Zoology جزئية الفاينل كاملة PDF

ANIMAL BIOLOGY 36 Characteristics of the Phylum: Platyhelminthes are Acoelomate, Triploblastic animals The body wall consists of three layers (endoderm, mesoderm, and ectoderm) The mesoderm occupies the...

ANIMAL BIOLOGY 36 Characteristics of the Phylum: Platyhelminthes are Acoelomate, Triploblastic animals The body wall consists of three layers (endoderm, mesoderm, and ectoderm) The mesoderm occupies the place of mesoglia in diploblastic animals. 1- The body flattened dorsoventrally. 2- The digestive system is incomplete (gastrovascular type); there is one opening "mouth" and no anus. 3- Most forms are hermaphrodite. 4- No internal space other than the digestive tube (Acoelomate). 5-Free-living or parasitic animals. 3.4.1. Class: Turbellaria Characteristics of the class: Includes worms that are free-living in saltwater or freshwater. It looks like a plant leaf, have suckers and the body covered by cilia. 3.4.1.1. Planaria: Lives in freshwater seeking for its food, hide between water plants and under rocks and avoids light. It has a frontal region occupied by the head, and back region at the end of the animal. It has a dorsal surface which directs upward and a ventral surface which directs downward. - The Digestive system: The mouth is in the centre of the underside of the body. The pharynx connects the mouth to the gastrovascular cavity. The gastrovascular cavity (intestine) branches throughout the body, allowing food nutrients to reach all extremities. Food passes from the mouth through the pharynx, then, into the intestines, where it is digested by the lining cells. Then the nutrients diffuse to the rest of the Planaria digest No anal opening. me - The Nutrition: Planaria consume living or dead, small animals that sucked up with their muscular mouths. Digestive enzymes are secreted from the mouth to begin external digestion. Then the pharynx projects out from the mouth to fragment the food into small pieces by sucking moves. The food passes inside the intestines, where it reaches all parts of the body by diffusion. - The Excretory system: The excretory system is made of a network of tubes extend along body sides and have many side branches opened on the dorsal surface by excretory pores. The side branches end by a swelling consist of flame cells. Flame cells have bundles of cilia that move to eliminate excess liquids from the body through the ducts, which lead to the excretory pores, then the waste is released on the dorsal surface of the body. ANIMAL BIOLOGY 37 The Nervous system: Consists of two ganglions at the head region under the eyespots, sometimes they referred to as the planarian brain. From the ganglion two lateral nerve cords extend along the body length till the body end. There are many transverse nerves connected to the two nerve cords, making the nerve system look like a ladder. The Genital and Reproductive system: Planaria is hermaphrodite but with cross-fertilization. The female genital system consists of two ovaries lies just behind eyespots. Two oviducts come out from each ovary, which extends to the end of the animal and is surrounded by vitelline glands that open into the oviduct. The male genital system consists of numerous testes, Vasa efferentia get out from every single testis which union together to form vasa deferens that extends beside the oviduct. Vasa deferens lead to vesicular seminalis then the muscular penis The penis opens into the genital atrium, which opens to the outside by the genital pore. The Reproduction: The two worms attached ventrally, The penis of each worm project out and release their sperms to the other worm, later the worms separate. After that the fertilized egg is surrounded by a shell forming egg pouch, each pouch contains about ten fertilized egg, Egg pouches release to the outside through the genital pore and stuck to the water plants or anything in the water. After some time, the eggs hatch and give rise to small worms resemble the parents but with incomplete genital system. Some types of Planaria reproduce asexually by binary fission. The Planaria, which reproduce asexually rarely reproduce sexually. Planaria can regenerate, it can be cut into pieces, and each piece can regenerate into a complete organism. ANIMAL BIOLOGY 39 - The body wall structure: It consists of three layers; Ectoderm from outside, Endoderm from inside, and Mesoderm between