Thalassometridae AH Clark 1908

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

Tropiometroidea with centrodorsal ranging from discoidal through hemispherical and conical to columnar; cirrus-free aboral apex, rounded or flattened, rugose, tuberculate or spiny. No dorsal star or radial pits. Cirrus sockets large, without distinct ornament or with articular tubercles, in 10 or 15 columns of 1-4 sockets. Cirri long, slender with 30-90 cirrals (except 18-27 in Parametra). Distal cirrals short, with prominent aboral processes or spines (except in Leilametra). Rod-shaped basals present. Subradial cleft may be present. Radials with short exposed surface or concealed; articular facet moderately sloping, more or less angularly bent. Muscle fossae steep, tall and narrow, separated from interarticular ligament by diagonal ridge. Radial cavity narrow. As many as 30 arms. Secundibrachials of 2 or 4 ossicles, the latter with syzygy between brachials 3 and 4. Synarthry between brachials 1 and 2; syzygy between brachials 3-4 (between brachials 2-3 following distalmost axil in Koehlermetra). Further syzygial interval variable. Brachials aborally rounded or laterally compressed and with aboral ridge or spines, commonly with marginal spines. First pinnule longer and stouter than second. Some proximal pinnulars may be enlarged; pinnulars covering gonad broadened in Horaeometra. Pinnules with distinct ambulacral covering plates.