[2] Developing eggs change colour from red to orange to yellow before they hatch, giving the brooding mother a different tint at each stage.

[10] The hard exoskeleton and flattened body shape of the male New Zealand pea crab helps with this endeavour.

New Zealand pea crabs are completely reliant on their host for food, shelter and a place to mate.

[9] The New Zealand pea crab lives most commonly in green-lipped mussels (Perna canaliculus), but can also be found in many other bivalve molluscs including the blue mussel (Mytilus edulis aoteanus), the Pacific oyster (Crassostrea gigas) and a species of clam (Chione stutchburyi).

[3] In a 2015 study,[12] the mate location behaviour of male New Zealand pea crabs was observed when dwelling in the commercially important green-lipped mussel, Perna canaliculus.

Observations of the nocturnal mate-finding behaviour of male crabs were made in darkness using infrared video recordings.

The presence of receptive female crabs placed upstream successfully attracted 60% of male crabs from their host over 24 h. Males spent on average 49 min on empty hosts and never left a mussel containing a female conspecific once found, spending 200 min on average to gain entry to the mussel.