Aphelochaeta cincinnata

Aphelochaeta cincinnata (Ehlers, 1908)

Figure 8

Heterocirrus cincinnatus Ehlers, 1908: 129, pl. 17, fig. 15.

Tharyx cincinnatus: Bellan 1974:791; Hartman 1966: 31, pl. 8, fig. 8.

Not Chaetozone cincinnata Augener, 1923. New Zealand, Auckland Islands. Unresolved homonym.

Not Tharyx cincinnatus: Richardson & Hedgpeth 1977: 185–185; Hartman 1978: 167; Hartmann-Schröder 1986: 83–84; Hartmann-Schröder & Rosenfeldt 1989: 71; 1990, 115; Cantone & Sanfilippo 1992: 375; Cantone 1994: 40–41; Gambi et al. 1997: 199, 201–202, 207–209; Knox & Cameron 1998: 70–71, fig. 136; Cattaneo-Vietti, R. et al. 2000: 509; Cantone et al. 2000: 551, 554; San Martin et al. 2000: 87; Siciński 1986: 71–73, Table 2; 2000: 163; 2004: 82; Siciński et al. 2012: 355, 359–365; Pabis & Siciński 2010: Table 2; 2012: 188, 190, 192; Angulo-Preckler et al. 2017: 68–69.

Not Tharyx cf. cincinnatus: Bromberg et al. 2000: 179, 182.

Not Aphelochaeta cincinnata: Parapar et al. 1997: 509; Hilbig 2001: 540; Cantone & Di Pietro 2001: Table 1; Hilbig et al. 2006: 711–725; Souza Barbosa et al. 2010: Table 1; Parapar et al. 2011: 719–724; Paiva et al. 2015: 1348–1351; Pabis & Sobczyk 2015: 117–118: 722 –728; Montiel et al. 2016: 1238–1240, Appendix 1.

Material Examined. Kerguelen Islands, Östlich Bank, collected by trawl from 88 m; Deutsche Tiefsee Expedition, Sta. 161, 48°57ʹS, 70°0ʹE, 88 m, holotype of Heterocirrus cincinnatus Ehlers, 1908 (ZMB 4491).— Off Argentina, Staten Island, South end of Puerto Cook, R / V Hero Sta. 712-668, 54.772°S, 64.048°W, Petersen Grab, 23 m (1, USNM 1013887).

Description of the holotype. Holotype of Aphelochaeta cincinnata (originally described as a species of Heterocirrus) light brown in color, exhibiting evidence of having been partially dry at some time. Specimen posteriorly incomplete, precluding any confirmation of posterior spines. Some areas of body, especially prostomium considerably shrunken and distorted, likely due to drying.

Prostomium and peristomium together relatively long and narrow, smooth, with no evidence of two ventrolateral peristomial grooves as originally figured by Ehlers (1908). First pair of branchiae originates slightly anterior to setiger 1 with second pair slightly more medial and directly on setiger 1. Dorsal tentacles arise from a medial position just posterior to first branchial pair on posterior border of peristomium. Tentacles thick, larger than branchiae. Each subsequent pair of branchiae arises dorsal to notosetae, continuing on subsequent segments. Most anterior setigers with branchiae or a scar of one.

All setae simple capillaries, although posterior most segments missing. Setae number up to eight in anterior fascicles, relatively long suggesting a natatory condition. Eggs, however, not observed anywhere along body. Parapodia reduced to low setal tori, best developed in anterior segments.

Methyl Green stain. No effort to stain this specimen with Methyl Green was made owing to its age and somewhat deteriorated state. However, given the relatively long prostomial/peristomial region, the position of the first branchiae and dorsal tentacles, it should be relatively easy to identify additional specimens of this species should they be encountered in new collections.

Description of a specimen from Staten Island, off Argentina. Specimen small, mostly complete with 32 setigers, ovigerous, measuring 5 mm long, 0.4 mm wide across anterior setigers, and 0.9 mm wide across expanded middle segments. Anterior 10–12 setigers narrow not expanded. Middle body segments expanded, filled with eggs (Fig. 8B) measuring 100–125 µm in largest diameter. Color in alcohol: tan.

