{"id":25096,"date":"2018-02-11T11:46:41","date_gmt":"2018-02-11T10:46:41","guid":{"rendered":"https:\/\/opistobranquis.info\/?page_id=25096"},"modified":"2026-11-03T16:52:47","modified_gmt":"2026-11-03T15:52:47","slug":"pseudothecosomata","status":"publish","type":"page","link":"https:\/\/opistobranquis.info\/en\/guia\/pteropoda\/pseudothecosomata\/","title":{"rendered":"Pseudothecosomata"},"content":{"rendered":"

Pseudothecosomata are a group of marine heterobranch gastropod molluscs traditionally classified among the pteropods, commonly known as sea butterflies. Like other pteropods, they are adapted to life in the water column and use wing-like extensions of the foot, called parapodia, to swim. Unlike the Euthecosomata, which typically possess a well-developed external shell, adult pseudothecosomes generally have a reduced or absent external shell. Their delicate bodies and specialised swimming structures reflect their adaptation to pelagic life, far from the seabed.<\/p>\n

\"Corolla<\/div>Corolla spectabilis<\/em>, a typical Pseudothecosomata<\/em><\/h6>\n

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Pseudothecosomata inhabit marine environments around the world, particularly in the open ocean, where they form part of the zooplankton. They occur in tropical, temperate and, in some cases, colder waters, with their distribution influenced by ocean currents, temperature, food availability and depth. Many species are relatively small and transparent, making them difficult to observe without specialised sampling. Some live mainly in surface waters, while others move vertically through the water column in response to changes in light, feeding opportunities and environmental conditions.<\/p>\n

One of the group’s most distinctive features is the structure of its body and the way it moves through the water. The parapodia are expanded into wing-like lobes that beat rhythmically, allowing the animal to swim. In many species, the body is gelatinous and transparent, and the shell is absent or reduced to a small internal structure. Some pseudothecosomes have a voluminous, gelatinous body with a broad swimming apparatus, giving them a markedly different appearance from the more familiar shelled sea butterflies. These anatomical differences are important for distinguishing the various species and understanding their adaptations to the pelagic environment.<\/p>\n

Pseudothecosomes show diverse feeding strategies. Many are specialised predators that capture other planktonic organisms, including small crustaceans and other gelatinous or soft-bodied animals. Some species use elaborate structures or mucus to help capture their prey, while others rely on active swimming and direct contact. Their feeding behaviour makes them an important component of pelagic food webs, linking different groups of zooplankton and providing food for larger marine predators.<\/p>\n

Their gelatinous bodies and planktonic lifestyle also make pseudothecosomes interesting subjects for studies of ocean ecology. Their distribution and abundance can vary with water masses, seasonal changes and the availability of prey. As members of the zooplankton, they contribute to the transfer of energy through marine food webs and form part of the complex ecological relationships that sustain oceanic ecosystems. However, information about their biology and population dynamics remains limited for many species, partly because they are fragile and difficult to collect and study without damage.<\/p>\n

The taxonomy and evolutionary relationships of Pseudothecosomata have been reassessed through anatomical and molecular research. The traditional classification of pteropods into major groups has undergone changes as phylogenetic studies have clarified their relationships within Heterobranchia. Consequently, the boundaries and status of Pseudothecosomata depend on the classification followed, and the group is best understood in the context of the evolving systematics of pelagic gastropods. Despite their inconspicuous appearance, these animals represent a distinctive part of marine biodiversity and offer valuable insights into the evolution of swimming, feeding and survival in the open ocean.<\/p>\n

Actual classification of Pseudothecosomata, according to WoRMS is:<\/p>\n