Chaetocirratulus andersenensis Blake 2018, new combination

Chaetocirratulus andersenensis (Augener, 1932), new combination

Figures 28–29

Heterocirrus andersenensis Augener, 1932: 46–47, fig. 3a–e.

Caulleriella andersenensis: Hartman, 1959: 401.

Chaetozone andersenensis: Hartman 1966: 26–27, pl. 7, figs. 1–3; 1967: 116–117; Cantone et al. 2000: 554; Hilbig et al. 2006: 724.

Tharyx fusiformis Monro, 1939: 129–130, fig. 18a–b. Hartman 1966: 32, pl. 8, figs. 5–6. New synonymy.

Material Examined. Antarctic Peninsula, Western sector, Off Peter I Island, 68°50ʹS, 90°35ʹW, 226–380 m, syntypes of Heterocirrus andersenensis: lectotype (ZMO C668), 2 paralectotypes (ZMO C669), and 1 paralectotype (ZMH V-11882).— Scotia Sea, Burdwood Bank, USNS Eltanin, Cr. 6. Sta. 344, 4 Dec 1962, 54.07°S, 58.75°W, Menzies trawl, 119 m (7, USNM 187626).— Drake Passage off South Shetland Islands, R / V Polarstern, ANDEEP I (ANT-XIX/3), Sta. 114-6, 18 Feb 2002, 61°43.55ʹS, 60°43.87ʹW, box corer, 2905 m (1, SMF 24914).— South Shetland Islands: 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, (6, SMF 24911); Sta. 300, 14 Mar 1998, 62°16.8ʹS, 58°42.1ʹW, MG, 423 m (1 SMF 24912); Sta. 325, 17 Mar 1998, 62°21.9ʹS, 58°42.6ʹW, MG, 805 m (1, SMF 24913).— West Antarctic Peninsula, Marguerite Bay, USCG Eastwind Sta. 4A, 24 Jan 1966, 67°53ʹS, 69°10.5ʹW, 300 m, coll. D. Pawson and Squires (13, USNM 1490727); Palmer Archipelago, Wiencke Island, Port Lockroy, R / V Hero Sta. 721-969, 7 Dec 1971, 64.8183°S, 63.53672°W, Petersen grab, 100 m, (2, USNM 187646); Sta. 721-970 7 Dec 1971, 64.8172°S, 63.5467°W, Petersen grab, 102 m (4, USNM 187634); Gerlache Strait, Two Hummock Island, R / V Hero Sta. 824-24-1, 23 Mar 1982, 64.248°S, 61.445°W, trawl, 540–605 m (1, USNM 1490731); Lion Island, Gerlache Strait, R / V Hero Sta. 721-729, 27 Dec 1971, 64.6967°S, 63.0417°W, Petersen grab, 318 m (1, USNM 187604); Graham Land, Paradise Harbor, Hero Sta. 731-1946, 11 Mar 1973, 64.88389°S, 62.88222°W, Blake trawl, 262–274 m (1, USNM 187983); off Graham Land, R / V Hero Sta. 721-1075, 23 Feb 1972, 64.790°S, 64.370°W, Blake Trawl, 91–110m (1, USNM 1490728); Argentine Islands, Penola Strait, R / V Hero Sta.; 824-13-1, 19 Mar 1982, 65.23°S, 64.20°W, Blake trawl, 310–360 m (3, USNM 1490729); Biscoe Islands, Grandidier Channel, Larrouy Island, R / V Hero Sta. 824-5-1, 16 Mar 1982, 65.94°S, 65.297°W, Blake trawl, 246–270 m (1, USNM 1490730).— East Antarctic Peninsula, Prince Gustav Channel, RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, Sta. 35A, 25 May 2000, 64°10.471ʹS, 058°28.505ʹW, SM grab, 651 m (2, LACM-AHF Poly 10213).— Ross Sea, Victoria Land, west of McMurdo Station, USNS Eltanin Cr. 32, Sta. 2059, 25 Jan 1968, 77.97°S 178.08°E, trawl, 655 m (1 USNM 1490732)— East Antarctica, off Mac Robertson Land, R / V Discovery Sta. 107, coll. 16 Feb. 1931, 66°45ʹS, 62°03ʹE, dredged, 219 m, 2 syntypes of Tharyx fusiformis (BMNH ZK 1941.3.3.97-98).

Description. Body large, a robust species, with smaller specimens distinctly fusiform (Fig. 28A), larger specimens more elongate but thickened, expanded in middle segments. Lectotype (ZMO C668) complete, twisted, about 33 mm long, with about 80 setigers (Fig. 28C). Largest paralectotype (ZMH V-11882) about 36 mm long, 4 mm wide at chaetiger 8, with about 80 setigers; one specimen from USCG Eastwind Sta. 4A, 14 mm long, with first 2 mm narrow, consisting of 10–12 setigers, followed by a 10 mm section up to 4 mm wide and with 22 setigers, then narrowing in last 2 mm (ca. 12 setigers) (Fig. 28A). Larger specimens elongate, one from Eltanin Sta.

32-2059 (USNM 1490732) 34 mm long, 2.2 mm wide along anterior and middle segments, narrowing posteriorly with about 80 setigers; similar specimens from EASIZ II, Sta. 299 (SMF 24911), about 35 mm long (Fig. 29 A–B). Some elongate specimens with venter flattened with shallow groove in middle segments replaced by low midventral ridgeline in posterior segments. Specimens with most robust and fusiform appearance usually filled with ova averaging 150 µm in diameter. Color in alcohol light tan or greyish brown; no additional body pigment observed.

