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Homotryblium plectilum
Homotryblium plectilum Drugg and Loeblich, 1967
Taxonomic senior synonym: Hystrichosphaeridium (as Homotryblium) floripes, according to Bujak in Bujak et al. (1980, p.64) — however, Stover in Lentin and Williams (1985, p.168) retained Homotryblium plectilum.
Taxonomic junior synonym: Areoligera digitata, according to Jain and Garg (1991, p.77).
Holotype: Drugg and Loeblich, 1967, pl.2, fig.1
Paratypes: Drugg and Loeblich, 1967
Locus typicus: Hinds County, Mississippi, U.S.A.
Stratum typicum: Oligocene
Original description: Drugg and Loeblich 1967, p. 184-185
Spherical chorate cyst with thin endophragm and periphragm, the latter giving rise to the processes. The wall is about 1 micron thick with the periphragm slightly thinner than the endophragm. Wall smooth to faintly and delicately granulate. Both layers commonly granulate or only the endophragm may exhibit this feature. The processes intratabular, buccinate, entire to secate, open distally but not opening into the central cavity. The walls of the processes are striate and may be faintly fibrous. The striations are formed by three or four nerve-like delicate thickenings which extend from the distal terminations to the basal areas where they radiate outwardly for a short distance. The distal ends of the processes are entire or else may be secate with from two to six lobes. The archaeopyle is epitractal with the line of separation just above the cingular processes. The morphology of the archaeopyle is the same as that described and illustrated by Evitt (1967,p. 49, pl. 9, figs. 7-16) and termed " Type 2A+6P"" ". The epitract usually fragments into its constituent plates. The apex consists of three plates (2-4") joined ventrally by a faint triangular thickening, the latter possibly reflecting an apical pore. These three plates commonly remain together as aunit. The six precingular plates and plate 1" usually separate as individual entities. The hypotract exhibits three series of processes, a circle of seven at the top, then a circle of six, and finally a group of three at the antapex. Those at the top of the hypotract clearly consist of six cingular plate processes and one anterior sulcal process. The latter is of considerable smaller size than the other processses of this series. It occurs on, or slightly below, a small projection or tab on the rim of the hypotract. Tiny notches on the upper edge of the hypotract are commonly visible between the cingular processes and, rarely, faint lines are visible which outline the cingular plates. The terminology for the remaining nine processes on the hypotract is problematical since the tabulation is only inferred. The most probable tabulation for this species is 4", 6"", 1a.p, 1s.p, 6""", 1p, 1"""". Some specimens exhibit one or more peculiar ring-shaped internal structures. These thickenings of the endophragm are about 10 Ám in total diameter with a somewhat variable rim width, Rarely, a small hole is present in the center of the ring. As many as three of these structures have been seen on one specimen, but only one is usual and this ocurs at the antapical end opposite the projection on the hypotract rim. Dimensios: Holotype, body 43 Ám, process 14 Ám. Range, body 37-70 Ám with most being about 50 Ám. The processes range from 14-26 Ám in length, usually about 20 Ám. Several hundred specimens examined.
Affinities:
Drugg and Loeblich, 1967, p. 185-186
Homotryblium plectilum is probably close to H. tenuispinosum Davey and
Williams, bult the shape and arrangement of the epitractal plates were not given for that species. An exact comparison with H. plectilum is therefore not possible. Davey and Williams give two different formulae for the hypotract (p. 100, 101), one of which is no doubt a misprint. That shown for H. tenuispinosum is essentially the same as that of H. plectilum as regards the basic number of processes but the interpretation differs slightly. Such inferred tabulations, however, are to some extent a matter for conjecture. Aside from these questions, H. plectilum differs from H. teinuispinosum in possessing striate processes, more robust singular processes, and at best only a weakly granulate wall. Homotriblium tasmaniense Cookson and Eisenack differs from H. plectilum most obviously in that it possesses a coarsely granulate to spinose wall. Once again epitractal plate patterns are not given so further comparison is not possible. The relationships of H. plectilum are not known, but the tabulation of the epitract and the apparent tabulation of the hypotract are suggestive of the extant genus Gonyaulax.
