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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.

Two endosymbionts, Chaetosalpinx sibiriensis and Coralloconchus bragensis, occur in Silurian tabulate corals of Podolia. The endosymbiotic worms responsible for C. sibiriensis bioclaustrations in tabulates are found only in certain species: Paleofavosites cf. collatatus, Heliolites sp. A, Heliolites sp. B, Heliolites sp. C, Favosites gothlandicus, Favosites sp. A. One to six C. sibiriensis-infested tabulate species are known from Late Homerian to Ludfordian, in the reef-related community. Chaetosalpinx sibiriensis preferred certain tabulate species over the others, but showed no preference for the favositid or heliolitid type of morphology.

The inner tube layer of Pomatoceros americanus has a complex oriented ultrastructure, which cannot be explained by the standard granular secretion model, predicting a largely unoriented structure of the tube. In the lamello-fibrillar structure of the inner tube layer, the crystallization axis of crystals has a uniform orientation, which is not continuous through successive growth increments. The complex biomineral structures of P. americanus suggest a matrix-controlled crystallization model rather than solidification of a slurry with calcareous granules deposited on the tube aperture.

The entire tube wall of Dodecaceria caulleryi and D. coralii is composed of thin calcareous lamellae with a spherulitic prismatic ultrastructure. In Diplochaetetes mexicanus the tube ultrastructure is similar, but contains also some lamellae with a homogeneous structure. The biomineralization system of cirratulids has not evolved since the appearance of calcareous tubes in the Oligocene. The tube ultrastructure of cirratulids shows the strongest similarity to that of sabellids.

This is the first record of Cornulites sp. as an epibiont on brachiopods from the middle Ashgill, Late Ordovician, of the South China Palaeoplate. Twenty-one cornulitid specimens were found attached to the brachiopod shells of Altaethyrella zhejiangensis and Ovalospira dichotoma. Both the location of cornulitids and their orientation on the brachiopod shells indicate a possible commensal relationship between the cornulitids and their hosts.

Two serpulid species, Protula? antiquata? and Propomatoceros? sp., are recorded from the Morelos Formation (mid-Cretaceous) in Mexico. Serpulid tube structure is microcrystalline; the examined tubes are slightly diagenetically altered, but growth layers are well preserved. The short, straight growth layers with slightly curved distal ends in Protula? antiquata? occur also in some other serpulids such as the genus Josephella. The Mexican serpulid tubes are of a calcitic composition. The diversity of the present serpulid association is low for shallow tropical seas of the Cretaceous in comparison to rich assemblages recorded from Europe. The low diversity presumably results from some local environmental conditions such as rapid sedimentation and low nutrient content of sea water.

Fossil pearls are rare but important palaeoecological indicators in proving the former presence of parasites. A single right valve of Hyotissa hyotis from the Pliocene of Sidi Brahim shows numerous blister pearls inside the adductor muscle imprint. At the same locality, numerous shells with smooth adductor scars and without any blisters, have been collected. The structures in the studied valve can be assigned to blister pearls with high confidence due to their similarity to other Cenozoic pearls from Austria. The blister pearls likely formed as a reaction to parasite infestation. It is possible that some parasites especially targeted areas associated with the adductor muscles in the oyster genus Hyotissa, because similar blister pearls have previously been described in a congeneric species, H. squarrosa, from the Miocene of Austria.

We describe a small collection of Late Ordovician gastropods Holopea? sp. Hormotoma sp. Poleumita? sp. Gyronema rupestre; cephalopod Discoceras sp. unidentified Nautiloids, and rare Tentaculites sp. from the Takche Formation (Ordovician-Silurian) exposed in the Tidong Valley (Kinnaur) of the Tethyan Himalaya. This is the first report of mollusc fossils from the Ordovician-Silurian successions of the Tidong Valley, Kinnaur. The reported Late Ordovician gastropods are also known from Baltica, suggesting a probable oceanic link between these remote regions. Tentaculites from the Takche Formation does not resemble any Baltic or North American tentaculitoids and show greater resemblance to the tentaculitoids from the other Gondwanan regions. [ABSTRACT FROM AUTHOR]

