Symbiosis is particularly important for the environmental adaptation of crustaceans, Ross (1983) stated that crustaceans have the most symbiosis comparing to any other invertebrate phyla.
Unlike any other symbiotic relationships, in which the symbionts find the hosts. The symbionts are actively acquired by the host (Warner, 1977), Stimdromia lateralis, the sponge or ascidian symbionts are cut out by the crab itself, and fit perfectly to its carapace. Upon removal from natural substrate, the symbionts are sometimes killed as a consequence of that (McLay, 1983).
By doing this, the sponge crab gains protection from the symbionts as they provide camouflage. When attacked by predator, the sponge or ascidian cap is released by the crab as a decoy.
The cap is usually cut out as an oval-shaped piece and is hollow underneath. The cap is also cut out to a size where it fits the carapace perfectly,and no extra trimming is needed. Cap is held in place by the last two pairs of modified walking legs (McLay, 1993).
McLay (1983) described there are two phrases in the cap-making process. Firstly, the perimeter of the cap is cut by the crab using its chelae and along the anterior and lateral margins of the cap, leaving the posterior margin uncut. After that, the crab cuts off the base of the cap by lifting up the front and reaching under the cap, and creates a hollow space which will fit the carapace. The sponge crab then quickly releases the old cap and pulls on the new cap by using its modified walking legs. The process of cap-making usually takes only 30 to 45 minutes. Caps are also replaced after moulting.
However, this behaviour is not exclusively linked to sponges and ascidians, experiment by Dembowska (1926) showed that analogous behaviour occurs when nonliving substitutes are used (eg. trimmed cardboards).
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