BIO 102 (General Biology II)
Courseware
Mr. B.M. Macaulay’s Aspect
RECAP (1)
Kingdom: Animalia
Sub-Kingdom: Invertebrata
Phyla:
1. Porifera
2. Coelentrata
3. Platyhelminthes
4. Nematoda
5. Annelida
6. Arthropoda
7. Mollusca
8. Echinodermata
RECAP (2)
Kingdom: Animalia
Sub-Kingdom: Vertebrata
Phyla:
* Protochordata (Usually an intermediate
between Invertebrata and Vertebrata)
1. Pisces
2. Amphibians
3. Reptiles
4. Mammals
5. Aves
Description and Characteristics of the Phyla:
• Platyhelminthes
• Nematoda
• Annelida
Phylum Platyhelminthes
The Flatworms
PLATYHELMINTHES
General Description:
From the Greek origin, ‘platy’ means flat and
‘helminthes’ means worms, hence, flat worms.
Generally, classes of flatworms either live freely
in rivers, lakes, seas (for example, Planaria) or as
parasitic organisms in the body of animals (for
example, flukes and tapeworm).
Characteristics of Platyhelminthes (1)
• They are generally dorso-ventrally flattened.
• They are bilaterally symmetrical.
• Having three body layers, i.e. triploblastic, with
organs and organelles.
• Body contains no internal cavity, i.e. Aceolomate.
The space between the body wall and gut are
filled with parenchyma composed of loose cell
masses.
• Possesses a blind gut (i.e. it has a mouth but no
anus)but well branched to transport food all over
the body.
THE EVOLUTION OF BODY CAVITIES
Characteristics of Platyhelminthes (2)
• Nervous system is ladder-like. It is in the form
of a brain and two main longitudinal nerve
cords connected at intervals by transverse
commissures.
• The reproductive system is well organized.
Most of them are hermaphrodites.
(Hermaphroditism is a phenomenon where
both male and female sex organs are situated
within the same body).
• They feed mostly on animals and other
smaller life forms.
Characteristics of Platyhelminthes (3)
• Flatworms generally possess nephridial tubules
called protonephridia, usually distributed
throughout the body – Such structures consist of
an external opening and a tubule that branches
internally, terminating in a number of blind, bulbshaped structures called flame bulbs, which bear
tufts of cilia. They function as excretory and
osmoregulatory organs.
The Structure of Protonephridium
Characteristics of Platyhelminthes (4)
• The Body is devoid of true metameric
segmentation.
• Circulatory and respiratory systems are absent.
• Many flat worms undergo regeneration of certain
parts of their body.
PLAYHELMINTHES (2)
There are three broad classes in the phylum,
platyhelminthes. They are:
• Class: Turbellaria
• Class: Trematoda
• Class: Cestoda
TURBELLARIA (1)
• They are mostly free-living and primarily
carnivorous.
• They are characterized by a soft epidermis that is
ciliated on the ventral surface. The movement of
the cilia propels the smaller forms.
• They possess a pair of fused cerebral ganglia
which forms a rudimentary brain, with two
interconnected parallel nerve cord running
length of body.
• Ocelli (simple eyes) are present in some.
TURBELLARIA (2)
• Turbellarians are generally divided into five groups
based on the different forms of their digestive cavity.
They are:
• Acoels: have no digestive cavity.
• Allocoels: Sack-like or branched digestive cavity.
• Rhabdocoels: Straight and unbranched digestive
cavity.
• Triclads: Possess three-branched gut. The
commonest example of turbellaria, Planaria, is a
triclad.
• Polyclads: gut sub-divided into numerous branches.
Planaria (Dugesia tigrina)
TREMATODA (1)
• These are parasitic flatworms and are often
referred to as Flukes. For example, Blood fluke,
Liver fluke, etc.
• They have oral suckers, sometimes supplemented
by hooks, with which they attach to their
vertebrate hosts.
• Trematodes have retained the same body form
and digestive cavity as the turbellarians.
However, practically the entire interior is
occupied by the reproductive system; the
organism is capable of producing huge numbers
of offspring.
