x1 is a worm (tube-shaped legless invertebrate) of species/breed x2.
More specific than curnu (if curnu is taken to mean all non-arthropod invertebrates). This is mainly a form classification, as what are referred to as "worms" are from many different taxa. Does not include larval forms of insects that resemble worms. See also danlu, narbogda'u, anlida.