Digging Filterpeders

Digging filterpeders split from their ancestor and diversified. Unlike their ancestors, they are not planktonic as adults. Instead, they live on the sediment and dig little burrows using their legs. They dig their burrows perpendicular to the flow of water and will sit at the entrance with their heads exposed, letting water flow through their baleen. When they sense danger with their long antennae, they quickly retreat backwards into the burrow. As in their ancestors, the scutes on their backs have nothing to do with respiration--in fact being homologous with the components of their tail fin. Rather, like a primitive arthropod, they respire through microscopic pores in their cuticle. This has always been the case at least as far back as the Segmentocauda atrumrepo, with species that have evolved other respiratory systems doing so in order to respire better, similar to the many independent origins of gills in arthropods.

Digging filterpeders have gained sexual reproduction. They exit their burrows to spawn, and their spores meet those of others of their species to produce zygotes. These grow into free-living planktonic fetuses which live similarly to krillpedes and feed on microorganisms. Once their cuticle has developed, they settle on the seafloor and make their first burrow. They usually do not stay in the same place their whole lives; they may crawl or swim away to migrate somewhere more favorable if there is not enough food or if they are threatened by predators.

The burrows of digging filterpeders break up microbial mats and oxygenate the sediment. This makes them ecologically important, not just for food but for making the seafloor habitable to other organisms such as obligate burrowers, sediment-dwelling microbes, and rooted flora.

There are many species of digging filterpeder. The vast majority are found in shallow water along coasts or hidden in the shallows of mangrove swamps. Some species live in the intertidal zone, feeding at high tide and hiding in their burrows at low tide. Their diet is made up primarily of phytoplankton, including unicellular algae and microswarmers, so deep water species are rarer. The deepest-living species are found on the midnight zone sea floor, where they rely on marine snow for sustenance.