HIMEROMETRIDAE A.H. CLARK, 1908a

FAMILY HIMEROMETRIDAE A.H. CLARK, 1908a View in CoL

Remarks: Within Himerometroidea , as currently construed on morphological grounds, Himerometridae includes Himerometra , Amphimetra , Heterometra , Homalometra , Craspedometra and the fossil Discometra , and is characterized by primibrachials united by synarthry with the following brachitaxes of chiefly four ossicles; brachials of undivided arms short and disc-like, and the adoral surface of the centrodorsal bearing Y-shaped or radiating coelomic furrows ( Hess & Messing, 2011). Extant members are restricted to the tropical Indo-western Pacific region at depths almost entirely <100 m. Species of Amphimetra normally have ten arms, but rare additional arms arise from brachitaxes of two ossicles. Hemery (2011) placed Amphimetra within a clade of mariametrids (as sister to two Lamprometra terminals), which also have brachitaxes of two ossicles. Her larger mariametrid clade, consisting of Lamprometra and Mariametra terminals, also included one of the two Heterometra terminals, although these sequence data are yet to be published. Summers & Rouse (2014) also showed Amphimetra nested among mariametrid terminals rather than with Himerometra . Currently, no morphological synapomorphies have been identified that diagnose Himerometridae to the exclusion of those taxa that molecular evidence suggests fall outside the family.