| Home> Miocene>

List species

Larcopyle weddellium Lazarus et al, 2005

Description - Add description

Relatively small, elongate, ellipsoidal test, generally elliptical in outline but a few specimens almost diamond-shaped but with rounded corners; end views of test circular to subcircular or nearly elliptical in outline. Internal structure similar to that of Lithelius minor, i.e., 4-5 closely spaced, concentric, trizonal shells which appear as a single or double spiral in certain orientations; shells more closely spaced (6-12 µm) than in Lithelius minor and with a more elongate elliptical outline. Surface of test regular to slightly irregular, generally with thorns but without conical spines except for polar spines. Pores of each shell subcircular to subpolygonal, subequal, subregularly arranged, 8-15 on half the minor circumference of the outer shell. At one or both poles of the principal axis of most tests there is developed a portion of an outer shell, similar to the inner shells; in most specimens at one or both of these poles there is a group of 1-6 thin conical spines which are more or less parallel to the principal axis of the test and are of variable length (2-37 µm, generally 6-15 µm); the structures developed at each pole resemble, but do not represent, a pylome.
Measurements; based on 30 specimens from stations 27 and 71: major diameter (principal axis) of test 77-122 µm, minor diameter 62- 92 µm.
Remarks. Because this species has an internal structure similar to that of Lithelius minor, it was placed in the genus Lithelius. Both species, however, are not planispirally coiled; therefore, a new generic name should be proposed for them. Other species of the Family Litheliidae likewise may not be planispirally coiled. Restudy of all representatives of this family is needed before taxonomic revision is possible.
Except for the lack of a true pylome at one or both poles, the presence of larger pores, and their tests being ellipsoidal, not discoidal, specimens of this species from the Gulf resemble Stomatodiscus spiralis Dreyer (1889, p. 114, Pl. 10, fig. 63). Several specimens appear to be discoidal, but when rolled over under the microscope their ellipsoidal shape becomes apparent. Study of Dreyer's type material should be made before a new name is proposed for this taxon.
Distribution. This species has a rare but spotty distribution in the Gulf. It is present as far north as station 206; therefore, it is to some extent cosmopolitan. It is absent at stations 64, 90, 91, 92, 130, 133, 151, 194, 203, 208, and 214. Its distribution apparently is not influenced by upwelling. Its greater frequency in the southern half of the Gulf indicates its preference for more nearly oceanic water masses.
Benson 1966
Remarks. As noted by Benson (1966, p. 265), this species has an internal structure similar to that of Lithelius minor, i.e., four to five closely spaced, concentric, trizonal shells which appear as single or double spirals or as concentric shells, depending upon the orientation of the test. On the other hand, the genus Spongurus is more closely allied with species consisting of closely spaced, concentric ellipsoidal (not trizonal) shells such as Spongocore puella and Spongurus sp. cf. S. elliptica.
Benson 1983
Derivation of name. The species is named after the Weddell Sea, where this morphotype was first encountered.
Holotype. Plate 10, figs 1, 2; 745B-10-2,53 (Pleistocene, Kerguelen). Museum für Naturkunde, Mikropaläontologie No. ECO-22.
Description. The small shell (about 110 µm) has a rather asym- metrical, ellipsoidal shape. The large pores are arranged close together, frames are absent in most specimens. A double spiral with closely spaced whorls gives the shell a compact appearance. Characteristically there are distinct caps on one or both poles and the whorls are not completely smooth, but have sharper bends and flattened regions. A wide pylome, often with teeth or a cluster of short spines, is usually present.
Occurrence. Late Miocene–Pleistocene, scattered occurrences in the Mid Miocene.
Remarks. Larcopyle weddellium is superficially similar to Lithelius minor Jörgensen, 1900, and/or similar lithelid forms, such as Lithelius spiralis Haeckel, 1887, in that all of these forms are built of compact spiral whorls of lattice shell. L. weddellium, however, is consistently ellipsoidal, has somewhat angular whorls, frequently has partially formed whorls at the pole ends of the shell and appears to possess a pylome, as indicated by the weakly expressed cluster of short spines or teeth at one end of the ellipsoidal shell. Larcopyle weddellium is also similar to incomplete specimens of Larcopyle pylomaticus n. comb., but can be distinguished by the characteristically asymmetrical shape of the shell – which is absent in L. pylomaticus – and its larger pores. The specimens illustrated by Nigrini & Lombari (1984) appear to be conspecific with L. weddellium described here, but they will not be formally synonymized without the actual material being examined.
Lazarus et al 2005











Discussion / Comments


Web links