radiolaria - rads_cat - Sethoconus martini

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Sethoconus martini

Citation: Sethoconus martini Campbell & Clark 1944

Type repository: University of California, Museum of Paleontology, San Francisco

Family (traditional): Actinommidae

Shell bell-shaped, rather large; apical horn stout, vertical, four-bladed, terminally sharp (apically broken in our figured specimens); cephalis small, conical (43°), set off from thorax by an internal septum and externally hardly distinct, its basal diameter about same as its length, and its sides convex; thorax generally subconical (60°) in upper 0.5 and reduced (40°) in lower portion, sides full and change in contour between two sections distinct but not emphatic; shell-aperture badly torn in our specimens, possibly toothed; wall thinner in cephalis than in thorax; surface of cephalis smooth, of thorax, spiny in upper 0.67 where there are thin, needlelike, freely branched and anastomosed nodes of porous framework forming a thorny or cactuslike surface, lower 0.3 smooth, framework of shell a basketlike network enclosing pores, this framework relatively strong (stronger than in recent species in which it is arachnoidal); pores of cephalis tiny, dotlike, probably not more than 50, well separated, single-contoured, shallow, and elliptical, pores of thorax very large, often hexagonal and commonly elliptical, graduated in size to some extent from margin to apex, about a dozen large ones around ultimate part of thorax, and in eight to nine vertical, alternated tiers.

Length (broken), 180µm, of thorax, 110µm; diameter, maximum (broken), 110µm. Distinguishing characters (rw): Sethoconus martini n. sp. differs from all described species, which are recent, in heavy framework. Recent species (five) have a delicate, spider-weblike framework instead. Yet, martini n. sp. agrees with latter in essential subgeneric characters and should be included in subgenus Plebarachnium [sic] unless, perhaps, heavier framework is a sufficient character to separate it from them. This heavy framework maybe derived from a special mode of life; Haeckel (1887) states that all recent species are surface dwellers.

[Campbell and Clark here list the species under the subgeneric name Phlebarachnium and include the subgeneric name in the species name.

References:

Campbell, A. S. & Clark, B. L. (1944a). Miocene radiolarian faunas from southern California. Geological Society of America, Special Papers. 51: 1-76. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Sethoconus martini Campbell & Clark 1944

Sethoconus martini

References:

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