dcsimg

Description

provided by NMNH Antarctic Invertebrates

"Flabellum impensum Squires, 1962

Flabellum inconstans; Pax, 1910, pp. 66-72, pi. 11, figs. 3-9, pi. 12, figs. 1-6.

Flabellum thouarsii; Gravier, 1914b, pp. 125-128, pi. 1, figs. 5, 6.—Wells, 1958, p. 268 (part : Discovery sta. 34, 39), pi. 2, figs. 5, 6.

Flabellum transversale: Thomson and Rennet, 1931, p. 41.

Flabellum harmeri; Gardiner, 1939, pp. 326, 327.

Flabellum curvatum; Gardiner, 1939, pp. 327, 328 (part: Discovery sta. 162).

Flabellum manneri; Niino, 1958, p. 257, pi. 2, fig. 1 (misspellings).

Flabellum sp. Squires, 1961, pp. 29, 38.

Flabellum impensum Squires, 1962b, pp. 14, 17-19, pi. 2, figs. 4-7, text fig. 3; 1969, p. 18 (part), pi. 6, map 3.—Podoff, 1976, pp. 31-38, pi. 2, figs. 9, 10.—Sorauf and Podoff, 1977, p. 4 (part: pi. 1, figs. 1, 2, not pi. 3, figs. 1, 2)—Cairns, 1979, p. 206.

Flabellum distincturn; Eguchi, 1965, pp.. 10, 11, text fig. 3.

Description. Corallum variable in shape, ranging from flabellate to almost conical (ceratoid to trochoid). Largest flabellate corallum 128 x 45 mm in CD and 80.2 mm tall (Plate 12, fig. 4). Ceratoid to trochoid coralla usually smaller, with GCD/LCD ratio as low as 1.1. Angle of lateral edges of flabellate coralla often about 40°-50° for first 10 mm, then lateral edges flaring out ward up to 150°, maintaining constant inclination of lateral faces of 30°-40°. In ceratoid to trochoid coralla, angle of lateral edges remaining constant with growth. All intergrades occurring between extreme flabellate and ceratoid shapes. Round pedicel never reinforced by external stereome and 3.5-6.0 mm in diameter. Small coralla usually attached to pebbles or gastropod shells; when over 30 mm tall, coralla usually becoming free of original attachment and pedicel often eroding to a point. Theca thin and usually worn. Often a thin, incised costal line corresponding to each septum and closely spaced chevronate growth lines circling theca. Principal costae on lateral edges sometimes slightly carinate. Calicular profiles of flabellate coralla strongly arched; those of trochoid coralla more even.

Septa hexamerally arranged in smaller coralla up to 96 septa stage. Additional septa irregularly added in groups of three, up to at least 300 septa (S7). Full fourth cycle achieved at GCD of about 11 mm, fifth cycle by about 19 mm, and sixth cycle by about 55 mm. Flabellate coralla usually having more septa than more slender coralla because of their increased calicular perimeter. In corallum with six full cycles of septa, relative septal sizes may be either S1 = S2 = S3 = S4 ≥ S5 ≥ S6 or Sl = S2 = S3 ≥ S4 ≥ S5 ≥ S6. Septa not exsert and very thin. Larger septa usually sloping concavely away from calicular edge, producing shallow notch, this notch usually finely dentate. Toward center of calice, septum forming shoulder before dropping vertically into fossa. Inner edges of larger septa slightly sinuous and thickened; deep within fossa, lower inner edges fused into rudimentary columella. Septal granules fine and pointed, often arranged in widely

spaced lines parallel to septal edge. Fossa very deep, elongate in flabellate coralla. Small amounts of internal stereome sometimes present in base.

