Ascidian

How to Distinguish from Similar Species: Molgula pacifica has much foreign material incorporated into the tunic and the atrial siphon is about twice as long as the oral. The tunic of Ascidia paratropa is covered with many large papillae. Ciona intestinalis is several times taller than wide and has visible longitudinal muscle bands. Corella willmeriana is very similar to this species but has a rectum more than 3/4 the length of the body and its atrial siphon is not expanded into a brood chamber.

Common on floats, plus can be found intertidally and subtidally

Geographical Range: British Columbia and the San Juan Islands

Depth Range: 0 to 20 m

This solitary ascidian has a smooth, transparent or translucent tunic. Its body is about twice as tall as wide. Its oral and atrial apertures are about the same length as one another and are not extended into distinct siphons. Its longitudinal muscle bands are not obvious. The rectum is half or less the height of the body, and part of the atrial siphon is expanded into a pocket for brooding embryos.

Biology/Natural History: This species has sometimes been mistaken for Corella willmeriana, which has a larger geographic range and lives deeper. The eggs of this species float and are thus trapped in the atrial pocket, which extends upwards. After hatching as tadpole larvae, they swim for a short time then settle and metamorphose. Many larvae often settle in the same place, leading to aggregated adults. At Friday Harbor, the species becomes mature at 3-4 months and lives for 5-8 months. Breeding is year-round. They have 12 chromosomes. Predators include the flatworm Eurylepta leoparda and the seastars Mediaster aequalis, Solaster dawsoni, and Pteraster tesselatus. The colonial tunicate Diplosoma macdonaldi may overgrow it in the winter months. White flecks seen in the mantle are uric acid crystals. The species concentrates iron but not vanadium. One can observe the periodic reversal of blood flow in this species.