Search Results for: nematocysts



When people think of jellyfish, the first thing that comes to mind is usually something about their sting. This capability is characteristic of most jellies and their relatives in the phylum Cnidaria. The name of the group is actually derived from their possession of structures known as cnidae. Each is located within a specialized cell that houses the cnida, which is a capsule with an attached hollow thread. Nematocyst is the more familiar term applied to specialized cnidae that are characteristic of scyphozoan and other types of jellies, and other cnidarians.

Imagine trying to capture live prey without the aid of teeth, a jaw and hard protective body parts. What if your body also consisted of delicate gelatinous tissue that would easily be destroyed by a struggling prey. That’s the challenge that jellies face every time they attempt to feed. Nematocysts come handily to the rescue. Rather than being designed for attacking people, stinging nematocysts function primarily for the capture of prey, and secondarily as a defense mechanism. A wide variety of nematocysts have been classified.  Many function to inject toxins to immobilize prey, while others serve to entangle and hold onto the intended meal by wrapping around it.


An undischarged nematocyst is housed within a cell known as a nematocyte. Most nematocytes are located on the tentacles of the jelly, which are the primary food capturing part of the body. Scyphozoan jellies also concentrate them around the mouth and on the gastric filaments of the stomach. The nematocyst capsule within the nematocyte is covered by a trapdoor-like operculum. Inside the capsule is the long, cylindrical tubule of the nematocyst. At the base of the tubule is an enlarged area known as the shaft. Both the shaft and the tubule may be endowed with an impressive set of spines (at least when viewed with scanning electron microscopy!). Characteristics of the tubule, spines and shaft are used in classifying the bewildering array of nematocyst types. You may see terms such as heterotrichous (tubule spines of unequal size), homotrichous (spines of equal size), atrichous (tubule without spines), eurytele (shaft dilated at its far end), haploneme (tubule without a well-defined shaft), heteroneme (tubule with a well-defined shaft), and isorhiza (tubule diameter the same throughout). Obviously there were some dedicated early researchers who didn’t have much of a social life! Species of cnidarian jellies vary in the types of nematocysts they possess, and this can be used to some extent in classifying and identification. A common nematocyst style among scyphozoan jellies is the heterotrichous microbasic eurytele (say that fast 3 times), one in which the shaft is relatively short and has a widened portion at the far (distal) end, with the spines largest near the shaft.

Nematocysts are continuously produced within cells known as nematoblasts. Since they are not reused following discharge and it is energetically costly to produce them, it’s to the advantage of the jelly to fire only when necessary. Both mechanical (touch) and chemical stimuli may act to trigger nematocyst firing. Contact with members of their own species generally doesn’t result in firing, which makes sense when you see a dense swarm of sea nettles that are frequently touching. When a potential prey item, such as a larval fish or another type of jelly makes contact, the result is quite different. Discharge is initiated by the opening of the capsule operculum. Immediately the tubule begins to evert out with a twisting motion. Although not completely understood, discharge appears to involve an increase of osmotic pressure within the capsule and perhaps a release of tension within the capsule wall. Combined with the spines, the twisting acts to drill the tubule into the unfortunate victim. The tubule then separates from the capsule and remains imbedded in the flesh.


Within a fraction of a second, hundreds or even thousands of nematocysts discharge with sufficient force to penetrate the skin or exoskeleton of the prey.  Nematocysts can discharge independently of each other in certain cases, or be influenced by interactions with surrounding cells or even the simple nerve net system. They can discharge even after the jellyfish has been dead for hours or days, much to the chagrin of beachgoers with a penchant for fondling beached gelatinous blobs.

