Chaetozone shackletoni, 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 : 96-98

publication ID

https://doi.org/ 10.11646/zootaxa.4537.1.1

publication LSID

lsid:zoobank.org:pub:169CBE5C-3A6E-438B-8A81-0491CBFBAC85

DOI

https://doi.org/10.5281/zenodo.3798526

persistent identifier

https://treatment.plazi.org/id/03A2CB16-FFAA-A22B-FF36-FE2AFAECFCBB

treatment provided by

Plazi

scientific name

Chaetozone shackletoni
status

sp. nov.

Chaetozone shackletoni View in CoL new species

Figures 51 View FIGURE 51 B–C, 52, 53

Material Examined. Scotia Sea, Powell Basin, R / V Polarstern, ANDEEP III (ANT-XXII/3), Sta. PS67/121-10, 14 Mar 2002, 63°41.74ʹS, 50°42.99ʹW, box corer, 2621 m, holotype ( SMF 24934) and 2 paratypes with fragments ( SMF 24935).— Drake Passage , off South Shetland Islands GoogleMaps , R / V Polarstern, ANDEEP I (ANT-XIX/3), Sta. PS61/105-5, 14 Feb 2002, 61°23.72ʹS, 58°50.04ʹW, box corer, 2266 m, 5 paratypes, ( SMF 24936).— Weddell Sea off Cape Norvegia GoogleMaps , R / V Polarstern, ANDEEP III (ANT-XXI/3), Sta. PS67/78-6, 21 Feb 2005, 71°09.45ʹS, 14°0.32ʹW, box corer, 2168 m, 1 paratype on GoogleMaps SEM stub ( MCZ149853 About MCZ ); off Coats Land , USCG Glacier, S ta. 69- 19, 11 Mar 1969, 74.105°S, 32.605°W, 1622 m, 1 paratype ( USNM 1490775 About USNM ); Sta. 69-20, 12 Mar 1969, 73.823°S, 31.682°W, 2288 m, 2 paratypes ( USNM 1490776 About USNM ). Detached posterior ends present. Some specimens photographed alive during ANDEEP I cruise complete (Sta. PS 67/121-10) but fragmented during preservation GoogleMaps .

Description. A small to moderately-sized species; holotype mostly complete, 10.9 mm long, 0.35 mm wide across anterior setigers, 0.8 mm wide across expanded middle segments, with about 50 setigerous segments; incomplete paratype from Glacier Sta. 69-19, 9.5 mm long, 0.4 mm wide across anterior setigers, 1 mm wide across expanded middle segments, with 43 segments. Body with distinctive shape, including narrow anterior thoracic region of about 15–20 setigers, enlarged middle body “stomach” area, and narrow posterior setigers ( Fig. 52A, C View FIGURE 52 ). Anterior and middle segments generally cylindrical in cross section, with narrow, shallow mid-dorsal groove present ( Fig. 53A View FIGURE 53 ) or absent in anterior thoracic segments; venter of thoracic segments weakly flattened, or with shallow groove present or absent; posterior segments somewhat dorsoventrally flattened; weakly developed. Expanded middle segments prominent, with enlarged stomach area filled with fine sediment ( Fig. 52A, C View FIGURE 52 ), also swollen with eggs in mature specimens. Color in life: deep green, darkest in posterior setigers; color in alcohol light tan, with distinctive brown to reddish pigmentation throughout body.

Prostomium short, conical, tapering to narrow rounded tip ( Figs. 51B View FIGURE 51 , 52A View FIGURE 52 , C–D, 53A–C); eyespots absent; circular ciliated nuchal organ present dorsolateral to oral opening ( Fig. 51C View FIGURE 51 inset); peristomium with three annular rings, first two rings merged dorsally, divided laterally, third ring largest, with pair of dorsal tentacles arising from near posterior margin ( Figs. 51B View FIGURE 51 , 53 View FIGURE 53 A–B); first pair of branchiae located posterior to tentacles, but anterior to setiger 1 ( Figs. 51B View FIGURE 51 , 53 View FIGURE 53 A–B). Second pair of branchiae on setiger 1, dorsal to notosetae on posterior margin, subsequent branchiae in similar location ( Figs. 51B View FIGURE 51 , 53A View FIGURE 53 ). In most specimens, dorsal tentacles and branchiae relatively short throughout body ( Figs. 51B View FIGURE 51 , 52A View FIGURE 52 ).

