Chaetozone bransfieldensis ( Hartmann-Schröder & Rosenfeldt, 1989 ) Blake, 2018

Blake, James A., 2018, Bitentaculate Cirratulidae (Annelida, Polychaeta) collected chiefly during cruises of the R / V Anton Bruun, USNS Eltanin, USCG Glacier, R / V Hero, RVIB Nathaniel B. Palmer, and R / V Polarstern from the Southern Ocean, Antarctica, and off Western South America, Zootaxa 4537 (1), pp. 1-130 : 77-80

Chaetozone bransfieldensis ( Hartmann-Schröder & Rosenfeldt, 1989) new combination

Figure 42

Tharyx spp. Hartman 1967: 118 (in part).

Chaetozone setosa: Hartman 1978:166 (in part). Not Malmgren, 1866.

Caulleriella bransfieldensis Hartmann-Schröder & Rosenfeldt, 1989: 67 , figs. 3–5.

Material Examined. Antarctic Peninsula, Bransfield Strait, R / V Polarstern, Cr. ANT-III/2, Sta. 207, coll. 3 Dec. 1984, 62°59ʹS, 57°05ʹW, 68 m, holotype ( ZMH P-19615) ; USNS Eltanin Cr. 6, Sta. 436, 8 Jan 1963, 63.23°S, 58° W, Otter trawl, 73 m (1, USNM 1129132 ).— South Shetland Islands, south of Low Island , R / V Hero Sta. 691- 26, 10 Feb 1969, 63.425°S, 62.250°W, 119–124 m, (1, USNM 187652 ); NE of Clarence Island , USNS Eltanin Cr. 12, Sta. 1089, 17 Apr 1964, 60.78°S, 53.507°W, 641 m (1, USNM 56078 ); Deception Island , R / V Hero, Sta. 721- 797, 12 Jan 1972, 62.972°S, 60.83°W, Petersen grab, 81 m (1, USNM 1490769 ).— Ross Sea, off Cape Adare , USNS Eltanin Cr. 27, Sta. 1869, 13 Jan 1967, 71.267°S, 171.667°E, trawl, 1565–1674 m, (1, USNM 1490768 ).— Weddell Sea, Coats Land, off Halley Bay , USCG Glacier, Sta. 69-1, 24 Feb 1969, 74.468°S, 30.528°W, Anchor dredge, 513 m (3, USNM 46788 ) .

Description. A small to moderate-sized species, holotype approximately 10 mm long, 1.0 mm wide for 82 setigers; paratypes reported larger, 22 mm long, 1 mm wide with up to 122 setigers ( Hartmann-Schröder & Rosenfeldt 1989). Body enlarged, somewhat fusiform anteriorly, then narrowing posteriorly. Color in alcohol: light tan, with some faint dusky pigment on anterior end especially in grooves of peristomial annuli.

Prostomium triangular, narrowing to rounded tip ( Fig. 42A ); a single pair of reddish eyespots present ( Fig. 42A inset), or absent; each eyespot when present round with distinct lens surrounded by red pigment cup; nuchal organs not observed. Peristomium wide, with two annuli, second trapezoidal in shape, narrowing posteriorly and terminating in middle of setiger 1. Dorsal tentacles arising from setiger 1, lateral to end of peristomium ( Fig. 42A ); first pair of branchiae lateral and posterior to dorsal tentacles on setiger 1; second pair of branchiae on setiger 2; subsequent branchiae dorsal to notosetae on each segment; most branchiae short or limited to stubs ( Fig. 42C ).

Parapodia reduced to simple setal tori; postsetal lamellae absent. Setal fascicles of noto- and neuropodia close to one another throughout body. Notosetae long capillaries anteriorly, partially replaced by a pair of heavy curved spines from about setiger 22–24; capillary neurosetae mostly replaced by 1–2 heavy spines from setiger 9–12, spines increasing to 4–5 in far posterior setigers; noto- and neuroacicular spines in pairs throughout middle setigers ( Fig. 42B ); posterior spines forming partial cinctures with 4–5 opposing spines arising from thin membranous elevated podial lobes ( Fig. 42C ); 8–10 spines on a side. Spines heavy, with those most medial and newest thicker and more curved ( Fig. 42D ). Some specimens epitokous with long, natatory setae. Pygidium a rounded disk ventral to anal opening.

Methyl Green stain. Body staining uniformly; no distinct pattern or speckling apparent.

Remarks. Caulleriella bransfieldensis is here transferred to Chaetozone because it has simple blunt-tipped spines in the noto- and neuropodia instead of bidentate hooks. The spines form partial cinctures in posterior segments as in several related species ( Blake 1996, 2015). Furthermore, the setal fascicles of noto- and neuropodia are set close together instead of widely separated as in species of Caulleriella (see Blake 1996; this study). The species is readily distinguished from Antarctic congeners by the presence of a single pair of eyespots (when present) and the heavy noto- and neuropodial spines that form partial cinctures in posterior segments.

On a global basis C. bransfieldensis is similar to C. acuta Banse & Hobson, 1968 from the Puget Sound, Washington (see Blake 1996). Both species have a pair of eyespots and acicular spines first present from anterior setigers; posterior spines are developed into partial cinctures. In C. acuta , some anterior notopodial spines are of an unusual oblique shape with fibrils present along one edge; such setae are absent in C. bransfieldensis . In C. acuta the dorsal tentacles and first pair of branchiae arise from the posterior part of the peristomium; in C. bransfieldensis , they first appear on setiger 1.

Distribution. Antarctic Peninsula, Ross Sea, Weddell Sea, shelf and slope depths, 73–1674 m.

Figures

FIGURE 42. Chaetozone bransfieldensis (Hartmann-Schröder & Rosenfeldt, 1989). A, anterior end, dorsal view, arrow indicates detail of eyespot, not to scale; B, mid-body segment, setiger 40, with paired noto- and neuroacicular spines and companion capillaries; C, far posterior segment, with partial cinctures of noto- and neuroacicular spines; D, neuroacicular spines. A, C, holotype (ZMH P-19615); B, D, specimen from Hero, Sta. 721-797 (USNM 1490769). C, modified from Hartmann-Schröder & Rosenfeldt 1989.