Animal Biology Basics

Animal Biology Basics

• ABCS 101 is the course code for Introductory Animal Biology, which is worth 3 credits
• Dr. Daniel Oduro can be reached via email at [email protected]
• Office hours are Monday to Friday, 8:30am - 2:00pm, at office number 84

Learning Outcomes

• Explain the basis for animal classification
• Describe/differentiate the external and internal features of flatworms, roundworms, and molluscs
• Discuss features indicating advancement in animal groups
• Describe flatworm and roundworm lifecycles related to human health
• List control measures for parasitic flatworms and roundworms impacting humans

Taxonomy

• Taxonomy is derived from the Ancient Greek taxis (arrangement) and nomia (method)
• Taxonomy is the science of naming and classifying species
• Organisms are organized using a hierarchical structure

Binomial Nomenclature

• Carolus Linnaeus developed the two-name system or binomial nomenclature in 1758
• Homo sapiens and Schistosoma haematobium are examples of binomial nomenclature

Animal Classification: Physical Characteristics

• Animal classification relies on physical traits, including the number of germ layers
• Diploblastic organisms have two germ layers
• Triploblastic organisms have three germ layers
• Type of body cavity is indicated by the germ layers
• Acoelomates lack a body cavity and are completely filled (e.g., sponges, jellies, flatworms)
• Pseudocoelomates feature a body cavity not surrounded by muscles/tissues (e.g., roundworms)
• Coelomates possess a true body cavity surrounded by muscle/other tissues (e.g., segmented worms, arthropods, mollusks, chordates, echinoderms)

Nature of Digestive System

• Animals are classified by the nature of their digestive system
• Some have one opening that is both mouth and anus
• Other animals have two openings

Body Segmentation

• Body segmentation is a physical characteristic used to classify animals
• Segmentation can be viewed as anterior, posterior, dorsal and ventral
• Body segments can be Head, Thorax and Abdomen

Body Symmetry

• Body symmetry can be radial or bilateral

Skeleton

• Type of skeleton (exoskeleton or endoskeleton) and nature of the skeleton are physical characteristics used to classify animals

Appendages

• Number and arrangement of appendages are physical characteristics used to classify animals

Animal Systematics

• Classification systems should reflect the evolutionary relationships of organisms Taxonomists support this viewpoint
• A taxonomic group should include all descendants of a particular ancestor and no other organisms

Significance of Classification

• Classification provides specific organism names
• It identifies different species
• Classification establishes relationships among organisms to understand their evolution
• Aids memory, grouping animals by shared characteristics
• Enhances communication using globally recognized scientific names

Flatworms

• Flatworms belong to the Kingdom Animalia and Phylum Platyhelminthes
• Examples include planaria, flukes, and tapeworms
• The name Platyhelminthes comes from "platus" (flat) and "helmins" (worm)
• About 25,000 known flatworm species are parasitic

Platyhelminthes Characteristics

• Flatworms have dorso-ventrally flattened bodies
• Sizes range from a millimeter to many meters in length
• Flatworms exhibit bilateral symmetry
• Flatworms are triploblastic

Platyhelminthes: Body Cavity and Organs

• No internal body space; they are acoelomates
• Organs are embedded in parenchyma (specialized connective tissue)
• Flattened shapes facilitate effective gaseous exchange
• Flattened shapes help with nutrient distribution by simple diffusion

Digestive System

• The digestive tract has a single opening, a mouth/anus
• Food is taken through the mouth
• Undigested waste is ejected through the mouth
• Some flatworms possess a digestive system with a branching intestine so nutrients are absorbed

Phylum Platyhelminthes Classes

• Class Turbellaria includes free-living flatworms like Planaria
• Class Trematoda includes parasitic flukes such as Schistosomes
• Class Cestoda includes parasitic tapeworms such as Taenia saginata

Class Turbellaria

• "Planaria" is a common name and a genus within the family Planariidae
• Turbellaria's scientific classification includes:
  • Kingdom: Animalia
  • Phylum: Platyhelminthes
  • Class: Turbellaria
  • Order: Seriata
  • Suborder: Tricladida
  • Family: Planariidae

Turbellaria Characteristics

• Mostly free-living flatworms with ciliated epidermis
• Habitats include marine, fresh-water, or terrestrial (moist soil)
• Generally creeping worms, 5mm to 50cm
• Use muscular and ciliary movement for locomotion
• Voracious carnivores, feed on small animals, usually worms and crustaceans

