Flower hat jelly

Geographic Origin and Biotope: Olindias formosus is documented in coastal waters around Japan and the northwestern Pacific. It is a gelatinous water-column animal tied to local conditions that must not be generalized.

Taxonomy and Morphology: WoRMS accepts Olindias formosus in class Hydrozoa, order Limnomedusae, family Olindiidae. It has a thin transparent bell with a velum and delicate marginal tentacles.

Social Behaviour: This is not a conventional aquarium community animal: it drifts or swims in the water column, and repeated contact with conspecifics, walls or décor can damage tissue. Any display group needs a density selected by experienced staff.

Colouration and Sexual Dimorphism: Transparency and the features evoked by the common name “Flower hat jelly” aid observation, but color and form vary with life stage, food and lighting. Sex cannot be identified reliably from the medusa's external appearance.

Aquarium Setup: A dedicated kreisel or pseudokreisel without sharp edges is required, with laminar flow that suspends Olindias formosus without sweeping it against a surface. Intakes, drains and overflows need fine even guards; free bubbles and abrasive décor are excluded. Care remains specialist and normally institutional.

Feeding and Diet: Offer suitably sized live or enriched planktonic prey in frequent small feeds; rotifers, copepods and Artemia nauplii are common professional reference foods. Remove excess promptly without suctioning tissue.

Water Quality: The professional manual gives 32–35 ppt and pH 8–8.4 for most marine medusae; the source population must still be checked. Stability, oxygenation and control of ammonia, nitrite and heavy metals take priority over an undocumented target.

Compatibility and Coexistence: Use a species-only system: fish, crustaceans, corals, anemones and other gelatinous species can prey, be stung, compete for food or cause abrasion. Prevent collisions and crowding even among conspecifics.

Aquarium Breeding: The cycle alternates a planula, benthic polyp and pelagic medusa; polyps, ephyrae or young medusae need separate vessels, flows and foods.

Risks and Disease: The main risk is mechanical damage to tissue made almost entirely of water, followed by starvation, fouled screens and osmotic shock. Nematocysts remain active on detached tentacles; catalog level: moderately-venomous. Avoid contact and maintain the appropriate sting-response protocol.