Classification of Gelatinous Zooplankton
The groups represented in this classification include most of the orders containing gelatinous zooplankton. Not all gelatinous animals are necessarily in this grouping (such as certain pelagic polychaete worms). Also, some orders (Anthomedusae, Leptomedusae, Limnomedusae, Stauromedusae, Mesogastropoda and Nudibranchia) include species that lack any kind of gelatinous or free-swimming stage in the life cycle. The information presented here gives only a few of the basic distinguishing characteristics for each order.
Phylum Cnidaria: Corals, anemones, hydrozoans, scyphozoans, cubozoans
Class Hydrozoa / Subclass Hydroidomedusae
Order Anthomedusae: Medusae with a bell that is usually taller than wide; gonads situated on the walls of the stomach; all with a sessile hydroid part of the life cycle (but not necessarily with free-swimming medusae); hydroids not enclosed in a chitinized cup (Amphinema, Annatiara, Catablema, Cladonema, Euphysa, Leuckartiara, Maeotias, Neoturris, Polyorchis, Sarsia, Scrippsia, Stomotoca, Velella)
Order Leptomedusae: Medusae with a bell that is usually wider than tall; gonads situated on radial canals; many bioluminescent around bell margin; all with a sessile hydroid part of the life cycle (but most do not produce medusae); hydroids are thecate since they are enclosed in a protective chitinized cup (Aequorea, Clytia, Eutonina, Foersteria, Mitrocoma, Modeeria, Ptychogena)
Order Limnomedusae: Small group of hydromedusae with a bell usually about as tall as they are wide; gonads either on stomach wall or on radial canals; small hydroids that lack a chitinized cup (Aglauropsis, Gonionemus, Vallentinia)
Order Narcomedusae: Medusae with a thick, relatively stiff umbrella; solid tentacles that often are held above the bell margin; holoplanktonic life cycle (lack hydroid stage); most found in open ocean and deep-sea habitats (Aegina, Pegantha, Solmaris, Solmissus)
Order Trachymedusae: Medusae with gonads situated on radial canals; holoplanktonic life cycle with fertilized eggs that develop directly into another medusa; tentacles usually long and easily broken off; most found in open ocean and deep-sea habitats (Aglantha, Benthocodon, Colobonema, Crossota, Geryonia, Halicreas, Haliscera, Liriope, Pantachogon, Ptychogastria)
Class Hydrozoa / Subclass Siphonophorae (Siphonophores)
Order Cystonecta: Siphonophores with an apical gas-filled float; lack swimming bells; tentacles of most with a painful sting (includes the Portuguese man-of-war, Physalia); float at surface, unlike the other 2 orders
Order Physonecta: Siphonophores with an apical gas-filled float and swimming bells; long stem region with feeding and reproductive components; most are hermaphrodites (Apolemia, Nanomia, Physophora)
Order Calycophora: Siphonophores that lack an apical gas-filled float, but with swimming bells; stem with multiple identical units that can detach and become free-swimming sexual fragments (known as eudoxids); some species small and inconspicuous, others with lengths exceeding 30 meters (Muggiaea, Praya)
Class Cubozoa - Cubomedusae (box jellies)
Primarily tropical species that resemble hydromedusae; often called box jellies due to the shape of the bell; bell transparent with 4 tentacles; have well developed eyes that can respond to nearby movements; some species known as "sea wasps", including the potentially deadly Chironex fleckeri of Australia (Carybdea, Chiropthalmus)
Class Scyphozoa
Order Stauromedusae: Lack a free-swimming medusa phase; polyp develops into stalked, attached form (Haliclystus, Manania)
Order Coronatae: Medusae with groove (coronal furrow) in the exumbrella of the bell; most with stiff, non-contractile tentacles that are often held above the bell; temperate species typically inhabit deep-sea waters (Atolla, Linuche, Nausithoe, Periphylla)
Order Semaeostomeae: Includes most of the conspicuous, familiar West Coast species; typically with 4 or more frilly oral arms used in feeding; most with polyp (scyphistoma) stage that produces ephyrae by strobilation (Aurelia, Chrysaora, Cyanea, Pelagia, Phacellophora, Poralia)
Order Rhizostomeae: Medusae that typically inhabit tropical and subtropical shallow seas; lack oral arms and marginal tentacles, and instead have 8 branched, lobed appendages used for feeding; many with zooxanthellae in the tissue (Mastigias, Phyllorhiza, Stomolophus)
