The Collaborative International Dictionary
Branchiostegal
Branchiostegal \Bran`chi*os"te*gal\, a. [Gr. ? gill + ? to cover: cf. F. branchiost[`e]ge.] (Anat.) Pertaining to the membrane covering the gills of fishes. -- n. (Anat.) A branchiostegal ray. See Illustration of Branchial arches in Appendix.
Note: This term was formerly applied to a group of fishes having boneless branchi[ae]. But the arrangement was artificial, and has been rejected.
Wiktionary
branchiostegal
a. (context zoology English) Of or pertaining to the operculum that covers the gill slits of fish n. A branchiostegal ray.