See nematocyst discharge in action, from the Pacific Cnidaria Research Institute: box jelly nematocysts

Nematocysts inject a complex slew of chemical agents into their prey or human victim. The numerous spines help to anchor the tubule into the prey and also serve as sites for the discharge of the toxic brew. Toxins and other substances may have a direct deleterious effect, or cause an immune reaction. It’s not clear whether different nematocyst types have characteristic toxins. Different species of jellies do, however, vary greatly in the suite of toxins they inject. Those that specialize in preying on fish, such as the sea wasp (Chironex) or the Portuguese man-of-war (Physalia), will tend to have very potent toxins that quickly immobilize the prey (and hence are quite painful to humans). Jellies that favor more gelatinous fare, like the egg-yolk jelly (Phacellophora), don’t need to concentrate on subduing the prey. Instead they often have nematocysts that are quite sticky and good at holding slimy blobs. Others like the moon jelly (Aurelia) rely more on bell mucus to capture zooplankton and thus have a comparatively reduced reliance on nematocysts.



Jellyfish toxins include a poorly understood array of complex chemicals, many of which are proteinaceous. Many have deleterious effects on cell membranes and cause them to rupture. This may, for example, lead to the breaking up of red blood cells, certainly not a desirable response to a sting. Other toxins have disruptive effects on the action of nerve and muscle cell membranes and impair their normal function. Throw in toxins that degrade collagen, break down proteins and lipids, and disrupt cellular influx of ions like calcium, and you can see why jellyfish mean business.

So behold the amazing nematocyst. Although small in stature, the combined efforts of multitudes of these microscopic workhorses is sufficient to subdue creatures that seemingly should have no problem against a delicate gelatinous blob. Nematocysts are one more reason to admire our gelatinous friends, and they are key to the success that jellyfish and their cnidarian relatives have had in conquering all marine habitats.

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Vallentinia adherens  Hyman, 1947
Phylum Cnidaria / Class Hydrozoa / Order Limnomedusae / Family Olindiasidae

Unless you’re really determined, don’t try to find this tiny hydromedusae unless you have lots of time and know where to look. It’s only known from the waters off Pacific Grove in Monterey Bay, and lives quite inconspicuously attached to seaweeds in shallow nearshore habitats. The transparent bell only reaches a diameter of about 8 mm. Each of the 4 radial canals holds a ruffled golden-brown gonad. The central squarish stomach has a creamy white color. Four long tentacles, each with a terminal adhesive disc, and about 40 shorter tentacles, usually with a terminal disc, ring the bell margin. The rings of nematocysts on the tentacles are very distinctive. One or two statocysts lie between each of the tentacles.

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Liriope tetraphylla (Chamisso & Eysenhardt, 1821)
Phylum Cnidaria / Class Hydrozoa / Order Trachymedusae / Family Geryoniidae

This tiny gelatinous jewel is a master of the fine art of transparency. Even when abundant near the surface, it’s difficult to know that they’re even there. If you do see them, identification of this trachymedusa is fairly easy. The transparent, colorless bell may be up to 3 cm diameter but is usually less. A long conical peduncle, to which is attached the stomach, extends from beneath the bell. Four radial canals continue along the length of the peduncle, and 4 flat gonads lie on the canals in the bell area. A total of 8 tentacles (4 long alternating with 4 short ones) are attached to the bell margin. Apparently the sting of the nematocysts can be mildly irritating, particularly if large numbers of individuals are involved.

Like other trachymedusae, this species lacks an attached polyp. Gonads release eggs or sperm into the water and the fertilized eggs develop into planulae. These form free-swimming actinula larvae, which develop directly into medusae. In nearshore waters of central and southern California, Liriope can occur in massive surface aggregations during periods of warmer oceanic water intrusion. This typically happens during fall months in Monterey Bay. This widespread species occurs worldwide from about 40 degrees N to 40 degrees S latitude, and ranges into northern California on the West Coast. It is a fairly common jelly in Mexico’s Sea of Cortez.

All images in the JelliesZone © David Wrobel and may not be copied or used in any form without permission.

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Haliscera conica Vanhoffen, 1902, top; H. bigelowi Kramp, 1947, bottom
Phylum Cnidaria / Class Hydrozoa / Order Trachymedusae / Family Halicreatidae

Both of these deep-water species are commonly collected in mid-water trawls. They are characterized by a bell width no more than 2.5 cm, and a rounded to conical apical projection (more pronounced in Haliscera conica). The mouth and stomach are circular, and connect to 8 broad radial canals. The canals are typically swollen in their midsection by flat. oval gonads. The velum is quite broad. About 160 tentacles (lost in these trawl collected specimens) line the bell margin. They have nematocysts concentrated in the distal (farthest) ends, and are about 1 to 3 times as long as the bell width. Both species are transparent and colorless, but may have an orange tinge to the canals and gonads, or rose-pink stomach and mouth (as seen in the photo of Haliscera bigelowi). They inhabit mid-water zones in both the Atlantic and Pacific Oceans.

