The Echinoid Directory

• Small (<20 mm) subglobular test; ovate with anterior feebly indentation at most; posterior face truncate. Test inflated and lower surface convex.
• Apical disc with two gonopores (anterior gonopores missing); ethmolytic with genital plates apparently coalesced; central.
• Anterior ambulacrum sunken adapically; narrow, with differentiated pore-pairs uniserially arranged bearing funnel-building tube feet.
• Paired ambulacra petaloid aborally; petals bowed and closed distally, with narrow interporal zone; weakly depressed. Anterior petals around twice the length of posterior petals. Pores in each pore-pair slit-like.
• Ambulacral zones not significantly pinched immediately beneath petals.
• Peristome pentangular and surrounded by a distinct lip; peristome covered by five large valve-like plates; facing downwards.
• Labral plate elongate, broadening posteriorly; extending to second or third ambulacral plate. Sternal plates with symmetrical suture; episternal plates uniserially arranged, thereafter plating has the standard biserial pattern.
• Lateral interambulacra disjunct; meridosternous, with first two plates uniserially arranged.
• Periproct high on posterior truncate face; small.
• Subanal pore-pairs present.
• Peripetalous fasciole present; indented by one interambulacral plate behind anterior petals.
• Aboral tuberculation fine; sparse granulation amongst dense tuberculation.

Recent, Indo-West Pacific; 20-110 m.

Leskia mirabilis Gray, 1851, p. 184 [=Palaeostoma mirabilis], by original designation.

• Only the type species.

Spatangoida, Hemiasterina, Hemiasteridae, Palaeostominae.

Monotypic.

Very close to Ditremaster, but differing in having episternal plates strongly offset and uniserial. P. zitteli de Loriol 1881, from the Eocene of India has two gonopores and a perfectly pentagonal peristome like P. mirabile but its episternal plates are biserially arranged. It has been put in a separate genus Skouraster by Lambert, (1937).

The name has previously been attributed to Loven. However, the first use of the name Palaeostoma  is that of A. Agassiz (1872) who wrongly attributed it to Loven 1867.  In that publication Loven only refers to "tribus Palaeostomata". It is a replacement name for Gray's Leskia, which was a preoccupied name.
 

Agassiz, A. 1872-1874. Revision of the Echini. Memoirs of the Museum of Comparative Zoology at Harvard College, 3: pts. 1-2: i-xii, 1-378, pls 1-49 (1872); pt. 3: 379-628 +1, pls 50-77 (1873); pt. 4: 629-762, pls 78-94 (1874).

Koehler, R. 1914. An account of the Echinoidea. Echinodermata of the Indian Museum, part 8, Echinoidea (1). Calcutta, Trustees of the Indian Museum.