radiolaria - rads_cat - Lophocyrtis galenum

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Lophocyrtis galenum

Citation: Lophocyrtis (Paralampterium) galenum Sanfilippo 1990

Type specimens: Plate III, 14, 15; Holotype (Plate III, 14)

Type sample (& lithostrat): DSDP Site 515B-35-3, 75-77 cm

Type age (chronostrat): Lychnocanoma elongata Zone in the Early Miocene

Description: Three-segmented theoperid with a weakly developed apical horn, pronounced collar and lumbar stricture and three strongly ridged, pored feet. The cephalic wall is perforated by 15-25 small circular to subcircular pores, in some specimens covered by a thick cap - the reduced apical horn. Thorax campanulate to approximately subspherical with a rough surface, sometimes tuberose proximally and about 26-32 pores on the maximum circumference, arranged quincuncially. Abdomen open, short, with rough surface and about 12- 32 pores around the maximum circumference. Three prominent feet with pores proximally depart from the distal abdomen. In many specimens, the abdominal lattice continues beyond the origin of the feet, with smaller pores. The feet are composed of usually four robust ridges that arise from the abdomen, proximally bordering three single rows of pores, the middle row longer than the lateral ones and distally merging to an elongated conical foot. In some specimens the middle two of these ridges enclose two pores while still on the abdominal surface, and sometimes there is an additional short ridge proximally. The outer two (lateral) ridges of each foot in some specimens extend into the abdominal wall sufficiently distinctly to form a thickened peristome (only rarely complete around the circumference )...

(based on 35 specimens from DSDP Site 78 core 14, Site 281 Core 12, Site 296 Cores 29-37 and Site 515B Cores 10-47): total length (excluding horn and feet) 195-295 m (median 220 µm); length off thorax 75-105 µm (median 90 µm), width 135-190 µm (median 155 µm); length of abdomen 75-180 µm (median 95 µm), width 190-260 µm (median 195 µm)

The name is derived from the Greek adjective galenos, calm, a reference to the mid (horse) latitudes in which most specimens have been found

Distinguishing characters: Lophocyrtis ( Paralampterium) ? galenum is distinguished from L. (P.) dumitricai, L. (P.) ? longiventer, L. (Cyclampterium) pegetrum and L. (C.) milowi by its shorter abdomen terminating in an incipient peristome and the ridged pored feet. The feet in L. (C.) milowi form an integral part of the abdomen since there is no differentiated termination of the abdominal wall.

Remarks: Although the evolutionary ancestors and descendants of L. (P.) ? longiventer and L. (P.) ? galenum are not yet known, the two forms have overlapping ranges at DSDP Site 296 in the late Oligocene Dorcadospyris ateuchus Zone (296-37 through 296-39). Near the top of its range at DSDP Site 296 in the late Early Miocene Calocycletta costata Zone, L. (P.) ? galenum co-occurs with tropical L. Cyclampterium) leptetrum. At the high southern latitude DSDP Site 281 the last occurrence of L. (P.) ? longiventer coincides with the earliest occurrence of L. (P.) ? galenum (in the interval 281-12-3 to 281-14-2 ), possibly indicating a shift from an Antarctic plankton province to a Subantarctic province in the middle of the Oligocene (Sancetta, 1979). The range of L. (P.) ? galenum at the North Atlantic DSDP Site 398D is very short (398D-12 through 398D-13 ) in the late Oligocene to Early Miocene and it is succeeded by the tropical forms L. (Cyclampterium) pegetrum and L. ( C.) leptetrum in the late Early Miocene. Similarly, tropical forms of Cyclampterium (leptetrum and tanythorax) replace L. (P.) ? galenum in the Middle Miocene Dorcadospyris alata Zone at DSDP Site 206. At the Atlantic mid latitude DSDP Site 356 L. (P.) ? galenum has been observed in sample 356-6-1 together with L. (C.) milowi and in the younger samples 356-5 through -4 it is also accompanied by L. (C.) pegetrum and L. (C.) leptetrum. As a result of a hiatus, the Oligocene and Late Eocene are not represented and the origin of L. (P.) ? galenum can not be observed.

Occurrence: This species has been found only in the middle latitudes, in the Late Oligocene to Middle Miocene, Dorcadospyris ateuchus into the D. alata Zone. The only Atlantic mid latitude, middle Miocene sequence available during this study is DSDP Site 515B, where radiolarians are not known in sediments younger than the D. alata Zone (Riedel and Sanfilippo, 1970; Johnson, 1978). In addition to the localities listed under Measurements, L. (P.) ? galenum has been observed in the Pacific DSDP Site 206 Cores 34-45; in the Atlantic Site 356 Cores 4-6 and Site 398D Cores 12, 13. The occurrence at the tropical Pacific Site 78 is anomalous and probably due to mixing of low and mid latitude faunas in the Lychnocanoma elongata Zone - this would be confirmed by finding other mid latitude species.

References:

Sanfilippo, A. (1990). Origin of the subgenera Cyclampterium, Parampterium and Sciadiopeplus from Lophocyrtis (Lophocyrtis) (Radiolaria, Theoperidae). Marine Micropaleontology. 15(3-4): 287-312. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Lophocyrtis (Paralampterium) galenum Sanfilippo 1990

Lophocyrtis galenum

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