Turbellaria: Internal Structure

• Triploblastic
• Gut (endoderm)
• Skin and muscles (ectoderm)
• Mesoderm makes up the rest

Planarian Anatomy

• Two ocelli (eyespots) can be found on the triangular head .
  • They are pigmented areas sensitive to light
• Two auricles (earlike projections) are sensitive to touch and chemicals

Turbellaria: Feeding and Digestion

• They detect food by chemoreceptors
• They wrap themselves around prey
• Small prey are taken into the gut and surrounded with digestive enzymes
• Fats are directly broken down (extracellular digestion)
• Proteins and carbohydrates are absorbed and digested by the cells lining the gut (intracellular digestion).

Class Turbellaria: Excretion

• Flame cells remove unwanted liquids through ducts to excretory pores
• Waste is released via excretory pores on the dorsal side
• No respiratory organs
• Gas exchange occurs through the body surface

Turbellaria: Reproduction

• Some species of Planaria are exclusively asexual
• Some reproduce both sexually and asexually
• During asexual reproduction, the planarian detaches its tail end
• Each half regrows lost parts by regeneration, requiring pluripotent cells or neoblasts
  • Regeneration can take a few weeks
  • It can result in two heads or tails if not fully detached

Turbellaria: Sexual Reproduction

• Turbellarians are monoecious (hermaphroditic)
• They practice cross-fertilization, giving and receiving sperm
• Fertilized eggs and yolk cells are enclosed in a cocoon after copulation
• Embryos emerge as juveniles

Class Trematoda (Flukes) Objectives

• The goal of the lecture is to describe the features of the phylum
• You should know:
  • Define flukes by their internal and external features
  • List some examples of the two main groups, blood and tissue flukes,
  • Describe life cycles of selected health-related flukes
  • List the control measures for selected flukes of importance to humans

Classification of Trematodes

• Major groups:
  • Blood flukes
    • Schistosoma mansoni
    • S. japonicum
    • S. haematobium
  • Tissue flukes
    • Intestinal
      • Fasciolopsis hepatica, F. buski
    • Liver
      • Clonorchis sinensis, Opistorchis
    • Lung
      • Paragonimus westermani
• Flukes are also classified by the environment, e.g., pond flukes

Trematodes (Flukes) Characteristics

• Estimated 18,000-24,000 species
• Flattened, leaf-like bodies (few mm to 8 cm long)
• Unsegmented
• Nearly all are parasitic, internal or external

Trematodes: Suckers and Tegument

• They have one/two suckers which serve as organs for feeding or attachment in most species
• The outer tegument is armed with tiny spines for attachment (e.g. Fasciola spp.)
• These inhabit digestive, respiratory, or circulatory systems, and urinary or reproductive tracts

Trematodes: Alimentary Canal

• They have a well-developed alimentary canal, but incomplete, and no anus
• They do not have a coelom or body cavity
• They lack blood vessels and have a simple ladder nervous system
• Flukes are oviparous and lay operculated eggs, except schistosome eggs
  • Also, hermaphroditic, except blood flukes

Generalized Life Cycle of Flukes

• Complex life cycles that differ depending on the species
• The definitive host is a man
• The intermediate hosts are freshwater snails, fish, or crabs
• Some trematodes have 2 or 3 intermediate hosts before reaching the definitive host
• Hermaphroditic ones are both male and female
• Fasciola hepatica (sheep liver fluke) and F. gigantica are examples. Metacercariae are infective for humans
• Bisexual ones have separate sexes
• Examples include Schistosoma japonicum, S. mansoni, and S. haematobium
• Cercariae are infective for humans

Fasciola hepatica

• In humans, maturation from metacercariae into adult flukes happens in approximately 3-4 months

Fasciola hepatica Symptoms

• This sheep liver fluke may be asymptomatic
• It can be coughing and vomiting
• It may result in generalized abdominal rigidity, headache and sweating
• It may lead to irregular fever, diarrhea and anaemia

Blood Flukes (Schistosomes): Traits summary

• Only bisexual flukes infect humans
• Body structure same as hermaphroditic flukes
• Both sexes live in lumen of blood vessels (close association)
• Male worm broader & heavier with large ventral groove, i.e. gynaecophoral canal
• Female lies within a tegumental fold or gynaecophoral canal

