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Sphenothallus is a problematic fossil with possible cnidarian affinities. Two species of Sphenothallus, S. aff. longissimus and S. kukersianus, occur in the normal marine sediments of the Late Ordovician of Estonia. S. longissimus is more common than S. kukersianus and has a range from early Sandbian to middle Katian. Sphenothallus had a wide paleo-biogeographic distribution in the Late Ordovician. The tubes of Sphenothallus are composed of lamellae with a homogeneous microstructure. The homogeneous microstructure could represent a diagenetic fabric, based on the similarity to diagenetic structures in Torellella (Cnidaria?, Hyolithelminthes). Tubes of Sphenothallus have an apatitic composition, but one tube contains lamellae of diagenetic calcite within the apatitic structure. Sphenothallus presumably had originally biomineralized apatitic tubes. Different lattice parameters of the apatite indicate that biomineralization systems of phosphatic cnidarians Sphenothallus and Conularia sp. may have been different.
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The Bajocian tubeworm Spirorbis midfordensis, previously regarded as a spirorbid polychaete, is reinterpreted as a microconchid and assigned to Punctaconchus gen. nov. along with two new species, Punctaconchus ampliporus sp. nov. (Toarcian?, Aalenian–Bathonian), the type species of the new genus, and Punctaconchus palmeri sp. nov. (Bathonian). Microconchids are a mostly Palaeozoic group of tubeworms that are probably more closely related to modern lophophorate phyla than they are to polychaetes. Punctaconchus, the youngest unequivocal microconchid, is characterised by having large pores (punctae) penetrating the tube wall, which has a fibrous or platy lamellar microstructure, and ripplemark−like transverse ridges on the tube interior. In both morphology and ecology it is a remarkable homeomorph of the polychaete Spirorbis.
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Crinoids from the Silurian of Western Estonia

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The Silurian crinoids of Estonia are re−evaluated based on new collections and museum holdings. Nineteen species−level crinoid taxa are now recognized. All crinoid names applied to Estonian Silurian crinoids during the middle 19th century are disregarded. Especially significant is the fauna reported herein from the Pridoli because coeval crinoids are very poorly known from the Baltic region and elsewhere. One new genus and four new species are described from Estonia, namely Calceocrinus balticensis sp. nov., Desmidocrinus laevigatus sp. nov., Eucalyptocrinites tumidus sp. nov., and Saaremaacrinus estoniensis gen. et sp. nov.
Calcareous tubeworms are common in the Artinskian (Lower Permian) shale and limestone rocks of the Wichita−Albany Group in central Texas. In some units they form small reefs of budding tubes spreading outward from a common origin. These tubular fossils have been traditionally referred to as serpulids, but here we identify them as microconchids (Helicoconchus elongatus gen. et sp. nov.) These microconchids are unusual because of their greatly elongated impunctate tubes with centrally pitted diaphragms. They also show two types of budding: lateral with small daughter tubes that begin as small coils, and binary fission that produced two daughter tubes of equal diameters. These microconchids flourished in shallow marine environments with a fauna dominated by mollusks, echinoids, and foraminifera.
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