them. - The Ectoderm layer: The outermost layer of the body layers consists of one layer of cells settling on a basement membrane and containing small bodies called Rhabdites. Rhabdites extend outside towards water forming a mucous layer that covers the animal to assist in prey catch and protect from enemies, Ectoderm has many cilia to utilize locomotion. - The Endoderm layer: The innermost layer of the body layers, it consists of large epithelial cells with glandular cells in between It forms the digestive canal epithelium. - The Mesoderm layer: The middle layer of the body layers, it formed of ameboid cells gather to form cellular net called Parenchymal tissue. Mesoderm also contains muscles. - The Muscle layer: A circular muscle layer below the basement membrane followed by a layer of longitudinal muscles and vertical muscle fibers. ANIMAL BIOLOGY 40 3.4.2.Class: Trematoda: Characteristics of the class: Ectoparasitic or endoparasites. The body shape is usually leaf-like covered with a cuticle layer or tegument. The body is unsegmented. They have adhesive organs in the form of suckers (Oral sucker, Ventral sucker) by which they attach to the tissues of their hosts. The Digestive tract is incomplete and the mouth is located in the frontal part of the body. The class includes liver flukes, and has two hosts, one vertebrate and the other is invertebrate (shells). There are two types of liver flukes: 1- Fasciola hepatica 2- Fasciola gigantica 3.4.2.1. Fasciola gigantica: It is the parasite of the bile ducts of the sheep liver and causes marked animal loss if they severely infected. It also can infect humans. - The External features: It is composed of an anterior small conical portion and a large leaf-shaped posterior portion with parallel sides. The cuticle is provided with numerous small spines. It has two suckers (Oral sucker; Ventral sucker) by which they cling to the tissues of their hosts. - The Digestive system: Fasciola has a single mouth located within the anterior sucker on the ventral side of the fluke. The mouth leads to the pharynx, which is then followed by a narrow esophagus. The esophagus, which is lined with a thin layer of epithelial cells, opens up into the intestinal caecum, extending along the sides of the body. As no anus is present (blind gut), the outer edge of intestine branches and each branch ending blindly near the posterior end of the body while the inner edge takes the V or U shape. - The Excretory system: It consists of a network of tubules surrounding one central excretory canal that leads to the excretory pore at the posterior end of the body. The central canal branches into four sections within the dorsal and ventral regions of the body. Each excretory tubule is connected to a flame cell, with cilia covering the cup's inner surface. The beating of these flagella resembles a flame and push the wastes to the excretory canal and then to the excretory pore. - The Genital system: Adult flukes are hermaphrodite; each contains both male and female reproductive organs. The male genital system consists of testes formed of two-branched tubules located in the middle third of the body. ANIMAL BIOLOGY 42 o 3.4.2.2Fasciola hepatica: Resemble Fasciola gigantica but smaller in size and has equal-sized suckers with elementary intestinal branches. - The Live Cycle: Fertilization is mixed, either between two worms or self-fertilization. The life cycle of Fasciola hepatica starts when a female lays eggs in the bile ducts of the liver of an infected human. The immature eggs are discharged in the biliary ducts and released in the feces. If landed in the water, the eggs become embryonated and develop larvae called miracidia. (which is conical in shape covered by cilia, has a short gut and two eyespots and a pair of flame cells). Miracidium invades an aquatic snail (Lymnaea) and develops into cercaria, a larva that is capable of swimming with its broad tail. The cercaria exits and finds aquatic vegetation where it forms a cyst called metacercaria. Infection of humans is through eating the raw freshwater plant containing the cyst. The metacercaria exits in the first part of the small intestine, duodenum. Metacercaria may penetrate the intestinal wall and gets into the peritoneal cavity, where it finds its way to the liver and starts invading liver cells. This phase of life circle happens only a few days after the initial contact with