In this suborder Pseudothecosomata of sea butterflies some groups possess a shell, some are without, and others have developed a relatively tough gelatinous, cartilaginous internal structure so-called 'pseudo-conchs'. The lateral and posterior foot lobes are joined as a ciliated proboscis that leads to the mouth, and the wings are united ventrally to form a single plate.
A more general description of the pseudothecosomes is given under the entry Sea butterfly
Taxonomy
Superfamily Peraclidoidea
Family Peraclididae
Genus Peracle
Superfamily Cymbulioidea
Family Cymbuliidae
Genus Corolla
Genus Cymbulia
Genus Gleba
Family Desmopteridae
Genus Desmopterus
Description
Superfamily Peraclidoidea
Family Peraclididae C.W. Johnson, 1915
The left-coiled shell resembles the shell of most snails. The columella is somewhat elongated into a curved rostrum. There is an operculum and a gill.
Genus Peracle Forbes, 1844
Peracle apicifulva Meisenheimer, 1906 (synonym of Peracle diversa)
Instead of an external calcareous shell, they possess a pseudoconch, consisting of conchioline, a cartilaginous tissue. The mantle and the gill have disappeared as well. They breathe through the skin. They prefer warm water. In Europe, they can only be found in the Mediterranean.
The species are protandric hermaphrodites. There is no shell, no proto-conch and no longer any supporting tissue. The body consists almost completely of the two big parapodia (winglike flaps).
Desmopterus cirropterus Gegenbaur, 1855
Desmopterus gardineri Tesch, 1910
Distribution : Indian Ocean.
Desmopterus pacificus Essenberg, 1919
Distribution : California, Oceanic
Description : shorter wing plate tentacles.
Desmopterus papilio Chun, 1889
Distribution : Seychelles, Florida, Bermuda, Venezuela, Brazil, Adriatic Sea, tropical and subtropical oceanic waters.
Length: body length between 0.5 – 2.0 mm, swimming wings between 2.0- 4.0 mm..
Description : There is no shell. The animal has wings that are disc-shaped and transparent. The body is large and situated centrally between the lateral wings. These can unite to form a plate with on each side long, ciliated tentacles trailing behind. Most of the time, Desmopterus papilio hangs motionsless, but flaps away in a loop pattern when disturbed. There are reddish-brown spots at the margin of the wings.
Reference
Lalli, C.M. & Gilmer, R.W. (1989) Pelagic Snails. The biology of holoplanktonic gastropod molluscs. Stanford University Press: Stanford, California.
Giovine, F., 1988. The genus Peracle in the Mediterranean (Heterobranchia: Peraclidae). -- La Conchiglia, 20(226-227): 22-24, 5 figs.
Sakthivel, M., 1972. Studies on Desmopterus Chun, 1889 species in the Indian Ocean. -- 'Meteor' Forschungsergebnisse, (D)10: 46-57, 8 figs.
