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Zoology

• The branch of biology related to the animal kingdom.
• Focuses on the structure, embryology, evolution, classification, habits and distribution of all animals, both living and extinct.
• Term derived from Ancient Greek (zōon "animal" + logos "knowledge").
• Areas of study include: Helminthology, Entomology, Ichthyology, Ornithology, Theriology, Malacology, and Mammology.

Taxon

• Systematic unit
• Hierarchy of biological classification's eight major taxonomic ranks includes: Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Species: Described vs Global Estimate

• Invertebrates described: ~1,359,365 and the global estimate is ~6,755,830.
• Insecta described: ~1,000,000 (965,431–1,015,897) and the global estimate is ~5,000,000.
• Arachnida described: 102,248 and the global estimate is ~600,000.
• Mollusca described: ~85,000 and the global estimate is ~200,000.
• Annelida described: ~16,763 and the global estimate is ~30,000.
• Nematoda described: <25,000 and the global estimate is ~500,000.
• Platyhelminthes described: 20,000 and the global estimate is ~80,000.
• Chordates described: 64,788 and the global estimate is ~80,500.
• Mammals described: 5,487 and the global estimate is ~5,500.
• Birds described: 9,990 and the global estimate is >10,000.
• Reptiles described: 8,734 and the global estimate is ~10,000.
• Amphibia described: 6,515 and the global estimate is ~15,000.
• Fishes described: 31,153 and the global estimate is ~40,000.
• Agnatha described: 116 and the global estimate is unknown.
• Cephalochordata described: 33 and the global estimate is unknown.
• Tunicata described: 2,760 and the global estimate is unknown

Relationships of the medically important parasites

• Parasites split into Protozoa and Metazoa (helminths)
• Protozoa include Sarcodina (amebas), Sporozoa (sporozoans), Mastigophora (flagellates), and Ciliata (ciliates).
• Metazoa(helminths) include Platyhelminthes (flatworms) and Nemathelminthes (roundworms)
• Platyhelminthes (flatworms) include Trematoda (flukes) and Cestoda (tapeworms).

Phylum: Flatworms (Platyhelminthes)

• The taxon name derives from the Greek word platy, meaning "flat", and helminth meaning "worm".
• Includes 20,000 known species that are categorized under four classes.
• Class Turbellaria: Flatworms that are ciliated and free living.
• Class Monogea: Ectoparasitic and constitute monogenetic flukes.
• Class Trematoda: Includes common flukes.
• Class Cestoda: Endoparasitic worms also know as tapeworms.
• Class Monogea: Is a class of Platyhelminthes

Parasitism vs Ectoparasite vs Endoparasites

• Parasitism: Association where one organism is harmed and the other benefits
• Ectoparasite: A parasitic organism that lives on the outer surface of its host.
• Endoparasites: Parasites that live inside the body of their host.

Flatworm Key Aspects

• Bilaterally symmetrical and triploblastic worms
• Body flattened dorsoventrally; oral and genital apertures mostly on ventral surface.
• Lack a body cavity other than the gut and lack an anus; the same pharyngeal opening both takes in food and expels waste.
• Larger examples have a highly branched gut for food distribution because of the lack of any other body cavity.
• Respire via diffusion, and no cell can be too far from the outside because of lack of cavity

Body Cavities

• One of the primary ways zoologists group animals through the presence or absence of coelom.
• A coelom is a fluid-filled cavity between the alimentary canal and the body wall.
• Three structural types of body plans related to the coelom are: Acoelomate, Pseudocoelomate, Coelomate.
• Acoelomate: No coelomic cavity exists.
• Pseudocoelomate: A coelom exists, but it is lined by mesoderm only on the body wall, not around the gut.
• Coelomate: The coelom is lined both on the inside of the body wall and around the gut by mesoderm and possess mesenteries.