All images in the JelliesZone © David Wrobel and may not be copied or used in any form without permission.

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Hitchhikers on Gelatinous Zooplankton


For creatures of the open sea realm, there are precious few protective sites. Many gelatinous animals serve as convenient traveling homes or resting places for a variety of other creatures. Certain types of larval fish and crustaceans are the primary users of this resource. Careful observation of gelatinous zooplankton will often reveal the presence of one or more hitchhikers.

Hitchhiking serves a number of purposes, including protection, a source of food, and distribution. Some larval or juvenile animals use their gelatinous host as a platform for development to adulthood. Other species may spend their entire lives on a jelly after settling down. Juvenile fishes, such as the medusafish (Icichthys lockingtoni), Pacific butterfish (Peprilus simillimus), and walleye pollock (Theragra chalcogramma) often lurk in the vicinity of large jellies. When danger approaches, they dive into the protective confines of the bell or among the tentacles. On the West Coast, purple-stripe jellies, sea nettles, moon jellies, lion’s mane and egg-yolk jellies frequently harbor piscine joyriders. Medusafish are even occasionally seen inside large salps. In some cases the relationship is commensal, in which case the jellyfish is not apparently effected by the association. Some fishes, however, may be ectoparasitic or even predatory on their host jelly. It’s not entirely clear how the fish avoid becoming a meal for the jellyfish. One possible mechanism is avoiding contact with the tentacles. It does seem hard to believe that a fish could somehow avoid touching the ever-moving tentacles while diving deep beneath the bell when danger approaches. Others include immunity to the nematocyst stings and production of mucus that reduces firing of nematocysts.

Crabs, such as the slender crab (Cancer gracilis), often associate with jellyfish before assuming a benthic existence. Pelagia colorata seem particularly favored by these crabs. Many hitchhikers grab food that the host has collected, but they may also consume host tissue. For this reason the association can be somewhat deleterious to the gelatinous host. An association that is certainly unfavorable to the host is that between the larval sea anemone, Peachia quinquecapitata, and certain hydromedusae.


A large number of amphipods in the family Hyperiidae are associated with many gelatinous animals. Medusae, siphonophores, ctenophores, pteropods and salps all serve as homes for these crustaceans. Often an amphipod will excavate a protective pit in the tissue of the host, or may be embedded deeper inside the animal. Females of one hyperiid amphipod, Phronima sedentaria, actually take over the tests of certain pelagic tunicates and swim while covered in their modified protective “barrel.” Phronima broods eggs within the barrel, and the hatchlings then consume their home before searching for more salp victims. This has to be one of the creepiest associations in the marine world! Certain salps are also used by males of the epipelagic octopus, Ocythoe tuberculata. The octopus uses jet propulsion to swim, even while inside its protective gelatinous home.


Juvenile fishes, such as the Pacific butterfish (Peprilus simillimus) seen in these two photos, often lurk in the vicinity of large jellies. When potential danger approaches, they dive into the protective confines of the bell or among the tentacles and oral arms. Somehow the fish manage to avoid the nasty sting of the ever-moving tentacles. Some jellies may harbor an entourage of a dozen or more fish. The silvery butterfish appear pretty conspicuous, but within an always moving jellyfish, the hitchhikers seemingly disappear in the mass of oral arms. Juvenile butterfish and other hitchhiking fish dine on zooplankton that the jelly has collected, and probably nibble on gelatinous tissue when captured prey are scarce. Eventually the fish decide that it’s time to strike off on their own, and they begin an independent adult existence. It’s not clear whether the jellyfish host benefits from this association, but the advantages to the hitchhiking fish seem apparent.

