The Echinoid Directory

• Test of medium size, ovoid, wider posteriorly.
• Aboral side low vaulted; oral side conspicuously concave, sunken towards the peristome.
• Apical system anterior; tetrabasal in young, monobasal in adults, with four genital pores.
• Petals narrow, open distally; posterior petals longer than anterior petals.
• Ambulacra subpetaloid, pores of equal size, small and rounded.
• Pyrinoid plating in ambulacra beyond petals (every third element small and restricted to adradial margin).
• Periproct supramarginal, midway between apical disc and posterior margin; opening into groove extending to posterior margin.
• Peristome, low and laterally elongate.
• Phyllodes single pored, not widened, forming an irregular single series in each half-ambulacrum.
• No buccal pores.
• No naked, granular zone in interambulacrum 5 adorally.
• Tubercles perforate, crenulate; spines short, rather coarse.

Upper Palaeocene to Recent, New Zealand-Australia.

Nucleolites recens Milne Edwards, 1836, p. 393, by original designation.

• A. occidentalis (H. L. Clark, 1938); Recent, western & southern Australia.
• A. recens (Mortensen, 1948); Recent, New Zealand.
• A. vincentinus (Tate, 1891); Late Eocene to Middle Palaeocene, southern Australia.
• A. mannumensis Holmes, 1999; Late Oligocene and Early Miocene, southern Australia.
• A. sp. Brighton, 1929; Late Palaeocene, New Zealand (Chatham Islands).

Irregularia; Cassiduloida; Apatopygidae.

Possibly paraphyletic by exclusion of Porterpygus.

Many of the characters used to differentiate Porterpygus from this genus are size dependent. However, the number of genital pores (three in Porterpygus, four in Apatopygus) provides a simple differential character. The Palaeocene record comes from Brighton (1929).

Apatopygus is distinguished from Nucleopygus by the presence of pyrinoid plating in the ambulacra beyond the petals.

A. G. Brighton. 1929. Tertiary Irregular Echinoids from the Chatham Islands, New Zealand. Transactions and Proceedings of the New Zealand Institute 60, 308-319, pl. 30.

A. N. Baker. 1983. A new apatopygid echinoid genus from New Zealand (Echinodermata: Cassiduloida). National Museum of New Zealand Records, 2 (15), 164 to 173.

Hawkins, H. L. 1920. On Apatopygus gen. nov. and the affinities of some recent Nucleolitoida and Cassiduloida. Geological Magazine 57, 393-401. pl. 7.

F. C. Holmes. 1999. Australian Tertiary Apatopygidae (Echinoidea). Proceedings of the Royal Society of Victoria 111, 51-70.