Remarks. An analysis of the living orientation of F. impensum similar to that of Squires (1964a) for other flabellids was made. The presence of filter feeders (usually Bryozoa) on both sides of a specimen was interpreted as an indication of an upright position, filter feeders on one side and borers on the other as a prone position, and absence of organisms from one or both sides as inconclusive. In an examination of 96 specimens which were alive when they were collected, 71 were found to be inconclusive, 24 indicated an erect posture, and 1 indicated a prone posture. The implication is that after _F. impensum becomes free of its original attachment, it maintains itself in an upright position, perhaps by submergence of the pedicel in the substrate. Consistent absence of filter feeders from near the base and of erosion of the base supports this theory. Two gastropods, believed to be of the families Volutidae and Muricidae (J. Houbrick, personal communication, 1979), have deposited large egg cases near the calicular edges of living specimens (Plate 12, figs. 4 and 5). Bryozoans and serpulids also commonly encrust the theca. Pax (1910) describes and illustrates some histology of a tentacle, including nematocysts.

Discussion. The extreme forms of F. impensum might easily be mistaken for separate species: one a large flabellate corallum with almost seven cycles of septa, the other a ceratoid to trochoid corallum with less than six cycles of septa. Furthermore, each form usually occurs homogeneously when it is collected. However, several suites show a continuous gradation of corallum shape. No other morphological differences are apparent. Even the type-specimens show this corallum variation: the holotype is flabellate, and the illustrated paratype is ceratoid. Finally, there are no geographic or bathymetric differences, except that the few records from the Weddell Sea and Eastern Hemisphere are mostly slender forms. The variation in corallum shape is believed to be a response to a localized environmental factor which could vary over a short distance, such as substrate type or current pattern. Early records of F. impensum were usually as signed to more northern temperate species. F. inconstans Marenzeller, 1904, reported by Pax (1910), Is a South African species with a basal fracture. F. thouarsii Milne Edwards and Haime, 1848, is a distinct species known from relatively shallow water only off eastern South America. F. harmeri Gardiner, 1929, has been synonymized with the New Zealand F. rubrum by Squires (1963b), and F. transversale Moseley, 1881, reported by Thomson and Rennet (1931), is a southern Australian species. Gardiner's (1939) single Antarctic record of F. curvatum is F. impensum.

Material. Eltanin sta. 272 (6), USNM 45636; sta, 410 (4), USNM 45634; sta. 426 (3), USNM 45635; sta. 428 (5), USNM 45632; sta. 437 (5), USNM 45637; sta. 444 (1), USNM 47330; sta. 499 (1), USNM 47347; sta. 992 (7), USNM 47335; sta. 993 (2), USNM 47323; sta. 997 (10), USNM 47341; sta. 1005 (1), USNM 47327; sta. 1079 (7), USNM 45640; sta. 1083 (9), USNM 47331; sta. 1084 (3), USNM 47368; sta. 1089 (1), USNM 47542; sta. 1870 (8), USNM 47346; sta. 1871 (33), USNM 47361, and (1), MCZ; sta. 1878 (12), USNM 47356; sta. 1880 (6), USNM 47349; sta. 1885 (2), USNM 47344; sta. 1898 (1), USNM 47367; sta. 1916 (1), USNM 47362; sta. 1922 (1), USNM 47545; sta. 1930 (2), USNM 47339; sta. 1933 (3), USNM 47355; sta. 1996 (1), USNM 47343; sta. 2005 (2), USNM 47371; sta. 2006 (1), MCZ; sta. 2016 (4), USNM 47370, and (3), MCZ; sta. 2018 (3), USNM 47375, and (1), MCZ; sta, 2021 (1), USNM 47369; sta. 2025 (2), USNM 47357; sta. 2031 (1), USNM 47372; sta. 2045 (3), USNM 47354; sta. 2063 (4), USNM 47353; sta. 2065 (2), USNM 47352; sta. 2068 CD, USNM 47351; sta. 2070 (1), USNM 47540; sta. 2085 (2), USNM 47348; sta. 2088 (4), USNM 47350; sta. 2097 (1), USNM 47342; sta. 2099 (6), USNM 47358; sta. 2115 (1), USNM 47365; sta. 2117 (9), USNM 47374; sta. 2124 (9), USNM 47376; sta. 2143 (9), USNM 47373; sta. 5761 (1), USNM 47366; sta. 5765 (4), USNM 47326. Islas Orcadas sta. 575-53 (11), USNM 47383; sta. 575-65 (9), USNM 47336; sta. 575-66 (4), USNM 47379; sta. 575-67 (1), USNM 47380; sta. 575-70 (2), USNM 47384; sta. 876-107 (3), USNM 47334; sta. 876-108 (6), USNM 47378; sta. 876-110 (2), USNM 47332; sta. 876-113 (2), USNM 47381; sta. 876-114 (3), USNM 47324; sta. 876-118 (6), USNM 47337; sta. 876-124 (1), USNM 47329; sta. 876-126 (4), USNM 47340; sta. 876-127 (1), USNM 47382. Hero sta. 691-20 (15), USNM 47333; sta. 702-465 (1), USNM 47543; sta. 721-1084 (1), USNM 47325; sta. 721-1102 (1), USNM 47390; sta. 721-1110 (20), USNM 47363; sta. 731-1842 (1), USNM 47328. Edisto sta. 16 (1), USNM 47391; sta. 28 (2), USNM 45641. Atka sta. 23 (2), USNM 47345. EW sta. 9 (86), USNM 45629; sta. 16 (1), USNM 47385; sta. 23 (73), USNM 45627; sta. 28 (3), USNM 45644; sta. 32 (1), USNM 47387; sta. 35 (1), USNM 47386; sta. 36 (2), USNM 45667; sta. 37 (8), USNM 45666; sta. 38 (13), USNM 45630; sta. 39 (4), USNM 45628. Westwind sta. 4 (1), USNM 47389. Vema sta. 18-32 (2), USNM 47338. NZOI sta. A-537 (1), USNM 47364; sta. A-625 (20), USNM 47392. Specimen identified as F. transversale from station 10 (Thomson and Rennet, 1931), Australian Museum G

