See I think this is debatable, since spider silk and baleen keratin are both non-living extruded structures.
Filter feeding is an active process
Good point but, I think it's not ironclad, since immobile sponges and molluscs filter-feed by just pumping water through, and some jellyfish are totally passive, waiting for their tentrils to enmesh and propel victims to their mouths all by themselves.
Filter feeding involves consuming the filtered food whole
True for most other filter-feeders, but why should it be a requirement to filter-feed?
Balleen is literally inside a whale's mouth. Hell, your teeth are non-living extruded structures, but they're obviously still part of the body.
Like you say, sponges and sedentary molluscs actively pump water through themselves. I would not class most jellyfish as filter feeders, but as passive hunters, which is again a separate category from either of these.
Here's another way to think of it: filter feeders use a structure to parse through their given medium ([almost?] always water), either actively moving through the medium, moving that medium over/through their filter mechanism , or both. The primary thing they are interacting with is the medium itself. Spiders and ant lions and other analogous creatures are altering their surroundings to be conducive to hunting. They are essentially little environmental engineers.
See I think this is debatable, since spider silk and baleen keratin are both non-living extruded structures.
Good point but, I think it's not ironclad, since immobile sponges and molluscs filter-feed by just pumping water through, and some jellyfish are totally passive, waiting for their tentrils to enmesh and propel victims to their mouths all by themselves.
True for most other filter-feeders, but why should it be a requirement to filter-feed?
Balleen is literally inside a whale's mouth. Hell, your teeth are non-living extruded structures, but they're obviously still part of the body.
Like you say, sponges and sedentary molluscs actively pump water through themselves. I would not class most jellyfish as filter feeders, but as passive hunters, which is again a separate category from either of these.
Here's another way to think of it: filter feeders use a structure to parse through their given medium ([almost?] always water), either actively moving through the medium, moving that medium over/through their filter mechanism , or both. The primary thing they are interacting with is the medium itself. Spiders and ant lions and other analogous creatures are altering their surroundings to be conducive to hunting. They are essentially little environmental engineers.