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)
Description:  This hydromedusa has a bell that is at least as high as it is wide, with many (around 100) evenly-spaced, unbranched tentacles around the bell margin.  The tentacles may be contracted to very short (especially when the animal is actively swimming) or extended to twice the bell length (especially when the animal is drifting).  As with many hydromedusae, it has a clearly developed velumNematocysts on the tentacles are not grouped into rings.  Ocelli (eyespots) 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 (15-25 pairs of) lateral diverticula.  The ring canal may or may not have several short centripetal diverticula.  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 (photo).  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 (10) cm tall.  Older individuals may have green algae growing on the exumbrella.

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.

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Dichotomous Keys:
  Flora and Fairbanks, 1966
  Kozloff 1987, 1996
  Smith and Carlton, 1975

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:

General Notes and Observations:  Locations, abundances, unusual behaviors:

In this closeup view the red spots at the ocelli, the pendant gonads, the long manubrium can be clearly seen.  The lateral diverticula are also visible on
several radial canals.

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. 

Takes two to tango
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.

Authors and Editors of Page:
Dave Cowles (2006):  Created original page