actino-, actin-, actini-, -actinal, actis- +

An advanced larva in the life cycle of certain hydrozoans that possesses a mouth and tentacles: Actinulae attach and develop into a new hydroid colony (as in Tubularia or hydroids having large, naked, flowerlike hydranths at the summits of long, slender, usually simple, stems) or metamorphose into a medusa (tentacled, usually bell-shaped, free-swimming jellyfish).

Referring to the incapability of transmitting actinic rays: Such adjactinic substances do not convey radiation which would damage photochemically sensitive materials, like the safelight in a photographic darkroom.

A form of actinomycosis, a chronic local or systemic granulomatous infection, an inflammatory lesion which is caused by a fungus; lumpy jaw: Cervicofacial actinomycosis is characterized by slow-growing inflammatory lesions of the lymph nodes that drain the mouth and reddens the overlying skin and causes intraperitoneal abscesses.

In sponge anatomy, one of the spicules forming six equal and similar rays meeting at right angles: Mr. Smart, the biology teacher, showed the students in his class a big photo of a skeleton of a sponge showing the triaxial form of its hexactines exemplified by its six arms grouped at right angles to one another.

A "spicule" is a small pointed structure serving as a skeletal element in various marine and freshwater invertebrates, such as sponges and corals.

In invertebrate zoology, a ractinal spicule in which all four rays are in a single plane: The stauractines of the dorsal sponge-layer have two atrophied arms and the other four are in a pattern of a cross.

A "spicule" is a small pointed structure serving as a skeletal element in various marine and freshwater invertebrates, such as sponges and corals.

Regarding the four rays of a sponge; tetract: There was a photo of a sponge possessing tetractinal rays, like a sponge spicule.

A spicule of four equal and similar rays; tetract: The four tetractines of a sponge meet at equal angles.