Chaetozone homosetosa ( 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 : 89-93

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

Figures 48–49

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

Caulleriella homosetosa Hartmann-Schröder & Rosenfeldt, 1989: 67–68 , figs. 6–8; 1990: 11.

Chaetozone sp. 1: Hilbig 2001: 540; Hilbig et al. 2006: 715, 717–719, 724 (in part); Ellingsen et al. 2007: 1269; Montiel et al. 2016: Appendix 2.

Chaetozone sp. 3: Hilbig 2001: 540; Hilbig et al. 2006: 715, 717, 719, 724 (in part); Montiel et al. 2005: 197; 2016: Appendix 2.

Material Examined. South Shetland Islands, King George Island, Admiralty Bay, R / V Polarstern Cr. ANT-III/ 2, 03 Dec 1984, Sta. 203, 62°05.30ʹS, 57°39ʹW, 265 m, holotype ( ZMH 196329 ) and 24 paratypes ( ZMH 196330 ); Collins Harbor , USCG Staten Island , coll. W.L. Schmidt , 28 Feb 1963, Sta. 64-63, 62.2°S, 58.93°W, 86 m (1, USNM 187606 ); Martel Inlet , R / V Hero, Sta. 721-809, 15 Jan 1972, 62.0933°S, 58.3683°N, Petersen grab, 142 m 1 ( USNM 187627 ); Deception Island, R / V Hero Sta. 824 44-1, 03 April 1982, 62.9867°S, 60.5775°W, VV grab, 60 m (3, USNM 187647 ).— Off King George Island , R / V Polarstern , EASIZ II (ANT-XV/3) , coll. B. Hilbig, Sta. 299, 14 Mar 1998, 62°15.8ʹS, 58°42.7ʹW, MG , 207 m (7, SMF 24938); Sta. 300 , 14 Mar 1998, 62°16.8ʹS, 58°42.1ʹW, MG , 423 m (26, SMF 24939); Sta. 330 , 18 Mar 1998, 61°20.6ʹS, 58°15.1ʹW, MG , 2009 m (2, SMF 24940).— Drake Passage , R / V Polarstern , EASIZ II (ANT-XV/3) , coll. B. Hilbig, Sta. 48-341, 19 Mar 1998, 61°34.5ʹS, 58°07.0ʹW, MG , 429 m (4, SMF 24941); Drake Passage , R / V Polarstern , EASIZ II (ANT-XV/3) , coll. B. Hilbig, Sta. 48-345, 20 Mar 1998, 61°53.3ʹS, 59°06.9ʹw, MG , 218 m (9, SMF 24942); Sta. 48-356 , 20 Mar 1998, 62°00.3ʹS, 59°14.9ʹW, MG , 103 m (2 SMF 24943).— West Antarctic Peninsul a, Palmer Archipelago , Anvers Island, Arthur Harbor: R / V Hero Sta. 721-758, 2 Jan 1972, 64.7658°S, 64.1106°W, Petersen grab, 73 m (1, USNM 187630 ); Sta. 721-759 , 2 Jan 1972, 64.765°S, 64.1142°W, Petersen grab, 84 m (1, USNM 1129131 ); Sta. 721-771 , 2 Jan 1972, 64.76°S, 64.12331°W, Petersen grab, 82 m (1, USNM 1129135 ); Sta. 824-38-1 , 29 Mar 1982, 64.7567°S, 64.1439°N, VV grab, 193 m (400+ USNM 1129127 ); Janus Island , R / V Hero, Sta. 731-1798, 18 Feb 1973, 64.7889°S, 64.1172°W, OP grab, 105 m (1, USNM 1129133 ); Wilhelm Archipelago , Petermann Island, R / V Hero Sta. 721-990, 10 Dec. 1971, 65.170°S, 64.125°N, Petersen grab, 64 m (1, USNM 1129134 ); Argentine Islands, Meek Channel, R / V Hero, Sta. 824-3-3, 15 Mar 1982, 65.2333°S, 64.2583°W, VV grab, 59 m (210, USNM 187978 ); Sta. 824-3-4 , 15 Mar 1982, 65.2333°S, 64.2583°W, VV grab, 60 m (215, USNM 187986 ); Sta. 824-3-5 , 15 Mar 1982, 65.233°S, 64.258°W, VV grab, 60 m (40+ USNM 1490750 ); Melchior Island , R / V Hero, Sta. 824-16-2, 22 Mar 1982, 64°19.50ʹS, 62°59.58ʹW, VV grab, 85 m (23, USNM 1490751 ); Sta. 824-16-3 , 22 Mar 1982, 64°19.50ʹS, 62°59.58ʹW, VV grab, 85 m (20, USNM 1490752 ); Sta. 824-16-4 , 22 Mar 1982, 64°19.50ʹS, 62°59.58ʹW, VV grab, 87 m (10, USNM 1490753 ).— East Antarctic Peninsula , Prince Gustav Channel, RVIB Nathaniel B. Palmer, Cr. 2000-3, coll. J.A. Blake, SM grab, Sta. 01, 14 May 2000, 64°17.625ʹS, 058°34.678ʹW, SM grab, 768 m (4 + 50 juvs,, LACM-AHF Poly 10232); Sta. 33 , 24 May 2000, 64°11.959ʹS, 058°41.857ʹW, 587 m (3, MCZ 149859 ); Sta. 34 , 24 May 2000, 64°10.995ʹS, 058°34.140ʹW, 865 m (5, MCZ 149860 ); Sta. 35 , 24 May 2000, 64°10.471ʹS, 058°28.505ʹW, 651m (4, JAB).— East Antarctic Peninsula , former Larsen Ice Shelf A area, border with Larsen B, RVIB Nathaniel B. Palmer, Cr. 2000-3, coll. J.A. Blake, SM grab, Sta. 11, 18 May 2000, 64°56.669ʹS, 060°19.281ʹW, 350 m (2, MCZ 149861 ); Sta. 22 , 20 May 2000, 64°46.632ʹS, 060°21.557ʹW, 868 m (5, MCZ 149866 ).— Weddell Sea , USCG Glacier, Sta. 69-2, 25 Feb 1969, 75.517°S, 30.133°W, 412 m (1, USNM 1490778 ); Weddell Sea , SW of Vestkapp, R / V Polarstern , EASIZ II (ANT-XV/3) , coll. B. Hilbig, Sta. 48-092, 04 Feb 1998, 73°34.2ʹS, 22°38.0ʹW, MG , 994 m (9, SMF 24944); Sta. 48-131 , 08 Feb 1998, 73°23.7ʹS, 22°09.1ʹW, MG , 1985 m (1, SMF 24945); off Halley Bay , Sta. 48-136 , 09 Feb 1998, 74°33.0ʹS, 27°13.1ʹW, MG , 2012 m (10, SMF 24946).— Ross Sea , Victoria Land, off Ross Island, USNS Eltanin Cr. 27, Sta. 1907 , 22 Jan 1967, 77.058°S, 166.233°E, Blake trawl, 891 m (3, USNM 1129136 ).— East Antarctica, Wilkes Land , Budd Coast, Wilkes Sta. 24 , 24 Dec 1961, 66.26569°S, 110.56833°E, trawl, 73 m (2, USNM 187603 ) .

