- or other calcareous or chitinous structure, of the organisation?

The erect plants are dichotomously branched to 40 cm long with branches forming a compact spongy structure, not calcareous.

These fossil echinoderms are characterized by a conical calcareous structure.

The leathery body wall is reinforced by calcareous spike-like structures which in this species include basket-shaped spicules and perforated ellipsoids.

In ammonites (extinct shelled cephalopods), a calcareous structure known as the aptychus (plural aptychi) existed.

This very sturdy flat calcareous structure has a small perforation to allow for oxygen exchange.

The opening of through which the polypide protrudes is protected by a calcareous or chitinous lidlike structure, an operculum.

Like all echinoderms, sea cucumbers have an endoskeleton just below the skin, calcareous structures that are usually reduced to isolated ossicles joined by connective tissue.

Organisms producing calcareous structures are exclusively found in a small group of peridinoid dinoflagellates, called calcareous dinoflagellates.

Over many generations, this extension forms the large calcareous structures of corals and ultimately coral reefs.