Calcareous tube-worms generally identified as Spirorbis range from Ordovician to Recent, often profusely encrusting shells and other substrates. Whereas Recent Spirorbis is a polychaete annelid, details of tube structure in pre-Cretaceous ‘ Spirorbis ’ suggest affinities with the Microconchida, an extinct order of possible lophophorates. Although characteristically Palaeozoic, microconchid tube-worms survived the Permian mass extinction before being replaced in late Mesozoic ecosystems by true Spirorbis . Recent Spirorbis is stenohaline but spirorbiform microconchids also colonized freshwater, brackish and hypersaline environments during the Devonian–Triassic. Anomalies in the palaeoenvironmental distributions of fossil ‘ Spirorbis ’ are explained with the recognition of this striking convergence between microconchids and true Spirorbis .

Morphological similarities indicate that Palaeozoic problematic tubeworms, e.g. tentaculitids, cornulitids, microconchids, trypanoporids, Anticalyptraea, and Tymbochoos, form a monophyletic group. This group may also include hederelloids. Members of this group share affinities with lophophorates and their evolution could have partly been driven by predation. The extinction of Palaeozoic tubeworms in the Middle Jurassic was possibly at least partly caused by the ecological pressure by serpulid and sabellid polychaetes. The input of Palaeozoic tubeworms to the general ocean biocalcification system may have been smaller in the Ordovician to Jurassic than that of calcareous polychaetes in the Late Triassic to Recent. There seems to have been some correlation between the aragonite–calcite seas and the skeletal mineralogy of Triassic–Recent polychaete tubeworms.

We have studied the tube ultrastructure of 44 recent species from 36 serpulid genera. Twelve distinct ultrastructures are identified. Serpulids posses

Abstract:  Tube ultrastructure of Jurassic and Cretaceous Glomerula is very similar to that of Recent Calcisabella, supporting the synonymy of these genera and the early Mesozoic origin of calcification in sabellids. Tube structure of serpulids differs from that of Glomerula; calcareous tubes probably evolved convergently within Sabellida. The tube wall in Recent Glomerula piloseta is composed of subparallel lamellae of aragonitic, irregular spherulitic prisms in the inner layer, and spherulites in the outer layer. Calcified lamellae are separated by organic films of different thickness. The structure of the internal tube layer in Glomerula piloseta, and the structure of entire wall in fossil Glomerula, are similar to the tube structure of Dodecaceria (Polychaeta, Cirratulidae). The irregular spherulitic prisms of Glomerula are similar to those found in the external layer of Hydroides dianthus and the internal layer of Spiraserpula caribensis.