Phylum Cnidaria
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name means “Stinging Cells”
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9,000 sp (precambrian- present)
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Phylum name means stinging cell; derived from cnidoblast cell which gives rise to the
nematocyst or “stinging cell”
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Old Phylum name Coelenterata means “hollow gut”
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Many familiar forms: jellyfish, sea anemone & coral
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Most primitive of the “true multicellular animals”; tissue is present
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All aquatic, most are marine (saltwater)
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Exhibit radial symmetry; body designed in a circular fashion
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Body plan is sac-like; digestive cavity with one opening
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Two body forms
Medusa
Polyp
-solitary
-can be colonial
-free-swimming
-sessile
-sexual
-asexual
-adult
-immature
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*Changing from one form to another is Alternation of Generation
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Members of this group have two distinct tissue layers
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Epidermis: outer cells (derived from ectoderm); collectively act as muscles
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Gastrodermis: lines stomach
(derived from endoderm)
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Mesoglea: middle layer of gelatinous material; can be thick or thin
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They have developed primitive type of nervous network called the nerve net; no ganglia
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Two Types of Nematocysts
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Penetrant: penetrates
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Glutinent: sticks
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Poison: proteinaceous neurotoxin; highly effective in stopping prey varies greatly between
species
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Class Hydrozoa (2700 sp.)
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Can have both polyps and medusa stages; usually both
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Colonies have two types of polyps: feeding and reproductive
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Only class to have freshwater forms
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Ex: Hydra- has been extensively studied
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Most species have colonial polyps (usually both)
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Ex: Obelia, Pennaria, Tubularia
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Siphonophores: these are colonial polyps with specialized polyps
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Ex: Portuguese Man-of-War; Physalia physalia
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Ex: “By the Wind Sailor”; Vellela vellela
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The hydromedusa is usually smaller
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manubrium: with mouth @ end
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Velum: inner collar of tissue no oral arms
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Class Scyphozoa (200 sp.)
99% Water
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Considered to be true jellyfish; all are marine
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Emphasis on medusa
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Polyp is reduced or non-existent and is always solitary; NON-COLONIAL
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Medusa is different from hydromedusa
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No velum
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Margin of bell with sensory organs
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Oral arms on manubrium
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Life Cycle; refer to diagram!
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Some species are very toxic, and poisonous and can kill humans.
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Ex: Sea wasp (Box jelly), Sea nettle
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A few species can be up to 8 feet wide, with 200 foot tentacles
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Some medusoids are sessile (bottom dwelling)
Class Cubozoa (15 sp.)
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Medusa with bells having four evenly spaced out tentacles, and well-developed eyes.
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Extremely toxic; found primarily north of Australia - Chironex fleckeri
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Class Anthozoa ( 2000 sp.)
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Largest class, 2/3 of all Cnidarians are in this class
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All are polyploid; some solitary, most colonial
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Name means “flower animal”
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Body more advanced
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Muscular pharynx for food capture
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Gastrovascular cavity (digestive cavity) with many muscular septa that helps to increase surface
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Septal filaments separate from septa and extend down into coelentron are called acontia.
These are loaded with nematocysts and are usually brightly colored.
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Gonads are located in Gastrovascular cavity
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Subclass Alcyonaria- Soft Corals
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8 part symmetry; both internally and externally
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Pinnate tentacles, not tubular (feathery)
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Internal arrangement of septa in multiples of eight
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All are colonial; many have an organic endoskeleton that is flexible and composed of the protein
gorgon
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Ex: sea whip, sea fan, sea pansy, sea pen
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Often called Gorgonians
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Subclass Zoantharia- name means “animal flower”
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Sea anemones and hard coral
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Have hexamerous or six part symmetry; called hexa corals
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Have totally tubular tentacles (TTT)
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Some form CaCO3 exoskeleton
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Hard or stony corals
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Major reef formers
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Order Scleractinia- modern corals
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First appeared in the Triassic, survived to present
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Individual animals (polyps) are called corallites
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Can range from very small to large
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Live in warm, clear shallow water that forms a band around the world from 30o N to 30o S
latitudes
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Most members of this group contain a symbiotic algae called zooxanthellae;
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The algae photosynthesizes and produces food for the coral and the coral gives nutrients and
protection for the algae
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A true mutualism
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6 part symmetry; evident in calcareous exoskeleton remains
- Pedal (basal) disc has grooves which CaCO3 is deposited
- Zooxanthellae algae lives in tissues of polyp must have light for photosynthesis
- Produces O2 and sugars for the polyp
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Aids in precipitation of CaCO3
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Algae often gives coral its color
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Most corals could not exist without this relationship
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Closest coral reef to Texas is East Flower Garden about 200 miles S.E. of Galveston
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Since corals precipitate CaCO3; they take C02 out of the water and air: helps to limit greenhouse
effect – a carbon sink
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Astrangia- only hard coral found along Texas coast
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Coral reefs produce highly varied and productive ecosystems: very delicate and sensitive to
change – results in “coral bleaching” events
Paleocorals
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Order Rugosa
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First appeared in the Ordovician to Permian when Pangaea was forming; caused obliteration of
shallow marine environment
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Called “horn” or cup corals
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Usually solitary; sometimes colonial
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Order Tabulata
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Also lived in the Ordovician to Permian
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Major Paleozoic reef formers
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Have horizontal partitions called tabulae
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Order Actinaria: (Sea Anemones)
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Have 6-part (hexamerous) multiples of six; internally and externally
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Many internal partitions or septa increase surface area
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Primary septa are muscular and connected to pharynx
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Secondary septa have septal filaments that continue into coelenteron called acontia
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Acontia filaments are loaded with nematocysts and are often brightly colored
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The body wall has many small pores called cinclides that helps to release water during rapid
contraction.
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Occasionally the acontia may be squirted out; this may be a defense strategy