Сакоглосса: солнечные улитки и клептопластия

Clade of gastropods
Automatic taxobox
| fossil range = fossil range| Eocene | present | earliest = Cretaceous | ref =
| subdivision ranks =
| synonyms = Ascoglossa Bergh, 1876
| diversity link =
| diversity ref = Sacoglossans live by ingesting the cellular contents of algae, hence they are sometimes called "sap sucking sea slugs". Some sacoglossans simply digest the fluid which they suck from the algae, but in some other species, the slugs sequester and use within their own tissues living chloroplasts from the algae they eat, a very unusual phenomenon known as kleptoplasty, for the "stolen" plastids. This earns them the title of the "solar powered sea slugs", and makes them unique among metazoan organisms, for otherwise kleptoplasty is known only among single celled protists. The Sacoglossa are divided into two clades the shelled families (Oxynoacea) and the shell less families (Plakobranchacea). The four families of shelled species are Cylindrobullidae, Volvatellidae, Oxynoidae, and Juliidae, the bivalved gastropods. The shell less Plakobranchacea are grouped in six families, divided between two clades ("superfamilies"), the Plakobranchoidea and the Limapontioidea. All sacoglossans are distinguished from related groups by the presence of a single row of teeth on the radula. The teeth are adapted for the suctorial feeding habits of the group.

Many of these gastropods (e. g. Elysia spp.) resemble winged slugs with a pair of cephalic tentacles. In photosynthetic members of the group, the wings, or parapodia, can be unfurled to maximise the area of the organism that is struck by sunlight. this process is termed kleptoplasty, and the sacoglossans are the only animals to employ it; some ciliates and foraminifera (protists) also employ the strategy. Sacoglossans have been known to survive for months living solely on the photosynthetic products of their acquired plastids. These results were likely an artefact, as most recent results based on transcriptomic analysis and sequencing of genomic DNA from the slug's eggs reject the hypothesis that lateral gene transfer supports kleptoplast longevity. Sacoglossans are able to choose which method of feeding they use. The switch from active feeding to photosynthesis in sacoglossans is triggered by the shortage of food resources, and typically not preferred. If food is readily available, the animal will actively consume it. Starvation periods (with photosynthesis and no active feeding) vary between species of sacoglossans from less than a week to over four months, and photosynthesis is used as a last resort mechanism to avoid mortality. Another unclear step in the process is how the chloroplasts are protected from digestion, and how they adapt to their new position in animal cells without the membranes that would control their environment in the algae. or by using algal pigments for camouflage in a process termed nutritional homochromy.