Calcarea (Order: Heteractinida)
Petaloptyon is considered a calcareous sponge belonging to the Family Eiffeiliidae (Rigby and Collins, 2004). Calcarea sponges are the only sponges with calcium carbonate (calcite or aragonite) spicules. They are thought to be an early branch within the phylum Porifera and are mainly found in the tropics today.
Petaloptyon – from the Greek, petalon, meaning “leaf,” and ptyon, meaning “fan.” This name refers to the broad open petal-like shape of this sponge.
danei – from the Greek dan, “torch.” This name may refer to the torch-like shape of this sponge.
Holotype – MCZ 101624, in the Museum of Comparative Zoology at Harvard University Cambridge, USA.
Burgess Shale and vicinity: none.
Other deposits: none.
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
The Trilobite Beds and the Tulip Beds (S7) locality on Mount Stephen. The Walcott Quarry on Fossil Ridge.
Brief history of research:
Raymond (1931) named Petaloptyon danei based on a couple of specimens collected during his visits to the Trilobite Beds with Harvard students. At the time, Raymond classified this new animal as an octocoral (soft coral). In 1986, Rigby described a new sponge Canistrumella alternata, but it was later discovered that this was essentially the same form that Raymond had described in 1931 (Rigby and Collins, 2004) and Canistrumella was made a junior synonym of Petaloptyon.
Petaloptyon has a very distinct and unusual globlet-like shape. It has an open conical to basket-like skeleton that is composed of alternating triangular shaped panels (up to 12) that may or may not have circular to elliptical gaps within them. The walls of this sponge are very thin and composed of spicules with five rays. At the top, the oscular margin has a scalloped appearance. At the base of the sponge there is a stalk and an attachment structure.
Petaloptyon is a very rare sponge with only a handful of specimens known.
Petalopyton would have lived attached to the sea floor. Food particles were extracted from the water as it passed through canals in the sponge’s wall.