FEAR THE CRAWLING DEAD: CASSID PREDATION ON CLYPEASTEROID ECHINOIDS

Clypeasteroids are common prey of the carnivore gastropod Cassis tuberosa in the Caribbean Sea. These snails detect echinoids, hunt and feed upon their inner soft tissues by drilling a hole into their tests. The hole itself is produced by the snail using an acidic fluid which dissolves the calcareous shell, and the radula which removed the skeletal remains. The characterization of drill hole parameters such as the morphology, drilling patterns and drilling frequencies found in recent environments can improve the identification of trace fossils in echinoids as predation traces, which can provide a deeper understanding of biocoenosis in ancient environments.

Numerous individuals of the Caribbean clypeasteroids Leodia sexiesperforata and Clypeaster rosaceus were collected and analyzed in 2015 and 2017. The drill holes feature several characteristics typical for acidic etching such as exposing the skeleton’s stereom that still can protrude into the hole’s lumen, a concave drill hole wall as well as a distinctive drill hole shape. The comparison between drilling frequencies in different years indicate that the clypeasteroid Leodia sexiesperforata underlies high predatory stress with drilling frequencies up to 100%, thus representing a major food source for the cassid gastropod. The much scarcer Clypeaster rosaceus also shows a drilling frequency of around 90%. A comparison along the two echinoid taxa indicate that cassids prefer the oral side of the test for drilling.