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Description

"Flabellum curvatum Moseley, 1881

 

Flabellum curvatum Moseley, 1881, pp. 174, 175, pi. 6, figs. 3a-3d.—Gardiner, 1939, pp. 327, 328 (part: WS sta. 839 only) .—Squires, 1961 (part: not Vema sta. 14-18), pp. 7, 9, 29, 38, 39, figs. 5, 11-13, 20, 22, 30.—Not F. curvatum; Squires, 1962a, pp. 1-11, figs. 1-3 (is F. thouarsii Milne Edwards and Haime, 1848).—Squires, 1962b, p. 14; 1964a, p. 13; 1964c, pi. 1, fig. 1; 1969, p. 18, pi. 6, map 3.—Cairns, 1979, p. 206.

 

Flabellum antarcticum; Keller, 1974, pp. 203-205, pi. 5, figs. 1-7.

 

 

Description. Corallum ceratoid to trochoid, rarely attached above GCD of 12 mm. Pedicel long, slender (2.5-3.3 mm in diameter), and usually bent; base of pedicel often worn to a point in older specimens. Corallum usually curved, enlarging gradually from pedicel to calice. Largest specimen examined 44 x 30 mm in CD and 47 mm tall. Theca usually worn or encrusted with bryozoans, serpulids, or other corals; sometimes thin, incised costal lines present, one corresponding to each septum. Calice elliptical, with GCD/LCD ratios of 1.4-1.6; calicular profile arched. Septa hexamerally arranged in five cycles. S1

 

and S2 equal in size and usually slightly larger than S3. S4 about half size of S3; S5 rudimentary and sometimes fenestrate because of weakly calcified trabeculae. Septa not exsert; upper edge of each larger septum forming shallow, concave notch near calicular edge. This notch often dentate but not always. Inner edges of larger septa straight to slightly sinuous and thickened lower in fossa. This thickening, along with

 

loose fusion of irregular processes from lower inner edges of larger septa, forming rudimentary columella. Septal granulation variable, ranging from low and rounded to high, slender, pointed granules, usually arranged in rows subparallel to septal edges. Fossa elongate and relatively shallow. Stereome present in elongate specimens.

 

 

Remarks. F. curvatum usually settles on pebbles 3-4 times the diameter of its original attachment. Its bent pedicel and curved corallum probably reflect a reorientation of the polyp after it detaches from its substrate or when it becomes so heavy that it topples sideways. It also attaches to coralla of its own species, echinoid spines, and branching bryozoans. In turn, the theca of the living coral provides a substrate for numerous species of Bryozoa, serpulid polychaetes, barnacles, hydrocorals, and other scleractinians. F. curvatum probably occurs in fairly high density off East Falkland island, indicated by the recovery of over 2500 specimens from a 68-min trawl.

 

 

Discussion. As is indicated by the synonymy, F. curvatum has often been confused with F. thouarsii, a closely related species. In fact, both Wells (1958) and Keller (1974) have synonymized these species. After thorough reexamination of this species complex I find that F. curvatum can be distinguished by a combination of the following characters: (1) the pedicel is usually bent and the corallum is usually curved; (2) the pedicel is longer; (3) the maximum size of the corallum is larger; (4) the septal notch is sometimes dentate; (5) the S4 are relatively larger than those of F. thouarsii; and (6) the fossa is usually shallower, sometimes partially occupied by a crispate columella. Characteristics of attachment and pedicel diameter mentioned by Squires (1961) are of no diagnostic value. Furthermore, although their depth ranges overlap, F. curvatum is usually found deeper than F. thouarsii. F. curvatum is distinguished from F. impensum by its coarser septal granulation, smaller PD, usually curved corallum, shallower fossa, and geographical distribution.

 

 

Material. Eltanin sta. 339 (73), USNM 47238; sta. 340 (139), USNM 47253; sta. 556 (8),. USNM 47243; sta. 558 (about 2500), USNM 47254; sta. 740 (6), USNM 47239; sta. 1536 (11), USNM 47242. Hero sta. 715-875 (126), USNM 47251; sta. 715-885 (1), USNM 47245; sta.715-895 (35), USNM 47252. Vema sta. 14-12 (4), USNM 45652, and (8), AMNH; sta. 15-PD3 (5), USNM 47240; sta. 15-PD4 (39), USNM 47250; sta. 15-PD9 (3), USNM 47241; sta. 15-PD10 (5), USNM 45626, and (11), AMNH; sta. 17-59 (2), USNM 45653; sta. 17-100 (24), USNM 45621, and (37), AMNH; sta. 17-101 (9), USNM 45624, and (32), AMNH; sta. 18-8 (7), USNM 45620; sta.. 18-12 (16), USNM 45622. Calypso sta. 171 (2), USNM 47246; sta. 172 (4), SME. BR sta.. 25149 (5), USNM 47244. Specimens of Squires (1961, 1962a), USNM; specimens of Gardiner (1939) from WS sta. 839, BM 1939.7.20.129. Two syntypes (BM 1880.11.25.85 and 1974.8.5.10).

 

 

Types. The eight syntypes of F. curvatum are deposited at the British Museum. Type-locality: 37°17’S, 53°52'W (off Rio de la Plata, Uruguay); 1097 m.

 

 

Distribution. Off southeastern South America from Rio de la Plata, Uruguay, to Cape Horn; Burdwood Bank; off Falkland Islands (Islas Malvinas); off South Georgia. Depth range: 115-1137 m; however, most

 

common between 400 and 800 m." Cairns 1982, pp. 35-38, Plate 10, figs. 10, 11; Plate 11, figs. 6-9.

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© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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