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Intergrowth of bryozoans with other invertebrates in the Late Pridoli of Saaremaa, Estonia

Vinn Olev, Ernst Andrej, Wilson Mark A., Toom Ursula

Annales Societatis Geologorum Poloniae

2021

Vol. 91, No. 2

102--111

Nine invertebrates intergrew with bryozoans in the latest Pridoli of Saaremaa, Estonia, namely: cornulitids (Cornulites baranovi and Conchicolites sp.), hydrozoans, rugosans (Tryplasma sp. and Entelophyllum sp.), Anoigmaichnus, microconchids (Tuberoconchus wilsoni), unknown tubicolous organisms and unknown soft-bodied organisms. The most common host of endobionts was Fistulipora przhidolensis, but trepostomes also participated in symbiotic associations. Solitary rugosan-cystoporate and hydrozoan-cystoporate associations were common in the Pridoli of Saaremaa, while other cases of intergrowth are rare. The rugosan-cystoporate, hydrozoan-cystoporate, hydrozoan-trepostome and Anoigmaichnus-cystoporate associations most likely were not a result of accidental intergrowth, whereas other associations presumably resulted from accidental intergrowth of two organisms. New data from the Pridoli of Saaremaa indicate that the Pridoli probably was not a time of lowered symbiosis levels in the regional ecosystem. Symbiosis levels in the Pridoli of Baltica were comparable to those in the Ludlow and Early Devonian worldwide.

A crustoid graptolite lithoimmured inside a Middle Ordovician nautiloid conch from northern Estonia

Vinn Olev, Wilson Mark A., Toom Ursula

Annales Societatis Geologorum Poloniae

2019

Vol. 89, No. 3

285--290

A light grey nautiloid conch has a dark brown colony attached to its internal surface. This colonial fossil resembles hederellids and bryozoans, but is in fact a crustoid graptolite (Hormograptus? sp.). The colony has been lithoimmured inside this nautiloid conch by early cementation. Crustoid graptolites were a part of the encrusting communities in the Middle Ordovician of Baltica, but their abundance among encrusters of biogenic substrates reached a peak in the middle Sandbian. The cryptic mode of life appeared very early in the evolution of the crus- toids. The discovery of this crustoid graptolite in a nautiloid conch indicates that the Baltic Middle Ordovician cryptic communities were taxonomically more diverse than was known previously. The nautiloid conch studied is sparsely encrusted with an encrustation density that is similar to those of other Middle Ordovician cryptic surfaces described from Estonia.