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During low tide, up to 50% of Mya arenaria values were observed in the unstable concave-up position on a tidal flat of the Dutch Wadden Sea. These shells were overturned by foraging birds (turnstones, Arenaria interpret L.). During high tide most of these shells are overturned again by the flood current. Turnstones overturned more left than right Mya arenaria values. This cannot be explained by selectivity of the bird, but left Mya values have a projecting chondrophore that acts as an anchor in the concave-down position. Therefore, more left than right values remain on the tidal flat. This, together with turnstone activity, can also explain high left/right ratios in floating and eolian transported Mya shells

Hatchery-reared juvenile Mya arenaria L. were grown for 11 wk in replicated gravel, sand, mud, and pearl net treatments under flow-through sea-water conditions in Maine. Analyses of variance showed significant differences between sediment treatments for final shell length, dry meat weight, chondrophore growth increment, and percent shell weight. Growth of juvenile M. arenaria was more rapid in fine sediments than in coarse sediments or nets. Regression slopes of shell length-shell height and shell length-shell depth varied significantly between sediment treatments. Slower-growing clams from nets and gravel were more globose than clams from sand or mud treatments. Clams grown in sand were longer and narrower than those from mud. Differences in growth rates and shell form were attributed primarily to the physical properties of the substrata, and their effects on the scope for growth of M. arenaria.

The genus Chondroplon, known from only 2 specimens worldwide, is re-interpreted as a deformed Dickinsonia.

Yochelson, Ellis L. & Stanley, George D., Jr. 1981 12 15: An early Ordovician patelliform gastropod, Palaelophacmaea, reinterpreted as a coelenterate. Lethaia, Vol. 15, pp. 323–330. Oslo. ISSN W24–1164. The fossil Palaelophacmaea criola Donaldson, from the early Ordovician Stonehenge Formation of central Pennsylvania, was described as a patelliform gastropod. A reinterpretation of the type lot and study of a few additional specimens provide the basis for an alternative placement. Palaelophacmaea is here assigned to the Hydrozoa, as a possible chondrophore. It has an exceptionally thin shell or test and concentric but irregular corrugations. Cambrian univalve genera having a more or less circular outline that are currently assigned to the Gastropoda or Monoplacophora should be reexamined to see whether they have the features of fossil chondrophore coelenterates rather than those of molluscs. The late Cambrian Palaeoacmaea Hall & Whitfield is removed from the monoplacophoran Mollusca and left unassigned as to phylum. We judge that at least some early Cambrian species of Scenella are probably coelenterate remains. *Early Ordovician, Palaelophacmaea, Gastropoda, Monoplacophora, Hydrozoa.