Polyorchis penicillatus (Eschscholtz, 1829) Common name(s): Red-eye jellyfish, bell medusa, bell-shaped jellyfish
Synonyms:  Polyorchis penicellata
Phylum Cnidaria  Class Hydrozoa   Order Hydroida     Suborder Athecata      Family Polyorchidae
	Polyorchis penicillatus from Rosario Bay.  About 3 cm long.
	(Photo by: Dave Cowles, June 2006)

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.

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

Depth Range:

Habitat:  A coastal species (nearshore), especially in bays.

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. 

The normal life cycle of hydrozoans is for male and female medusae to release sperm and eggs. After fertilization, the fertilized egg divides and becomes a small, ciliated planula larva. The planula settles to a surface and grows into a branched colony of attached polyps. Medusae bud from some of the polyps in the colony to complete the life cycle. Another athecate hydrozoan, Turritopsis dohrnii, however, which is widespread in warm oceans, has recently been discovered to have an unusual skill. If the sexually mature medusae are injured or encounter unfavorable conditions such as warmth, modified salinity, or pinching, the mature, differentiated cells of the medusa can de-specialize and form into a cyst, which is a ball of pluropotent stem cells. The cyst settles to the bottom and grows back into a new polyp colony. This behavior thus allows them to take a shortcut backwards to an earlier stage in their life cycle. Currently this is the only known sexually mature, multicellular animal that can do this. Not even Turritopsis rubra, a member of the same genus, appears to be able to do this. Some of the main scientists who discovered this phenomenon include Maria Pia Miglietta, Maria Pascual-Turner, and Stefano Piraino. A summary of their research and a list of several key references can be found here in the journal "The Scientist". Whether other athecate  hydroids such as Polyorchis can do this is not known.

References:

General References:
  Gotshall, 1994
  Harbo, 1999
  Johnson and Snook, 1955
  Kozloff, 1993
  Morris et al., 1980
  Niesen, 1994
  Niesen, 1997
  Ricketts et al., 1985
  Wrobel and Mills, 1998

Scientific Articles:
 

Web sites:

This freely swimming individual has its tentacles extended out farther than the one above does.  Photo by Dave Cowles, July 2008

Another individual, photographed 2012.  Note the long, dangling gonads inside the bell. 

Two individuals dancing in a planktonkreisel. Photo by Dave Cowles, July 2020

Click HERE for a 1-minute movie of this species swimming in a planktonkreisel, taken summer 2020. Some individuals are greenish-colored due to algae adhering to their outer surfaces.