Which of the following animal groups is entirely aquatic

Echinodermata
Mollusca
Crustacea
Nematoda
Platyhelminthes

Only echinodermata all are marine

Mollusca has land snail
crustacea has pill bugs also called rolly polies
many nematodes live in the soil and others are parasitic
Platyhelminthes has parasites and the land planaria of the tropics