Tree Germ Layers (triploblastic)

• Endoderm, mesoderm and ectoderm, encompass the precursors of all structures and organs
• Generated by gastrulation, occurring at the early stage of embryonic development.
• Ectoderm: Epidermis of skin and derivatives, epithelial lining of mouth and anus, cornea and lens of eye, nervous system, sensory receptors in epidermis, adrenal medulla, tooth enamel, and epithelium of pineal and pituitary glands.
• Mesoderm: Notochord, skeletal system, muscular system, muscular layer of stomach and intestine, excretory system, circulatory and lymphatic systems, reproductive system (except germ cells), dermis of skin, lining of body cavity, and the adrenal cortex.
• Endoderm: Epithelial lining of digestive tract, epithelial lining of respiratory system, lining of urethra, urinary bladder, and reproductive system, liver, pancreas, thymus, and thyroid and parathyroid glands.

Symmetry

• Animals show body symmetry patterns.
• Porifera phylum shows no particular symmetry(asymmetry).
• Cnidaria and Echinodermata show radial symmetry.
• A third pattern seen in most animal phyla, is bilateral symmetry.
• Flatworms (Platyhelminthes): Worm-like animals are bilaterally symmetrical; right and left sides are the mirror images of each other with distinct head and tail ends.

Flatworms (Platyhelminthes) Cell Layers

• Triploblastic: Possess three main cell layers: outer ectoderm, middle mesoderm and inner endoderm just like the other bilateral animals.
• The middle layer in these animals is made up of spongy mesoderm cells called parenchyma.

Flatworms (Platyhelminthes) - Internal Structure

• Epidermis: Cellular or syncytial; rhabdities in epidermis of most Turbellaria; epidermis a syncytial tegument in Monogenea, Trematoda (flukes), and Cestoda (tapeworms).
• Muscular system: Primarily of a sheath form and of mesodermal origin with layers of circular, longitudinal, and sometimes oblique fibers, beneath the epidermis.
• Internal Body: No internal body space other than digestive tube (acoelomate); with space between organs filled with parenchyma, a form of connective tissue or mesenchyme
• Circulatory and Respiratory Organs: These animals lack circulatory and respiratory organs, and have flat bodies that permit the flow of oxygen and nutrients to reach all parts of the body by simple diffusion
• Carbon dioxide leaves animals through the same diffusion process.
• Gut structure facilitates nutrients: It is branched profusely to facilitate adequate the diffusion.

Flatworms (Platyhelminthes) Digestion

• The system is incomplete with a single opening serving as the mouth and anus.
• A single layer of endodermal cells line the gut, to absorb and digest the food materials.
• Some species feature secretion of enzymes in the gut or pharynx to soften and break up the food.
• Undigested materials are regurgitated through the mouth because an anal opening is absent.
• Large species possess an anal opening and some with exceptionally profusely branched guts possess more than one anal opening

Flatworms (Platyhelminthes) Excretory System

• Well-developed system called protonephredia
• Protonephredia structure: A network of tubules within the animal's body tissues.
• Tubules: One end of the tubule extends into an exterior pore on the surface of the body, and the other end leads into spherical structure called flame cells.
• Flame cell function: Possess long cilia which carry out a beating function which gives it the appearance of flickering candle
• Waster removal: Excess water and body wastes enter the flame cells, are pushed by cilia into the tubules and through on excreted the in exterior surface pore

Flatworms (Platyhelminthes) Nervous System

• Marked at the head region is of the primitive type.
• Includes a pair of anterior ganglia or a nerve ring connected to 1-3 pairs of longitudinal nerve chords with transverse commissures.
• Their ganglia serve as the brain.

Flatworms (Platyhelminthes) Reproductive System

• Can reproduce asexually and sexually.
• Asexual reproduction results from the ability to regenerate tissues by transversal bipartition.
• Individual function: They attach to a substrate and induce a constriction in the body's mid region and divide.
• Results of division: Two divided body parts each regenerate.
• Most are hermaphrodite: Possess female and male reproductive organs.
• Rarely, individual sex are found, but they do process highly developed reproductive Organs.
• Self-fertilization: fusion of male and female gametes from the same animal, but in the absence of self fertilization cross fertilization can occur (fusion of sex cells from two individuals.)

