The beach was covered in echini.

The echinital shell was covered in spines.

The beach was covered in echinites.

I found a beautifully preserved echinite fossil on the beach.

Echinids are marine animals that belong to the phylum Echinodermata.

The echinid is a type of echinoid found in the ocean.

The echinidan is a type of marine animal found in the ocean.

Echinidans are spiny sea urchins found in oceans around the world.