COELENTERATA GENERAL CHARACTERS AND CLASSIFICATION PRESENTED BY Dr. Y. SAVITHRI LECTURER IN ZOOLOGY GOVT. COLLEGE FOR MEN(A), KADAPA. HISTORY OF COELENTERATA 1. COELENTERATA – HOLLOW GUT 2. CNIDARIA – NETTLE
Aristotle Knew the stinging qualities of coelenterates and considered hese organisms as intermediate between plants and animals and termed them Acalephe or cnide (Gr., akalephe =nettle; cnodos = thread). They were included in the Zoophyta ( Gr; zoon= animal; phyton= plant) together with various forms from sponges to ascidians. The animal nature of coelenterates was established by Peyssonel (1723) and Trembley (1744). Linnaeus, Lamarck and Cuvier grouped the coelenterates under Radiata which included the echinoderms also because of their symmetry. Finally, Leuckart (1847) separated the coelenterates from echinoderms and created a separate phylum Coelenterata (Gr., koilos = cavity; enteron – intestine). GENERAL CHARACTERS
Hatschek (1888) splitted Leuckart’s Coelenterata into three distinct phyla – Spongiaria (Porifera), Cnidaria (Coelenterata) and Ctenophora.
Sea Anemone
Hydras Jellyfish Sea Coral CONNECTING LINKS
Proteospongia: Ctenoplana: Protozoa and Porifera Coelenterata and helmenthes Coelenterates are Metazoa or multicellular animals with tissue grade of organisation.
These are aquatic, mostly marine except few freshwater forms like Hydra.
These are sedentary or free-swimming and solitary or colonial.
Individuals are radially or bi-radially symmetrical with a central gastro vascular cavity communicating to the exterior by the mouth.
Diploblastic animals; body wall consists of an outer layer of cells called ectoderm and inner layer of cells the endoderm cemented together by an intermediate layer of non-cellular gelatinous mesogloea.
These animals exhibit the phenomenon of polymorphism with very few exceptions; the main types of zooids in polymorphic forms are polyps and medusa. Polyp is sessile and asexual zooid, while medusa is free- swimming and sexual zooid. Skeleton, either exoskeleton or endoskeleton is of common occurrence.
Acoelomate animals because they do not possess a second body cavity,
the coelom.
Short and slender tentacles encircle the mouth in one or more whorls
and helps in food capturing, ingestion, locomotion and protection.
The tentacles are provided with nematocysts; tentacles serve for food
capture, its ingestion and for defence. These are also present on body
layers, these are adhesive organs.
These are usually carnivorous; digestion is extracellular as well as
intracellular. Anus is not found. Nervous system is primitive , consisting of diffuse nerve net.
Respiratory, circulatory and excretory systems are wanting.
Reproduction is both by asexual and sexual methods.
Asexual reproduction occurs by budding and sexual reproduction by the formation of gametes.
A ciliated planula larva usually present in the life history.
The life history exhibits the phenomena of alternation of generations or metagenesis in which the asexual polypoid, sessile generation alternates with sexual medusoid, free- swimming generations. FEEDING
Cnidarians are carnivores that use tentacles to capture prey. The tentacles are armed with cnidocytes – unique cells that function in defense and the capture of prey. Nematocysts contain toxins used for prey capture and defense. FEEDING
Extracellular digestion begins in the gastrovascular cavity, but is completed within the cells of the gastrodermis.
Some cnidarians supplement their diet with nutrients collected from algal symbionts (zooxanthellae). LOCOMOTION
A. Medusa: motile, free-swimming
B. Polyps: sessile Exceptions: 1. Hydra tumbles on tentacles 2. Sea anemones glide on pedal disc RESPONSE
Sensory cells 1. Chemoreceptors (chemicals)
2. Thigmoreceptors (touch)
3. Photoreceptors (light)
Ocelli (eyespots)
4. Statocysts (balance) NERVE NET
Cnidarians have a diffuse nervous system.
Nerve cells forming two interconnected nerve nets in the epidermis and gastrodermis.
No concentrated grouping of nerve cells forming a central nervous system.
