BIO 102 Courseware-1
Transcript BIO 102 Courseware-1
BIO 102 (General Biology II)
Mr. B.M. Macaulay’s Aspect
2. Coelentrata (Cnidaria and Ctenophora)
* Protochordata (Usually an intermediate
between Invertebrata and Vertebrata)
Description and Characteristics of the Phyla:
General Description: PLATYHELMINTHES
• 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)
1. They are generally dorso-ventrally flattened.
2. They are bilaterally symmetrical.
3. Have three body layers, i.e. triploblastic, with
organs and organelles.
4. Body contains no internal cavity, i.e.
Acoelomate. The space between the body wall
and gut are filled with parenchyma composed of
loose cell masses.
5. 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)
6. Nervous system is ladder-like. It is in the form
of a brain and two main longitudinal nerve
cords connected at intervals by transverse
7. 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).
8. They feed mostly on animals and other
smaller life forms.
Planaria and the flame cell
Characteristics of Platyhelminthes (3)
9. Flatworms generally possess nephridial tubules
called protonephridia, usually distributed
throughout the body.
• Protonephridia consist of an external opening
and a tubule that branches internally,
terminating in a number of blind, bulb-shaped
structures called flame bulbs, which bear tufts of
• Protonephridia function as excretory and osmoregulatory organs.
The Structure of Protonephridium
Characteristics of Platyhelminthes (4)
10. The Body is devoid of true metameric
11. Circulatory and respiratory systems are absent.
12. Many flat worms undergo regeneration of
certain parts of their body.
There are three broad classes in the phylum,
platyhelminthes. They are:
• Class: Turbellaria
• Class: Trematoda
• Class: Cestoda
1. They are mostly free-living and primarily
2. They are characterized by a soft epidermis that is
ciliated on the ventral surface. The movement of
the cilia propels the smaller forms.
3. They possess a pair of fused cerebral ganglia
which forms a rudimentary brain, with two
interconnected parallel nerve cord running
length of body.
4. Ocelli (simple eyes) are present in some.
Turbellarians are generally divided into five groups
based on the different forms of their digestive cavity.
Acoels: have no digestive cavity.
Allocoels: Sack-like or branched digestive cavity.
Rhabdocoels: Straight and unbranched digestive
Triclads: Possess three-branched gut. The
commonest example of turbellaria, Planaria, is a
Polyclads: gut sub-divided into numerous branches.
Planaria (Dugesia tigrina)
1. These are parasitic flatworms and are often
referred to as Flukes. For example, Blood fluke,
Liver fluke, etc.
2. They have oral suckers, sometimes
supplemented by hooks, with which they attach
to their vertebrate hosts.
3. Trematodes have retained the same body form
and digestive cavity as the turbellarians.
4. The entire interior of trematodes is occupied by
the reproductive system; the organism is capable
of producing huge numbers of offspring.
5. The are majorly hermaphrodites. For some such
as S. haematobium, the female (larger) houses
the male (smaller) in a gynaecophoric canal.
Trematodes can be divided into two broad groups
based on the number of host:
Monogenea: trematodes parasitising a single host
Digenea: trematodes parasitising two or more
• 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.
• These flukes hold on to the fish by the use of
hooks and attachment organs at the posterior
end. E.g. Gyrodactylus sp. (Gill fluke).
• 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
Schistosoma haematobium (Blood fluke)
Female houses male in a gynaecophoric canal
Fasciola hepatica (Liver fluke)
Gyrodactylus sp. (Gill fluke)
1. Cestodes are parasitic flatforms also known as
tapeworms as a result of their tape-like body
2. The body of Cestodes has lost the typical turbellarian
3. A typical cestode body (known as strobila) consists of
series of linearly arranged reproductive segments
called proglottids which may be immature, mature or
4. They are mostly hermaphrodites.
5. There is no mouth or digestive system; food is
absorbed through the body cuticle.
6. Adults live in the digestive tract of vertebrates,
and larval forms encyst in the flesh of various
vertebrates and invertebrates.
7. The tapeworm’s head called scolex, bears a
crown-like rostellum and four circle of
hooks/suckers which are attachment organs.
8. 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 an intermediate host.
The Scolex of the Tapeworm (Taenia
Tapeworm (Taenia sp.)
T. Saginata vs T. solium
Nature of the
Has a rostellum;
2 rows of spiny
hook; 4 suckers. hooks (22-32); 4
• 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
• Examples include the common roundworm of
man (Ascaris lumbricoides), hookworm,
Pinworm, Guinea worm, whipworm, etc.