slender crab-chrysaora

Crabs, such as the slender crabs seen here (Cancer gracilis), often spend their formative months in association with a jellyfish before assuming a benthic existence. Chrysaora colorata seem particularly favored by these crustaceans. It is not unusual to see an older, battle-worn Chrysaora with 50 or more tiny crabs hitching a ride. Unfortunately for the jelly, the relationship is not totally benign. The crabs dine on food that the jellyfish has labored to collect, and probably have no qualms about nibbling on delicate gelatinous flesh. They even can enter the stomach of the jelly without apparent harm. After drifting for many miles, the juvenile crabs somehow determine that the time is ripe to jump free and begin the perilous journey to the ocean bottom. These in turn produce the planktonic zoea larvae that seek out gelatinous traveling hosts.


Pelagic barnacles (Family Lepadidae) will attach to just about anything floating in the open ocean. One species, Alepas pacifica, has taken things a step further and sets up shop on the bells of large jellies, such as egg-yolk jellies (seen here in the photo), purple-stripe jellies, and at least 5 other scyphozoan species. Typically the barnacles, which may occur singly or in clumps of up to 8 to 10 individuals, are attached at the top of the bell in the center. To lighten the load on their gelatinous host, the hard shell component characteristic of other barnacles is very thin and reduced. It’s hard to say whether the jelly is harmed by it’s crustacean hitchhikers, but once attached, there’s not much it can do. With certain scyphozoan species, it appears that the barnacles are parasitic, feeding on gonadal tissue of the jellyfish. Most large jellies however do seem to avoid the extra load – it’s relatively uncommon to see an egg-yolk jelly wearing a pelagic barnacle cap.


A large number of crustaceans known as amphipods (mainly those in the Family Hyperiidae) are associated with gelatinous animals. Hyperiid amphipods often have species-specific relationships, such that a particular species of amphipod may be found only on one or perhaps several related species of gelatinous zooplankton. Medusae, siphonophores, ctenophores, pteropods and salps all serve as homes for these crustaceans. The unfortunate comb jelly in the photo here (Hormiphora) is burdened by over a dozen of the pesky hitchhikers. Often an amphipod will excavate a protective pit in the tissue of the host, or may be embedded deeper inside the animal. Some living amphipods can even be found inside the stomachs of hydromedusae. It’s not clear if these amphipods typically consume host tissue and what other harm they may present. With a load like the comb jelly pictured here, it would appear that there must be some disadvantage to hosting a throng of amphipods. If disturbed excessively, hyperiid amphipods will swim away from the host and seek another gelatinous home.


An association that is certainly unfavorable to the jellyfish host is that between the larval sea anemone, Peachia quinquecapitata, and certain hydromedusae including Mitrocoma and Clytia. Young planktonic anemone larvae are ingested by the jellyfish, and then feed on the gonads and stomach of their hapless host. Eventually the anemones (two are seen in this photo) drop off and assume a more typical benthic lifestyle as adults.


When you’re a juvenile fish, cast into the dangerous waters of the open ocean, predators are an ever-present threat. Everywhere, it would seem, there is someone seeking a tasty meal. With shelter at a precious premium, anything goes. That’s where large jellies, like the egg-yolk jelly (Phacellophora), can come in quite handy. In addition to providing a place to hide, the jelly’s stinging ability is probably an effective deterrent for many would be predators. Here a tiny juvenile fish finds comfortable accommodations among the tentacles and oral arms of an egg-yolk jelly. Eventually it will abandon its gelatinous host and assume an independent existence.

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Mollusc References

Listed here are a variety of scientific papers that relate to the study of gelatinous molluscs. These papers are published in scientific journals that are not available in public libraries – you will need access to a university library or online sources. Note that references with author names in color are links to abstracts (summaries) provided by several publishing companies that produce scientific journals. In most cases, the full journal papers are available online by paid subscription (check the home page of each publishing company for details).

To search for online literature, use the new Google tool below (About Google Scholar). Use any information available – author, topic, title, words that appear in title, etc. If you see a reference below that strikes your fancy, use that information for the search. Make your query as specific as possible to limit the number of search results. If you’re lucky, you’ll come up with a link to the complete research paper, or at least an abstract. This is a new service so don’t expect everything to be online, but with time it should improve.

