Thank you for the interesting contribution! I believe there is a misinterpretation regarding the apertures in Thyasiridae. Thyasirids have only one exhalant aperture (see Allen, 1958 "On the Basic Form and Adaptations to Habitat in the Lucinacea (Eulamellibranchia)"). What is shown here appears to be the inhalant aperture, which is reduced to a ciliary connection in this family. Sometimes ciliary connection is preserved after fixation (see description of Axinus grandis in Payne & Allen, 1991 "The morphology of deep-sea Thyasiridae (Mollusca: Bivalvia) from the Atlantic Ocean".

Best regards, Valentin