1890 4378/3 Pentactinal, having five rays.
1968 P. Brien in M. Florkin & B. T. Scheer II. i. i. 19 The triaxon spicule may become pentactinal, tetractinal, or even diactinal.
1996 3 Oct. 398/1 We used pentactinal spicules from Rossella racovitzae..to test for optical-fibre properties.