Phylum Ctenophora: Comb jellies
Order Cydippida: Solid spherical or ovoid body with a pair of long, retractable tentacles in both larval and adult stages; tentacles with sticky side branches used for zooplankton prey capture; includes the common sea gooseberry (Euplokamis, Hormiphora, Lampea, Pleurobrachia)
Order Thalassocalycida: Small order of comb jellies with body shaped like a broad medusa; short comb rows on upper surface of the "bell" (Thalassocalyce)
Order Lobata: The "lobed" comb jellies - possess a pair of large mucus-covered oral lobes used in zooplankton prey capture; most with very delicate tissue; tentacles typically small and inconspicuous; pass through a cydippid-like larval stage with tentacles (Bolinopsis, Leucothea)
Order Cestida: The "Venus's girdle" comb jellies; body flattened in one plane and elongated in the other to form a ribbon-like shape; comb rows along the aboral edge (opposite the mouth); pass through a cydippid-like larval stage (Cestum, Velamen)
Order Beroida: Body resembles a sac; lack tentacles throughout the life cycle; large mouth used to engulf prey whole, or can use macrocilia (fused teeth-like structures) lining the pharynx to bite off pieces (Beroe)
Phylum Mollusca: Clams, cephalopods (squid, octopus), snails, nudibranchs, pteropods, heteropods
Class Gastropoda / Subclass Prosobranchia
Order Mesogastropoda / Suborder Ptenoglossa / Superfamily Heteropoda - Heteropods: Visual predators with single swimming fin along the midline of the body; typically swim with fin held upward; holoplanktonic life cycle; well developed eyes and mouth with radula used in prey capture; shell greatly reduced or absent (Atlanta, Carinaria, Firoloida, Pterotrachea)
Class Gastropoda / Subclass Opisthobranchia
Order Thecosomata: Pteropods (for "wing foot") with greatly enlarged portion of molluscan foot used for swimming; certain species known as "sea butterflies"; feed by producing an external mucous web that traps small zooplankton prey; some species with a thin shell; protandrous hermaphrodites (start as males) (Cavolinia, Clio, Corolla, Creseis, Desmopterus, Gleba, Limacina)
Order Gymnosomata: Highly specialized predators that use a radula, unique hook sacs and a jaw to capture thecosome pteropod prey; use pair of muscular swimming wings derived from portion of foot for relatively rapid swimming ability; lack any kind of shell; simultaneous hermaphrodites with internal fertilization (Clione, Cliopsis, Crucibranchaea, Pneumodermopsis, Thliptodon)
Order Nudibranchia: The familiar, often colorful and primarily benthic ophisthobranchs; a few species are capable of swimming, and some have an entirely planktonic life cycle (Dendronotus, Fiona, Glaucus, Melibe, Phylliroe)
Phylum Chordata: Vertebrates (mammals, birds, reptiles, amphibians, fishes), tunicates, hemichordates
Subphylum Urochordata (Tunicata)
Class Thaliacea
Order Salpida: Pelagic tunicates with body wall containing circular muscle bands; rhythmic contractions of muscle bands pump water through body which functions for swimming and feeding; internal mucous net filters tiny planktonic particles out of passing water; individual and population growth rates can be very rapid; complex life cycle with alternating aggregate (sexual) and solitary (asexual) phases (Cyclosalpa, Helicosalpa, Iasis, Pegea, Salpa, Thalia, Thetys)
Order Doliolida: Generally inconspicuous pelagic tunicates that swim using rapid contractions of the circumferential muscle bands; feed by pumping water through an internal mucous net using gill cilia; capable of very rapid population increases; complex life cycle with sexual and asexual phases (Dolioletta, Doliolum)
Order Pyrosomatida: Colonial pelagic tunicates that use cilia to pass water through an internal mucous net within each individual; many are brightly bioluminescent; some species are quite large, forming colonies several meters in length (Pyrosoma)
Class Larvacea (Appendicularia)
Order Copelata: Unique among the tunicates in retaining the larval "tadpole" form as mature adults; tail used for locomotion and in feeding; produce a complex external mucous net (the house) to collect tiny planktonic food; most shallow water species are small and inconspicuous; typically are hermaphrodites (except for Oikopleura)
