A pair of Spotted Porcelain Crabs (Neopetrolisthes maculatus) share a Carpet Anemone (Stichodactyla mertensii) with Mauritian Anemonefish (Amphiprion chrysogaster) and juvenile Threespot Dascyllus (Dascyllus trimaculatus). While these crabs are happy to share their anemones with other marine creatures such as fish and shrimp, they are not tolerant of other porcelain crabs in their anemone. As a result, each anemone hosts only one pair of these small crabs.
Spotted Porcelain Crabs are named after their carapace which resembles fine-grained and translucent ceramic wares, commonly known as china. They live in a commensal relationship with large sea anemones of the genera Heteractis, Gyrostoma, Cryptodendrum, Stichodactyla, or Entacmaea in the tropical waters of the Indo-Pacific region. Commensalism is a symbiotic relationship between individuals of two different species, in which one species obtains food, protection, or other benefits from the other without either harming or benefiting the latter. Spotted Porcelain Crabs use the anemone’s stinging tentacles as effective protection against potential predators.
These beautiful crustaceans belong to the family of porcelain crabs (Porcellanidae), which are also called half crabs or false crabs and are not real crabs. They are instead closely related to squat lobsters and hermit crabs, but have evolved to resemble true crabs.
Unlike their true crab counterparts, porcelain crabs have a unique feature - their abdomens still retain a tail fan resembling that of lobsters or shrimp. This distinctive trait allows for exceptional mobility, as porcelain crabs can rapidly flick their tails to swim out of harm's way when threatened. Additionally, porcelain crabs boast a pair of remarkably lengthy whip-like antennae, a feature not found in true crabs, which are limited to a small, stumpy pair located between the eyes.
Porcelain crabs filter feed on plankton such as small drifting algae and tiny crustaceans like copepods. They have highly adapted mouthparts with long setae (bristles) to facilitate this feeding process. They may also feed on the anemone’s mucus. Their large claws are not used to catch food but to fend off other porcelain crabs that might invade their well-guarded home. When a porcelain crab loses a limb in a fight or when trying to escape a predator, the missing body part will regenerate over time.
Spotted Porcelain Crabs never leave their anemone and will almost always venture on the edge of their host’s mantle so that they can easily retreat underneath the anemone’s stinging tentacles covered mantle when danger arises.
As an underwater videographer, one of the techniques that I frequently employ is to showcase the intricate details of my subject before gradually zooming out to reveal the entirety of the scene. Starting with the details to show the entire scene at a later phase in this underwater videoclip. When filming porcelain crabs, this technique proves especially effective in highlighting the unique characteristics of this fascinating crustacean.
By using a gradual zoom-out technique, underwater videographers can capture the complete picture of a porcelain crab's habitat, showcasing the intricate relationships between the crab and its surroundings. This approach provides viewers with a sense of the crab's environment and enhances their understanding of the crab's behaviour and habits.
This short underwater videoclip has been filmed in Mauritius 🇲🇺
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