the parasite. Usually, the larva spends a few weeks just browsing and eating the liver. Then it relocates to the bile ducts where it begins its final, stage and becomes an adult. It takes about three to is four months for the metacercaria to develop into an adult. Adult flukes start to produce eggs (up to 25,000 eggs per fluke per day). The eggs pass out via stools and into freshwater. The eggs become embryonated while in fresh water, allowing them to hatch as miracidia and repeat the life cycle. ANIMAL BIOLOGY 43 2. Class: Cestoda surface - Characteristics of the class: All Cestoda are endoparasites body They lack an alimentary canal, so they absorb digested food through their body surface. They have long flat bodies composed of a linear series of reproductive units or proglottids. Most forms hermaphrodite (has both male and female organs in the same worm). Zhost I Cestodes require at least two hosts: a. The adults are parasites that live in the digestive tract of hosts. 8 b. The larvae stage parasitizes in the tissues of vertebrates and invertebrates. For examples: Taenia saginata reproductive It lives as an adult in the human intestine. cells (a mature adult may reach a length of 10-12 meters, which may consist of 1000-2000 proglottids) The body consists of a small scolex (head) follows by a narrow neck by the continuous growth of which new proglottids are budded off. 1 -The Scolex (head): It has four suckers for the attachment to the intestinal wall but without any hooks. 2- The Neck: It is a narrow-unsegmented region followed by a linear series of reproductive units or proglottids. The mature segments followed neck immature segments, then mature segments. Finally, gravid segments are formed. fortaenia if - The Nervous system: The nerve system of Tania spp. comprises a pair of ganglia in scolex and two lateral longitudinal nerve cords, which extend longitudinally through each segment. - The Excretory system: It is composed of flame cells attached to small canals, which lead to the excretory canals Excretory canals in the scolex aré continued along the body's length by a pair of dorsolateral and ventrolateral, excretory canals. A trans verse excretory canal connects these paired canals near the posterior end of each proglottid. hermaphrodite - The Reproductive system : The worms are hermaphrodite. if Every proglottid segment contains two sets of genitalia, the male genital system and the female genital system. - The Male reproductive system: 2 It consists of numerous small scattered spherical testes connected to vasa efferentia that join to become a single vas deferens. The vas deferens commonly lead into a seminal vesicle and hence to a papilla-like penis and open by the male genital opening. 2 become single I event  Cestoda ANIMAL BIOLOGY Taea IT 44 I - The Female reproductive system: 61W 0 It consists of one large bilobed ovary located at the base of each mature segment, which is posterior in position and connected to an oviduct. Oviducts pass backward and unite with the vitelline duct, draining the vitelline gland, which lies posterior to the ovary. There is a small enlargement, the Ootype, at the place of union of the vitelline duct and oviduct. The uterus is simple, but in more mature (gravid) proglottids, it becomes much branched on becoming full of eggs. The gravid proglottid is longer than the mature proglottids, with a much-branched uterus (15-20 main branches on each side) packed with eggs. I WI Mature proglottis of taenia ‫أﺳﻠﺔ ﻧﺎﺿﺟﺔ ﻟﻠﺗﯾﻧﯾﺎ‬ ANIMAL BIOLOGY - The Life cycle: cestoda ftp.foit 45 Taenia Fertilization in this worm is cross or self-fertilization (auto-fertilization), but the latter is rare. The ova may be fertilized by the sperms of the same proglottid, from other proglottids of the same individual or both The sperms travel down the vagina to fertilize the ova in the lower part of the oviduct. On their passage to the uterus, the eggs become enclosed with a large yolk cell, in a thin eggshell. In the uterus, the egg development begins to form a six hooked larva (hexacanth embryo), surrounded by hard radially striated embryophore. When the terminal gravid proglottids with their eggs break off and pass out with the feces, the proglottids disintegrate, and the eggs with the embryos may be scattered on the soil, grass dust, etc.where grazing cattle may pick them up. When the cattle swallow the eggs or proglottids, the