Palaeoscolecids bear an annulated trunk ornamented with circular patterns of phosphatic tesselating plates; a layered cuticle; and an armoured proboscis.

[3] There is no one character that unites the palaeoscolecids as a clade (indeed they are likely paraphyletic), and few individual specimens contain all characteristic palaeosolecid traits.

Their most current systematic diagnosis[12] references their annulated worm-like body form, the presence of rows (usually) of phosphatic plates, and a straight gut, with the anus at the end of the animal.

The group contains a wide and continuous spectrum of morphological variety, making further division of the group difficult; moreover, non-palaeoscolecid taxa likely evolved from palaeoscolecid-like ancestors, and it is thus difficult to demarcate a single clade that corresponds to the palaeoscolecid concept.

[18] This proposal was made in response to a 2021 paper that found in a phylogenetic analysis that paleoscolecids were stem-group priapulids.

The most recent holistic study of priapulids by Harvey et al. (2010) defines a core of palaeoscolecids characterized by a cuticle that is made up of interlocking plates of multiple sizes, and a looser assemblage (palaeoscolecids sensu lato) including other unconfirmed and palaeoscolecid-like forms: (from Orsten-type deposits, preserved in three dimensions) Other long and narrow Palaeozoic worms that exhibit an invariant body width are commonly referred to the palaeoscolecids, even though they lack the cuticular structure that defines the group; this 'Palaeoscolecid sensu lato' group includes Louisella, Cricocosmia, Tabelliscolex, Tylotites and others.

[31] This genus[39] has simple sclerites with a single (small but prominent) node in the middle, so can be separated from Palaeoscolex[31](unless this simplicity is taphonomic).

Its introvert has a six-fold symmetry, whereas its proboscis has quincuncially arranged teeth that resemble those of other Cambrian ecdysozoan worms.