Description. A large species, holotype 23 mm long, 6 mm wide, for about 128 setigerous segments; R/V Hero specimens similar, up to 24 mm long with about 110–130 setigerous segments. Body narrow, thin throughout ( Fig. 48A ) slightly enlarged from about setiger 15, narrowing in posterior segments ( Figs. 48B , 49C ). Anterior region rounded dorsally in cross section, flattened ventrally, with no distinct ventral groove or ridge; middle and posterior segments cylindrical in cross section, but not moniliform. Color in alcohol: light tan, most specimens with inconspicuous black pigment speckles on posterior lateral margins of peristomium ( Fig. 49A , D–E), often absent.

Prostomium small, triangular, narrowing to rounded tip ( Figs. 48A , 49A ); eyespots absent; nuchal organs shallow grooves on posterior lateral margin of prostomium, sometimes everted. Peristomium narrow, elongate, about 2/5 longer than wide with three annular rings apparent, best observed laterally, but extending on to but not across dorsum on some specimens ( Fig. 49A ); dorsum elevated as a relatively smooth dorsal crest ( Figs. 48A , 49A ); in some specimens, annular rings only vaguely obvious laterally with grooves visible after staining ( Fig. 49 A–B, D). Dorsal tentacles missing on most specimens, but these narrow, not unusually long when present, arising from posterior border of peristomium ( Figs. 48A , 49A ). First pair of branchiae arising posterior to and

lateral to dorsal tentacles ( Fig. 48A ); subsequent branchiae on posterior border of each setiger, just dorsal to notosetae ( Fig. 48A ); most branchiae short.

