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Helicoplacus gilberti

Helicoplacoidea - Helicoplacidae

Helicoplacus gilberti was named by Durham and Caster (1963) [see also Durham 1993.]. Its type specimen is UCMP 37847 and is a 3D body fossil. It is the type species of Helicoplacus.

Synonymy list
YearName and author
1963Helicoplacus curtisi Durham and Caster p. 822 fig. 1
1963Helicoplacus gilberti Durham and Caster p. 822 figs. figs. 1A, B, E, F
1967Helicoplacus curtisi Durham p. 100
1967Helicoplacus everndeni Durham p. 100 figs. Pl. 14, fig. 6
1967Helicoplacus gilberti Durham p. 100
1967Helicoplacus firbyi Durham p. 101 figs. Pl. 14, fig. 3
1993Helicoplacus gilberti Durham p. 600 figs. Figures 3.2, 4.1, 5.2, 6.3, 6.8, 7.3, 7.7
1993Helicoplacus casteri Durham p. 601 figs. Figures 5.1, 5.5, 5.6, 7.1
1993Helicoplacus everndeni Durham p. 601
1993Helicoplacus guthi Durham p. 601 figs. Figure 7.4, 7.6
1993Westgardella curtisi Durham p. 601
1993Westgardella firbyi Durham p. 601 figs. Figure 2.3.
1993Westgardella blancoensis Durham p. 603 figs. Figure 6.6, 6.7
2006Helicoplacus gilberti Wilbur p. 290

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familyHelicoplacidaeDurham and Caster 1966

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

J. W. Durham and K. E. Caster 1963Interambulacra with about four turns; plates of medial column slightly longer than those of lateml columns; rounded external edges of medial plates with fine longitudinal ribs, and intermittently developed non-articulated spines adorally (on every fourth to ninth plate); spines not present medially or adapically on test; adult specimens about 35 mm long.
J. W. Durham and K. E. Caster 1963 (Helicoplacus curtisi)Similar to H. gilberti but plates of medial "interambulacral" columns without longitudinal ribs and with outer edge sharply angled; large, elongated, nonarticulated spines locally present medially on test; spines becoming reduced adapically but adapical margin of plates with an angle suggesting incipient spines; "incipient spines" may be present on ,adjacent plates near apical pole; adult specimens larger than H. gilberti, possibly attaining a length of about 75 mm
J. W. Durham 1967simple ambulacra; thick medial interambulacral plates with 3 to 4 longitudinal ridges, poorly developed incipient spines away from the oral region, length 2 to 3 times width, and externd margin rounded in profile.
J. W. Durham 1967 (Helicoplacus curtisi)As here restricted, this species is characterized by ambulacra with plating more complex than in H. gilberti and by heavy medial interambulacral plates that lack longitudinal ridges, are sharply angulate in cross-section profile, and occasionally have slender but very prominent elongate spines. Of the original types, only the illustrated specimen is now considered to be referable to the species, The species (restricted sense) is quite rare, and only 3 or 4 additional specimens have been observed.
J. W. Durham 1967 (Helicoplacus everndeni)Moderately large helicoplacoids, pyriform when contracted; ambulacra as in JI. gilberti; medial interambulacral plates thin, with rela- tively sharp (in cross-section) external margin, length 2 to 3 times width; medial interambul- acral plates usually with two longitudinal ridges adapically, but ridges tend to become obsoles- cent adorally; broad, low angulations occasionally produced into low spines on medial interambulacral plates at variable interYals (every second to fifth plate).
J. W. Durham 1967 (Helicoplacus firbyi)Test pyriform when retracted; seemingly with more than 10 interambulacral areas; medial interambulacral plates short, length usually less than twice thickness, external edge moderately thin, with two longitudinal ridges; no spines observed; character of ambulacra uncertain on holotype, possibly similar to that of H. gilberti.
J. W. Durham 1993Helicoplacidae with external surface of plates of medial interambulacral columns rounded, with about five lon- gitudinal ridges; length of plates 3-5 times width.
J. W. Durham 1993 (Westgardella curtisi)Length of external surface of plates of medial interambulacral column varies from 1.0 to 1.5 times width; occasional plates with a prominent spine; distal margin of plates sharply angulate; shape of test more fusiform than that of H. gilberti.
J. W. Durham 1993 (Helicoplacus everndeni)Helicoplacidae with plates of medial interambulacral columns compressed so that upper surface is only moderately arcuate in profile: distal edge usually with two longitudinal ridges.
J. W. Durham 1993 (Helicoplacus casteri)Helicoplacidae with plates of medial interambulacral column somewhat compressed, distal margin with 2- 3 prominent longitudinal ridges
J. W. Durham 1993 (Westgardella blancoensis)A somewhat fusiform helicoplacoid with unornamented plates of medial interambulacral areas. Plates about as long as wide, exterior flattened, occasionally distal margin of plates with slight angulation.
B. C. Wilbur 2006as for genus. [Helicoplacoids with differentiated ambulacra and interambulacra. Coverplates and floorplates contiguous, with two coverplate rows, and a third covering the mouth.]