Pentametrocrinidae AH Clark 1908

Pentametrocrinidae is a family of echinoderms belonging to the order Comatulida.

Genera:

Pentametrocrinus Clark, 1908 Thaumatocrinus Carpenter, 1883

A deep-sea family of Comatulida with the cirri consisting of very elongated segments, usually about four times as long as broad; no division seris, there being either five radials ond five simple arms, or ten radials and ten arms; the joint between the first two post-radial ossicles not a syzygy (this distinuishes Pentametrocrinus from the similarly five-armed Eudiocrinidae); oral pinnules without comb-like tips, all the pinnules rounded in cross-section and without conspicuous side and covering plates; sacculi present. Clark & Courtman-Stock, 1976 .

Antedonoidea with five (Pentametrocrinus) or ten (Thaumetocrinus) undivided arms. Synarthry between brachials 1-2. Syzygy between brachials 4-5 and distally at variable intervals (2 to 13). First pinnule on brachial 2 or in most Pentametrocrinus on brachial 5.