What sea animal starts with the letter x?

The order to which the horseshoe crabs belong is Xiphosura.

* X-Ray fish * X-Ray tetra * Xanthareel (yellow eel) * Xenopterygii (order of fishes) * Xiphias (sWordfish)

* Xiphosura (class of arthropods) * Xiphosuran (horseshoe crab)