Schistosomiasis

• Parasitic disease caused by blood trematodes of the genus Schistosoma
• Main human-infecting species:
  • S. haematobium: causes urinary schistosomiasis, prevalent in Africa
  • S. mansoni: causes intestinal schistosomiasis, found in Africa and America
  • S. japonicum: causes intestinal schistosomiasis, found in Far East

Schistosomiasis: Symptoms

• S. mansoni and S. japonicum cause bloody diarrhea with abdominal pain
• Schistosoma eggs cause ulceration and abscesses in the intestinal wall
• S. haematobium
• Eggs cause bladder wall ulceration, bloody urine, and pain during urination
• Eggs in capillary bed impede circulation and cause cirrhosis of the liver
• The eggs in the liver can causes fibrosis
• Ultimately an enlarged liver and spleen can occur, known as hepatosplenomegaly
• Control of Schistosomiasis includes:
  • Praziquantel
  • Avoiding contaminated water
  • Filtering drinking water
  • Sanitary disposal of water

Schistosomiasis: Treatment

• Praziquantel is effective against all species
• Contaminated water should be avoided
• Drinking water should be filtered
• Control measures include sanitary disposal of sewage
• No vaccine is available

Schistosomiasis: Taxonomic Classification

• Kingdom: Animalia
• Phylum: Platyhelminthes
• Class: Trematoda
• Subclass: Digenea
• Order: Strigeidida
• Family: Schistosomatidae
• Genus: Schistosoma
• Species: haematobium

Platyhelminthes, Class Cestoidea (Tapeworms): General Characteristics

• Multicellular animals are flat and bilaterally symmetric
• They are dorsoventrally flattened and solid without a body cavity
• Most tapeworms are hermaphroditic
• Overall size varies from 1 mm to 20 meters
• Tapeworms are endoparasites with sexually mature worms in the alimentary tract and associated ducts
• All vertebrate species can be parasitized by at least one species of tapeworm in the digestive tract

Types of tapeworms

• Taenia solium ('pork' tapeworm)
• Taenia saginata (Beef Tapeworm)
• Diphyllobothrium spp. (fish tapeworm)
• Hymenolepis nana (The Dwarf Tapeworm)
• Hymenolepsis diminuta (The Rat Tapeworm)
• Echinococcus granulosis- The Hydatid Tapeworm (Causes Echinococcosis)
• Dipylidium caninum - The Double-Pored Tapeworm

Cestodes (Tapeworms): Anatomy

• Flat and ribbon-like
• It consists of an interior attachment or scolex, the main body called the strobila consisting of a chain of segments or proglottids
• The Scolex or head is characterized by sucking disks or lateral grooves for attachment
• Rostellum
  • Small button-like structure on the scolex of “armed” tapeworms from which the hooks protrude
  • It may be retractable
• Tapeworms have the complete absence of an alimentary canal
  • no mouth
  • no gut
  • no anus
• All nutrients are acquired through a specialized tegument
• The flat & large surface area helps with nutrient absorption
• They lack sense organs and covering the entire surface of the tegument is a layer of carbohydrate is the glycocalyx
• It protects from the parasite host digestion as well as enhances nutrient absorption and maintains the parasite's surface membrane
• Excretion -Flame cells (protonephridia), located in the proglottids are used

Cestodes: Reproduction

• Hermaphroditic; Each proglottid contains a set of reproductive organs of both sexes
  • either through self-fertilization, or cross-fertilization (to permit hybridization) Asexual
  • by breaking off proglottid segments at the end of the trunk

Cestodes – Life cycle of Taenia spp.

• Humans consuming undercooked food, especially pork, or water contaminated with tapeworm eggs,

Dipylidium caninum

• The dog tapeworm mainly infects dogs and cats
• Is occasionally found in humans when infected flea is ingested

Cestodes (tapeworms): Symptoms of taeniasis

• Symptoms may be absent or mild
• abdominal pain, headache
• increased appetite (Tesfa-Yohannes, 1990)
• epilepsy when the brain is infected with cysticerci (develops in skin and brain)

Taxonomic Classification for Taenia

• The kingdom is animalia
• The Phylum is platyhelminthes
• The class is Cestoidea/Cestoda
• The order is Cyclophyllidea
• The family is Taeniidae
• The Genus is Taenia
• The Species is Solium