eggshells are dissolved in the intestine, and the hexacanth embryos burrow through the intestinal wall into the blood or lymph vessels After passing through the heart to the muscles, especially active muscles as the tongue, neck,shoulder, and leg muscles, they become a bladder worm (cysticerci). Here is a period of ten to twenty weeks the larvae develop an invaginated scolex with suckers Infection to man takes place by epting insufficiently cooked beef meet containing the cysticerci. When man's digestive juices dissolve off the cyst wall, the bladder is digested, the scolex evaginates and becomes attached to the intestinal wall, and new proglottids begin to develop. It takes 2-3 weeks for a mature worm to form. When a man is infected with,one of these tapeworms, many single proglottids are expelled daily from his intestine. ANIMAL BIOLOGY 46 3. Class: Nemathelminths ÉÉ Phylum: Nemathelminthes Class: Nematoda Order: Order: Strongylata m neat Ascaridat Ancylostoma Ascaris Characteristics of the phylum: They are cylindrical, or roundworms where the body pointed from both ends. They are Triploblastic and Acoelomate animals. They have a peri-visceral cavity, and the alimentary canal is straight, simple, opens by a mouth and an anus. It lacks muscles and glands. Sexes are usually I separate, and the gonads are tubular. The body is covered with a rigid, smooth elastic cuticle. They 000 live parasitic or free-living. Order: Ascaridata: I They have lips around the mouth, and males have curved posterior ends, two spicules, and no bursa copulatrix. Order: Strongulata: The males have two spicules and bursa copulatriX. Ascaris: To This worm is an intestinal parasite that inhabits man's small intestine and several other mammals such as pigs, cattle, and horses. These parasites cause abdominal pain, neuropathy, and bronchitis when their larvae invade the lungs. Ascaris have a yellowish-white color. Male length varies from 15-25 cm, and the female is bigger than 20-30 cm. or roundworms 1 cylindrical ANIMAL BIOLOGY 48 - The External surface: The body surface is smooth with two longitudinal, lateral lines inside both extends an excretory canal, ventral.and dorsal lines extending in both nerve cord. Males have curved posterior ends, two copulatory spicules. The genital opening in the female has situated on ventral sides some distance from the anterior end (at about one third the length of the body, the excretory opening lies on the ventral side behind the mouth and anus at the end of the body. The mouth lies at the body's anterior end and is guarded by three finely papillated lips, one dorsal and two ventrolateral. 7 dorsal 2 Ventral - The alimentary canal and nutrition They feed on the food inside the host's intestines, i.e., digested food, so the alimentary canal of Ascaris very simple is a straight tube inside the body cavity and connected to the wall the body at the mouth and anus only. The anterior portion of the alimentary canal is the muscular pharynx, followed by midgut. The posterior portion is a rectum, which excretes the waste through the anus open - The Excretory system: It consists of two excretory canals, gach extending along a lateral line. Two excretory canals are connected at the anterior end, which found the excretory pore. There are four amoeboid cells around the site of connection for two excretory canals, which collect the excretory fluid then absorbed by the excretory canal walls and four ameboid cells. - The Nervous system: It formed from a ring of nerve tissue around the pharynx gives rise to small nerves to the anterior end and two nerve cords to the posterior end, one dorsal and one ventral, which extended through the dorsal line and ventral line. - The Reproductive system: - The Male reproductive system: It consists of a single thread-like, much-coiled testis and passes out into a coiled vas deferens, dilating a broader but straight vesicula seminalis opens with short, muscular ejaculatory ducts which unite with the rectum and open together in one aperture. -The Female reproductive system: It consists of two thread-like coiled ovaries, each lead into a coiled, and somewhat less opaque oviduct leads into a complete straight uterus. The oviduct dilates into a spherical chamber, the receptaculum seminis, before leading into the uterus. The two uteri unite together and form the single vagina, which tapers anteriorly and opens by the genital aperture.  