Pleurobrachia bachei A. Agassiz, 1860

Common name(s): Sea gooseberry, Comb jelly, Cat's eye, Sea walnut

Synonyms:
Class Tentaculata
Order Cydippida
Family Pleurobrachiidae
Pleurobrachia brachei, about 1 cm diameter, captured from Rosario Strait.  This is a side view with the mouth to the right.  Some ctene rows, which are beating, can be seen glistening and the row at the top can be seen in side view.  The tentacular sheaths and retracted tentacles are to the left.
(Photo by: Dave Cowles July 2007)
Description: Ctenophores such as this one look similar to jellyfish but have 8 rows of fused cilia (ctenes) along their sides which beat for propulsion.  Pleurobrachia bachei is elliptical in shape with no large lobes.  The comb rows (ctenes) are nearly equally spaced and extend nearly the entire length of the body.  Two long (up to 15 cm), branched tentacles trail back from sheaths which angle out from near the gut toward the aboral pole (photo).  The tentacle branches (tentillae) are abundant (photo), are only from one side of the tentacle, and are not coiled (though the tentacles can be retracted into the sheaths).  The animal is clear, but organs and tentacles may be pink, yellow, white, or orange-brown.  There may be purplish blotches near the pharynx.  Diameter to 1.5 cm; length slightly longer than diameter.

How to Distinguish from Similar Species:Euplokamis dunlapae is similar shape but the body is more ovoid and flattened plus the tentacle branches (tentillae) are sparse and coil into bundles when contacted.

Geographical Range:  Alaska to Acapulco, Mexico

Depth Range:

Habitat:  Pelagic, especially in nearshore water

Biology/Natural History:  Ctenophores have no nematocysts so they cannot sting.  Instead, they have colloblast cells which produce a sticky substance to snare prey.  Pleurobrachia bachei feeds on almost anything small enough for it to engulf, and may consume many copepods, eggs, and larval fish.   It is a sit-and-wait predator.  It swims horizontally in a semicircle while gradually extending its two tentacles until the tentillae hang down evenly spaced (photo).  Then it stops and waits suspended with its mouth upright.  When prey (usually a copepod) contacts the sticky net of tentillae and is snared, Pleurobrachia begins swimming forward while retracting its tentacles until the prey is close to its body.  Then it begins rotating its body so the prey is brought around to the mouth and ingested (see movie).  This species is the most common species of ctenophore likely to be encountered in the Northwest.  Large aggregations may be seen in spring and summer.  Individuals are hermaphrodites (both male and female).  Eggs and sperm are released through the mouth and fertilized in the water.  Not bioluminescent.  May harbor a small colored symbiotic amphipod, Hyperoche sp.

An extensive review article about cilia, swimming, neural circuitry, and behavior in ctenophores including Pleurobrachia can be found in Tamm (2014)



 

References:

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

General References:
  Brusca and Brusca, 1978
  Harbo, 1999
  Hinton, 1997
  Kozloff, 1993
  McConnaughey and McConnaughey, 1985
  Niesen, 1994
  Niesen, 1997
  Ricketts et al., 1985
  Sept, 1999
  Smith and Johnson, 1996
  Wrobel and Mills, 1998

Scientific Articles:
Haddock, S.H.D. and J.F. Case, 1995.  Not all ctenophores are bioluminescent:  Pleurobrachia.  Biol. Bull. 189: 356-362

Greene, C.H., M.R. Landry, and B.C. Monger, 1986.  Foraging behavior and prey selection by the ambush entangling predator Pleurobrachia bachei.  Ecology 67: 1493-1501

Haddock, Steven H.D., 2007.  Comparative feeding behavior of planktonic cenophores.  Integrative and Comparative Biology 47:6 847-853

Moss, A.G., 1991.  The physiology of feeding in the ctenophore Pleurobrachia pileus.  Hydrobiologia 216: pp 19-25

Moss, A.G. and S.L. Tamm, 1981.  Properties of the unilateral ciliary reversal response during prey capture by Pleurobrachia (Ctenophora). Biological Bulletin 161: p 308 (abstract)

Sleigh, M.A., 1968.  Metachronal coordination of the comb plates in the Ctenophore Pleurobrachia.  Journal of Experimental Biology 28: pp 111-125

Tamm, Sidney L., 2014.  Cilia and the life of ctenophores.  Inverterate Biology 133:1 pp 1-46

Tamm, S.L. and A.G.Moss, 1985.  Unilateral ciliary reversal and motor responses during prey capture by the Ctenophore Pleurobrachia.  J. Exp. Biol. 114: 443-461

Web sites:


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

This species is common pelagically during the summer.



In this view the mouth is facing the camera and one tentacle trails off to the left.  The ends of the beating comb (ctene) rows can be seen.



The long, retractable tentacles have branches (tentillae) along one side.



This closeup view of the aboral end shows how the tentacle sheaths angle out from the pharynx.  A partly retracted tentacle can be seen on the lower left. 

Wide
Tall
A few images of Pleurobrachia bachei swimming.  A short movie of the movements the species can make while deploying and manipulating its tentacles can be viewed by clicking here.




Authors and Editors of Page:
Dave Cowles (2007):  Created original page
Jonathan Cowles (2007):  Updated page with CSS