Demospongea (Order: Monaxonida)
Halichondrites is considered a primitive demosponge (Rigby, 1986). Demosponges, the same group that are harvested as bath sponges, represent the largest class of sponges today.
Halichondrities – from the Greek hal, meaning “belonging to the sea,” chon, meaning “funnel” or “tube,” and dri, meaning “thicket.” The name refers to the shape of this marine sponge with a thicket of long hair-like spicules.
elissa – from the Greek eliss, meaning “to roll, or to turn about.” This name may refer to the spiral pattern of the small spicules of this sponge.
Holotype –USNM66447 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Burgess Shale and vicinity: An unidentified species, Halichondrites sp. from Mount Stephen (Rigby and Collins, 2004).
Other deposits: H. confusus Dawson, 1889 from the Ordovician of Quebec at Little Métis.
Lower Cambrian, Wutingaspis-Eoredlichia Zone to Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 510 to 505 million years ago).
Burgess Shale and vicinity: The Walcott and Raymond Quarries on Fossil Ridge.
Other deposits: H. elissa from the Lower Cambrian Chengjiang fauna (Chen et al., 1997; Luo et al., 1999).
Brief history of research:
Walcott assigned this species to the genus Halichondrites in 1920. Ribgy (1986) re-described this genus and hypothesized that Halichondrites probably evolved from an early species of Leptomitus and established a new family called Halichondritidae to include this genus. New specimens collected by the Royal Ontario Museum were subsequently described by Rigby and Collins in 2004.
This sponge has a cone shaped base that extends upwards to form a long tube. The walls of the sponge are smooth with a thatch of small spicules that are vertically arranged in a clockwise spiraling pattern. There are no canals visible in the wall; they may be very small or run parallel to the wall. The most distinctive part of this sponge is the long thick, densely arranged spicules that emerge from the wall. These spicules are orientated upwards and may be up to 8.5 cm long. This sponge can be over 20 cm tall and is one of the tallest and most hirsute (densely covered in hair) of the Burgess Shale sponges. Water would have entered though small pores in the wall, moving into the central cavity and out the circular osculum at the top of the sponge.
Halichondrites is very rare and represents only 0.01% of the Walcott Quarry community (Caron and Jackson, 2008).
Halichondrites would have lived attached to the sea floor. Particles of organic matter were extracted from the water as they passed through canals in the sponge’s wall.