CNS does not provide advantage for radially symmetrical animals where stimuli approach from all sides. REPRODUCTION
1. Asexual budding from polyps or medusae 2. Sexual a. Medusae release sperm & eggs b. Some monoecious, some dioecious c. Larvae free-swimming CLASSIFICATION OF COELENTERATA:
The classification followed here is given by Hyman, L.H,. (1940). According to Hyman, Phylum Coelenterata has been divided into three classes, viz., Hydrozoa, Scyphozoa and Anthozoa. Sub Phylum
Ex: Ex: Ex: Hydra: (Sea Fur) Aurelia, Gorgonia Physalia: Rhyzostoma, Adamsia (Portuguese man of Lucernaria, Meandrina war) Pericolpa Metridium Velella, Porpita, Periphylla Madripora Halistemma Class: Hydrozoa (Gr: Hydra=water, zoon=animal
BROWN HYDRA EATING Hydrozoa are solitary and freshwater or mostly colonial and marine, sessile and free- swimming forms.
They exhibit tetramerous or polymerous radial symmetry.
Body wall consists of an outer ectoderm and an inner endoderm separated by non- cellular mesogloea.
Gastrovascular cavity without stomodaeum, septa or nematocysts bearing gastric filament.
Skeleton or horny structure is horny peri- sarc in some forms, while coenosarc secretes a skeleton of calcium carbonate forming massive stony structure or coral in other forms.
They exhibit polymorphism, There are two main types of zooids, the polyp and medusa.
Medusa is provided with true muscular velum. Many Hydrozoa exhibit alternation of generations.
Reproductive products or sex cells are usually ectodermal in origin and discharged externally. Cleavage is holoblastic, embryo ciliated planula.
Ex: Hydra, Obelia, Porita, physalia (Portugese an of war), Velella (Little sail) Millipora. CLASS: SCHYPHOZOA: GR: SKYPHOS= CUP, ZOON= ANIMAL
Fried egg jelly Scyphozoa include large jelly-fishes or true medusae are exclusively marine. Medusae are large, bell or umbrella-shaped, without true velum, free swimming or attached by an aboral stalk. Marginal sense organs are tentaculocysts having endodermal statoliths.
Polypoid generation absent or represented by small polyp, the scyphistoma which gives rise to medusae by strobilisation or transverse fission.
Gastrovascular system without stomodaeum with gastric filaments and may or may not be divided into four inter-radial pockets by septa. Mesoglea is usually cellular.
Gonads are endodermal and the sex cells are discharged.
Ex: Aurelia, Cassiopea, Rhyzostoma, Lucrnaria, Periphylla. CLASS: ANTHOZOA GR: ANTHOS=FLOWERS, ZOON = ANIMAL OR ACTINOZOA: GR: ACTIN = RAY, ZOON = ANIMAL. Solitary or colonial exclusively marine forms.
They are exclusively polypoid. Medusoid stage is altogether absent.
Body usually cylindrical with hexamerous, octomerous or polymerous biradial or radio bilateral symmetry.
The oral end of the body is expanded radially into an oral disc bearing hollow tentacles surrounding the mouth in the centre.
The stomodaeum is present, often provided with one or more ciliated grooves the siphonoglyphs.
Gastro vascular cavity is divided into compartments by complete or incomplete septa or mesenteries. Mesenteries bear nematocysts at their inner free edges.
Mesogloea contains fibrous connective tissue and amoeboid cells. Skeleton either external or internal.
Exoskeleton is formed from calcium carbonate which often form massive corals.
Nervous system is in the form of typical nerve net without a concentrated central nervous system.
Gonads are endodermal, develop in the mesenteries.
The ripe sexual products are discharged into coelenteron.Fertilisation is external.
The fertilised egg develops into a planula larva, which after a short free life settles down and develops into an adult.
Ex: Metridium(Sea anemone), Adamsia (sea anemone), Corallium (Precious coral or red coral), Gorgonia (Sea fan), Pennatula (Sea pen). ECOLOGICAL ROLE
A. Predators and prey
B. Neurotoxins in medical research
C. Coral – jewelry, building, reefs (surfing!)
D. Coral reefs - habitat for many
-great biodiversity
- protect coastline
E. Symbiosis with other organisms