Polyorchis penicillatus (Eschscholtz 1829)

How to Distinguish from Similar Species: Ptychogena lactea and Staurophora mertensi are similar except that their bells are much wider than high and their gonads do not hang down into the subumbrellar space. Polyorchis haplus does not have lateral diverticula on the radial canals.

Biology/Natural History: This is a common hydromedusa along the west coast. It can often be seen in midwater but more often swims near the bottom, especially around eelgrass. The jelly eats caprellid amphipods and other small crustaceans which are common on eelgrass, as well as worms and crustaceans from the bottom and small plankton. Sexes are separate. The polyp stage of this species is either very small or unknown, and the medusa may develop directly from a planula larva. This species is large for a hydromedusa, and some of the largest hydromedusae are in this genus. The medusa is common in some years and nearly absent in others.

Geographical Range: Aleutian Islands, Alaska to Sea of Cortez, Mexico

This hydromedusa has a bell that is at least as high as it is wide, with many evenly-spaced, unbranched tentacles around the bell margin. The tentacles may be contracted to very short or extended to twice the bell length. As with many hydromedusae, it has a clearly developed velum. Nematocysts on the tentacles are not grouped into rings. Ocelli around the bell margin, at the base of the tentacles, are ringed with red which can be clearly seen. It has 4 unbranched radial canals which have many lateral diverticula. The ring canal may or may not have several short centripetaldiverticula. The fingerlike or sausagelike gonads hang down from the subumbrellar surface, under the radial canals near the juncture of the stomach with the radial canals, in 4 groups. Usually there are less than 15 gonads. The bell is transparent with white parts but the gonads and some other internal organs may be yellow, yellow-brown, reddish-brown, or purple. The manubrium, which is long and has 4 short frilly lips, hangs from a rounded "gastric peduncle". Average size is 2-3 cm, and up to 5 cm tall. Older individuals may have green algae growing on the exumbrella.

A coastal species, especially in bays.

polyp unknown, large medusae