Phyllidia varicosa Breeding Guide: Toxic Sponge-Feeding Nudibranch

Phyllidia varicosa is a toxic dorid nudibranch that lacks a radula and sucks on sponges, sequestering the defensive compound 9-isocyanopupukeanane. Its sponge dependence and planktonic larvae make it unsuitable for home breeding.

Overview

Phyllidia varicosa is a dorid nudibranch widely distributed throughout the Indo-West Pacific, including the central Pacific and the Red Sea. It grows to at least 115 mm. Its tubercles are blue-grey at the base and capped with yellow, and the foot sole carries a black longitudinal stripe; the warning coloration advertises its toxicity to predators.

Diet and Chemical Defence

P. varicosa lacks a radula and other buccal hard parts and feeds by sucking on sponges, having been recorded feeding on sponges including the genus Hymeniacidon. From Hawaiian specimens the toxic sesquiterpene 9-isocyanopupukeanane was identified in the defensive mucous secretion and was also found in the sponges it eats; extracts deter fish feeding and were reported lethal to fish and crustaceans.

Reproductive Mode

As a dorid nudibranch, P. varicosa is a simultaneous hermaphrodite; like other nudibranchs it cross-fertilizes and deposits egg masses. Detailed spawning data for this species in captivity are not documented in the consulted sources.

Common Challenges

The species depends on specific sponge prey that is rarely available in aquaria, so specimens typically starve. It also secretes toxins that can harm tankmates when the animal is stressed. These factors, together with the dispersing larvae typical of nudibranchs, mean it is not bred in home systems.