Transcript BIO 102 PPT_4 - Futabase.com

BIO 102: GENERAL BIOLOGY II
UNIT: 4
INVERTEBRATES
COURSE LECTURER: AFOLABI, O.J.
PUBLIC HEALTH & PARASITOLOGY UNIT,
DEPARTMENT OF BIOLOGY,
FEDERAL UNIVERSITY OF TECHNOLOGY
AKURE,NIGERIA.
TIME: 8.00A.M-10.00A.M ON FRIDAYS
VENUES: ETF LECTURE THEATRE
What is invertebrate?
• Invertebrates are group of
animals(and animal like organisms)
that do not have a backbone.
• They are divided into four groups
based on their cellular composition
and organisation
Groups of Invertebrates
• There are four groups of invertebrates, these are:
• Protozoa
• Mesozoa
• Parazoa
• Metazoa
Protozoa
• They are unicellular i.e. made up of one cell
• They are acellular or non-cellular i.e. not divided
into cells
• Their vital functions are carried out by organelles
• They are animal-like
• They are simple and primitive
• They occur in watery or moist environments
• They are found in the sea, freshwater, soil, body fluids
e.t.c
• They are cosmopolitan (distributed worldwide)
• They are at the protoplasmic level of organisation i.e.
specialised portions of the cytoplasm called organelles
carry out particular functions within their single cell
• Their organelles include cilia, flagella, pseudopodia,
contractile vacuoles e.t.c.
• The protozoa are distinctly animal in their feeding,
obtaining their nutrition from ready made sources
including other animals.
• Because of their size, they can only prey on others
smaller organisms than themselves. There are those
that live on bacteria, others feed on diatoms and
small protozoans.
Divisions of Protozoa
• Protozoa are broadly divided into four phyla based
mainly on their organelles and modes of
locomotion
1.Phylum: Rhizopoda
2. Phylum: Apicomplexa
3. Phylum : Sarcomastigophora
4. Phylum: Ciliophora
Phylum : Rhizopoda
• Rhizopoda or Sarcodina has a naked undifferentiated surface
• They lack chromatophores (pigment containing cells)
• They possess a single nucleus
• They do not have rigid shape due to the absence of a rigid
pellicle
• Asexual reproduction is by binary fission
• They possess pseudopodia (false feet) as locomotory
organelles and can be withdrawn into the body
• E.g. Arcella, Amoeba, Entamoeba e.t.c
Amoeba proteus
Phylum: Apicomplexa
• Also known as sporozoa posses apical complex which
specialize in producing spores to ensure infection to
their host.
• They lack external locomotory organelles.
• They are characterised by their reproductive process
rather than by their locomotory organelles as in other
two groups.
• They are parasitic and absorb food in solution from
their host.
• They are uninucleate
• They form many spores during asexual and sexual
reproduction. This is their most distinctive
characteristics
• They are economically important in that they cause
diseases in humans and in organisms useful to
humans
• E.g Plasmodium causes malaria, Eimeria causes
coccidiosis, Toxoplasma causes toxoplasmosis e.t.c
Plasmodium trophozoites in red blood cells
Phylum: Sarcomastigophora
• Some members possess chromatophores while
others do not.
