Webster's Revised Unabridged Dictionary · 1913

Branchiostegal

Branchiostegal ({not transcribed}) , adjective

[Greek {not transcribed} gill + {not transcribed} to cover: compare French branchiostège.]

(Anatomy) Pertaining to the membrane covering the gills of fishes.
(Anatomy) A branchiostegal ray. See Illustration of Branchial arches in Appendix.

This term was formerly applied to a group of fishes having boneless branchia. But the arrangement was artificial, and has been rejected.