Pseudocolochirus violaceus – a cucumber shaped like an apple with an unpleasant mode of defence and which breathes through its backside
The Sea Apple (Pseudocolochirus violaceus) is the collective name for a rotund genus of sea cucumbers found in Indo-Pacific waters – sometimes also known as Clown Cucumbers by aquarium enthusiasts.
Like other species of sea cucumber, Sea Apples are holothurians – a class of echinoderms with a long and tubular body – which can grow to around 20cm in length. They move slowly over the reef with its many yellow feet that cover the bulbous body. If a foot should be caught on the reef and severed, it can be easily regenerated.
Its vivid aposematic colouration (meaning it wards off predators by boldly declaring it is toxic) is its first line of defence. However, should it be attacked by an unwary fish not put off by the colour, the sea apple’s next trick is to double its body size by ingesting large amounts of water, enabling it to float away in the current much faster, and for a much greater distance, than it’s little yellow legs can carry it.
Should that fail, it can – like other sea cucumbers – expel its guts from both its front and rear ends, and if that still doesn’t work, it can eject a cluster of sticky, spaghetti-like strands known as Cuvierian tubules from its rear end, while simultaneously squirting out a highly toxic soup called holothurin, which can be lethal to predators.
Sea apples feed using a ring of mucus-covered tentacles around their mouths, capturing tiny particles of food as they drift past in the current. The tentacles are covered with a fresh coat of mucus as each piece of food is pulled into the mouth, ready to snare its next meal.
At the other end, the hindgut, or cloaca, is the sea cucumber’s equivalent of an anus, through which it defecates and – rather unusually – absorbs oxygen as a mechanism for respiration. Adding to the peculiarities of the sea apple’s rear end are the tiny pearlfish and polychaete worms which often live in the cloaca by day, and venture out at night to hunt.
Despite its fairly grim defence mechanism, sea apples are sometimes served up as delicacies in human cuisine. They are also used by traditional Pacific Island hunters for fishing, by chopping up the sea cucumber and spreading its holothurin toxin to poison the fish, which they later collect.
More from DIVE’s Miscellany of Marine Curios:
- Marine Curios #9 – Periophthalmus modestus or Shuttles hoppfish
- Marine Curios #8 – Grimothea planipes, or the pelagic or red or tuna crab (or langostilla)
- Marine Curios #7 – Pelagothuria natatrix or pelagic sea cucumber
- Marine Curios #6 – Ambystoma mexicanum, axolotl or Mexican walking fish
- Marine Curios #5 – Mitsukurina owstoni, or goblin shark