Parapodia reduced to simple setal tori; postsetal lamellae absent. Setal fascicles of noto- and neuropodia close together throughout body. Notosetae long capillaries, about ten per fascicle in anterior setigers, decreasing to 7–8 posteriorly; long natatory-like setae throughout body in most specimens, absent in smaller specimens; in posterior segments 3–4 sharply curved narrow notoacicular spines present in last few pre-pygidial segments; neurosetae all capillaries for first 30–60 setigers, 8–10 per fascicle, then transitioning to mixture of short weakly curved spines and capillaries, followed by all spines in last 20 or so setigers, these numbering 5–6 per fascicle ( Fig. 48C ). Neuroaciculars relatively simple, shorter than notoaciculars, most blunt-tipped ( Fig. 48D ), curved toward notopodia; notoaciculars longer, also curved, most sharply pointed, a few blunt-tipped; spines not alternating with capillaries but some notoaciculars accompanied with capillaries. Noto- and neuroacicular spines together in posterior setigers forming partial cinctures numbering about 8–9 spines on a side ( Fig. 48C ).

Pygidium tapering, conical with dorsal anus and ventral lobe; opening of anus bordered dorsally by 6–8 small papillae ( Figs. 48B , 49C ).

Methyl Green stain. Methyl Green imparts a pattern to the peristomium with the annular rings and dorsal crest staining ( Fig. 49 E–F); individual segments with stain concentrating as bands on the venter of some anterior setigers; many specimens not staining or only weakly, probably due to the more than 40–50 years storage in alcohol.

Remarks. Caulleriella homosetosa is transferred to Chaetozone because it has short, curved, sigmoid acicular spines in the neuro- and notopodia instead of bidentate hooks. Furthermore, the setal fascicles of noto- and neuropodia are set close together instead of widely separated as in species of Caulleriella (see Blake 1996). In the original description, Hartmann-Schröder & Rosenfeldt (1989) indicated that the dorsal tentacles and first branchiae originated on setiger 1. However, examination of the holotype indicates this to be in error and they are confirmed as originating on the achaetous posterior part of the peristomium.

Chaetozone homosetosa is similar in overall appearance to Tharyx obtusus , also redescribed in this study (see below). The two species are difficult to separate superficially and sometimes occur in the same samples. Both have a similar morphology to the pre-setiger region with a peristomium having three annular rings and the dorsal tentacles and first pair of branchiae occurring on the posterior ring just anterior to setiger 1. The two species differ, however, in the nature of the posterior noto- and neurosetae. In C. homosetosa , the posterior neurosetae are short, curved, blunt-tipped and arranged into partial cinctures; in T. obtusus , the short spines have classic Tharyx -like knobbed or sub-bidentate tips together with short barbs along the shaft that create a weakly serrated edge on the concave side below the main fang; in C. homosetosa the posterior notosetae include capillaries and thicker spines with blunted tips thus agreeing with the definition of Chaetozone instead of Tharyx .

The overall appearance of the body and relatively few posterior acicular spines of C. homosetosa were initially thought to represent a kind of Tharyx with simple spines instead of with knob-tipped spines typical of most Tharyx species. Chaetozone homosetosa is similar in this respect to C. castanea n. sp. By having reduced cinctures with thin blunt-tipped spines. Both C. homosetosa and C. castanea n. sp. depart in this respect, from most species of Chaetozone that have heavier golden-colored sigmoid posterior spines.

Chaetozone homosetosa has long, natatory-like notosetae present from anterior setigers in most specimens; Hartmann-Schroder & Rosenfeldt (1989) observed these from about setiger 15. These setae appear to be associated with sexual maturity; they are absent in small specimens.

Habitat. Tharyx homosetosus is one of several bitentaculate cirratulids that occur in the vicinity of the Prince Gustav Channel and former Larsen Ice Shelf A. The surficial sediments at these locations collected in May 2000 consisted of 20–40% sand in the upper 0–5 cm ( Gilbert & Domack 2003).

Distribution. East Antarctica, 73 m; West Antarctic Peninsula, 59–429 m; East Antarctic Peninsula, 350–868 m; Weddell Sea, 994–1988 m.

Figures

FIGURE 48. Chaetozone homosetosa (Hartmann-Schröder & Rosenfeldt, 1989). R/V Hero Sta. 8-24, 38-1 (USNM 1129127): A, anterior end, dorsal view; B, posterior end, dorsal view; C, noto- and neurosetae of posterior setiger; D, posterior neuroacicular spine.

FIGURE 49. Chaetozone homosetosa (Hartmann-Schröder & Rosenfeldt, 1989). Photomicrographs: A, anterior end, dorsal view; B, anterior end, right lateral view; C, posterior end, dorsal view; D, anterior end, ventrolateral view; E, anterior end, dorsal view; F, anterior end, ventrolateral view. A–D, R/V Hero Sta. 824 16-2 (USNM 1490751), stained with Shirlastain A; E–F, R/V Hero Sta. 824 3-5 (USNM 1490750), stained with Methyl Green.