Endobionts on modern and fossil Turritella from the northern Gulf of California region

Abstract

Turritellid gastropods are diverse and abundant in Mesozoic to Cenozoic marine assemblages. Despite their ubiquity and biostratigraphic utility, little is known about their ecology, paleoecology, or taphon‐omy. Living positions of fossil turritellids, for example, are not well known. Additionally, encrusting and boring organisms (epi‐and endobionts) present on fossil Turritella shells are interpreted to occur exclusively on empty shells. Living snails, hermit crabinhabited shells, and empty shells of Turritella gonostoma were examined from Cholla Bay, northern Gulf of California, for the presence of endobionts to determine if bioerosion (via endobionts) is limited to empty shells. Living T. gonostoma, which are semi‐infaunal to infaunal, had three types of endobionts in low frequencies associated with the shell: microborers (green algae/blue‐green bacteria), spionid polychaetes (ichnogenus Caulostrepsis), and clionid sponges (ichnogenus Entobia). Biont distribution on the shells indicate life positions. Hermited shells of T. gonostoma had similar endobionts in higher frequencies, with the addition of the spionid trace fossil (Helicotaphrichnus) and coralline algae (which appears to decalcify the shell). Empty shells had extensive clionid borings. Empty shells were also more likely to have drill holes (ichnogenus Oichnus) from predatory gastropods. Thus, endobiont infestation is not restricted to empty shells, nor may it be a reliable guide for “time‐since‐death” for fossil turritellids. Fossil Turritella from this region had primarily clionid borings; the patchy occurrence and distribution of these bionts indicate diverse burial histories for turritellid shells.

Key words:

• Turritella gonostoma
• turritellids
• taphonomy
• bioerosion
• Helicotaphrichnus
• trace fossils
• Oichnus