Google Scholar

Bé, A.W.H. and R.W. Gilmer. 1977. A zoogeographic and taxonomic review of euthecosomatous pteropoda. Pp. 733-808 In: Oceanic Micropaleontology, Vol. 1. A.T.S. Ramsey (ed.). Academic Press, London.

Bertsch, H. 1969. A note on the range of Gastropteron pacificum. Veliger, 11:431-433.

Conover, R. J. and C. M. Lalli. 1972. Feeding and growth in Clione limacina (Phipps), a pteropod mollusc.
Journal of Experimental Marine Biology and Ecology, 9: 279–302.

Dadon, J.R. and S.F. Chauvin. 1998.  Distribution and abundance of (Gymnosomata Gastropoda:
Opisthobranchia) in the Southwest Atlantic.  Journal of Molluscan Studies, 64(3):345-354.

Dales, R.P. 1952. The distribution of some heteropod molluscs off the Pacific coast of North America. Proceedings of the Zoological Society of London, 122:1007-1015.

Davenport, J. and A. Bebbington. 1990. Observations on the swimming and buoyancy of some thecosomatous pteropod gastropods. Journal of Molluscan Studies, 56:487-497.

Farmer, W.M. 1970. Swimming gastropods (Opisthobranchia and Prosobranchia). Veliger, 13:73-89.

Gilmer, R.W. 1972. Free-floating mucus webs: a novel feeding adaptation for the open ocean. Science, 176:1239-1240.

______. 1990. In situ observations of feeding behavior of thecosome pteropod molluscs. American Malacological Bulletin, 8:53-59.

Gilmer, R.W. and G.R. Harbison. 1986. Morphology and field behavior of pteropod molluscs: feeding methods in the families Cavoliniidae, Limacinidae and Peraclididae (Gastropoda: Thecosomata). Marine Biology, 91:47-57.

Høisæter, T. 1989. Biological notes on some Pyramidellidae (Gastropoda: Opisthobranchia) from Norway. Sarsia, 74:283-297. 

Kattner, G., W. Hagen, M. Graeve and C. Albers. 1998.  Exceptional lipids and fatty acids in the pteropod Clione limacina (Gastropoda) from both polar oceans.  Marine Chemistry, 61(3-4):219-228.

Lalli, C.M. 1970. Structure and function of the buccal apparatus of Clione limacina (Phipps) with a review of feeding in gymnosomatous pteropods. Journal of Experimental Marine Biology and Ecology, 4:101-118.

Lalli, C.M. and R.W. Gilmer. 1989. Pelagic Snails: The Biology of Holoplanktonic Gastropod Mollusks. Stanford University Press, Stanford, California, 259 pp.

Marcus, E. 1971. Range of Gastropteron pacificum Bergh, 1893 [sic]. Veliger, 13:297.

McGowan, J.A. 1967. Distributional atlas of pelagic molluscs in the California Current region. CALCOFI Atlas No.6 (California Marine Research Committee, 218 pp.

______. 1968. The Thecosomata and Gymnosomata of California. Veliger, 3 (Supplement):103-125.

Mills, C.E. 1994. Seasonal swimming of sexually mature benthic opisthobranch molluscs (Melibe leonina and Gastropteron pacificum) may augment population dispersal. Pp. 313-319 In Reproduction and Development of Marine Invertebrates. S. A. Stricker, W. H. Wilson Jr. and G. L. Shinn (eds.). Johns
Hopkins University Press, Baltimore.

Noji, T.T., et al. 1997Clearance of picoplankton-sized particles and formation of rapidly sinking
aggregates by the pteropod, Limacina retroversa. Journal of Plankton Research, 19(7):863-875.

Norekian, T.P. 1997. Coordination of startle and swimming neural systems in the pteropod mollusk Clione
: Role of the cerebral cholinergic interneuron. Journal of Neurophysiology, 78(1):308-320.

