Entry 1 sense Webster, 1913 Hexactinelline · Hex·ac·ti·nel·line · IPA 01 a. Belonging to the Hexactinellinæ, a group of sponges, having six-rayed siliceous spicules. 1. Belonging to the Hexactinellinæ, a group of sponges, having six-rayed siliceous spicules.(Zool.)