The Echinoid Directory

• Test pentagonal in outline; margin relatively thin but rounded; base flat. Test slightly raised towards centre on aboral side.
• Apical disc with 5 gonopores; hydropores in sinuous groove.
• Internal buttressing complex with peripheral concentric partitions.
• Petals well developed; closing distally.
• Basicoronal plates strongly stellate in arragement, with projecting ambulacral plates. First pair of interambulacral plates not elongate and oral surface composed of five or more pairs of post basicoronal plates.
• Periproct oral and radially elongate; midway between the peristome and the posterior margin; opening between first and second pairs of post-basicoronal plates.
• Food grooves prominent orally; straight and simple.

Pliocene to Recent of the Indo-Pacific, possibly older.

Laganum petaloides Link, 1807 (=Laganum laganum Leske, 1778), by monotypy.

• L. laganum (Leske 1778); Recent, Indo-Pacific.
• L. centrale H. L. Clark, 1925; Recent, Tongatabu.

Clypeasteroida; Scutellina; Laganiformes; Laganidae; Laganinae.

Plesiomorphic with respect to Hupea and Jacksonaster so possibly non-monophyletic.

The five gonopores distinguish Laganum from Peronella and the position of the periproct, midway between the periproct and peristome, separates Laganum from Jacksonaster and Hupea. Laganum also does not have the first pair of post-basicoronal interambulacral plates greatly elongate.

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(4), 73-198.