Panchin, Y.V., P.V. Zelenin and L.B. Popova. 1997. Regeneration of central and peripheral synaptic connections in the locomotor system of the pteropod mollusc Clione limacina. Invertebrate Neuroscience, 3(1):27-40.

Satterlie, R.A., T.P. Norekian and K.J. Robertson. 1997. Startle phase of escape swimming is controlled by pedal motoneurons in the pteropod mollusk Clione limacina. Journal of Neurophysiology, 77(1):272-280.

Seapy, R.R. 1985. The pelagic genus Pterotrachea (Gastropoda: Heteropoda) from Hawaiian waters: A taxonomic review. Malacologia, 26:125-135.

Seapy, R.R. and R.E. Young. 1986. Concealment in epipelagic pterotracheid heteropods (Gastropoda) and cranchiid squids (Cephalopoda). Journal of the Zoological Society of London (A), 210:137-147.

Smith, K.L. Jr. and J.M. Teal. 1973. Temperature and pressure effects on respiration of thecosomatous pteropods. Deep-Sea Research, 20: 853-858.

van der Spoel, S. 1967. Euthecosomata. J. Noorduijn en Zoon N.V., Gorinchem, The Netherlands.

______. 1968. The shell and its shape in Cavioliniidae (Pteropoda, Gastropoda). Beaufortia, 15:185-189.

______. 1972. Notes on the identification and speciation of Heteropoda (Gastropoda). Zoöl. Meded., Leiden, 47:545-560.

______. 1976. Pseudothecosomata, Gymnosomata and Heteropoda (Gastropoda). Bohn, Scheltema and Holkema, Utrecht, The Netherlands, 484 pp.

Suarez-Morales, E. and R. Gasca. 1998. Thecosome Pteropod (Gastropoda) Assemblages of the Mexican Caribbean Sea (1991). Nautilus, 112(2):43-51.

Tarling, G.A.,  J.B.L. Matthews, P. David, O. Guerin and F. Buchholz. 2001. The swarm dynamics of northern krill (Meganyctiphanes norvegica) and pteropods (Cavolinia inflexa) during vertical migration in the Ligurian Sea observed by an acoustic Doppler current profiler.  Deep Sea Research Part I : Oceanographic Research, 48(7):1671-1686. 

Tesch, J.J. 1949. Heteropoda. “Dana” Report ,34:1-53.

______ 1950. The gymnosomata II. “Dana” Report , 36:1-15.

Thiriot-Quievreux, C. 1973. Heteropoda. Oceanography and Marine Biology Annual Review, 11:237-261.

______ and R.R. Seapy. 1997. Chromosome studies of three families of pelagic heteropod molluscs (Atlantidae, Carinariidae, and Pterotracheidae) from Hawaiian waters. Canadian Journal of Zoology, 75(2):237-244.

Thompson, T.E. and I. Bennett. 1969. Physalia nematocysts: utilized by mollusks for defense. Science, 166:1532-1533.

Wang, L., Z. Jian and J. Chen. 1997.  Late Quaternary pteropods in the South China Sea: carbonate
preservation and paleoenvironmental variation.  Marine Micropaleontology, 32(1-2):115-126.

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Cnidarian References

Listed here are a variety of scientific papers that relate to the study of cnidarian jellies. These papers are published in scientific journals that are not available in public libraries – you will need access to a university library or online sources. Note that references with author names in color are links to abstracts (summaries) provided by several publishing companies that produce scientific journals. In most cases, the full journal papers are available online by paid subscription (check the home page of each publishing company for details).

To search for online literature, use the new Google tool below (About Google Scholar). Use any information available – author, topic, title, words that appear in title, etc. If you see a reference below that strikes your fancy, use that information for the search. Make your query as specific as possible to limit the number of search results. If you’re lucky, you’ll come up with a link to the complete research paper, or at least an abstract. This is a new service so don’t expect everything to be online, but with time it should improve.

Google Scholar

Abe, Y. and M. Hisada. 1969. On a new rearing method of common jellyfish, Aurelia aurita. Bulletin Marine Biol. Stn. Asamushi, 13: 205–209.