Class. Flukes (Trematoda) Species. Liver Fluke (Fasciola hepatica)

• Also known as sheep liver fluke
• It is a parasitic flatworm and can infect sheep, cattle, humans, and other animals across the world.
• One of the largest of its kind, can reach an average body length of 1.1 inches and a width up to 5 inches.
• Its shape is worm-like, and it has a wider front end and sometimes wider individuals. backs
• Front end with a cone like extension, under which the oral sucker can be found.
• Acetabulum of this organism is larger than its oral sucker, but is also located near the front.
• Its body, body is covered with large spines resembling spines

Class. Flukes (Trematoda) Liver Fluke (Fasciola hepatica) Additional Characteristics

• The alimentary canal has a single mouth that leads into the blind gut; it has no anus, the mouth is located within anterior sucker on the ventral side of the fluke which leads to the pharynx, followed by a narrow oesophagus.
• The oesophagus, lined with a thin layer of epithelial cells, opens into the large intestine.
• Intestine branches, with each branch ending blindly near the posterior end of the body.
• Lacks respiratory organs: adult flukes respire anaerobically (without oxygen).
• An excretory system contains of tubules surrounding one main excretory canal and connects to a flame cell known as protonephridia.
• The nerve system consists of a pair of nerve ganglia located on either side of the oesophagus around which is a nerve ring that connects the two nerve ganglia together.
• Nerves stem and reach the posterior end of the body.
• Adult flukes are hermaphroditic, male and female reproductive organs open up into the same chamber called the genital atrium.
• The genital atrium is an ectodermal sac which opens up to the outside via a genital pore.
• The testes consist of two branched tubules, located in the middle and posterior regions. From here epithelium lining of the tubules make sperm, and sperm passes into the vas deferens then the seminal vesicle.
• The seminal vesicle projects the ejaculatory duct, opens into the genital atrium.
• The anterior testis right side has a branched tubular ovary connected to vitelline duct via a short oviduct to the junction of the ovaries,the uterus, plus yolk reservoir.
• From this junction the uterus opens into genital atrium, and an opening is surrounded by Mehlis glands where terminal end of uterus's ends
• The liver fluke reproduces sexually.

Host Types

• Definitive host: A host that harbors a parasite in the adult stage or where the parasite undergoes a sexual method of reproduction.
• Intermediate host: Harbors a parasite in the larval stages or when an cycle of asexual development takes place.
• Multiple intermediate host: Larval development is completed in two different intermediate hosts, referred to as the first and second.

Life Cycle - Fascioliasis

• Caused by Fasciola hepatica, also known as the common liver fluke or the sheep liver fluke.
• Eggs are passed in the feces of definitive hosts.
• Free-swimming miracidium hatches from egg and penetrates a suitable snail intermediate host.
• After penetration, the miracidium undergoes developmental stages (sporocysts, rediae) and develops into many cercaria.
• Cercaria exit the snail and swim until contacting aquatic vegetation and encyst and develop into metacercaria.
• Humans ingest the metacercaria on plants such as watercress.
• Metacercaria hatch, penetrate the intestinal wall, and migrate through peritoneal cavity until contacting liver.
• Once there, they penetrate liver and migrate to bile ducts where to grow to adult worms

Class. Tapeworms (Cestoda)

• Parasitic cestodal flatworm species.
• Includes Tapeworms
• Also medically important cestodes: Taenia solium, Taenia saginata, Diphyllobothrium latum, and Echinococcus granulosus.

