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"Flabellum apertum Moseley, 1876
Flabellum apertum Moseley, 1876, p. 556 (part: off Prince Edward Islands); 1881, pp. 167, 168 (part: Challenger sta. 145), pi. 6, figs. 7a-7c—Not F. apertum; Marion, 1906, pp. 120, 121, pi. 11, figs. 9, 9a (is F. angulare Moseley, 1876).—Wells, 1958, p. 262.—Not F. apertum Squires, 1958, p. 68.—Squires and Keyes, 1967, p. 26, pi. 4, figs. 4, 5.—Squires 1969, pp; 16, 18, pi. 6, map 4.—Zibrowius, 1980, p. 154.
Flabellum patagonichum Moseley, 1881, pp. 166, 167, pi. 15, figs. 1-7.—Fowler, 1885, pp. 585-590, figs. 1-12.—Wells, 1958, p. 262. —Squires, 1961, p. 30; 1969, pp. 17, 18, pi. 6, map 4.—Squires and Keyes, 1967, p. 27.—Cairns, 1979, p. 206.
Description. Corallum campanulate and distinctly compressed. Pedicel short and cylindrical (2.0-2.5 mm in diameter); originally attached to small object, becoming free early in ontogeny. Largest specimen examined (USNM 47444) 57.2 x 39.3 mm in CD and 37.2 mm tall. The two principal costae ridged and continuous from pedicel to calice. They diverge from pedicel at an apical angle between 130° and 170° until a GCD of about 30 mm, whereupon epitheca turns upward to continue almost vertical growth. At point of inflection, the four lateral C1 usually well developed, sometimes forming spurs, and. may continue as ridges to calice. C2 sometimes ridged from point of inflection to calice, but much less than C1. Epitheca porcelaneous, with chevron-shaped growth lines extending between each septum. Calicular profile scalloped, a large apex corresponding to each S1 and S2 and a smaller peak corresponding to every S3. Septa hexamerally arranged in four cycles, with rudiments of fifth cycle only in larger specimens. S5 first appearing in end half systems, only rarely in lateral half systems; largest specimen with 68 septa. Si and S2 equal in size and
slightly exsert. Their inner edges thickened and fusing in center of fossa, forming elongate, solid or trabecular columella. S3 and S4 progressively smaller and do not reach columella. S5, if present, rudimentary. All septa having straight inner edges and bearing numerous, small, pointed granules.
Stereome infilling sometimes at bottom of fossa.
F. apertum forma patagonichum differing from typical form primarily in its smaller size (maximum
size reported, 28 x 21 mm in CD) and more slender shape. Ridged principal costae diverging from pedicel at an apical angle between 90° and 110° and turning upward at GCD of about 15 mm, producing smaller, more slender corallum. Other four C1 not developed. Theca porcelaneous only in region 5-10 mm from calice. Remainder of corallum usually worn and white but may also be uniformly reddish-brown or white with diffuse reddish-brown stripes corresponding to S1 and S2. S4 often missing from half systems and stereome infilling more common.
Discussion. F. patagonichum is treated as a forma of F. apertum because both patagonichum and typical apertum as well as a continuous series of morphological intermediates were present in two lots. The series of 246 specimens from Eltanin station 283 was particularly helpful in tracing the morphological variation possible in one population.
Four other closely related species have been linked to F. apertum: F. angulare Moseley, 1876; F. conuis Moseley, 1881; F. japonicum Moseley, 1881; and F. raukawaensis Squires and Keyes, 1967. Gardiner (1929b) synonymized F. angulare, F. apertum, and F. conuis as F. japonicum, the incorrect senior synonym. He stated that F. patagonichum might prove to be a form of F. japonicum also. Keller (1974) synonymized F. japonicum and F. raukawaensis as F. apertum, which she reported from off South Africa and western India. Zibrowius (1980) distinguished F. angulare from F. apertum and discussed the nominal species. I have examined the type-specimens of all of the above species except F. raukawaensis, of which I have seen a specimen from very near the type-locality (Eltanin station 1403), and have made the following observations. F. japonicum can be distinguished from F. apertum by its possession of a full fifth cycle of septa at a calicular diameter at which F. apertum has only few S5. Yabe and Eguchi (1941a) have used this as a key character to differentiate the two species. F. japonicum has been widely reported from the northern Indian Ocean, off Indonesia, Japan, Philippine Islands, and Tasmania. F. angulare is known only from the
north Atlantic (1647-3186 m) and can be distinguished by its less compressed corallum and S3 that extend to the columella. F. conuis, known only from off the Admiralty Islands, is very similar to F. apertum forma patagonichum in shape but differs in having a deeper fossa, a more delicate corallum, slightly corrugated septa, and S3 that reach the columella. It is probably a separate species, but obviously more specimens are
needed before this can be determined with certainty. F. raukawaensis, known only from four specimens from off North Island, New Zealand, is very similar to typical F. apertum but differs in that it has more S5, a larger columella, and S3 that almost reach the columella. Other records of F. apertum that I have not verified include von Marenzeller (1904a), off Tanzania, East Africa, 863 m; Yabe and Eguchi (1941b), off
Japan, 307 m; Keller (1974), off South Africa, 1400 m, and off western India, depth unknown; Keller (1975), Caribbean, depth unknown.
Material. Forma apertum; Eltanin sta. 338 (2), USNM 45675; sta. 558 (1), USNM 47442; sta. 1412 (4), USNM 47444; sta. 1414 (2), USNM 47439; sta. 1422 (5), USNM 47441. Is las Orcadas sta. 575-6 (12), USNM 47445. Edisto sta. 7 (1), USNM 4736. WH sta. 64/68 (3), ZIZM. NZOI sta. D-166 (2), USNM 47437. Mixtures of formae apertum and patagonichum: Eltanin sta. 216 (28), USNM 45674; sta. 21-283 (246), USNM 47443. Specimen of Squires and Keyes (1967), USNM 47438. Syntypes of F. apertum and F. patagonichum.
Types. The eight syntypes of F. apertum, two from Challenger station 3 (number 18126.96.36.199) and six from Challenger station 145 (number 18188.8.131.52), are deposited at the British Museum. Because these specimens represent a mixed lot (Zibrowius, 1980), a lectotype is chosen from Challenger station 145 (Plate 13, figs. 8, 9). The remaining specimens are considered paralectotypes, those from Challenger station 3 being F. angulare (see Zibrowius, 1980). Type-locality: 46°40’S, 37°50'E (off Prince Edward Island); 567m. The syntypes of F. patagonichum are also de posited at the British Museum. Type-locality: 47°48’30’’S, 74°47'W (off Isla Penguin, Chile); 220 m.
Distribution. Circum-Subantarctic, including: off Prince Edward Islands; Hjort Seamount; Macquarie
Ridge; off Chile; off Falkland Islands (Islas Malvinas); Falkland Plateau; off southern Brazil; off southern New Zealand. Depth range: 220-1500 m." Cairns 1982, p. 44-46, Plate 13, figs. 8-11; Plate 14, figs. 1-4.