Achistrum sp.   scale in cms CLASS - Holothuroidea ORDER - Apodida FAMILY - Achistridae GENUS/SPECIES - Achistrum sp. ROCK UNIT - Francis Creek Shale Member, Carbondale Formation AGE - Pennsylvanian (300 million years old) LOCALITY - Peabody Coal Mine Pit 11, near Braidwood, Will Co., USA This small "sea cucumber" is one of many unusual fossils found in the area around Mazon Creek, in central Illinois. Although worm-like in appearance, it can be distinguished by a ring of plates around the mouth. This ring of plates corresponds to modified tube feet which form a ring of large "tentacles" around the mouth. Although sea cucumbers are common in today's shallow seas and deep oceans, complete fossils are extremely rare. Many other ancient echinoderm groups had large, heavily calcified plates which were easily preserved. In contrast, holothurians have a light skeleton made of tiny rods and plates which are loosely intermeshed. After death, the skeleton of sea cucumbers falls apart quickly and easily, leaving millions of the tiny skeletal elements scattered on the sea floor. PRI 42977

scale in cms

CLASS - Holothuroidea
ORDER - Apodida
FAMILY - Achistridae
GENUS/SPECIES - Achistrum sp.

ROCK UNIT - Francis Creek Shale Member, Carbondale Formation

AGE - Pennsylvanian (300 million years old)

LOCALITY - Peabody Coal Mine Pit 11, near Braidwood, Will Co., USA

This small "sea cucumber" is one of many unusual fossils found in the area around Mazon Creek, in central Illinois. Although worm-like in appearance, it can be distinguished by a ring of plates around the mouth. This ring of plates corresponds to modified tube feet which form a ring of large "tentacles" around the mouth.

Although sea cucumbers are common in today's shallow seas and deep oceans, complete fossils are extremely rare. Many other ancient echinoderm groups had large, heavily calcified plates which were easily preserved. In contrast, holothurians have a light skeleton made of tiny rods and plates which are loosely intermeshed. After death, the skeleton of sea cucumbers falls apart quickly and easily, leaving millions of the tiny skeletal elements scattered on the sea floor.