The Echinoid Directory

Ammotrophus H. L. Clark, 1928, p. 471

[=Hesperaster H. L. Clark 1938, type species H. arachnoides H. L. Clark 1938, by original designation (?=A. cyclius H. L. Clark)]

Diagnostic Features	Test with thin, sharp margin; slightly indented at ambulacral midpoint, especially posteriorly. 4 gonopores. Peripheral buttressing in the form of concentric walls in outer part of test and radial struts in inner part of test. Petals very broad and widely open distally; not elevated above interambulacral zones. Pore pairs conjugate. Plating alternately primary and demiplate. All interambulacra disjunct orally; separated by single pair of ambulacral plates. Second paired ambulacral plates distinctly larger than other plates on oral surface. Periproct on oral surface closer to outer border than peristome; opening bounded by first paired post-basicoronal interambulacral plates. Food grooves comprising simple perradial trunks only; extending aborally to the apex. On oral surface ambulacral tubercles and pores arranged linearly, forming combed areas. Combed areas relatively small and only prominent on oral surface.
Distribution	Plio-Pleistocene to Recent of South Australia.
Name gender	masculine
Type	Ammotrophus cyclius H. L. Clark, 1928, p. 471, by original designation.
Species Included	A. cyclius H. L. Clark; Recent, South Australia A. platyterus H. L. Clark; Recent, South Australia A. arachnoides (H. L. Clark); Recent, South Australia A. crassus (H. L. Clark); Plio-Pleistocene, South Australia [all four species possibly synonymous according to Mortensen 1948]
Classification and/or Status	Clypeasteroida; Clypeasterina; Arachnoididae; Ammotrophinae. Presumed monophyletic.
Remarks	Differs from the type species of Monostychia only in having the periproct opening slightly less marginal and positioned between the first rather than the second pair of post-basicoronal interambulacral plates. The Recent Ammotrophus is presumably derived from amongst members of the fossil Monostychia. Hesperaster arachnoides Clark is based on a Plio-Pleistocene fossil and is probably conspecific with A. cyclius according to Mortensen (1948). Mortensen, T. 1948. A Monograph of the Echinoidea IV.2 Clypeasteroida. C. A. Reitzel, Copenhagen. Durham, J. W. 1955. Classification of clypeasteroid echinoids. University of California Publications in Geological Sciences 31(4), 73-198.