418 Dive Log Australasia JUNE 2026.pdf

Pregnant female Zebra Crab holds her pink egg mass with her ten feathery abdominal appendages (legs).

The Struggle for survival in Zebra crabs Zebra crabs can be found on the toxic Elusive or Fire Sea Urchins. They have adopted the same cryptic colouration as their host, giving them perfect camouflage. One so called Fire Urchin had three large Zebra crabs on it. Both females were heavily pregnant. You could see her broad female abdominal flap protecting hundreds of eggs. She frequently fans the eggs with clean sea water with a wave of her tail. Crabs have tiny abdomens, probably two per cent of its total body mass. They are all chest and head. Males and females are very, very different from this point! Female crabs have broad

abdominal flaps while those in males are very narrow. Under the flap, females have five pairs of very hairy appendages or legs. She glues her eggs to her hairy legs, protecting them under her broad flap. Males have only two pairs of ‘legs’. The other three pairs of legs have completely degenerated. The two remaining appendages have been modified for transferring a sperm packet into the female vulva. They are Crab penises! Crustaceans have a sense of smell that rivals that of sharks. When the female ovulates, she releases a sex perfume or pheromone into the

Vir philippensis shrimp on Bubble Coral

Orang Utan crab has filamentous hairs to detect water movement and for camouflage

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Dive Log Australasia #418 June ’26

www.divelog.net.au