holotype with shallow dorsal groove along anterior end middle segments ( Fig. 28B ). All segments short, with anterior and middle segments crowded, about 8–9 times wider than long; posterior segments longer, about as long as wide, but not moniliform; cinctures not developed. Color in alcohol light tan without any pigment on body.

Pre-setiger region elongate, thick, about as long as first ten setigers, tapering anteriorly ( Figs. 27A–B , 28A–B ). Prostomium triangular, tapering to narrow pointed tip ( Fig. 27A–B ); eyespots absent; nuchal organs rounded raised openings on posterior lateral margin ( Fig. 27B ). Peristomium an elongate, single ring lacking any evidence of annular rings or grooves; paratype with two longitudinal grooves separated mid-dorsally by ridge producing dorsal crest ( Fig. 27A ). Dorsal tentacles arise near posterior margin of peristomium with first pair of branchiae on setiger 1; subsequent branchiae in similar location.All branchiae missing or reduced to stubs, except for a single thin branchia on one posterior segment of holotype.

Parapodia of anterior and middle segments located laterally, on raised ridges with noto- and neuropodia positioned close together ( Figs. 27A–B , 28B ); parapodia of posterior segments more widely separated, with podia reduced to low ridges or mounds from which setae arise. Anterior setae all long capillaries numbering about 10–12 per fascicle in notopodia and 6–8 in neuropodia, continuing through middle setigers; long natatory-like setae absent. Neuropodial acicular spines from setiger 44 in holotype; these spines number two per fascicle with capillaries at first; increasing to 5–6 spines in far posterior setigers accompanied by only 1–2 capillaries. Notopodia without separate acicular spines except last two setigers where two short, thickened, spinous capillaries occur among long thin capillaries. Thus, only up to seven or eight spines or spinous capillaries present in far posterior setigers; distinct posterior cinctures of spines not developed. Individual neuropodial spines unusual, with thickened shaft weakly curving to rounded tip; in lateral view, concave side of shaft with a groove and with apex of shaft expanded bearing same groove ( Fig. 28C ). In other views, groove and expanded shaft not clearly evident.

Body terminating in multilobed pygidium consisting of two rounded ventral lobes and two small dorsal lobes ( Fig. 27C ).

Methyl green staining. Prostomium retaining stain, otherwise no pattern.

Remarks. Chaetozone novagracilis n. sp. is unusual among bitentaculate cirratulids in having a multilobed pygidium and a unique grooved apical enlargement on the acicular spines. Although prominent and well-developed neuropodial acicular spines are present, notopodial spines are reduced to a pair of spinous capillaries. The absence of an equivalent number of notopodial spines and of distinct posterior cinctures of spines departs from the latest generic diagnosis of the genus. In this regard, Chaetozone novagracilis n. sp. is most similar to C. gracilis , a deepwater species from off California (depth 4016 m) that also has a reduced number of acicular spines that do not form distinct posterior cinctures and a multilobed pygidium ( Moore 1923; Blake 1996). Chaetozone novagracilis n. sp. differs from C. gracilis in having an undivided peristomium instead of one that has a smooth elongate ring followed by a separate achaetous segment that bears the dorsal tentacles and first pair of branchiae. In contrast, the peristomium of C. novagracilis n. sp. is undivided with the dorsal tentacles on the posterior margin and the first pair of branchiae arising from setiger 1. In addition, the neuropodial acicular spines of C. novagracilis n. sp. first occur on setiger 44 instead of 33, and the spines have an unusual apical enlargement that bears a longitudinal grove or channel that continues along convex side of the shaft. Such a spine has not been previously observed in cirratulids.

Biology. Cruise SA-5 was the only ACSAR survey on which samples were collected at Sta. 14A off South Carolina. The ecological results were presented by Blake et al. (1987) and Blake & Grassle (1994). The site was unusual in that the sediment consisted of 94–95% sand with low water content. The coarse grain size of the sediments appears to be important for Chaetozone novagracilis n. sp. because it was not encountered at other adjacent 600 m stations off Cape Lookout and Cape Hatteras where the sediments have a high silt + clay content. Other newly described polychaetes known only from Sta. 14A are the orbiniid Leodamas mucronatus Blake, 2021a and another cirratulid, Caulleriella pintada Blake, 2021b . The latter species, with 14% of the total number of individuals among three replicate 0.09 m 2 samples, was the most abundant benthic invertebrate species at the site ( Blake & Grassle 1994; Blake 2021b).

Etymology. The epithet is from novus, Latin for new or recent; and gracilis, Latin for slender or thin and is in reference to the close morphological similarity of the new species to C. gracilis ( Moore, 1923) .

Distribution. Off Charleston, South Carolina, 605 m.

Figures

FIGURE 27. Chaetozone novagracilis n. sp. Holotype (USNM 1661373): A, anterior end, dorsal view; B, anterior end, right lateral view; C, pygidium, dorsal view.

FIGURE 28. Chaetozone novagracilis n. sp. Holotype (USNM 1661373): A, entire worm, right lateral view; B, anterior end, right lateral view; C, neuropodial acicular spine. Stained with Shirlastain A.