Ascaris ANIMAL BIOLOGY 50 - The Life cycle: After mating, a female Ascaris may lay eggs. The fertilized ovum is oval, contains one cell (zygote), and is surrounded by a thin shell, an inner coat, and a thick brown shell at the outer surface with external papillae. Egg carried by the host's feces. Given suitable soil conditions, embryos develop into larvae that peel off into infective juvenile larva within two weeks, and the egg becomes infective. The direct sunlight and high temperatures are lethal, but the eggs have excellent tolerance to other adverse conditions, such as desiccation or lack of oxygen. Infection usually occurs when eggs are ingested with uncooked vegetables or when children put soiled fingers or toys in their mouths. When a host swallows embryonated eggs, the tiny juvenile larva hatch, they burrow through the intestinal wall into veins or lymph vessels and are carried through the heart to the lungs where the larva peels off twice. They break out into alveoli and are carried up to the trachea, then swallowed and go to the esophagus, stomach, and intestine again where it peels for the fourth time and develops into an adult worm. - not found circulatory system and respiratory system in Ascaris Ascaris Life Cycle Fertilzereegg round one zygote killed Temp  Amed an ANIMAL BIOLOGY 51 Phylum: Annelida Characteristics of the phylum: Annelids have a worldwide distribution. They live in marine, freshwater, and on land, active, sedentary, or ectoparasitic. Advantages of segmented worm: 1.The Annelida are metamerically segmented, Triploblastic, coelomate animals. 2.Their body is covered with a thin cuticle, and the body wall is muscular. 3. They possess chaeta but no exoskeleton. 4.They are hermaphrodite. I m 5.The excretory organs are metamerically arranged nephridia. T.es 6.The gonads develop from the coelomic epithelium. 7.The nervous system comprises a cerebral ring and a double ventral nerve cord with a double ganglion in each segment. 8. They have a closed circulatory system. The phylum divided into three classes: 1.Class: Oligochaeta, for example, Allolobophora (Earthworm). 2.Class: Polychaeta, for example, Nereis (Sandworm). 3.Class: Hirudinea, for example, Hirudo (medical leech). skin 1. Class: Oligochaeta: Segmented worms have few chaetae, and they are 'al ways hermaphrodite. Gonads are confined to a few of the anterior segments of the body. Gonaducts opened by funnel-shaped structures to body coelom I Eggs are deposited and develop in unique capsules There is no free larval stage. u Example: No larva The Earthworm (Allolobophora spp.): Earthworms live in damp soil. They abound in the fields and gardens where they build burrows, engulfing earth particles mixed with organic matter that they digest, thus aerating the soil Earthworms are nocturnal, that is, they become active by night and retire to their burrows during the day. The body form is cylindrical, pointed anteriorly, and dorsoventrally flattened posteriorly. The body is divided into a significant number of segments vary from 100-250 segment The mouth opening is found terminally at the ventral side; the mouth is surrounded by a peristomium and extends in front of the mouth a prostomium, dorsal, and forms an upper lip. a The clitellum is a swelling part lies on the dorsal and lateral sides concealing the segments. These, however, are distinct on the ventral side, where the edges of the clitellum are SPIT thickened at puberty on segments 31-33, forming puberty crests.  Annelidgigochaeta ANIMAL BIOLOGY 52 - The body apertures: 1.Mouth opening. 2.The anus lies at the posterior end of the last segment. 3.The dorsal pores are minute, fragile pores which lie mid dorsally between segmental grooves starting with segment 8 to the posterior end. 4. The excretory pores or nephridia pores are the minute pores of the nephridia to the outside. o They are ventral in position, two per segment, except the first three and the last segment where they are absent. o 5. The male openings are two slit-like apertures with thickened lips. They lie on the ventrolateral sides of segment 15. 6.The female has two small openings which lie ventrolateral on segment 14. 7. The spermathecal pores are two pairs of minute openings, the first pair lies in the intersegmental 0 grooves between segments 9-10, the second pair lies in the intersegmental grooves between 0 segments 10-11, each open extend to the pouch which stores the sperms. 