''Achistrum'' is an extinct genus of

sea cucumber Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothu ...

which existed in Poland during the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

period, and the United States during the Carboniferous period.Triassic Holothurian Sclerites from Tatra Mountains
Krystyna Zawidzka. It contains the species ''Achistrum nicholsoni'' and ''Achistrum ludwigi''.

References

Apodida Carboniferous echinoderms Triassic echinoderms Fossils of Poland Fossil taxa described in 1881 {{paleo-holothuroidea-stub