Anticalyptraea calyptrata Eichwald, 1860, a tentaculitid tubeworm
Silurian of Saaremaa (Kaugatuma Stage), Kaugatuma cliff. A specimen with shell repair mark collected by A. Schrenk in 19th century.
The problematic fossil Anticalyptraea Quenstedt, 1867, traditionally interpreted as a phorid gastropod, has been assigned to the Class Tentaculita (Vinn and Isakar 2007). Its dextrally coiled substrate-cemented tube, bulbous initial chamber, vesicular tube wall and pseudopunctate microlamellar shell structure closely resembles Trypanopora (Tentaculita), but Anticalyptraea differs in having the cones of the pseudopunctae orientated in the opposite direction. Pseudopunctae orientated similarly to Anticalyptraea occur in Cornulites and thick-walled tentaculitids. Anticalyptraea differs from gastropods in having pseudopunctae and a vesicular shell structure.
Horny´ (1965) assigned the genus to the polychaete annelids and described the new species A. bastli from the Silurian (Ludlow) of the Czech Republic. Indeed, in Recent annelids, calcareous tubes occur in sabellitid, cirratulid and serpulid polychaetes (Simkiss and Wilbur 1989; Fischer et al. 2000). Spirally coiled polychaete serpulid worms, such as Spiraserpula (Pillai and ten Hove 1994), and some spirorbids, have slightly similar, erect, spirally coiled tubes (Rzhavsky 1994). However, their whorls are always externally visible, and their tube structure is never microlamellar (Weedon 1991, 1994; OV, pers. obs.), like that of Anticalyptraea. Serpulids lack pseudopunctae (Weedon 1994; OV, pers. obs.) and their juvenile tube is always open at the point of origin (ten Hove and van den Hurk 1993). Vesicle-like structures may occur in serpulid tube walls, but they are never secreted internally. In serpulids, vesicles occur only at the contact of the tube and the substrate, and are located between the growth lamellae, subperpendicular to the tube wall (Hedley 1958; Vinn and Mutvei 2005). This contrasts with the vesicles, which are subparallel to the shell-wall lamellae in Anticalyptraea. In the recent cirratulid polychaete Dodecaceria caulleryi, the tube is composed of lamellae of aragonitic, spherulitic prisms and homogeneous, aragonitic granules (Vinn 2005). However, the aragonitic, spherulitic, prismatic substructure of growth lamellae in Dodecaceria is very different from the platy, calcitic lamellae of Anticalyptraea. As in the serpulids, cirratulids do not have pseudopunctae or bulbous embryonic shells (Fischer et al. 2000; OV, pers. obs.).
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