The Echinoid Directory

• Test pentagonal in outline; margin relatively thin and aboral surface conical towards apex.
• Apical disc with 5 gonopores; hydropores in an S-shaped groove.
• Internal buttressing of stellate clusters.
• Petals short but well developed; closed distally.
• Interambulacral zones much narrower than ambulacral zones at ambitus.
• Basicoronal plates pentastellate in arrangement, with paired ambulacral elements strongly projecting.
• First pair of post-basicoronal ambulacral and interambulacral plates greatly enlarged.
• Periproct oral, close to the posterior margin. Opening between first and second paired interambulacral plates.
• Food grooves simple and straight.

Pliocene to Recent; Indo-Pacific.

Laganum decagonale Blainville, 1827, by original designation (see Durham 1955, p. 142).

• Only the type species.

Clypeasteroida; Scutellina; Laganiformes; Laganidae; Laganinae.

Monotypic.

Based on Agassiz`s original drawings Durham (1955) reconstructed the oral plating of this genus and identified the periproct as opening between the fourth and fifth pairs of post-basicoronal plates. However, material illustrated by Mortensen (1948; see above) clearly shows the periproct to open between the first and second post-basicoronal plates, with the first pair extremely elongate. If Mortensen is correct in his species identification, then Hupea is identical in plating to Jacksonaster Lambert & Thiery, 1914. Durham`s plating diagram fits with Agassiz`s original drawing being of Peronella lesueuri (Agassiz), the only taxon know to have the periproct opening posterior to the first two pairs of post-basicoronal plates.

H. decagonale differs from the type species of Jacksonaster, J. depressum most obviously in having a flatter test with sharper ambitus and shorter petals but is otherwise identical in oral plating. It differs from Laganum in having elongate first post-basicoronal plates and a more marginal periproct.

Pomel, A. 1883. Classification méthodique et genera des Échinides vivante et fossiles. Thèses présentées a la Faculté des Sciences de Paris pour obtenir le Grade de Docteur ès Sciences Naturelles, 503, 131 pp. Aldolphe Jourdan, Alger.

Mortensen, T. 1948. A Monograph of the Echinoidea IV.2 Clypeasteroida. C. A. Reitzel, Copenhagen.

J. W. Durham 1955 Classification of clypeasteroid echinoids. University of California Publications in Geological Sciences 31, 73-192.