CHARACTERISTICS OF NEMATODA (1)
1. They are vermiform (worm-like), usually
cylindrical in shape.
2. Triploblastic and non-segmented, with bilateral
3. Size varies from microscopic to pencil-sized.
4. They are covered with thick cuticle, having no
5. Body cavity is pseudocoelomate, and the fluidfilled space functions as hydrostatic skeleton.
6. They have a complete digestive system (i.e. true
gut) but circulatory and respiratory organs are
CHARACTERISTICS OF NEMATODA (2)
7. Excretory system consists of one or more large
gland cells opening to an excretory pore or canal
8. Circular nerve ring with dorsal and ventral nerve
cords; sense organs include phasmid and ciliated
9. Sexes are usually separate (dioecious)
10. Male is smaller than the female and has a
characteristic curved or bent tail.
11. The phylum contains both free-living and parasitic
Nematode (Ascaris Sp.) – Male and female species
The phylum Nematoda is divided into two classes:
Characteristics of class Enoplea
1. Amphids pocket-like, not spiral, usually post-labial.
2. Cuticle smooth or finely striated.
3. Phasmids present or absent.
NB: Amphids are slits or openings above or below the
Phasmids are slits or openings at the posterior
Examples include: Trichuris trichiura, Mermis
nigrescens (Grasshopper nematode parasite), etc.
Characteristics of class Chromadorea
1. Pore-like or slit-like amphid apertures vary from
labial pores or slits to post-labial elaborate coils
2. Cuticle usually annulated, sometimes
ornamented with projections and setae.
3. Phasmids present or absent, generally posterior.
Examples include: Hookworm, pinworm,
whipworm, Common round worm of man, etc.
Ascaris lumbricoides (Ascariasis)
Ascaris life cycle
Ancylostoma duodenale (Hookworm)
Hook worm disease
Dracunculus medinensis (Guinea worm)
Trichuris trichiura (Whipworm)
Trichuris life cycle
Mermis nigrescens (Grasshopper nematode)
Grasshopper nematode disease
Enterobius vermicularis (Pin worm)
Enterobius Life cycle
Wuchereria bancrofti (Microfilarial worm)
Onchocerca volvulus (Microfilarial worm)
Blackfly (Simulium damnosum)
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.
• The Annelida (segmented worms) are a medium
sized phylum of more than 9,000 species of
• Most species prefer aquatic environments, but
there are also a number of well known terrestrial
• Only a few species of annelids are commonly
known to human beings. These include the
Earthworms, Ragworms, Medicinal leeches, etc.
CHARACTERISTICS OF ANNELIDA (1)
1. Bilaterally symmetrical and vermiform, i.e.
2. They are triploblastic with 3 body layers.
3. Body cavity is a true coelom, i.e. Eucoelomates.
4. They are metamerically segmented, i.e. divided
by internal septa.
5. Body possesses a true gut with mouth and anus.
6.Body possesses 3 separate sections, a
prostomium, a trunk and a pygidium.
CHARACTERISTICS OF ANNELIDA (2)
7. Has a true closed circulatory system.
8. Has no true respiratory organs.
9. Excretion is carried out by the nephridium in
10.Reproduction normally sexual or
11. Feed a wide range of materials.
12. Live in most environments, i.e. Ubiquitous.
13. Has a nervous system with an anterior nerve
ring, ganglia and a ventral nerve chord.
THE STRUCTURE OF NEPHRIDIUM
The phylum Annelida is currently under review
and there are lingering debates on it. However,
the phylum is traditionally divided into 3 broad
• Class Polychaeta
• Class Oligochaeta
• Class Hirudinea
• ‘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.
• ‘Oligo’ – Few; Chaete – Hair-like structure.
• Oligochaetae live in marine, freshwater and
• Generally, they have a more rounded cross-section
and a less distinct head.
• They are usually hermaphrodites but seldomly
undergo sexual reproduction.
• As adults, they possess a clitellum – an organ which
looks like a bandage of skin wrapped around the
anterior region of the animal. This clitellum has an
important function in sexual reproduction.
• Examples: Earthworm, Aelosomata worms (e.g.
Aelosoma hemprichi), Branchiobdella worms
Earthworm (Lumbricus terrestris)
1. Hirudinea occur in Fresh water, marine and
2. They are commonly known as leeches.
3. Leeches are well known for their blood sucking
habits and their head-to-tail looping mode of
4. 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.
5. Medicinal leeches (Hirudo medicinalis) have been
useful in treating blood circulatory illnesses.