Animal Taxonomy for Veterinary Medicine Lecture Notes PDF

Metazoa Phylum: Cnidaria. It takes its name from cells called cnidocytes, which contain the stinging organelles (nematocyst) characteristics of the phylum. The members of this phylum are radiate animals. The radial symmetry, in which the body parts are arrange...

Metazoa Phylum: Cnidaria. It takes its name from cells called cnidocytes, which contain the stinging organelles (nematocyst) characteristics of the phylum. The members of this phylum are radiate animals. The radial symmetry, in which the body parts are arranged concentrically around the oral -aboral axis, is particularly suitable for sessile or sedentary animals and for free, floating animals. Habit and habitat: Cnidarians are found in shallow marine water. There are no terrestrial species 1  Classsification of phylum: Cnidaria Eumetazoa Radiata Bilataria Phylum: Cnidaria (Coelonterata) Class: Hydrozoa Class: Scyphozoa Class: Anthozoa Alcyonium sp. Aurelia sp. Hydra sp. Sea anemones 2 (jelly fish) Obelia sp. Stony corals  Hydra with developing bud and ovary. Moon jellyfish Aurelia aurita  General characteristics of Phylum: Cnidaria (1) Diploblastic animals (two germ layers, ectoderm and endoderm) Epidermis - outer covering (ectoderm) Mesoglea - middle non-living jelly-like layer Gastrodermis - lines gastrovascular cavity (endoderm) 4 (2) Radial symmetry 5  (5) Mouth and Tentacles Mouth at oral end surrounded by tentacles (this opening act as mouth and anus). 6  Has two forms, medusa and polyp (3) (4) The presence of one opening (mouth) into and out of gastrovascular cavity 7 Gastrovascular cavity often branched or divided with septa 8 (5) Has Cnidocytes or nematocysts (stinging cell) 9 Cnidocyte (nematocyte)  (6) Nervous System Nerve cells, arranged in a nerve net. 11  Revision General characteristics of Phylum: Cnidaria 1. Radial symmetry. 2. Two types of individuals: polyp and medusa. 3. Their body is made up of different types of cells arranged in two tissue layers (diploblastic), an outer ectoderm and inner endoderm. Separated by a jelly like mesogloea. 4. There is a single gastrovascular cavity with a single opening which serves as both mouth and anus. 5. Tentacles usually encircling the mouth. 6. Special stinging cysts, known as the nematocyst in ectoderm and endoderm and are usually abundant on tentacles. 13 7) Respiration and excretion take place by simple diffusion through the body surface 8) Asexual reproduction by budding( in polyps) or sexual reproduction by gametes (in all medusa and some polyps) 9) Some colonial forms secrete a massive external calcareous skeleton (the stony corals). 14  Some Representative species Hydra sp. It has small cylindrical body with a closed lower (aboral) end known as the basal disc for attachment. This basal disc is provided with gland cells to enable the Hydra to adhere to a substratum and also to secrete a gas bubble for floating. The mouth on the oral cone, is encircled by 6 to 8 hollow tentacles. The mouth opens into the gastrovascular cavity. In some individuals buds may project from the sides. Testes or ovaries, when 15 present, appear on the surface of the body.  Some Representative species Hydra sp. Body wall:  The body surrounding the gastrovascular cavity consists of an outer epidermis (endoderm) and an inner gastrodermis (ectoderm) with mesoglea between them.  The epidermal layer contains epitheliomuscular, interstitial, gland, cnidocyte, and sensory and nerve cells.  Gastrodermis is made up of large nutritive-muscular, interstitial, and gland cells and they are lining the gastrovascular cavity.  Mesoglea, is a gelatinous or jelly like substance, helps to support the body and acts as a type of elastic skeleton. 16 17 Locomotion:  Unlike colonial polyps which are permanently attached, the Hydra can move from one place to another by gliding on its basal disc, using the mucous secretion.  It may even turn end over end or detach itself and, by forming a gas bubble on its basal disc, float to the surface. 18 Nutrition:  Hydra is a holozoic animal, It feeds on a variety of small crustacean, insect larvae and similar small aquatic animals.  The tentacles with its nematocysts cooperate to bring the prey to the mouth. Inside the gastrovascular cavity, gland cells discharge enzymes on the food. 19 The digestion is started in the gasterovascular cavity (extracellular digestion), Then the food particles are drawn by the pseudopodia of the nutritivemuscular cells, where intracellular digestion occurs. Ameboid cells may carry undigested materials to the gastrovascular cavity, where they are expelled. The soluble digested products are distributed by diffusion to all parts of the body.  Reproduction:  The Hydra reproduces sexually and asexually. Beside, it has a great capacity for regeneration.  In asexual reproduction, buds appear as outpocketing of the body wall and develop into young hydras that eventually detach from the parents.  The sexual reproduction is usually stimulated by the unfavorable condition, eggs in the ovary( gonads appear temporary) are fertilized by sperm shed into the water. ‫للمعرفة‬  The formed zygote undergoes cleavage to form a blastula.  The inner part of the blastula deliminates to form the endoderm and the mesoglea is laid down between the ectoderm and endoderm. A cyst forms around the embryo before it breaks loose from the parent, enabling it to survive the winter.  Young hydras hatch out in the spring when the weather is favourable. 21.Obelia sp.Obelia sp Medusa stage Polyp Stage  Aurelia sp. Habit and habitat:  occur in coastal waters of all the oceans of the world, swimming close to the surface of the sea. ‫للمعرفة‬ The medusa of Aurelia has a circular outline. It has a convex exumbrella and a concave sub-umbrella side. The margin is fringed with numerous small tentacles. In the center of the sub- umbrella side of the bell is a manubrium having a square mouth. The corners of the mouth has four long oral arms, the lower side of each arm has a ciliated exhalent groove which are studded with many nematocysts. The nematocyst is also found on the tentacles and 25 on the umbrella surfaces. 26