Acker, T.S. 1976. Craspedacusta sowerbyi: an analysis of an introduced species. Pages 219-226 in G.O.
Mackie, editor. Coelenterate ecology and behavior. Plenum Press, New York. 

Acuña, J. L., D. Deibel, and S. Sooley. 1994. A simple device to transfer large and delicate planktonic organisms. Limnology and Oceanography, 39: 2001–2003.

Afzelius, B.A. and A. Franzen. 1971. The spermatozoon of the jellyfish Nausithoe. Journal of Ultrastructure
Research, 37: 186-199.

Agassiz, A., 1883. Exploration of the surface fauna of the Gulf Stream. III. Part 1. The Porpitidae and Velellidae. Memoirs of the Museum of Comparative Zoology at Harvard College 8: 16 pp. + 12 plates.

Alvariño, A. 1971. Siphonophores of the Pacific, with a review of the world distribution. Bulletin of the Scripps Institution of Oceanography, 16:1-432.

Anderson, P.A.V.  1977.  Electrically coupled, photosensitive neurons control swimming in a jellyfish.  Science, 197: 186-188.

Arai, M. N. 1988. Interactions of fish and pelagic coelenterates. Canadian Journal of Zoology,  66: 1913-1927.

_____. 1991. Attraction of Aurelia and Aequorea to prey. Hydrobiologia, 216–217: 363–366.

_____. 1997. A Functional Biology of Scyphozoa. Chapman and Hall, London, 316 pp.

2001. Pelagic cnidarians and eutrophication: a review.  Hydrobiologia 451 (Developments in Hydrobiology, 155):1-9. 

Arai, M.N. and A. Brinckman-Voss. 1980. Hydromedusae of British Columbia and Puget Sound. Canadian Bulletin of Fisheries and Aquatic Sciences. 204, 192 pp.

_____. 1983. A new species of Amphinema: Amphinema platyhedos n. sp. (Cnidaria, Hydrozoa, Pandeidae) from the Canadian West Coast. Canadian Journal of Zoology, 61:2179-2182.

Arai, M.N., M.J. Cavey, and B.A. Moore. 2000. Morphology and distribution of a deep-water Narcomedusa (Solmarisidae) from the north-east Pacific. Scientia Marina, supplement 1:55-62. 

Arkett, S.A. and A.N. Spencer. 1986. Neuronal mechanisms of a hydromedusan shadow reflex.  I. Identified reflex components and sequence of events. Journal of Comparative Physiology,  159: 201-213.

Arkhipkin, A. and V. Bizikov. 1996. Possible imitation of jellyfish by the squid paralarvae of the family Gonatidae (Cephalopoda, Oegopsida). Polar Biology, 16(7):531-534.

Aerne, B.L. 1996. The hydrozoan life cycle: a small secreted protein is involved in specification of the polyp stage. Development, Genes and Evolution, 206(5):337-343.

Avian, M. 1986. Temperature influence on in vitro reproduction and development of Pelagia noctiluca (Forskal). Bollettino di Zoologia, 53: 385-391.

_____., L. Rottini Sandrini and F. Stravisi. 1991. The effect of seawater temperature on the swimming activity of Pelagia noctiluca (Forsskal). Bollettino di Zoologia, 58(2): 135-142.

Båmstedt, U.,  M.B. Martinussen  and S. Matsakis. 1994. Trophodynamics of the two scyphozoan jellyfishes, Aurelia aurita and Cyanea capillata, in western Norway. ICES Journal of Marine Science, 51(4):369-382.

Båmstedt, U., H. Ishii and M. B. Martinussen. 1997. Is the scyphomedusa Cyanea capillata (L.) dependent on gelatinous prey for its early development? Sarsia, 82:269-273.

Båmstedt, U., J. H. Fosså, M. B. Martinussen and A. Fosshagen. 1998. Mass occurrence
of the physonect siphonophore Apolemia uvaria (LESUEUR) in Norwegian waters. Sarsia:83:79-85. 