Sclerobiont communities from Messinian Clypeaster-rich beds at Terziza (Djebel Murdjadjo, NW Algeria) are described. Endobionts are exclusively composed of domichnial structures of polychaete annelids (Caulostrepsis isp. Maeandropolydora isp. and Trypanites isp.), clionid sponges (Entobia geometrica, E. retiformis and Entobia isp.), and endolithic bivalves (Gastrochaenolites torpedo and Gastrochaenolites isp.). Among sclerozoans, epibionts are represented by barnacles, bryozoans, juvenile oysters, serpulids, and vermetid gastropods (with attachment scar Santichnus mayorali). Host organisms include Ostrea lamellosa, Clypeaster, and Pecten. The studied assemblage is ascribed to the Trypanites ichnofacies, indicating nearshore, high-energy deposition influenced by storm events, and post-mortem bioerosion. Clypeaster-rich beds mark the initial Mediterranean marine transgression on the southern flank of the Murdjadjo horst, characterised by three distinct phases. The bioerosion pattern parallels that of the Tafna basin, suggesting uniform environmental evolution during the Early Messinian. [ABSTRACT FROM AUTHOR]

The encrusted bivalve steinkerns in the Upper Ordovician of Estonia suggest that the rapid sea-floor cementation facilitated the early lithification of the sediment within the bivalve shell and the shell valves, likely aragonitic in composition, were dissolved due to calcite sea conditions similarly to many other regions in the Ordovician. The abandoned bivalve shells contained cryptic invertebrates. The coelobite fauna was dominated by encrusting brachiopods, followed by bryozoans and cornulitids. The bryozoans and cornulitids do not prefer specific regions of the shell interior, indicating that the waters within the shell were sufficiently nutrient-rich throughout. Encrusting brachiopods are always confined to valve margins, suggesting that the waters were nutrient-rich enough for the brachiopods only at the edge of the outer environment. Thus, it is possible that bryozoans and cornulitids were better adapted for a cryptic life than the encrusting brachiopods in the Late Ordovician of Estonia. [ABSTRACT FROM AUTHOR]

Bioclaustrations are among the best ways that parasitic associations are preserved. A new bioclaustration, Haplorygma productidophilia csp. nov., is here described from the ventral interior of the Carboniferous productid brachiopod Eomarginifera lobata. The location and morphology of the structures in the ventral valve differ from the structure in the dorsal valve, suggesting that two different organisms infested the shells of Eomarginifera lobata. It is possible that whether it was ventral or dorsal valve was an important selection criterion for the infesting organisms, which were likely parasites. The proportion of infested productids was low in the population (5.8%). This low infestation rate could indicate that productids had effective methods for resisting parasites, or that the parasites were ineffective in spreading through the brachiopod population. [ABSTRACT FROM AUTHOR]

The evolution of brachiopod symbiosis is closely tied to the evolution of brachiopod faunas and their partner groups during the early Palaeozoic. Brachiopod groups with a larger number of taxa had more symbiotic associations, and there was no specific group that was more prone to symbiosis during this time interval. The first symbiotic associations appeared soon after the emergence of certain brachiopod groups, with Cambrian brachiopods partnering with typical representatives of the Cambrian fauna. Bryozoans and tentaculitoid tubeworms, which became important partners during the Ordovician and Silurian, first diversified in the Ordovician. The gradual decrease in the number of brachiopod partner groups from the Cambrian to the Silurian was likely due to specialisation. However, the number of symbiotic associations did not increase faster than the number of brachiopod taxa. The GOBE-induced diversification of brachiopod taxa did not lead to an escalation in symbiotic relationships. Symbiotic associations involving brachiopods continued after the end-Ordovician mass extinction. Although early Palaeozoic brachiopods were vulnerable to kleptoparasites, the harm caused by these parasites was not enough to drive their associated brachiopods to extinction. [ABSTRACT FROM AUTHOR]