TREMATODA (2)
• Trematodes can be divided into two broad groups
based on the number of host – Monogenea
(trematodes parasitising a single host) and
Digenea (trematodes parasitising two or more
hosts).
• Monogenetic flukes spend their entire life cycle as
parasites on a single host, often on the gills and
skin of fish; they include no human parasites.
They hold on to the fish by the use of hooks and
attachment organs at the posterior end. E.g.
Gyrodactylus sp. (Gill fluke).
TREMATODA (3)
• Digenetic flukes on the other hand, have complex
life cycles involving two or more hosts. The larval
worms parasitise one or more small animals
(typically snails and sometimes fishes) and the
adult worms further parasitises vertebrate hosts.
E.g. Schistosoma haematobium (Blood fluke) and
Fasciola hepatica (Liver fluke).
• In the case of S. haematobium, the larva initially
parasitises a snail (Bulinus sp.) and when the
adult emerges, it enters a vertebrate host (E.g.
Man) to complete its life cycle causing the
disease, Schistosomiasis.
Schistosoma haematobium (Blood fluke)
Fasciola hepatica (Liver fluke)
Gyrodactylus sp. (Gill fluke)
CESTODA (1)
• Cestodes are parasitic flatforms also known as
tapeworms as a result of their tape-like body
sturcture.
• The body of Cestodes has lost the typical turbellarian
form.
• A typical cestode body (known as strobila) consists of
series of linearly arranged reproductive segments
called proglottids which may be immature, mature or
gravid.
• They are mostly hermaphrodites.
• There is no mouth or digestive system; food is
absorbed through the body cuticle.
CESTODA (2)
• Adults live in the digestive tract of vertebrates,
and larval forms encyst in the flesh of various
vertebrates and invertebrates.
• The tapeworm’s head called scolex, bears a
crown-like rostellum and four circle of
hooks/suckers which are attachment organs.
• The body of an adult tapeworm is virtually a
reproductive factory; gravid proglottids (i.e. Filled
with fertilised eggs) are released with the faeces
of the definitive host to resume development in
the body of intermediate host.
The anterior section of the Tapeworm
(Taenia sp.)
Tapeworm (Taenia sp.)
Assignment
S/N
Taenia saginata
1.
Nature of the scolex
2.
Type of intermediate host
Taenia solium
Phylum Nematoda
The Roundworms
NEMATODA (1)
General Description:
Nematodes derived their name from the Greek
word, ‘Nema’, meaning, "thread" and ‘tode’
meaning, "like“, i.e. thread-like worms. This is the
second largest phylum in the animal kingdom
next to the Arthropods. Members are
approximately 80,000 species, of which 15,000
are parasitic. Examples include the common
roundworm of man (Ascaris lumbricoides),
hookworm, Pinworm, Guinea worm, whipworm,
etc.
CHARACTERISTICS OF NEMATODA (1)
• They are vermiform (worm-like), usually cylindrical
in shape
• Triploblastic and non-segmented, with bilateral
symmetry.
• Size varies from microscopic to pencil-sized.
• They are covered with thick cuticle, having no
external cilia.
• Body cavity is pseudocoelom, and the fluid-filled
space functions as hydrostatic skeleton.
• They have a complete digestive system (i.e. true
gut) but circulatory and respiratory organs are still
lacking.
CHARACTERISTICS OF NEMATODA (2)
• Excretory system consists of one or more large
gland cells opening to an excretory pore or canal
system
• Circular nerve ring with dorsal and ventral nerve
cords; sense organs include phasmid and ciliated
pits.
• Sexes usually separate (dioecious)
• Male is smaller than the female and has a
characteristic curved or bent tail.
• The phylum contains both free-living and parasitic
members.
Nematode (Ascaris Sp.) – Male and female species
NEMATODA (2)
The phylum Nematoda is divided into two classes:
• Enoplea
• Chromadorea
Characteristics of class Enoplea
1. Amphids pocket like, not spiral, usually postlabial.
2. Cuticle smooth or finely striated.
3. Phasmids present or absent.
NB: Amphids are slits or opens above or below the
lip.
