Terms in this set (37)

  • alternation of generations
    the interchanging sessile polyp and free-swimming medusa stages typical of the cnidarian life cycle
  • cnidocyte
    a specialized cell of a cnidarian that produces and contains a stinging nematocyst
  • coenosarc
    the living portion of the tubular connecting portions of colonial cnidarians like Obelia; consists of a simple cylinder of an outer epidermal tissue layer, an inner gastrodermal tissue layer, and an intermediate mesoglea surrounding a central gastrovascular cavity
  • colonial
    describes individual animals (usually produced asexually) living in a group, which often remain joined together by some physical connection
  • dioecious
    the condition of an animal with both male and female sex organs borne in different individuals
  • diploblastic construction
    a typical cnidarian body with two layers of cells: an outer epidermal tissue layer and an inner gastrodermal layer with an intervening noncellular mesoglea layer
  • epidermis
    the outer tissue layer protecting the surface of an animal from its environment
  • gastrodermis
    the inner tissue layer of animals bordering the digestive cavity
  • gastrovascular cavity
    a central internal body space of an animal that functions in both digestion and circulation; a type of incomplete digestive system that includes a single mouth opening acting as both an entrance and an exit
  • gonangium
    a type of reproductive individual polyp in colonial Hydrozoa, such as Obelia; produces free-swimming medusae
  • hydranth
    a feeding individual polyp in a colonial hydrozoan, as in Obelia
  • medusa stage
    a free-swimming stage in the life cycle of many cnidarians, usually bearing gonads and producing gametes
  • mesoglea
    the gelatinous layer between the epidermal and gastrodermal layers of cnidarians; simple and noncelllular in the Hydrozoa, containing cells and/or fibers in the Scyphozoa and Anthozoa
  • monoecious
    the condition of bearing both male and female sex organs in one individual; usually not self-fertilizing
  • nematocyst
    a stinging capsule produced by the cnidocytes of cnidarians; a key characteristic of the phylum
  • nerve net
    the diffuse, interconnected network of nerve cells in cnidarians; lacks ganglia or other nervous centers
  • perisarc
    the nonliving outer covering secreted by the coenosarc of colonial hydrozoans
  • planula larva
    a simple, ciliated, sausage-shaped form produced by many cnidarians; develops from the zygote or fertilized egg
  • polymorphism
    exhibiting two or more distinct body forms in a single species, like several types of specialized individual polyps found in Obelia, Physalia, and many other cnidarians
  • polyp stage
    the sessile (attached) phase in the life cycle of many cnidarians
  • radial symmetry
    a body plan in which the body parts are arranged around a central axis
  • scyphistoma
    the small, sessile, inconspicuous polyp stage in the life cycle of certain scyphozoans that lives attached to rocks and other submerged objects in shallow coastal waters
  • symbiosis
    an organism living in a close, continuing relationship with another organism of a different species, such as the algal cells living in the tissues of stony corals and other cnidarians
  • velum
    a thin, shelf-like membrane found in most hydromedusae, located on the subumbrellar surface just inside the perimeter of the bell; believed to aid in swimming
  • Class Anthozoa
    corals and sea anemones; solitary or colonial animals with only a polyp stage (the medusa is absent); gastrovascular cavity is partitioned with septa; mesoglea with many amoeboid cells; all marine; 6000 species
  • Class Hydrozoa
    hydroids and siphonophores; most with a colonial polyp stage and a free-swimming medusa stage; thin and gelatinous mesoglea; well-defined epidermis and gastrodermis; most species are marine, but a few live in fresh water; 3000 species
  • Class Cubozoa
    sea wasps or box jellyfish; all species have marine medusae with conical bells of four flattened sides; small polyps metamorphose directly into medusae; common in all tropical seas, especially in the Indo-Pacific and Western Pacific; stings are dangerous to humans, with nematocysts containing some of the strongest toxins known; 20 species
  • Class Scyphozoa
    true jellyfish; most are large marine jellyfish with an abundant mesoglea; polyp stage is reduced or absent; mesoglea contains fibers and amoeboid cells; all marine; 200 species
  • pedal disc
    structure found at the lower end of Hydra that contains mucus-secreting gland cells; used for attachment
  • hypostome
    an elevation between the bases of the radially arranged tentacles in Hydra
  • buds
    the products of asexual reproduction in Cnidaria
  • statocysts
    balancing organs located between the bases of the tentacles in hydrozoans
  • hydrotheca
    a delicate outer covering in hydrozoan hydranths
  • blastostyle
    a central structure in hydrozoan gonangia on which medusa buds develop
  • gonotheca
    a thin outer covering in hydrozoan gonangia
  • ephyrae
    small, free-swimming juvenile medusae in jellyfish that swim, grow, and metamorphose into small medusae
  • pedal laceration
    a type of asexual reproduction in anthozoans where bits of tissue split from the base of an anemone as the animal moves along the substrate; these tissue pieces later regenerate an entire small anemone