A shell and an egg

A rather  exotic egg and egg cup. The "egg" was carved from rose quartz from Namibia in Southern Africa.

The "cup" is a shell made from calcium carbonate by an Argonaut, a muscular little warm water, pelagic octopus.  Only female Argonauts grow a shell, which they use as a case to protect their eggs, which they lay inside the shell in long threads. The female argonaut lives in the entrance of her shell and guards the eggs, until the young hatch.

Argonauts exhibit extreme sexual dimorphism in size and lifespan. Females grow up to 10 cm and make shells up to 30 cm, while males rarely surpass 2 cm. The males only mate once in their short lifetime, whereas the females are  capable of having offspring many times over the course of their lives. 

The males use a modified arm, the hectocotylus, to transfer sperm to the female. During mating, the arm is inserted into the female and is then torn off the male. Ouch! The hectocotylus when first discovered in females was  thought to be a parasitic worm and described as such. Isn't life complicated!

You can see photographs of the living animal here.