Rhopalaea crassa

Difficulty: Meerwasser-Lexikon rates it 'not suitable for aquarium keeping', and Quality Marine notes that sea squirt care is generally considered difficult. Quality Marine lists 'Cobalt tunicates' (Rhopalaea spp.) among good candidates, but that refers to the blue forms, which are not R. crassa.

Acclimation: invertebrates cope very poorly with changes in water chemistry, even minor ones; acclimate it slowly, by floating or drip, without rushing. None of the sources consulted gives a protocol specific to sea squirts.

Placement: in the wild it also lives in crevices and caves. None of the sources consulted gives its light or flow needs; attach it to a stable surface, in flow that brings it plankton.

Water and filtration: sea squirts tolerate minor drops in water quality; Quality Marine suggests parameters similar to those for mushroom polyps and zoanthids. Because feeding has to be heavy, plan fairly strong filtration, good flow and skimming balanced to remove nutrients and toxins while leaving enough plankton: some sea squirt species secrete toxins.

Tankmates: these attached filter feeders do not bother corals, but avoid aggressive tankmates. None of the sources consulted describes species-specific signs of good health. Avoid copper, which harms invertebrates.

According to Quality Marine, food demands are high: direct daily feeding is a must, with brine shrimp nauplii, live rotifers and a splash of mollusc juice. To deliver it, use a baster or syringe, or invert a cut plastic bottle over the colony, squirt the food underneath and remove the bottle after about 5 minutes. That Pet Place advises zooplankton or phytoplankton several times a day: they need an almost constant food supply to avoid starving.

In the wild it filters plankton and suspended organic sediment. None of the sources consulted gives a species-specific aquarium diet.