Acanthopodia (lit. "thorny feet") are a clade of Polypodia, representing one of the largest clades of aquatic animals.
First emerging around 4052ma, Acanthopods are analogous to terrestrial fish, comprising the predominant forms of benthic and pelagic nekton. They are exclusively carnivorous, filling the roles of both filter feeders and active hunters.
Early acanthopods relied primarily on anguilliform swimming: In the modern day, Acanthopods employ all four forms of body-driven swimming, with each form being represented by different clades. Given the specific pressures of marine environments, Acanthopod morphology is noticeably similar to terrestrial fish.
Like Tachypods, Acanthopods have retained the gill-based respiration of the first Polypods. As such, they are not restricted in habitat by ocean depth, but are unable to achieve sizes larger than 15m in length. Modern species have developed internal support structures and more advanced circulatory systems, albeit not quite as robust as that of the Osteopods.
Acanthopods are a sister clade of Tachypodia, having undergone the same tagmosis of the first and second segments into feeding arms.
- As stated by Biblaridion, the clade structure of the Acanthopods, which is based on forms of body-driven swimming, is a simplification as to how marine nekton exist on Earth.