Parapodia reduced with setae emerging directly from body wall; in far posterior setigers parapodia formed into low membranes bearing partial cinctures of spines and capillaries ( Fig. 53D View FIGURE 53 ). Noto- and neurosetae from setiger 1 all capillaries ( Fig. 53B View FIGURE 53 , E–F), numbering 6–10 per fascicle; individual capillaries with numerous fibrils arising from shaft, best seen with SEM ( Fig. 53G View FIGURE 53 ). Some specimens with long, natatory-like capillaries along most of the body. Acicular spines first occur from setigers 20–25 in neuropodia and setigers 25–30 in notopodia; in smaller specimens, these spines occur more anteriorly, but usually associated with enlarged mid-body segments. In most posterior setigers noto- and neuroacicular spines formed into partial cinctures with spines emerging from low elevated membranes ( Figs. 52B View FIGURE 52 , 53D View FIGURE 53 ); notopodial spines numbering 6–7 and neuropodial spines 5–6, or with 11–13 spines on a side; spines accompanied by closely situated, thin, smooth capillaries; spines broad, tapering to a pointed tip ( Figs. 51C View FIGURE 51 , 52B View FIGURE 52 , 53H View FIGURE 53 ).

Pygidium simple rounded lobe ventral to anal opening ( Fig. 53D View FIGURE 53 ).

Variability. Most of the variability observed in C. shackletoni n. sp. is likely due to contraction during preservation. The peristomial rings are more obvious in specimens where the pre-setiger region appears shortened, likely due to contraction. The presence of a mid-dorsal groove on the anterior thoracic segments is difficult to observe and may be an artifact of preservation. The pigmentation present along most of the body in preservative is either reddish or brown; this pigment is faded in some specimens or entirely absent. In most specimens, the dorsal tentacles and branchiae are missing, but when present, they are often short, not elongate. In the largest specimens, the swollen middle section is also longer and encompasses more segments. In general, the prostomium is short, not elongate as in C. biannulata n. sp.

Methyl Green stain. Body stains uniformly throughout, with no distinct pattern.

Etymology. This species in named in honor of Sir Ernst Shackleton (1874–1922), Antarctic explorer of the Heroic Age, whose Imperial Trans Antarctic Expedition (1914–1917) was curtailed by ice in the Weddell Sea, resulting in his ship the HMS Endurance being trapped, eventually crushed, and sunk, leaving all hands with few options for survival. Shackleton, however, organized the crew and after hauling their life boats across the ice to open water, they eventually landed on Elephant Island. There being no hope for rescue, Shackleton led a small crew on his now-famous boat journey to South Georgia where eventually, after a trek over the mountains from the southern to northern side of the island to the whaling station at Grytviken, he was able to find a vessel, return, and rescue his crew with no loss of life. Years later, while on another expedition, he died on 5 Jan 1922 on South Georgia where he was buried.

Remarks. Chaetozone shackletoni n. sp. is a deep-water species that closely resembles C. biannulata n. sp. with which it may co-occur. Chaetozone shackletoni n. sp. differs in having a shorter prostomium, a distinctly enlarged middle section along the body, brown to red pigmented areas along the body, and partial posterior cinctures of acicular spines with up to 13 spines on a side instead of up to 24 in C. biannulata n. sp. In life, the body of C. shackletoni n. sp. is pigmented green; in preservative, it is brown to red, but fades considerably after long periods of preservation.

The enlarged middle body segments and pigmentation of C. shackletoni n. sp. is reminiscent of another deepwater species, C. brunnea , from the eastern North Pacific ( Blake 2006). In C. brunnea , however, the enlarged area is limited to only a few segments, which actually produce a twist on the body resulting in the posterior segments often being offset from the anterior segments. In C. brunnea , the enlarged segments function as a stomach that is filled with sediment. In C. shackletoni n. sp., the enlarged segments are more posterior on the body, occupy up to 10 segments, and, based on observations, may simply be a site where eggs are stored and mature. An enlarged stomach also occurs in C. australosetosa n. sp. and C. biannulata n. sp. but is rarely conspicuous.

Habitat. Sediments in areas where Chaetozone shackletoni n. sp. were collected were generally olive-grey sandy muds, with silt content being the highest fraction. At the Weddell Sea station the sediment was moderately to poorly sorted: sand (9%), silt (72%), and clay (19%) ( Howe et al. 2007).

Distribution. Antarctic Seas: Drake Passage, Scotia Sea, and Weddell Sea in slope depths, 1622–2288 m.

R

Departamento de Geologia, Universidad de Chile

V

Royal British Columbia Museum - Herbarium

SMF

Forschungsinstitut und Natur-Museum Senckenberg

USCG

Universidad de San Carlos de Guatemala

Kingdom

Animalia

Phylum

Annelida

Class

Polychaeta

Order

Terebellida

Family

Cirratulidae

Genus

Chaetozone

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