Helminth Life Cycle

• Progresses from egg to larva to adult.
• Egg - Containing an embryo, that upon hatching, differentiates into a larval form, which then matures into the adult form which produces more eggs.
• Hosts and specific terms according to the host's parasite development cycle is: definitive host and intermediate host.
• Definitive host: The sexual cycle occurs or where the adult itself is located
• Intermediate host: The cycle of larva and asexual.
• Dead-end hosts: Larval form in the example in the human are not transmitted to to other humans.
• Humans are dead-end hosts for a Taenia solium and Echinococcus.

Class. Cestoda (Tapeworms) Characteristics

• Platyhelminthes classified by: Cestoda and Trematoda
• Tapeworms: Contain a rounded head, a scolex, and a flat body with multiple segments called proglottids.
• Attachment capabilities: The scolex has suckers, hooks or grooves.
• The body develops by new proglottids near the scolex, and oldest are distal and gravid and hold eggs that are transferred to cattle, etc.
• Lack a digestive system.
• Their bodies use protonephredia for excretion.
• Contain well developed muscles and nervous systems, much like other flatworms.

Class. Cestoda (Tapeworms) Additional Aspects

• Have a cerebral ganglion as the main nerve center.
• Have sensory innervation dependent of complexity of a region.
• Their are nerves that supply endings, cirrus and vagina with plentiful nerve endings.
• Function with chemorecion and tactoreception
• All are hermaphrodites with male and female reproductive systems.
• Have one or more testes, cirri, vas deferens, seminal vesicles and a unlobed single ovary along the uterus.
• Both systems external opening referred to as external pore with atrial cup shape.
• A great example of hermaphrodites, these worms are not completely individual and some reproduction occurs because they are in one host.
• Often coupling with cirri of individual and sharing of exterior and sperm

Class. Cestoda (Tapeworms) - Tegument

• The body is covered by a special covering called tegument: This contains an absorptive layer called microtriches.

Taenia

• Two human pathogens: T. solium and T. saginata.

Taenia solium - Disease

• T. solium causes taeniasis.
• T. solium larvae cause cysticercosis.
• Structure: Identified by Scolex, which has four suckers and hooklets.
• Is identified by gravid proglottids that has 5-10 uterine.

Taenia solium and Taenia saginata - Infection & Features

• Contracted by humans pork(T. solium) or beef (T. saginata) containing cysticerci, and adults lay eggs in system.
• Both are transmitted by contact or fecal
• Cattle are infected with ingesting proglottids, which are passed by stool.

Beef Tapeworm (Taenia saginata)

• Causes taeniasis and doesn't have cysticerosis.
• Morphology includes: scolex with four suckers, in contrast to those in other organisms
• Proglottids have 15 to 25 primary uterine segments and lack hooklets, unlike T soliums.
• Life cycle: Humans contract infection by eating raw beef with larvae
• Larva development: attach to wall in small intestine and takes 3 months to full growth
• Reproduction:Gravids are detached and eggs eat be cattle
• Cysticercosis: is not caused by Sagginata, only by the undercooked beef.

Echinococcus granulosus and Larvae

• Tapeworms that cause disease and larvae cause cysts
• Properties: comprised of a scolex with proglottids, one of the smallest cestodes'

Echinococcus granulosus: Life Cycle

• Worms live in dogs intestines and release eggs ingested by sheep human and
• These worms are known for a cycle which happens in sheep intestines and migrate to liver
• Adults have tapeworm s contained on the intestines, the tapeform can form hyatiid cysts

Fish Tapeworm (Diphyllobothrium Latum)

• Worms that have sucking grooves, found from consumption of fish, and have longer lifespans
• Features 3000 4000 segment that makes a big tapeworm.
• Also is identified by the rosette parts
• D latum eggs are one million produced and come from stool

Diphyllobothrium latum: Life Cycle

• On reaching fresh water release a ciliated worm that are parasites that can get water.
• It can ingested when they find a genera.
• Most patients are asymptomatic, but some can develop worms.