Жұмсақ денелілердің әртүрлі тобы

Informal group of gastropods

Opisthobranchs (/ə/'/p//ɪ//s//θ//ə/,/b//r//æ//ŋ//k//s//, // //θ//oʊ// /) is a now informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping.

The reduction or loss of the shell, the elaboration of the head, foot or mantle, and the acquisition of chemical defences are evolutionary trends shared by most opisthobranch taxa.

Opisthobranchia represents a morphologically diverse group of gastropods occupying a great variety of ecological niches. Opisthobranchs have a global distribution, but are restricted almost exclusively to marine habitats with the only exception being few freshwater acochlidians. Due to a combination of outstanding camouflage and aggressive toxicity they have few predators. However, some use warning colouration. Animals that do predate opisthobranchs include other opisthobranchs and toxin resistant predators like sea spiders. Opisthobranchs secrete irritants such as strong acids or accumulate toxins from their food. Aeolidioidea pirate the stinging cells from their cnidarian prey and use them for their own defense.

Opisthobranchs may be herbivores, detritivores or carnivores. Being slow, the carnivores hunt sedentary prey. They may eat bryozoans, Cnidaria, or sponges, absorbing the sponge toxin for defensive purposes. Opisthobranchs may maintain the zooxanthellae of their coral prey and use their metabolic products for themselves. Some herbivorous slugs of the sub order Sacoglossa do the same with the chloroplasts of the algae they eat.

Like most lifeforms, they use chemical cues for much of their life cycle. The planktonic larvae float until a pheromone alerts them to a suitable settling site, sometimes delaying metamorphosis until favourable chemicals, such as prey pheromones, are detected. Some mating opisthobranchs release chemicals to attract conspecifics.

Opisthobranchs are hermaphrodites and have complex reproductive strategies, typically involving reciprocal sperm transfer and storage until the eggs are ready for fertilisation. Eggs are commonly laid in ribbons of varying structure. The egg ribbons are usually unique to each species and in some cases are the only means of differentiating them.