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Radiate Animals

Radiate Animals. Phylum Cnidaria. Phylum Ctenophora. Radiate Animals: General Characteristics. These phyla are characterized by radial or biradial symmetry. Their bodies are arranged around a central axis.

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Radiate Animals

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  1. Radiate Animals

  2. Phylum Cnidaria • Phylum Ctenophora

  3. Radiate Animals: General Characteristics • These phyla are characterized by radial or biradial symmetry. Their bodies are arranged around a central axis. • Biradial symmetry means that the body can be divided into mirrored halves ONLY along 2 planes that pass through the central axis.

  4. General Characteristics • Both phyla have two well-developed germ layers (endoderm and ectoderm). • A third layer, mesoderm, is present in some.

  5. General Characteristics • They have an internal body cavity (gastrovascular cavity) with a single opening that acts as both mouth and anus. • Most radiates have tentacles that aid in food capture.

  6. General Characteristics • Radiates have the simplest form of true nerve cells (protoneurons), but nerves are arranged as a nerve net, with no central nervous system. • Radiates have the simplest form of sense organs. • Statocysts maintain equilibrium and ocelli are photosynthetic. • Radiates can move by muscular contractions or ciliary comb plates, but most forms are best adapted for floating or being carried by currents.

  7. Phylum Cnidaria • Classes Hydrozoa, Scyphozoa, and Anthozoa

  8. Characteristics of Cnidaria • All are aquatic and have radial symmetry. • Primarily sessile or floating • More specialized than sponges • Contain nematocysts (stinging cells) that are found in cells called cnidocytes • Have two body forms: • Polyp – tubular body with tentacles; example – hydra • Medusa – bell shaped and free-swimming; example - jellyfish

  9. Class Hydrozoa • Representatives: hydra, obelia, and Portuguese man-of-war • Members of this class exhibit the polyp or medusa form. The medusa form has a velum (ring of tissue that is found at the base of the tentacles).

  10. The Hydra • Hydra are the freshwater Hydrozoa representative. • They are typically sessile polyps. • The normal habitat for hydra is the underside of aquatic leaves and lily pads in the water of ponds and streams. • Hydra are found throughout the world with 16 species in North America alone.

  11. Structure of the Hydra Body Plan • Its body can extend to a length of 25-30 millimeters. • It is a cylindrical tube with a stalk-like end and an attachment end. • The basal disk is the attachment end that contains gland cells to allow adhesion.

  12. Structure (continued...) • The mouth (hypostome) opens to the gastrovascular cavity. • Six to ten tentacles surround the mouth: • These are hollow and extendable. • They contain nematocysts (coiled stinging cells used to get food and provide protection).

  13. Structure (continued...) Body Wall • Ectoderm – outer layer or epidermis; contains many types of cells • Epitheliomuscular cells – responsible for muscular contractions • Interstitial cells – undifferentiated stem cells that become most other types of cells • Gland cells – secretes an adhesive substance that aids in the attachment process • Cnidocytes – contain nematocysts • Nerve cells – multipolar neurons

  14. Structure (continued...) • Endoderm – gastrodermis; inner layer that contains muscular, gland, and interstitial cells • Mesoglea – jelly-like substance found between ectoderm and endoderm

  15. Processes of the Hydra • Locomotion – floats and moves by somersaulting motion • Response – when disturbed, it will contract and form a small ball • Digestion • Food enters the gastrovascular cavity that is lined with gastrodermal cells. • Some secrete digestive enzymes that partially digest food. • Partially digested food is taken in by the gastrodermal cells when digestion is complete.

  16. Processes (continued...) • Excretion • Digestive wastes are expelled through the mouth. • Metabolic wastes and carbon dioxide are discharged into water. • Respiration – oxygen diffuses from water into cells

  17. Processes (continued...) • Nervous • Contains a nerve net that consists of interconnected nerve cells located at the base of the epidermis and gastrodermis • This is a primitive type of nervous system. • It controls movement of tentacles. • NO BRAIN!

