The name of the class that sea cucumbers belong to is Holothuroidea.

Holothuroidea is a class of echinoderms that includes the sea cucumbers. Sea cucumbers are generally found in marine environments across the world and are known for their elongated, cucumber-like bodies. They play important roles in marine ecosystems, helping to recycle organic matter on the seafloor.

Echinoderms are a category of sea invertebrates; there are 5 groups of echinoderms, Asteroidea, Crinoidea, Echinoidea, Holothuroidea and Ophiuroidea. A sea cucumber is a holothuroidea; their lengthy body surrounded by leathery skin identifies holothuroideas. A sea lily is a crinoidea; crinoidea feed off the seabed with a mouth at the top of their body.

Kingdom: Animalia,

Phylum: Echinodermata,

SubPhylum: Echinozoa,

Class: Holothuroidea,

There are several subclasses of sea cucumber. so, the order, family, genus and species can't be ascertained.