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"Flabellum truncum Cairns, 1982




Description. Corallum ceratoid to trochoid, compressed. Angle of lateral edges 45°-70°; inclination of lateral faces 22°-38°; ratio of GCD/LCD 1.4-2.2. Corallum (anthocyathus) proximally truncated, resulting from transverse fission from a presumably attached base (the anthocaulus). Scar of attachment from 9 to 14 mm long and from 5 to 9 mm wide; usually worn. Largest specimen 38 x 23 mm in CD; tallest specimen 39.4 mm in height. Theca thin, sometimes bearing low, rounded, longitudinal ridges, one corresponding to each S1-3. Lateral edges rounded, never carinate or spinose. Calicular margin entire; profile of margin arched. Septa hexamerally arranged in five cycles, rarely with additional S6. S1, S2, and S3 equal in size and extending to columella. S4 about half of size of S1; S5 about one fourth of size of S4. Sometimes lower inner edges of S4 bending toward and fusing with S3. Septa not exsert and bearing large, pointed or blunt


granules measuring as high as septal thickness. Lower inner edges of larger septa thickened and slightly sinuous; sinuosity corresponding to shallow undulations of currugated septa. Columella variable in structure, but usually slender, elongate, loose fusion of inner edges of S1-3; may sometimes be a slightly wider, flat, solid mass or a very wide (up to 25% of LCD), loose, spongy structure.



Remarks. Zibrowius (1974b) suggested that the truncated flabellids may reproduce asexually by transverse division (‘strobilation’) with one basal part (the anthocaulus stage (see Wells, 1966, p.226)), producing more than one corallum (the anthocyathus stage). Unfortunately, no attached specimens or specimens in the process of dividing were found among the lots of F. truncum. When the attached and free stages of the truncated flabellids are known, some species will probably be synonymized.



Discussion. F. truncum belongs to the flabella truncata section of the genus Flabellum (see Milne Edwards and Haime, 1848, p. 259), which is equivalent to Zibrowius's (1974b) 'second group’. Zibrowius listed 19 species from this group, which are all characterized by a transverse division, but none of these are known from the eastern Pacific or the Subantarctic. Many are distinguished by prominent costal spines or crests. Out of this group, F. truncum is most similar to F. inconstans Marenzeller, 1904, known from off South


Africa at 100 m. F. truncum is distinguished by its smaller size, lesser number of septa, and deeper bathymetric range.



Etymology. The specific name truncum (Latin: piece cut off, tip) refers to the detached distal anthocyathus stage of this species.



Material. Eltanin sta. 21-282 (1), USNM 47526; sta. 338 (1), USNM 47527. Islas Orcadas sta 575-5 (1), USNM 47528. Anton Bruun sta. 11-88 (2), USNM 47529.



Types. The holotype, collected at Eltanin station 21-283, is deposited at the United States National Museum (47174). Six paratypes from Eltanin station 21-283 (number 47175) and 19 from Anton Bruun station 18-714 (number 47176) are deposited at the United States National Museum. One paratype from Anton Bruun station 18-714 is deposited at the British Museum (1979.11.4.1). Type-locality: 53°13'S, 75°41'W (off Isla Desolacion, Chile); 1500-1666 m.



Distribution. Off western coast of South America from off Peru to off southern Chile; south of Falkland Islands (Islas Malvinas); Falkland Plateau (Map 11).



Depth range: 595-1896 m." Cairns 1982, p. 46, Plate 14, figs. 5-8.


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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