Crinoids

Crinoid Periechocrinus moniliformis, from the Silurian of England. Source: Museum Victoria.

These animals, sometimes called 'sea lilies', are actually primitive echinoderms, and so are related to sea stars, sea cucumbers and sea urchins.

Fossil crinoids date back almost 500 million years to the Cambrian Period. They were very abundant during the Palaeozoic Era and sometimes lived in large accumulations known as 'crinoid gardens'. They resembled long-stemmed flowers, with a central 'cup' containing the soft parts of the animal, numerous branching 'arms' and a stem up to 30 metres long which attached the animal to the ocean floor. When the animals died, the ocean currents often broke up the remains and rolled them together in vast amounts to form thick deposits of limestone.

Crinoid Helicocrinus plumosus, from the Upper Silurian of the Melbourne suburb of West Brunswick. Source: Museum Victoria.

Crinoidal limestone is found in the Lilydale, Kinglake and Buchan districts in Victoria.

Most modern crinoids have more flexible arms than the fossil species and do not have stalks (at least as adults), but are free to swim or crawl over the sea floor. These types of crinoids are sometimes called 'feather stars'.