Illustration of a generalized spinicaudatan “clam shrimp”. By Sarah Lyn Boyce as part of a PEET project funded by a U.S. National Science Foundation grant (DEB 9978193) to Joel W. Martin, Natural History Museum of Los Angeles County. All rights reserved.

This tiny branchiopod crustacean (clam shrimp) can be found in most Devonian sediments and indicates a shallow water environment. It is common in the Upper Stromness and Rousay Flagstone groups. Depending on the type of sediment and the conditions of fossilization Ipsilonia orkneyensis is preserved as a tiny (few mm) thin valve often with growth lines (concentric rings) visible, see photomicrographs below.

The crustacean belongs to the conchostracans, commonly called clam shrimps (the shrimp is housed between the two chitin valves). Conchostracans occur on all continents and have a full range from the Palaeozoic up to recent times. They are filter feeders but also scrape and tear their food and scavenge on all organisms in their environment. They live in temporary pools or other shallow water conditions.

Recently, the genus and species were renamed. It was first named Estheria membranacea (Pacht) (Jones, 1862 p. 14—18, Pl. Ⅰ, figs. 1—5). Later it was renamed in Asmussia murchisoniana (Jones) (Morris, 1980, p. 29).

The new name Ipsilonia orkneyensis was given by: Chen Pi-ji (Nanjing Institute of Geology and Palaeontology, Academia Sinica) and Samuel Morris (British Natural History Museum) in 1991.

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