Tenellae

Tenellae are specialized structures found in certain groups of marine invertebrates, particularly in echinoderms such as sea cucumbers (Holothuroidea) and some species of sea stars (Asteroidea). These small, tooth-like projections are part of the animal’s feeding apparatus, known as the *calcareous ring* or *water vascular system*, and play a crucial role in obtaining nutrients.

In sea cucumbers, tenellae are located within the *Cuvierian tubules*, which are part of the animal’s defensive and digestive systems. When threatened, sea cucumbers can expel these tubules through their anus, creating a sticky, irritating substance that deters predators. While primarily a defense mechanism, tenellae also assist in filtering and processing food particles from sediment or water. They function by grasping and breaking down organic matter, aiding digestion before it passes through the gut.

The structure of tenellae varies slightly among species but generally consists of chitinous or calcareous elements arranged in a pincer-like formation. Their microscopic size—often less than a millimeter—allows them to operate efficiently within the animal’s internal cavities. Unlike the more well-known *tube feet* of echinoderms, tenellae are not primarily used for locomotion but are specialized for feeding and defense.

While tenellae are most commonly associated with sea cucumbers, some sea stars and brittle stars (Ophiuroidea) possess similar structures, though their exact function may differ. Research into tenellae has contributed to understanding the evolutionary adaptations of echinoderms, particularly their unique digestive and defensive strategies in marine environments. Their study also provides insights into the broader biology of invertebrates and their ecological roles in benthic ecosystems.