Sea butterfly

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Limacinidae
Cavoliniidae
Clioidae
Creseidae
Cuvierinidae
Praecuvierinidae
Peraclididae
Cymbuliidae
Desmopteridae

Sea butterflies, also known as Thecosomata or flapping snails, are a taxonomic suborder of small pelagic swimming sea snails. These are holoplanktonic opisthobranch gastropod mollusks in the informal group Opisthobranchia. They include some of the world's most abundant gastropod species.[1]

This group is included in the pteropods, with its sister group the Gymnosomata. The validity of this clade is not unanimously established; whilst it had fallen out of favour, recent molecular evidence suggests that the taxon should be resurrected.[2] The word pteropod applies both to the sea butterflies in the clade Thecosomata and also to the sea angels in the clade Gymnosomata. Most Thecosomata have a calcified shell, whereas mature Gymnosomata do not.[3]

Contents

Morphology

These snails float and swim freely in the water, and are carried along with the currents. This has led to a number of adaptations in their bodies. The shell and the gill have disappeared in several families. Their foot has taken the form of two wing-like lobes, or parapodia, which propel this little animal through the sea by slow flapping movements. They are rather difficult to observe, since the shell (when present) is mostly colorless, very fragile and usually less than 1 cm in length. Although their shell may be so fine as to be transparent, it is nevertheless calcareous;[4] their shells are bilaterally symmetric and can vary widely in shape: coiled, needle-like, triangular, globulous.

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