The aboral side of body is inflated and the oral side flat. A supra dorsal membrane supported by the spines of the paxillae covers the true aboral surface to create a nidamental chamber. In the centre of this membrane is a large opening (osculum). Many smaller spiracles pierce the rest of the membrane. On each side of the ambulacral furrow is a wide actinolateral membrane supported by long spines; between the spines are small holes, each guarded by an operculum, which lead to the nidamental chamber; water enters here and is expelled through the osculum. No oral intermediate plates.
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Pteraster tesselatus is a stubby five-armed sea star with a central aboral pore. The ends of the arms are upturned to reveal the ambulacral furrow. When collected this species often produces copious amounts of clear mucus. Usually tan, but its colour varies from cream to yellow to a dull grey-purple. The aboral side is occasionally modified by a chequered pattern or dark brown markings in a rough star-shaped pattern. The tube feet are yellow or orange. The arms can grow up to 12 cm long, and the arm-to-disc ratio is from 1.1 to 1.9. The aboral surface is a supradorsal membrane supported by the pseudopaxillar spines with an opening, the osculum, in the centre. The pseudopaxillae have a low base and up to 26 long spines, and 7 or 8 on the periphery. Marginals and other skeletal plates are hidden by the supradorsal membrane. The adambulacrals have a webbed transverse series of 5 to 7 spines. An actinolateral membrane covers half the distance from the furrow to the edge of the arm. Each mouth plate has a membranous fan of 5 to 7 marginal spines and a single large sub oral spine. The fan of one plate is continuous with the fan of the adjacent one.
Pteraster tesselatus has shorter arms, a smoother aboral surface and generally is a darker colour than Pteraster.
The diet of Pteraster tesselatus includes encrusting sponges, bryozoans, hydroids and colonial sea squirts, and less frequently, sea anemones, the rock oyster Pododesmus macrochisma, scallops and solitary sea squirts.
P. tesselatus breeds from early July to the end of August. It does not brood its eggs in the so-called nidamental chamber. Instead, it releases yellow or orange eggs (1.5 mm in diameter) through the osculum two or three at a time or in a long string. The fertilized egg develops into a nonfeeding larva that passes directly into the adult without metamorphosis, which usually results in the axes of symmetry changing or the loss of larval structures. This is the only sea star known to have truly direct development. McEdward (1995) suspects that the larval form evolved in a brooding ancestor but did not revert back to a typical pelagic larva when the species evolved back to broadcast spawning. At 10°C in the laboratory, development from egg to young sea star took 25 days; the mouth formed on the 30th day. This implies that, in nature, this sea star does not feed until it settles on the substrate as a juvenile. Most settlement occurs between 10 and 12 days, often among the tubes of the polychaete Phyllochaetopterus. See McEdward 1992 for details of the unusual development of this species.
P. tesselatus shows a negative response to bright light and a positive response to moderate or green light. When it is disturbed, cells in its supradorsal membrane secrete copious amounts of mucus, which is forced out of the spiracles onto the top surface by water pressure in the nidamental chamber. This secretion is highly effective in repelling predation by Solaster dawsoni and Pycnopodia helianthoides; experimental removal of the supradorsal membrane allowed an S. dawsoni to eat a P. tesselatus in four days. If a clam is injected with P. tesselatus mucus and offered to the Sunflower Star, it is rejected. In an aquarium, this mucus will kill snails, hermit crabs and sea cucumbers that are submersed in it for 24 hours.
P. tesselatus flushes its gills by inflating its supradorsal membrane to draw in sea water through slits between the adambulacral spines, and contracting the membrane to force water out through the osculum. This allows the animal to regulate its oxygen intake. The scale worm Arctonoe vittata is commensal on P. tesselatus.
The Bering Sea to Washington (subspecies P. tesselatus arcuatus to central California) in 6 to 436 metres. Usually found on broken or solid rock along the coast of British Columbia. Common, but not abundant.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. E-Fauna BC:
Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab
for Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
16/09/2019 3:28:56 PM]
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