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Tetraplatia volitans Busch, 1851
Phylum Cnidaria / Class Scyphozoa / Order Coronatae / Family Tetraplatidae

Even a jellyfish expert may be thrown off by this bizarre little creature – it hardly resembles any other jellyfish. Looking more like a worm, and being 4 to 9 mm long, it’s easily overlooked. It feeds on small zooplankton, capturing prey without the aid of tentacles, which are lacking. The color is whitish to bluish white. The body is cylindrical with pointed ends, with a constriction closer to the aboral end. Its cnidarian affinities are revealed by the presence of nematocysts contained in 4 tracks that run the length of the body, and 4 shorter tracks between these. The coronal groove is divided into 8 pairs of lappet-like structures. Between the lappets are marginal sense structures (8 total). The four gonads are not easily visible. Tetraplatia is cosmopolitan, found worldwide in oceanic waters, from the surface down to about 900 meters.

All images in the JelliesZone © David Wrobel and may not be copied or used in any form without permission.

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Chrysaora colorata

Purple-stripe jelly, Chrysaora colorata, Monterey CA, Pacific Ocean

Of all the gelatinous creatures visiting Monterey Bay, the purple-striped jelly is certainly among the most recognizable and spectacular. Based on certain morphological characters, a taxonomic revision has placed this species (formerly Pelagia colorata) in the genus Chrysaora. With a bell of up to 70 cm diameter, usually streaked with a radial pattern of stripes, and long, flowing oral arms, this jelly is quite impressive. The four frilly oral arms have a coiled appearance. Eight marginal tentacles alternate with eight sensory rhopalia. The tentacles are well armed with nematocysts and can produce a relatively painful sting. Although large specimens are typically endowed with very distinct purple pigment patterns, younger individuals have a pale pinkish bell that lacks the dramatic stripes and patterns of adults. Youngsters also have long, thin, dark maroon tentacles that assume a more subdued coloration by adulthood. Young adults like the one in the second photo can be endowed with truly impressive oral arms, sometimes as long as 4 to 5 meters. Very old individuals often lack the long flowing oral arms and have thickened, pale tentacles. The photos here show a progression from a jelly toddler to a withered old-timer.

Unlike sea nettles and moon jellies, purple-striped jellies are not seen in large surface aggregations. Juvenile slender crabs (Cancer gracilis, bottom photo) often make homes of this jelly and travel with their host until ready to assume a benthic existence. A wide variety of zooplankton serve as prey, including copepods, larval fish, ctenophores, salps, other scyphomedusa, and fish eggs. Chrysaora colorata has a relatively limited range primarily off the coast of California. It is possible to establish polyps and culture this species in captivity, although it’s not as easy as some other species. When provided appropriate aquarium conditions (such as a kreisel tank), the medusae do well under captive conditions. Purple-striped jellies are a popular species for display at public aquariums, but cultured individuals never attain the spectacular dimensions or coloration of their wild counterparts.

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Physophora hydrostatica Forskal, 1775
Phylum Cnidaria / Class Hydrozoa / Subclass Siphonophorae / Order Physonecta / Family Physophoridae
Physonect siphonophore, Physophora hydrostatica, Point Lobos CA, Pacific Ocean

This stunning physonect siphonophore is easily distinguished from any other gelatinous West Coast animal. A conspicuous silvery apical gas-filled float is followed by a set of swimming bells that occupy about half the length. Finger-like dactylozooids, colored with beautiful tinges of orange and violet, attach at the base of the swimming bells. These structures house relatively potent nematocysts that can impart a strong sting on those careless enough to make contact. A mass of feeding gastrozooids and reproductive gonozooids lie inside the ring of dactylozooids. Typical length of the compact swimming bell / dactylozooid portion of the siphonophore is from 8 to 12 cm. Trailing behind are the highly extensible tentacles that usually exceed the length of the rest of the siphonophore. Physophora typically swims slowly with tentacles extended as it drifts for zooplankton prey. Look carefully at the whitish clumps spaced at regular intervals along the tentacles. They resemble swimming copepods as the tentacles are repeatedly contracted and extended. Perhaps this is a method for luring copepod-seeking predators that instead become prey for the siphonophore. Physophora is occasionally seen in surface waters of central California, but never in any great numbers.

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