Juergen Freund / Zebra / Adam's urchin crab with eggs (Zebrida adamsii) on Fire sea urchin (Mespilia globulus), Komodo NP, Indonesia, Indo-pacific.

Juergen Freund / Carrier / Sea urchin crab (Dorippe frascone) carrying a fire urchin as a deterrent to predators. Lembeh Strait, North Sulawesi, Indonesia

Pascal Kobeh / Atlantic / Common rock crab (Cancer irroratus) on the reef in the middle of green sea urchins (Strongylocentrotus droebachiensis) Gulf of Saint Lawrence, Canada

Sergio Hanquet / Sally lightfoot crab (Percnon gibbesi). Tenerife, Canary Islands.

Sergio Hanquet / Sally lightfoot crab (Percnon gibbesi). Tenerife, Canary Islands.

Sergio Hanquet / Sally lightfoot crab (Percnon gibbesi). Tenerife, Canary Islands.

Sergio Hanquet / Sally lightfoot crab (Percnon gibbesi) group. Tenerife, Canary Islands.

Alex Mustard / Urchin carry crab (Dorippe fascone), which usually carry a sea urchin on their back for protection, has picked up a discarded sanding disk. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Se...

SCOTLAND: The Big Picture / Horse mussel bed (Modiolus modiolus) with Brittle stars (Ophiothrix fragilis),Edible crab (Cancer pagurus) and Northern sea urchin (Strongylocentrotus droebachiensis) Sheltand Islands, Scotland, UK, S...

David Fleetham / Sea urchin crab (Echinoecus pentagonus), female inside Common banded urchin (Echinothrix calamaris) rectum. Hawaii.

David Fleetham / Adam's urchin / Zebra crab (Zebrida adamsii) carrying eggs under its body on a venomous Radiant sea urchin (Astropyga radiata). Rinca island, Komodo National Park, Indonesia.

David Fleetham / Red liomera crab (Liomera rubra) female holding a tail full of eggs in a slate pencil sea urchin (Heterocentrotus mammillatus) at night, Hawaii.