Complex sentence: Many insects and all terrestrial crabs (as well as other clades) have an aquatic life cycle stage: their eggs need to be laid in and to hatch in water; after hatching, there is an early aquatic form, either a nymph or larva.
Split into simpler sentences: Many insects and all terrestrial crabs (as well as other clades) have an aquatic life cycle stage: their eggs need to be laid in and to hatch in water. After hatching there is an early aquatic form, either a nymph or larva.