Taxonomic senior synonym: Hystrichosphaeridium (as Homotryblium) floripes, according to Bujak in Bujak et al. (1980, p.64) — however, Stover in Lentin and Williams (1985, p.168) retained Homotryblium plectilum.
Taxonomic junior synonym: Areoligera digitata, according to Jain and Garg (1991, p.77).
Holotype: Drugg and Loeblich, 1967, pl.2, fig.1
Paratypes: Drugg and Loeblich, 1967
Locus typicus: Hinds County, Mississippi, U.S.A.
Stratum typicum: Oligocene
Original description: Drugg and Loeblich 1967, p. 184-185
Spherical chorate cyst with thin endophragm and periphragm, the latter giving rise to the processes. The wall is about 1 micron thick with the periphragm slightly thinner than the endophragm. Wall smooth to faintly and delicately granulate. Both layers commonly granulate or only the endophragm may exhibit this feature. The processes intratabular, buccinate, entire to secate, open distally but not opening into the central cavity. The walls of the processes are striate and may be faintly fibrous. The striations are formed by three or four nerve-like delicate thickenings which extend from the distal terminations to the basal areas where they radiate outwardly for a short distance. The distal ends of the processes are entire or else may be secate with from two to six lobes. The archaeopyle is epitractal with the line of separation just above the cingular processes. The morphology of the archaeopyle is the same as that described and illustrated by Evitt (1967,p. 49, pl. 9, figs. 7-16) and termed " Type 2A+6P"" ". The epitract usually fragments into its constituent plates. The apex consists of three plates (2-4") joined ventrally by a faint triangular thickening, the latter possibly reflecting an apical pore. These three plates commonly remain together as aunit. The six precingular plates and plate 1" usually separate as individual entities. The hypotract exhibits three series of processes, a circle of seven at the top, then a circle of six, and finally a group of three at the antapex. Those at the top of the hypotract clearly consist of six cingular plate processes and one anterior sulcal process. The latter is of considerable smaller size than the other processses of this series. It occurs on, or slightly below, a small projection or tab on the rim of the hypotract. Tiny notches on the upper edge of the hypotract are commonly visible between the cingular processes and, rarely, faint lines are visible which outline the cingular plates. The terminology for the remaining nine processes on the hypotract is problematical since the tabulation is only inferred. The most probable tabulation for this species is 4", 6"", 1a.p, 1s.p, 6""", 1p, 1"""". Some specimens exhibit one or more peculiar ring-shaped internal structures. These thickenings of the endophragm are about 10 Ám in total diameter with a somewhat variable rim width, Rarely, a small hole is present in the center of the ring. As many as three of these structures have been seen on one specimen, but only one is usual and this ocurs at the antapical end opposite the projection on the hypotract rim. Dimensios: Holotype, body 43 Ám, process 14 Ám. Range, body 37-70 Ám with most being about 50 Ám. The processes range from 14-26 Ám in length, usually about 20 Ám. Several hundred specimens examined.
Affinities:
Drugg and Loeblich, 1967, p. 185-186
Homotryblium plectilum is probably close to H. tenuispinosum Davey and
Williams, bult the shape and arrangement of the epitractal plates were not given for that species. An exact comparison with H. plectilum is therefore not possible. Davey and Williams give two different formulae for the hypotract (p. 100, 101), one of which is no doubt a misprint. That shown for H. tenuispinosum is essentially the same as that of H. plectilum as regards the basic number of processes but the interpretation differs slightly. Such inferred tabulations, however, are to some extent a matter for conjecture. Aside from these questions, H. plectilum differs from H. teinuispinosum in possessing striate processes, more robust singular processes, and at best only a weakly granulate wall. Homotriblium tasmaniense Cookson and Eisenack differs from H. plectilum most obviously in that it possesses a coarsely granulate to spinose wall. Once again epitractal plate patterns are not given so further comparison is not possible. The relationships of H. plectilum are not known, but the tabulation of the epitract and the apparent tabulation of the hypotract are suggestive of the extant genus Gonyaulax.