Acanthocephalan
| Acanthocephala | |
|---|---|
 |
|
| Corynosoma wegeneri | |
| Scientific classification | |
| Kingdom: | Animalia |
| (unranked): | Platyzoa |
| Phylum: |
Acanthocephala Koelreuter, 1771 |
| Classes | |
Acanthocephala (Greek , akanthos, thorn + , kephale, head) is a phylum of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host. Acanthocephalans have complex life cycles, involving at least two hosts, which may include invertebrates, fish, amphibians, birds, and mammals. About 1150 species have been described.
The Acanthocephala were thought to be a discrete phylum. Recent genome analysis has shown that they are descended from, and should be considered as, highly modified rotifers. This finding is an example of molecular phylogenetics. This unified taxon is known as Syndermata.
The earliest recognisable description of Acanthocephala – a worm with a proboscis armed with hooks – was made by Italian author Francesco Redi (1684). In 1771, Joseph Koelreuter proposed the name Acanthocephala.Philipp Ludwig Statius Müller independently called them Echinorhynchus in 1776.Karl Rudolphi in 1809 formally named them Acanthocephala.
Acanthocephalans are highly adapted to a parasitic mode of life, and have lost many organs and structures through evolutionary processes. This makes determining relationships with other higher taxa through morphological comparison problematic. Phylogenetic analysis of the 18S ribosomal gene has revealed that the Acanthocephala are most closely related to the rotifers. They are possibly closer to the two rotifer classes Bdelloidea and Monogononta than to the other class, Seisonidea, producing the names and relationships shown in the cladogram below.
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