Phasmids are slits or openings at the posterior
region.
Characteristics of class Chromadorea
1. Pore-like or slit-like amphid apertures vary from
labial pores or slits to post-labial elaborate coils
and spirals.
2. Cuticle usually annulated, sometimes
ornamented with projections and setae.
3. Phasmids present or absent, generally posterior.
Ascaris lumbricoides (Ascariasis)
Ascaris life cycle
Ancylostoma duodenale (Hookworm)
Dracunculus medinensis (Guinea worm)
Dracunculiasis
Trichuris trichiura (Whipworm)
Enterobius vermicularis (Pin worm)
Wuchereria bancrofti (Microfilarial worm)
Elephantiasis
Onchocerca volvulus (Microfilarial worm)
Assignment
I have supplied you with enough examples of
parasitic nematodes; however, to complete your
knowledge of nematodes, you will have to supply
me with five (5) common examples of free-living
(non-parasitic) nematodes before the next class.
Phylum Annelida
Segmented worms
ANNELIDA (1)
General Description
• The Annelida (segmented worms) are a medium
sized phylum of more than 9,000 species of
worms.
Most
species
prefer
aquatic
environments, but there are also a number of
well know terrestrial species. Only a few species
of annelids are commonly known to human
beings, these include the Earthworms,
Ragworms, Medicinal leeches, etc.
CHARACTERISTICS OF ANNELIDA (1)
• Bilaterally symmetrical and vermiform, i.e. wormlike.
• They are triploblastic with 3 body layers.
• Body cavity is a true coelom, i.e. Eucoelomates.
• They are metamerically segmented, i.e. divided
by internal septa.
• Body possesses a true gut with mouth and anus.
• Body possesses 3 separate sections, a
prostomium, a trunk and a pygidium.
CHARACTERISTICS OF ANNELIDA (2)
• Has a true closed circulatory system.
• Has no true respiratory organs.
• Excretion is carried out by the nephridium in
many annelids.
• Reproduction normally sexual or hermaphroditic.
• Feed a wide range of material.
• Live in most environments.
• Has a nervous system with an anterior nerve ring,
ganglia and a ventral nerve chord.
THE STRUCTURE OF NEPHRIDIUM
ANNELIDA (2)
The phylum Annelida is currently under review
and there are lingering debates on it. However,
the phylum is traditionally divided into 3 broad
classes:
• Class Polychaeta
• Class Oligochaeta
• Class Hirudinea
CLASS POLYCHAETA
• ‘Poly’ – Many; ‘Chaeta’ – Hair-like structure.
• They are predominantly marine animals and are
divided ecologically into the Errantia and the
Sedentaria depending on whether or not they live
sedentary lives in holes or live more active lives.
• The Errantia have well developed heads and complex
parapodia (paddles) that they can use for swimming.
• Polychaetae are hermaphrodites; A reproductive
segment is often formed which dies immediately
after the release of gametes.
• Examples: ragworm, lugworm and bloodworm.
Ragworm
CLASS OLIGOCHAETA
• ‘Oligo’ – Few; Chaete – Hair-like structure.
• Oligochaetae live in marine, freshwater and
terrestrial habitats.
• Generally, they have a more rounded cross-section
and a less distinct head.
• They are usually hermaphrodites but seldomly
undergoes sexual reproduction.
• They possess a clitellum as adults, an organ which
looks like a bandage of skin wrapped around the
animal. This clitellum, has an important function in
sexual reproduction.
• Examples: Earthworm, Aelosomata worms (e.g.
Aelosoma hemprichi), Branchiobdella worms
(Branchiobdella astaci).
Earthworm
CLASS HIRUDINEA
• Hirundinea occur in Fresh water, marine and
terrestrial environments.
• They are commonly known as leeches.
• Leaches are well known for their blood sucking
habits and their head to tail looping mode of
locomotion.
• They have two suckers – In most cases, one is
located at the anterior (head) end of the body
composed of segments 1-4 and the other at the
posterior (tail) end composed of segments 25-33.
• Medicinal leeches (Hirudo medicinalis) has been
useful in treating blood circulatory illnesses.
Leeches