0 0 8. The openings of the copulatory gland are three pairs on the later side of the 9-11 segments.  ANIMAL BIOLOGY 53 - Nutrition and digestive system: Earthworms feed mainly on decaying organic matter, bits of leaves and vegetation, refuse, and animal matter. The alimentary canal start with the buccal region extends in segment 1-2 and opens with Isi o_0 the mouth in front followed by the pharynx in segment 3-5 is thick-walled, muscular tube and connected to the body wall by numerous muscle strands that can contract and relax for sucking digested food. Followed by the esophagus on segments 6-14 is narrow and thin walled. The crop on segment 15-16 is dilated and thin-walled follow by the gizzard on segment 3 17-19 is thick-walled, highly muscular and serves to grind the food. The intestine extends along the rest of the body opens to the exterior by the anus on the last segment. - The Circulatory system: It is a closed form, consisting of several tubular vessels in which blood flows. The main blood vessels are: 8182 1. The dorsal blood vessel extends mid-dorsally above the alimentary canal. It is contractile and blood flows inside it from behind forwards. 2. The ventral blood vessel extends medially below the alimentary canal. It is non-contractile and blood flows along its greater length from in front backwards. 3. The sub-neural blood vessel extends close below the nerve cord. 4. The pseudo hearts are 6 pairs of contractile transverse vessels which run on both sides of the esophagus, connecting the dorsal with the ventral blood vessels. 8 - The Excretory system: f It consists of a large series of segmentally arranged nephridia, one pair in each segment except the first three and the last. Note that the nephridium has a small inner opening found at the end of a ciliated funnel which lies in front of the septum between segments. The latter body is in the form of convoluted tube which is mostly ciliated and opens to the outside on its own segment by a nephridia pore. - The Nervous system: 0 It consists of the subpharyngeal ganglia form. a bilobed mass at the third segment which lies dorsal to the pharynx There are two nerve cords turn around the pharynx and join to form subpharyngeal ganglia which is also bilobed from which extend as nerve cord backwards to the last segment. It bears a swelling or ganglion in each segment. From each ganglion three pairs of nerves From the brain extend some nerves to first and second segments. ANIMAL BIOLOGY 54 - The Reproductive system: earthworms The earthworm is hermaphrodite. - The Male genital system, consists of: 1. The testes are two pairs of minute bodies and lie in segments 10 and 11 2. The seminal funnels are two pairs, large and ciliated. Each funnel lies behind a testis and extends laterally and backwards as a vas efferent. The two vasa efferentia on each side unite to form a vas deferens which extends backwards to open to the outside by the corresponding male genital aperture on segment 15. 3.Four pairs of seminal vesicles as empty bags very distinct, four pairs which lie one pair in each o segment the site of esophagus in from segments 9-12. o - The Female genital system, has the following: 1. The ovaries are tiny and pyriform in shape suspended from anterior septum. The two o ovaries lie in segment 13. The ovary has broad side full of immature eggs 2. The ovarian funnels are two in number and lay one behind each ovary. Each lead into an ovisac that opens to the exterior by a short oviduct which opens to genital aperture on segment 14. (ovisac stores eggs before release to outside) 3.The spermathecae are two pairs of small rounded sacs, one pair in each of segments 10 and 11. They receive the sperms. - The Reproduction: Although the worm is hermaphrodite, it doesn't fertilize itself, but fertilization occurs between two worms. The two worms adhere at their inferior surface, in this time sperms pass from spermathecae of each to the other where they stored, then the two worms separate from each other. When the time of laying egg is approaching clitellum, glands are activated and secrete liquid which freezes and forms a flexible tubal sheath around clitellum. At that the worm starts to move and shrink backwards to strip this sheath off. When the sheath reaches to segment 10, sperms exit from spermathecae and fertilize ova. Finally, when the