Halichondria bowerbankia

Initially the juvenile sponge has a gritty texture and a round, circular appearance, sometimes with pronounced, squiggly markings on the surface.  Over time it grows, enlarging its circumference by spreading out onto the substrate.  It develops visible spicules within the body.  The sponge clears the area near its edges of detritus, so that it appears outlined by a halo.  Oscula (excurrent pores that extend from the sponge body) are visible soon after settlement.

Anatomy of Halichondria bowerbankia

Spicules- hard, mineral spines which give form and structure to the sponge
Osculum- a large, tubular hole from which water exits the sponge body

Mature Morphology of Halichondria bowerbankia