Phylum Coelenterata Dr. Shivani Gupta, PGGCG-11, Chandigarh.

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1 Phylum Coelenterata Dr. Shivani Gupta, PGGCG-11, Chandigarh

2 General Characters -The coelenterates are mainly marine organisms
-Coelenterates can be classified two basic body forms the polyp (sessile) and the medusa (free swimming) -Have only one body opening. -The polyp is a radially, symmetrical individual having a longitudinal oral- aboral axis. -The mouth is at the free end and is surrounded by one to many whorls or sets of tentacles which may be hollow or solid. -The aboral end is commonly developed as an adhesive device for attachment and is conveniently referred to as a base. -The central body cavity is the gastrovascular cavity, also called the enteron or coelenteron.

3 General Characters polymerously radial individual.
-The medusa is a tetramerously or polymerously radial individual. -The body is usually bell- or bowl-shaped with the mouth suspended in the center of the underside of the bell on a stalk. -Instead of directly surrounding the mouth as in the polyp, the tentacles are located at the margin of the bell. -The outer or aboral part of the bell is recognized as the exumbrella and the under or oral part as the subumbrella. -The mouth leads to the central stomach which in turn gives rise to four or more radial canals. -These radial canals run through the umbrella, on the subumbrellar side, and commonly lead to a ring canal at the margin which is continuous around the margin

4 General Characters -Body two layered: outer ectoderm of epidermal
cells, inner gastrodermis(endodermis) which contains digestive cells and middle mesoglea which contains nerve net and jelly like substance. -Intracellular, independent effector organelles called nematocysts (also known as stinging cells or nettle cells) are present. -A coiled thread tube in each cell may be rapidly everted under proper stimulation and used for food gathering and for defense against predators, intruders, or enemies. -Nematocysts are produced within cells called cnidoblasts. -The morphologically simplest coelenterates, the Hydrozoa, have nematocysts limited to their outer epidermis whereas the more complex Scyphozoa and Anthozoa bear nematocysts in both the outer epidermis and inner gastrodermis.

5 General Characters 1. Prey touches a tentacle. Nematocysts fire, paralyzing prey, toxin is injected. Tentacle contracts, prey is forced into mouth. Prey is digested in gastrovascular cavity.

6 Types of nematocysts Nematocysts of Hydra: Upper figs. show discharged and lower figs. show undischarged nematocysts A. Penetrant. B. Volvent. C. Stereoline glutinant. D. Streptoline glutinant

7 General Characters -The coelenterate nervous system can be defined as consisting basically of an unpolarized network of bipolar and multipolar neurons. -The nervous system is subepithelial in location, both subepidermal and subgastrodermal, and may in some forms consist of two networks in only limited contact with one another and with each specialized either for rapid through conduction or for slower, more general spread of conduction. -Circulatory system absent. -Respiration by diffusion via cell surface. -Reproduction both sexual and asexual. Asexual reproduction-Budding

8 General Characters Sexual Reproduction in Hydra Life cycle of Obelia

9 General Characters Life Cycle of Aurelia

10 Classification Coelenterata divided into 3 classes:
Hydrozoa Scyphozoa Anthozoa Subclass (i) Leptolinae (ii) Trachylinae Cubozoa (ii) Staurozoa Alcyonaria (Octocorallia) (ii) Zoantharia (Hexacorallia) Hydrozoa -the hydroids, hydras, and hydrozoan or craspedote jellyfish (hydromedusae); An example is the Hydra. Scyphozoa -the acraspedote (they lack a velum -a shelf of tissue projecting inward from the margin of the bell in hydromedusae and cubomedusae). jellyfish, body shape resembles a bowl or cup, so that jellyfish is often called a bowl. Anthozoa -the sea anemones, corals, sea fans, sea pens, and sea pansies, the body shape resembles a flower. This class is forming sea anemones or coral reefs that can add to the beauty of the scenery of the sea.

11 Class Anthozoa -These organisms are marine, solitary or colonial, and exclusively polypoid coelenterates with no traces of a medusoid stage. -Most anthozoans live attached to some firm object of the shore or on the sea bottom; some embed in the soft sediment. -Anthozoans have a cylindrical body with an oral disk, mouth, stomodeum, hollow tentacles, endodermal gonad, and cellular mesoglea. -The gastrovascular cavity is partitioned longitudinally into radial compartments by endodermal mesenteries or septa whose free edges, particularly, thicken and differentiate into mesenteric or septal filaments. -Both sexual and asexual reproduction occurs. The germ cells are derived from the endoderm, and fertilization occurs either in the female gastrovascular cavity or in the sea. The zygote develops into either a ciliated swimming larva, the planula, or a young polyp. -The class Anthozoa includes the soft, horny, stony, and black corals, the sea pens, and sea anemones. The horny corals include the sea fans, sea whips, and sea feathers.

12 Class Anthozoa Sea Fan Brain coral Sea Whip Alcyonaria Sea Feather
Sea Pen Stony coral Giant green anemone

13 Class Hydrozoa -Includes the fresh-water hydras, the marine hydroids, many of the smaller jellyfish, a few special corals, and the Portuguese man-of-war. -The form of the body varies greatly among the hydrozoans. This diversity is due in part to the existence of two body types, the polyp and the medusa. A specimen may be a polyp, a medusa, a colony of polyps, or even a composite of the first two. -In a representative life cycle, the fertilized egg develops into a swimming larva which soon attaches itself and transforms into a polyp. The polyp develops stolons (which fasten to substrates), stems, and other polyps to make up a colony of interconnected polyps. -Medusae are produced by budding and liberated to feed, grow, and produce eggs and sperm. -Most hydrozoans are carnivorous and capture animals which come in contact with their tentacles. The prey is immobilized by poison injected by stinging capsules, the nematocysts. - Most animals of appropriate size can be captured, but small crustaceans are probably the most common food.

14 Class Hydrozoa Aglaophenia octodonta Craspedacusta sowerbyi Hydra
Sertularia Portuguese-man-of-war Obelia medusa Porpita Velella Tubularia

15 Class Scyphozoa -They are all marine and usually take two forms, the polyp, or scyphopolyp, and the medusa, or scyphomedusa. However, some are polyplike and sessile throughout their lives, while others are always pelagic and lack the sessile polyp stage. -Among the Coelenterata, the Scyphozoa are characterized by having well-developed medusae of large size and fairly well- organized polyps of small size.

16 Class Scyphozoa Chrysaora colorata Phyllorhiza punctata Aurelia Ephyra
Chrysaora melanaster Cyanea capillata Catostylus tagi Aurelia aurita