worm gets rid of the sheath permanently the edges of the sheath fuse and form a cocoon which contains fertilized ova. This cocoon remains in soil until hatching of egg and exit of young worms from cocoon and grows in soil. ANIMAL BIOLOGY Sandworm 56 2- Class: Polychaeta Example: *(The sandworm) Nereis: This class comprises the bristle-worms, which are nearly always marine, with obvious homonymous segmentation Their chaetae are numerous and borne on special prominences of the body called the parapodia. The sexes are usually separate, and gonads extend in most segments of the body They are live in temporary burrows in the sand, from between tidemarks to depth, which they occasionally leave to reconstruct anew The body form is cylindrical, pointed dorsally, and the body is divided into significant number similar segments, separated by intersegmental grooves. The body apertures: 1. The mouth 2. The anus 151 3. The nephridiopores, which are one pair open in each segment and lie below the parapodia. The body appendages: (A) The Tentacles: 1. One pair of Prostomial tentacles lies in the anterior and function as a tactile 2. One pair of Prostomial palps. lies in the posterior. They are longer and thicker than prostomial tentacles and delicate to taste. 3. Four pairs of long slender prostomial tentäcles lie around the mouth, which is considered two fused segments. Marapodia (B) The Lateral appendages : I Found in all body segments except, in the first and last segments called parapodia, consisting of two divisions. 1. The dorsal notopodium bears dorsal cirrus and a bundle of chaetae lodged in a chaetagerous sac. Also, a much stronger chaeta, the dorsal aciculum, appears deeply embedded in the notopodium. 2. The ventral neuropodium bears similar structures: ventral cirrus, which is longer than the dorsal one, a bundle of chaetae, and a tough ventral aciculum. The Movement: They are found in temporary hiding places, such as under stones, where they stay with their bodies covered and their heads protruding. They are most active at night when they wiggle out of their hiding places and swim or crawl over the sand, searching for food. 000 Parapodia are used in crawling, swimming, or for anchoring the animal in its tube.  ANIMAL BIOLOGY 57 - The Digestive system: Nereis feed on small animals, other worms, and a variety of larval forms They capture food with their chitinous jaws, which they protrude through the mouth as they evert their pharynx. Food is swallowed as the worm withdraws its pharynx. Movement of food through the alimentary canal is by peristalsis. - The Excretory system: 13 It consists of nephridia (like earthworm) segmentally arranged nephridia, one pair in each segment except the first three and the last. Note that the nephridium has a small inner opening found at the end of a ciliated funnel, which lies in front of the septum The latter body is in the form of a convoluted tube mostly ciliated and opens to the outside on its segment by a nephridia pore.  ANIMAL BIOLOGY 58 - The Circulatory system: D Blood red color and contain hemoglobin dissolved in plasma, and the system consists of: 1. Dorsal blood vessels 2. Ventral blood vessels These vessels run mid-dorsally above the alimentary canal and are connected through transverse vessels. Blood flows between these two vessels via segmental networks in the parapodia, septa, and around the intestine. - The Sense Organs: yd Sense organs are highly developed in polychaetas and include eyes, nuchal organs, and statocysts The eyes, when present, may range from simple eyespots to well-developed organs. - The Reproductive system: Polychaetas have no permanent sex organs. They usually have separate sexes Reproductive systems are simplex Gonads appear as temporary swellings of the peritoneum and shed their gametes into the coelom. The gametes are then carried to the outside through gonad ducts or by rupture of the body wall. Fertilization is external, and the early larva is a trochophore. - Transverse Section of Nereis: 3 The epidermis consists of goblet cells and sensory cells and is covered externally by a thin cuticle The muscular layer is built up of an outer continuous thin circular muscle layer and an inner thick longitudinal layer, interrupted along with a series of lines and therefore appears divided into four blocks and two pairs of oblique muscles in each segment In the center of the section (center of the body), a coelomic cavity is full of fluid and lined with coelomic or peritoneal epithelium and divided by transverse intersegmental septa. ANIMAL BIOLOGY 60 3 - Class: Hirudinea - Characteristics of the class: These are Annelida with a shortened body composed of a smaller and fixed number of segments without chaetae. They possess two suckers, an anterior which contains the mouth and a posterior at the end of the body. They are hermaphrodites; the embryos develop inside cocoons. The medical leech (Hirudo medicinalis) lives on vertebrates' blood, which goes down to where it lives in water of ponds, marshes, and streams. Man has long used the leech's power by letting it suck patients' blood, and so is called the medical leech. - The Body form: 1. The leech body has a greenish-brown color, paler below than above. The form of the body is dorsoventrally flattened (not rounded). The dorsal surface is marked with yellowish longitudinal bands spotted with black pigment, while the ventral surface irregularly matters. 2. The suckers: a cup-shaped anterior sucker with the mouth opening in its middle, and a larger imperforated disc-like posterior sucker, both are ventrally directed. 3. The body is externally divided into many rings or annuli. The worm has a fixed number of segments, only 33. Every five annuli correspond to one true segment except at the anterior and hind ends where the annuli number per segment is less than five. 4. The eyes are black and are five pairs on the dorsal surface of the first five segments. 5. The segmental papillae which bear on a ,certain annulus a transverse row of delicate elevations in each segment. 6. The nephridiopores are 17 pairs of minute openings on the ventral side, one pair in each of the segments 7-23 inclusive. 7. The anus opens mid-dorsally at the point of junction between segment 26 and the posterior sucker. 8. The Genital openings: A. The male genital opening lies in the mid-ventral line on the 4th annulus of segment 11. B. The female genital opening lies in the mid-ventral line on the 4th annulus of segment 12. - The Locomotion: 1. The worm swims in the water by vertical undulations. 2. It walks with the help of the suckers (like hydra). - The Digestive system and nutrition: The mouth is surrounded by a buccal region consisting of three serrated chitinous jaws, one dorsum, and two latero-ventral. The pharynx is muscular sucking. The crop is extended along 11 segments and comprises 11 thin-walled chambers, each project laterally into a diverticula or caeca pair.  ANIMAL BIOLOGY 61 swot The stomach is the small digestive region, and the intestine is a short narrow tube and opens through a short rectum to the outside by anus. The leech sticks the anterior sucker of the body of the host and uses the jaws to do characteristic tri-radiate wound on the body of the host and to suck the blood by muscular pharynx then the salivary gland which near to mouth opening secrete hirudin, an enzyme which prevents blood clotting through nitration. - The Excretory system: 0 The excretory system consists of 17 pairs of nephridia lying in segments 7-23. 0 Respiration takes place by diffusion through the skin. - The Circulatory system: 513 Its circulatory system is a reduced coelom consisting of several sinuses and vessels containing red blood. There are dorsal blood sinus, ventral blood sinus, and two lateral blood vessels. Fm - The Nervous system: The system consists of: An anterior nerve ring has one pair of cerebral ganglia. A ventral nerve cord has ganglion in each segment of the body. o 55 - The Reproductive system: The leech is a hermaphrodite. - The male reproductive system: 0 1. Nine pairs of testes lying along the sides of the ventral blood sinus in segments 13-21. 2. The vasa efferentia comes out from every testis. 3. Vasa deferens. 9284. Vesicula seminalis. 5. Ejaculatory duct, the two ejaculatory ducts open to the exterior by penis on segment 11. - The female reproductive system: It consists of two ovaries, and two short oviducts follow and unite in a common oviduct, which leads into the vagina, which bends anteriorly and opens to the outside on segment 12. Fertilization: is mixed, occurs interchangeably between 2 worms. Eggs are laid out in sacs at the side of rivers. The embryo forms and the eggs hatch, yielding little individuals look-alike the parents.  US a U classes o o o 00  b o o o o o t.ms