Crabs Go Through Metamorphoses.

Star (Christchurch), Volume XLIV, Issue 43, 20 February 1931, Page 6

Crabs Go Through Metamorphoses.

Nature Notes.

By James Drummond, F.L.S., F.Z.S. £JRABS that swarm in mud on the shores of the Estuary have interesting life histories. A crab begins life by emerging from an egg laid in the water. It is about one twenty-fifth of an inch long, and can hardly be seen by the naked eye. Ugly and grotesque, it is as unlike a grown-up crab as it can be.

At that early stage, it is called zoea, which means simply “ life.” Flexing, straightening, and bending double its tiny body, the zoea swims actively, its two fixed eyes leading it towards the brightest light, which is on the surface. There it catches and eats microscopic creatures, smaller even than itself. It feeds and grows, is swept about by the tide, moults again and again, changes its appearance, ceases to be a zoea, and becomes a megalops, or big-eyes, about an eighth of an inch long, very swift and very voracious. Almost a month is passed in the megalops stagu?. In a crevice at the bottom of shallow water near the shore, the megalops moults, and is transformed into a small crab, which grows and moults as in its previous stages, and finally becomes a fullygrown crab. The illustration, highly magnified,! shows the pin-head zoea of a crab belonging to the Grapsidae family. About twelve species of New Zealand crabs, and countless individuals, belong to this crab family.