Prostomium broadly triangular or wedge-shaped, rounded on anterior margin, wider than long (Figs. 28 A–C, 29C–E), sometimes with nuchal organs emergent, visible at lateral, posterior edges. Large peristomium with two distinct lateral grooves following prostomium resulting in three subequal annular rings (Figs. 28 A–C, 29C–D); dorsal tentacles dorsomedial in location, arising from groove between peristomium and setiger 1; tentacles thick, short in preservation (Fig. 28 A–B). First pair of branchiae lateral to dorsal tentacles on posterior margin of peristomium; subsequent branchiae on setiger 1 and following, arising dorsal to setal fascicles, continuing through first half of body (Fig. 28 A–C).

Parapodia simple, slightly expanded ridges with narrow podial lobes from which setae arise (Fig. 28C); smaller specimens with better development of parapodia in first few, non-expanded segments. Setae of anterior setigers all long, thin, simple capillaries, numbering 6–8 per fascicle in largest specimens. Neuropodia of the last 5–20 or fewer setigers bearing 1–4 heavy, straight acicular spines (Fig. 28E) and a few accompanying capillaries (Fig. 28D); spines clear or opaque, not colored; largest specimens also with few short spines in some posterior notopodia. Pygidium an expanded saucer or conical structure, sometimes pointed posteriorly, surrounding dorsally directed anal opening (Figs. 28A, 29B).

Variability. The shape of the body varies from a distinctly fusiform shape where the individual segments are short and crowded to more elongate thickened bodies that are widest in the middle and have more elongate segments that are not tightly crowded. The first appearance of neuropodial spines begins in posterior segments and may include the last 1–5 segments or up to the last 20 segments in large specimens. In all specimens, however, regardless of body shape and size, the distinctive MG staining pattern is evident.

Methyl Green stain. Specimens identified as C. andersenensis exhibit a defined staining pattern. The anterior end, including the posterior half of the prostomium, the peristomium, setiger 1, and the dorsum and interparapodial areas of 5–10 anterior setigers, takes up stain (Fig. 29 D–E). The anterior half of the prostomium is a narrow clear crescent (Fig. 29 C–E); anterior parapodia stain on their anterior and posterior borders and extend on to the venter as weak transverse bands of speckles; these are sometimes best developed in posterior segments. The middle expanded and fusiform part of the body is largely unstained or only stained weakly; the posterior segments take up stain similarly to those of the anterior segments. Some specimens exhibit a speckling of the branchiae, but in others, the branchiae do not take up stain. The dorsal clear crescent on the prostomium would appear to be diagnostic and should be evident in specimens that might be questionable or posteriorly incomplete. There is variability however; a specimen from Eltanin Sta. 344 (USNM 187626) lacked the clear crescent, with the stain on the prostomium extending all the way to the anterior end.

Remarks. Syntypes of Heterocirrus andersenensis were discovered in two different museums: Zoological Museum of Hamburg (1, ZMH V-11882) by me and the Zoological Museum, Oslo (1, ZMO C668 and 2, ZMO C669) by the late Dr. Mary E. Petersen. I was able to briefly examine the Oslo specimens during a visit with Dr. Petersen in 1997. I had previously examined the Hamburg specimen on loan from Dr. Gesa Hartmann-Schröder in 1986 and again during a visit to ZMH in May 2000. In correspondence dated 01 May 2001, Dr. Petersen convinced me that the specimen from Sta. 129 in 270 m (ZMO C668) was the one Augener referred to in his description and that should be designated as the lectotype, despite the specimen from ZMH being larger. Thus, the syntype (ZMO C668) is a complete specimen and is here designated the lectotype, the other syntypes are designated as paralectotypes.

Examination of the syntypes of Tharyx fusiformis reveals that short acicular spines are present in posterior neuropodia, indicating synonymy with Chaetocirratulus andersenensis. Monro (1939) had indicated that all setae were capillaries, an error that was perpetuated by Hartman (1966) resulting in misidentifications by subsequent workers. The overall Methyl Green staining pattern is more or less the same for all specimens examined, including a syntype of T. fusiformis (BMNH ZK 1941.3.3.97-98). The unstained crescent on the anterior border of the prostomium is definitely present on one paralectotype of C. andersenensis (ZMH V-11882). The ZMO specimens were not tested. The form of the prostomium, shape and degree of segmentation of the peristomium, placement of the dorsal tentacles, and the presence of short spines on posterior setigers are diagnostic for this species. The largest specimens have posterior spines in both noto- and neuropodia; whereas, smaller ones appear to have spines limited to the neuropodia.

There is considerable variability in the body form of this species, probably owing to the modification of body shape at times of sexual maturity. It appears that sexually mature specimens attain the greatest degree of expansion and elaboration of the fusiform shape. Atokous specimens are less extreme in expansion of the body, but all are thick and robust in appearance.

Habitat & biology. Little habitat data is available for the samples associated with Chaetocirratulus andersenensis. R/V Hero Stations 824-7-1, 13-1, and 24-1 from the West Antarctic Peninsula are from rocky seafloors containing pebbles, sponges and mud.

The size of the ova (ca. 150 µm) and the large number of these that fill the coelom suggest that this species spawns directly into seawater. It is likely that the resulting larvae disperse at some point in the water column. Larger eggs would be required for prolonged brood protection or direct development. Distribution. Widespread around Antarctica, in shelf depths, 120–840; Drake Passage, 2905 m.