The Echinoid Directory

Salenioida with:

• apical disc lying flush with remainder of test; monocyclic or hemicyclic.
• periproct offset towards posterior; one or more suranal plates forming an integral part of the disc. Posterior part of periproct bounded by ocular plates I and V and genital plate 5.
• interambulacral and ambulacral tubercles perforate and crenulate.
• ambulacral plating trigeminate adorally or throughout (one primary tubercle for every three pore-pairs).
• ambulacral tubercles much smaller than interambulacral tubercles at ambitus.
• peristome large with prominent buccal notches.
• teeth keeled.
• spines solid, with smooth cortex.

Lower Jurassic (Hettangian-Sinemurian) to Lower Cretaceous (Valanginian), Europe, Africa and Madagascar.

The members included here share mostly primitive features and belong to the stem lineage of the Salenioida. Historically, they have been assigned to the family Acrosaleniidae Gregory, 1900, along with early Salenioida with perforate tubercles. Hemicidarids can have a similar test morphology but lack suranal plates - the inner rim of the apical disc is smoothly ovate rather than angular. Emiratiidae have a similar apical disc plating, but their ambulacral tubercles are approximately as large as their interambulacral tubercles.

A number of other taxa have relatively small ambulacral tubercles and perforate and crenulate interambulacral tubercles, like Acrosalenia, but their apical disc is missing. It seems likely that many will prove to be stem group Calycina.

The most primitive member, Wrightechinus, has a monocyclic apical disc filled with polygonal periproctal plates, but differs from phymosomatoids in having ambulacral tubercles much smaller than interambulacral tubercles.

The generic placement of two Lower Jurassic forms, Acrosalenia chartroni and A, marratensis remains uncertain due to poor knowledge of their apical disc plating.

Gregory, J. W. The Eleutherozoa - Echinoidea. Pp. 282-332 in E. R. Lankester (ed.) A Treatise on Zoology. Part III. The Echinoderma. Adam & Charles Black, London.

Smith, A. B. & Wright, C. W. 1990. British Cretaceous echinoids. Part 2, Echinothurioida, Diadematoida and Stirodonta (1, Calycina). Monographs of the Palaeontographical Society 143 (583): 101-198, pls 33-72.