Prostomium and peristomium not distinctly separated, forming an elongate pre-setiger region lacking any annuli or evidence of peristomial rings (Fig. 8A); anterior end narrow, bluntly rounded on anterior margin. Peristomium posteriorly forming dorsal wedge onto setiger 1 (Fig. 8A); eyespots absent; nuchal organs not observed. First pair of branchiae anterior to dorsal tentacles along angular wedge at juncture of peristomium and setiger 1; dorsal tentacles medial and posterior to first pair of branchiae; second pair of branchiae on posterior margin of setiger 1 dorsal to notosetae; subsequent branchiae from setiger 2 and those following in same location.

Parapodia well developed in thoracic setigers, set off from dorsal and ventral surfaces by grooves (Fig. 8A), forming low shoulders; middle and posterior parapodia less distinct. Each parapodium with simple setal tori bearing fascicles of smooth bladed capillaries; setal fascicles with 5–7 setae throughout.

Methyl Green stain. No pattern.

Remarks. The original description of Aphelochaeta cincinnata was based on a single specimen, redescribed here, from 88 m in the Kerguelen Archipelago at latitude of approximately 49°S. Thus, the original specimen was from a low-latitude subantarctic locality, not the high Antarctic (i.e., about 59– 60°S or higher).

Ehlers (1908) was very specific in stating that the first pair of branchiae occurs on the peristomium anterior to the dorsal tentacles and not on setiger 1. This agrees with my examination of the holotype. The second pair of branchiae occurs on the posterior border of setiger 1 dorsal to the notosetae. The specimen collected as part the R/ V Hero Station 712-668 (USNM 1013887) from Staten Island off Argentina agrees well with the original description of A. cincinnata and my observations of the holotype.

Based on the geographic location of the original collection by Ehlers (1908) and after examining hundreds of specimens of Aphelochaeta as part of the present study, no specimens among the very extensive Hero, Eltanin, Nathaniel B. Palmer, and Polarstern collections at my disposal as well as the earlier collections identified by Hartman (1967, 1978) that I have reexamined agree with the branchial and tentacle placement that were originally reported by Ehlers (1908) and that are present on the type specimen of Aphelochaeta cincinnata. I am, therefore, of the opinion that A. cincinnata does not occur in the high Antarctic despite numerous reports to the contrary (e.g., Bellan 1972; Hartman 1978; Hartmann-Schröder & Rosenfeldt 1989, 1990; Cantone & Sanfilippo 1992; Knox & Cameron 1998; Siciński 2000, 2004; Hilbig 2001; Hilbig et al. 2006; and many others). The single specimen from Staten Island off Argentina, a subantarctic location, is the only one that agrees with the original concept of A. cincinnata. It is likely that the record of Bellan (1974) from Kerguelen is a correct identification because the position and depth (61 m) are nearly identical with that of the type locality.

Benthic surveys in Antarctica have typically recorded Aphelochaeta cincinnata (or Tharyx cincinnatus) as among the most abundant cirratulid polychaetes in their collections (see references in synonymy lists above). It is now obvious that these numerous records of A. cincinnata actually refer to several of the new species described in this study, with A. cincinnata not being present. For example, the collections from the EASIZ II survey provided by Dr. B. (Hilbig) Ebbe and identified as A. cincinnata, have been re-identified as A. aubreyi n. sp., A. dearborni n. sp., A. palmeri n. sp., and A. spectabilis n. sp., all of which are difficult to separate from one another if the specimens are fragmented. The most abundant species of Aphelochaeta in the EASIZ II materials that had been identified as A. cincinnata is A. palmeri n. sp. from samples off King George Island.

Distribution. Indian Ocean, Kerguelen Islands, 88 m; Staten Island off Argentina, 23 m; possibly other sub- Antarctic islands, shallow water.