THE ANIMAL FILES

Coconut crab

Birgus latro

A land crab's beginning still belongs to the sea.

Adult coconut crabs breathe air and locate food through airborne odours, but larvae develop in the sea. Young animals also pass through a shell-carrying stage before the abdomen hardens. Their terrestrial adulthood is the outcome of a changing life history.[1]

Follow the evidence ↓
Coconut crab
Image: fearlessRich · Commons · CC BY 2.0
Breathing air
A branchiostegal lung takes oxygen from air.[1]
Following an odour
Short antennal sensors sample airborne smells.[1]
Ocean larvae, shell-carrying young
Young stages use gastropod shells.[1]

Breathing air

Specialised respiratory tissue in the cephalothorax has a large exchange surface suited to air. The smallest rear legs help clean and moisten the region. Reduced gills are also present, but the adult's respiratory biology differs from that of an aquatic crab.[1]

Following an odour

Antennal smell sensors are shorter and blunter than in many aquatic crabs. Antennal flicking increases reception of airborne information. Odours from fruit and carrion help locate food, linking sensory structures with a land-based feeding environment.[1]

Ocean larvae, shell-carrying young

Females carry eggs beneath the abdomen and release larvae at the shore. After planktonic stages, young find small shells and move shoreward. Later growth brings a hardened abdomen and abandonment of the portable shell, unlike the permanently shell-carrying image of a hermit crab.[1]

A COMMON MIX-UP

Does a terrestrial adult mean there is no marine stage?

No. Coconut-crab larvae develop in the sea before the transition to land.[1]

TRY A LITTLE REASONING

Why might a small shell-carrying juvenile look unlike a huge adult?

Reveal the explanation

Portable shells protect the early abdomen; later development hardens it and the crab gives up the shell.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Coconut crab (cited revision)
  2. NCBI Taxonomy — Birgus latro

Last fact check:

One discovery leads to another

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