13538; specimen identified as F. harmeri (Gardiner, 1939), BM 1939.7.20.128; specimens (2) identified as F. curvatum from station 182 (Gardiner, 1939), BM 1939.7.20.271-272; specimens identified as F. thouarsii from Wells (1958) from stations 34 (2) and 39 (2), South Australian Museum H 63, H 65.

Types. The holotype and 61 paratypes of F. impensum are deposited at the New Zealand Oceanographic institute. Type-locality: 73°20'S, 174°00'E (Ross Sea); 369-384 m.

Distribution. Circumpolar continental Antarctic, including off South Shetland Islands, South Orkney Islands, and South Sandwich Islands, and one disjunct record off the Antipodes Islands. Depth range: 46-2260 m; however, temperature range probably very slight. Most records between 100 and 1000 m; one of deepest records (2010 m) at northernmost range (Eltanin sta. 2143, off Antipodes Islands)." Cairns 1982, pp. 38-41, Plate 10, figs. 8, 9; Plate 11, fig. 10; Plate 12, figs. 1-8.

Biology

provided by World Register of Marine Species
azooxanthellate
license
cc-by-4.0
copyright
WoRMS Editorial Board
bibliographic citation
van der Land, J. (ed). (2008). UNESCO-IOC Register of Marine Organisms (URMO). van der Land, J. (ed). (2008). UNESCO-IOC Register of Marine Organisms (URMO).
contributor
Jacob van der Land [email]
contributor
Jacob van der Land [email]

Depth range

provided by World Register of Marine Species
46-2260 m
license
cc-by-4.0
copyright
WoRMS Editorial Board
bibliographic citation
van der Land, J. (ed). (2008). UNESCO-IOC Register of Marine Organisms (URMO). van der Land, J. (ed). (2008). UNESCO-IOC Register of Marine Organisms (URMO).
contributor
Stephen Cairns [email]
contributor
Stephen Cairns [email]

Habitat

provided by World Register of Marine Species
bathyal
license
cc-by-4.0
copyright
WoRMS Editorial Board
bibliographic citation
van der Land, J. (ed). (2008). UNESCO-IOC Register of Marine Organisms (URMO). van der Land, J. (ed). (2008). UNESCO-IOC Register of Marine Organisms (URMO).
contributor
Jacob van der Land [email]
contributor
Jacob van der Land [email]