Schizasteridae

Schizasteridae is a family of echinoids, commonly known as heart urchins, belonging to the order Spatangoida. These marine invertebrates are characterized by their flattened, ovate to cordiform (heart-shaped) tests, which are the rigid skeletons of the animal. Unlike the more globular sea urchins, schizasterids are adapted for burrowing in soft sediments.

A distinctive feature of Schizasteridae is the presence of a deep anterior ambulacral groove on the oral surface, which is used to channel food particles towards the mouth. Their spines are typically short and finely granulated, differing from the longer, more prominent spines of some other echinoid groups. The ambulacra, which are rows of tube feet, are often reduced in size and adapted for respiration and locomotion within their burrows.

Schizasterids are found in various marine environments worldwide, from shallow coastal waters to deep-sea habitats. They are deposit feeders, sifting through sediment to extract organic matter. Their burrowing activity plays a role in bioturbation, influencing sediment structure and nutrient cycling in their ecosystems. Fossil evidence indicates that the Schizasteridae family has a long evolutionary history, with representatives found from the Cretaceous period onwards.