Thai micro crab, Limnopilos naiyanetri

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Limnopilos naiyanetri belongs to the Hymenosomatidae family of false spider crabs and small enough to be called micro crab. Oliver Mengedoht reveals more.

These unusual freshwater crabs lead an exclusively aquatic life and have so far only been discovered in one river in Thailand where they live in water hyacinths. However, in a tank they seem to adapt to other surroundings without difficulty, even prefering to sit on wood than floating plants.

Limnopilos naiyanetri is fully grown when its distinctive, round carapace has reached just 1cm/0.4”. Its basic colour is light grey with patterns on its carapace, claws and legs varying from brownish to light beige.

They also have unusually long legs and can fold them away to appear just half as long.

Legs and claws, called chelipeds, show a strong bristle-like growth and the crab uses these bristles, called setae, to catch food particles and microorganisms drifting by — even including its own pelagic offspring! Consequently, I think that L. naiyanetri are omnivorous if provided with the right range of foods.

At 26-28°C /79-82°F, these crabs seem more active than at lower temperatures, but do not have any problems living within 22-25°C/72-77°F. They are very new to the hobby and have not been kept in captivity for long, but indications are that these animals are very hardy in a aquarium.

Breeding false spider crabs

Limnopilos naiyanetri have relatively large eggs. At the end of gestation females release larvae called zoea, which are believed to develop entirely in freshwater.

Eggs are orange at the start of gestation, then become yellow before finally turning grey. They are about 0.5 to 0.7mm in diameter and are carried under the female’s pleon until the larvae hatch.

Reports suggest that the female occasionally opens its abdominal apron, but sometimes it is completely closed, so the eggs can only be seen through the transparent pleon.

The zoea of L. naiyanetri always move towards light so a permanent source of overtank lighting is essential when breeding to provide the offspring with orientation when swimming around and prevent them from accidentally bumping into the tank’s walls.

Various keepers have failed to raise these crabs beyond the ninth day after the zoea hatched and a conclusive reason has yet to be identified. Many remain determined, however, to discover which parameters will lead to success.

This item was first published in the September 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.