radiolaria - rads_cat - Stichomitra asymbatos

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.

Other pages this level: S. asymbatos, S. asymmetra, S. communis, S. compsa, S. wero

Stichomitra asymbatos

Citation: Stichomitra asymbatos Foreman 1968

Type age (chronostrat): Late Cretaceous, Mesozoic.

Type locality: LL10; LL459; LL460; LL461; LL462; LL463; LL464; LL465; LM1593

Type repository: Holotype USNM 158013,038/0, and paratypes USNM 158012, L38/3, and USNM 158013, 037/3 U.S. National Museum, Washington, D.C.

Shell of six to ten segments, conical except for last one or two which narrow and are subcylindrical. Cephalis with sturdy horn smooth proximally, generally with a few thorns distally or a slightly roughened tip; rarely the horn poorly developed as a thickened apex with a few, short, irregular protrusions. Cephalis either smooth hyaline or with shallow depressions and a few thorns apically; a tiny vertical horn frequently present where the internal vertical spine penetrates the cephalic wall. A single row of inward- and downward-directed pores almost always present at collar stricture. Internally, four collar pores, the vertical spine (which divides the cervical pore on many of the cyrtoids) rising so sharply that its distal end is markedly above the collar stricture. Internal apical spine prominent along dorsal cephalic wall. Thorax generally has pores or depressions quincuncially arranged, with angular frames and tiny nodes or spines at the angles; rare specimens have no pores or depressions, surface smooth except for a few irregular thorns. A single row of inward- and downward-directed pores present at lumbar stricture. Conical abdominal segments thick-walled, distal subcylindrical ones thin-walled. The thick-walled abdominal segments generally increase gradually in width and length, with the last, or next to last the widest and longest. Thin-walled abdominal segments very variably developed narrowing distally, the terminal one generally considerably longer than any of the other abdominal segments. Length of segments and depth of strictures vary considerably from specimen to specimen. Pores subcircular, rather regular in size on individuals but vary considerably among specimens, either irregularly arranged or tending toward a quincuncial arrangement with transverse rows. Surface rough with walls thickened by large blunt nodes or spines. These appear first on the third segment and are prominent, depending on length of specimen, to fourth or eighth segment. The one or two thin-walled segments generally have no nodes, and only occasionally downwardly directed spines on the proximal segment; the last segment, always incomplete, occasionally shows a portion of its distal edge with irregular downwardly directed teeth.

Length of well-developed apical horn 25-60µ, of cephalis 22-30 µm, of thorax 22-30 µm, of five segments 140-210 µm, of seven segments 202-310 µm, of fifth segment 30-60µ, of seventh segment 38-110µm; width of apical horn near base 10-18 µm, of thorax 43-50µm, of fifth segment 75-130 µm, of seventh segment 85-175µ; ratio of width to length of thick-walled fifth segments 1 9-2.5, of thick-walled seventh segments 2 1-3.5. (Dimensions based on thirty specimens.)

Distinguishing features: The larger size of the cephalis, high rising vertical spine, and sturdy apical horn make it not very likely that this species is closely related to the other two species here included under Stichomitra. However it seems even less likely to be related to t

References:

Foreman, H. P. (1968). Upper Maestrichtian Radiolaria of California. Special Papers in Palaeontology. 3: 1-82. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Stichomitra asymbatos Foreman 1968

Stichomitra asymbatos

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