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. 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 red 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:
Scientific Articles:
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, S.H.D. and J.F. Case,
1995. Not
all ctenophores are bioluminescent: Pleurobrachia.
Biol.
Bull. 189: 356-362
Haddock, Steven H.D., 2007. Comparative feeding
behavior of planktonic
cenophores. Integrative and Comparative Biology 47:6 847-853 Heimbacher
Goebel, Wyatt L., Sean P. Colin, John H. Costello, Brad J. Gemmell, and
Kelly R. Sutherland, 2020. Scaling of ctenes and consequences for
swimming performance in the ctenophore Pleurobrachia bachei. Invertebrate Biology 139:3 e12297. https://doi.org/10/1111/ivb.12297
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.
Authors and Editors of Page: Dave Cowles (2007): Created original page Jonathan Cowles (2007): Updated page with CSS |