  18. Processes (continued...) • Reproduction • Asexual reproduction occurs through budding or regeneration. • Miniature versions break off of mature organisms and grow to maturity. • Sexual reproduction occurs when temporary gonads develop in the autumn. • The ovaries produce eggs and the testis produce sperm. • The developing embryos are encased in a cyst to protect them from harsh winters. Warm weather stimulates the “hatching” of new hydras.

  19. Class Scyphozoa • Scyphozoa means “cup animal.” • The most common representative is the jellyfish (Aurelia).

  20. The Jellyfish • Contains both body forms – polyp and medusa • Medusa form is for sexual reproduction • Zygote develops into a PLANULA LARVA which swims around and then settles to form the polyp form • The polyp form produces more of the medusa form

  21. The Jellyfish • Tentacles of the medusa have nematocysts that give humans painful stings

  22. Most Deadly Jellyfish • All jellyfish contain a toxin, but some are more toxic than others. • Many of the box jellies are considered to be more dangerous. • Specifically, the Irukandji is considered the most deadly of the jellyfish. (There are actually multiple species.) • It is only one centimeter cubed at its largest, while many are 5mm or less in diameter. • It’s small size makes it almost invisible in the marine waters off of Australia’s coast.

  23. Class Anthozoa • Means “flower animal” • Common representatives are the sea anemone and coral

  24. Class Anthozoa • Anthozoans lack a medusa stage. • All anthozoans are marine, found in both deep and shallow water, and vary in size. • Anthozoans are solitary or colonial. • They contain a large gastrovascular cavity that is separated by divisions called septa, which are inward projections of the body wall.

  25. Sea Anemone • The polyps of sea anemones are larger and heavier than hydrozoan polyps • They attach to shells, rocks, or timber by pedal discs. Some burrow in mud or sand. • A crown of tentacles surrounds the flat oral disc. • A slit-shaped mouth leads into a pharynx. • The gastrovascular cavity is divided into six pairs of primary septa.

  26. Sea Anemone • When in danger, water is rapidly expelled through pores as the anemone contracts to a small size. • Some anemone fishes shelter in sea anemones and have a skin mucus that protects them from triggering nematocysts.

  27. Corals • Corals display only the polyp body form. • Coral reefs have great productivity, rivaled only by tropical rain forests. • Living plants and animals are limited to the top layer above the calcium carbonate deposits. • Coral reefs are suffering from global warming and high concentrations of carbon dioxide.

  28. Corals • Coral also has a large economic value. • When coral dies, the hard skeleton remains • The skeletons produce coral reefs and can also be used to create jewelry.

  29. Phylum Ctenophora • Class Tentacula

  30. Characteristics of Ctenophora • Composed of fewer than 100 species, all of which are marine and primarily found in warm waters • All are formed from 8 rows of comblike plates that function in locomotion • Has a combination of radial and biradial symmetry • Has endoderm and ectoderm, with mesoglea between • Does not contain nematocysts, but do contain adhesive cells called colloblasts that are used to capture prey

  31. Class Tentacula • Has tentacles that may or may not have sheaths into which they retract • Some have flattened tentacles for creeping • Representative - Pleurobrachia

  32. Pleurobrachia BODY FORM • Its body is 1.5-2 cm in diameter and has a sense organ called a statocyst near the mouth opening. • Its surface has 8 equally spaced bands called comb rows that have long fused cilia called comb plates. • Movement is accomplished by the wavelike beating of the cilia. • It has two tentacles that are very long and extensible that may also be retracted into tentacle sheaths. • The surface of the tentacles are covered with colloblasts (glue cells) that can catch or hold small animals.

  33. Pleurobrachia DIGESTION • It has a gastrovascular system that consists of a mouth, pharynx, stomach, and a system of gastrovascular canals. • Digestion is both extracellular and intracellular. • Undigested waste leaves the body through 2 anal canals. RESPIRATION and EXCRETION • Both occur through the body surface NERVOUS and SENSORY • The epidermis contains numerous sensory cells that allow the organism to be sensitive to chemicals and other stimuli.

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