Comprehensive Description

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"Flabellum areum Cairns, 1982



Description. Corallum trochoid to turbinate, sometimes campanulate; usually straight. Weakly attached by short pedicel 3.2-5.1 mm in diameter; pedicel often detached from substrate (usually a small pebble), allowing base and pedicel to erode gradually. Largest specimen 27.7 x 20.0 mm in CD and 21.2 mm tall. Theca usually worn, bearing thin, longitudinal striae corresponding to all septa, characteristic of most flabellids. Calice elliptical, with GCD/LCD ratio usually between 1.3 and 1.4; lateral edges rounded. Calicular margin entire, calicular profile straight to slightly arched. Septa hexamerally arranged in five cycles; how ever, fifth cycle never complete. One large specimen with 86 septa; holotype (adult specimen) with 80 septa. S1and S2 equal in size and meeting in center of calice. S1 and S2 not exsert and forming near calicular edge shallow, concave notch; notch may or may not be dentate. Upper thecal edge forming lip rising slightly above upper septal insertions. Size of S3 depending on presence of paired S5 in half system. If S5 present (which is more common in half systems adjacent to lateral edges), then S3 one half to three fourths of size of S1,2; when S5 absent, S3 about one third of size of S1,2. S4 and S5 progressively smaller, S4 expending only about halfway to base. Inner edges of septa usually straight but may be slightly sinuous. Septal granules low to moderately tall and arranged in lines parallel, or rows almost perpendicular, to septal edge, the latter corresponding to fine sinuosity of septal edge.


Fossa appearing spacious because of widely spaced septa and campanulate corallum shape. Lower, inner


edges of S1 and S2 greatly thickened and fused in center, forming rudimentary columella. Theca within calice often increased substantially by deposits of stereome, sometimes obscuring smaller septa. Stereome also filling in base of more elongate coralla.



Remarks. The maximum size of this species probably lies between a GCD of 25-30 mm, judging from


the extreme development of stereome and worn pedicels of specimens in this size range.



Discussion. F. areum is most similar to F. thouarsii, particularly in size, septal arrangement, and geographic distribution. It can be distinguished by its deeper fossa, larger pedicel diameter, lesser number of septa per centimeter (about 12 for F. areum, 18 for F. thouarsii), and much deeper bathymetric range.



Etymology. The specific name areum (Latin: open or vacant space) refers to the spacious fossa.



Material. Vema sta. 15-132 (25), AMNH; sta 17-57 (15), AMNH; sta. 17-61 (3), USNM 47913.



Types. The holotype, collected at Eltanin station 1592, is deposited at the United States National Museum (47167). Three paratypes from Eltanin station 1592 (number 47168), 14 from Eltanin station 973 (number 45639), 8 . from Vema station 17-57 (number 47169), and 15 from Vema station 15-132 (number 45616) are deposited at the United States National Museum. Type-locality: 54°43'S, 55°30'W (Scotia Ridge east of Burdwood Bank); 1647-2044 m.



Distribution. Off Mar del Plata, Argentina; off Cape Horn, Tierra del Fuego; Scotia Ridge southeast of Falkland Islands (Map 8). Unconfirmed depth range: 1647-2229 m." Cairns 1982, p.35., Plate 11, figs. 1-5.


Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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