• Chromatophores are cup-shaped masses of
protoplasm of a green, yellow or brownish colour,
due to the presence of the pigment:
• Chlorophyll, xanthophylls, carotenes e.t.c
• The cell is covered by a pellicle and it is semi-rigid
• They usually have a definite shape
• Adults use flagella as a means of locomotion
• They possess a single nucleus
• Asexual reproduction is by binary fission
• Members are divided into two classes
Classes of sarcomastigophora
• 1. Phytomastigophorea
• These are flagellates that are plant-like in that they
possess chlorophyll
• Most of the members are holophytic
(photosynthentic)
• E.g Volvox, Euglena, Chlamydomonas e.t.c
Euglena sp
• 2. Zoomastigophora
• They are animal-like and lack chromatophores
• They are holozoic (Food is ingested through
temporary or permanent openings)
• There is sexual reproduction in a few groups
• Some members of this class are parasitic
• They may possess one to many flagella
• They are amoeboid forms with or without flagella
• E.g. Mastigamoeba, Trichonymphia, Trypanosoma,
leishmania
Phylum : Ciliophora
• This phylum constitutes the largest group of protozoans
• They exhibit a high level of organelle development
• They possess cilia as locomotory organelles
• They have a constant body shape due to the presence
of firm pellicle covering their body
• They possess nuclei of two types, a large meganucleus,
which controls all cell activities except reproduction,
and a micronucleus which controls sexual reproduction
• Asexual reproduction is by transverse fission while
sexual reproduction is by conjugation, which
involves fusion of nuclei and not cells
• Most of the ciliates are free living and solitary, a few
are colonial and some are sessile, very few are
parasitic
• They feed on small organic particles or prey on
microscopic organisms
• E.g paramecium, vorticella, balantidium e.t.c
Paramecium
PARAZOA
• There is only a single phylum in this group, the
phylum Porifera
• Porifera is a latin word where Porus = pore,
• ferre= to bear, Porifera means animals that bear
pores
• Members of this phylum is commonly known as
sponges
• They are the most primitive and simplest of the
multicellular animals
• Their body consists of many cells, which due to the
absence of a nervous system and sense organs, are
more or less independent of one another
• Their cells are not organised into tissues and organs
hence they are at cellular level of organisation
• Adult sponges are sessile and attached to the rocks
and other hard surfaces in shallow water and they
are predominantly marine but some may occur in
freshwater
• The body of a sponge consists of many cells
arrange in two layers around a central cavity
• The central body cavity of a sponge is known as
spongocoele or paragaster
• The layer lining the internal cavity is known as the
gastral layer or choanoderm; it is composed of
collared flagellated cells known as the gastral layer
or choanocytes
• Numerous incurrent pores known as Ostia perforate
the body surface of a sponge, for which they were
named porifera
• Ostia are linked to inhalant canals
• Water enters by Ostia and passes along the inhalant
canals into spongocoele. It carries along with
various minute organisms that serves as food for
the sponge.
• The food particles are engulfed by the collared cells
(choanocytes) where digestion takes place and the
indigestible material is injected into the space
within the collar.
• The major opening of the sponge body is exhalant
and not a mouth, this is the osculum
• They are often coloured due to interaction with
symbiotic algae
• Individuals are hermaphroditic
• Reproduction is by sexual and asexual means
• One of different larval forms is amphiblastula
• The phylum Porifera is divided into four classes
Sponges
Classes of Porifera
• Class 1: Calcarea
• Class 2: Hexactinellida
• Class 3: Desmospongiae
• Class 4: Sclerospongiae
Class : Calcarea
• These are sponges with skeleton consisting solely
of calcareous spicules
• They have large choanocytes (Collared flagellated
cells)
• E.g Leucoslenia, Sycon, e.t.c
Class : Hexactinellida
• These are sponges with a purely siliceous skeleton
composed of six-rayed spicules of silica
• Choanocytes are small and lack jelly
• They are a deep –sea group
• E.g Euplectella, Hyalonema e.t.c
Class: Demospongiae
• They lack skeleton and if present it may be
siliceous and does not contain six rayed
spicule of silica
• Choanocytes are small and possess jelly
• E.g Spongilla, Oscarella e.t.c
Class: Sclerospongiae
• This is a very small class of leuconoid marine
sponges
• They are similar to demospongiae
• They are found in association with coral reefs
• Their skeleton is made up of siliceous spicules and
sponging fibres confined to a thin superficial layer
on top of a huge mass of calcium carbonate
Mesozoa
• Mesozoa (Greek mesos, “middle”; zōion, “animal”), phylum or
superphylum of life forms, sometimes thought to be
transitional from unicellular to multicellular organisms.
• The body consists of a layer of outer cells surrounding
internal reproductive cells;
• it contains no real organs.
• Except at the time of dispersal, mesozoans live as internal
parasites of marine invertebrates.
• The group contains about 50 species placed in two classes or
orders.
• They reproduce sexually and have a complex life
cycle involving more than one larval form.
• Its locomotion is carried out by cilia.
• Some time ago, mesozoa were considered as a link
between protozoan and metazoan, because they
do not possess true tissues and their structure is
very simple.
• E.g Rhopalura granosa
Classes of Mesozoa
• The Phylum includes two classes:
• Class Rhombozoa- Parasites of the renal bags of
cephalopods, like octopi, sepias and squids. Two orders:
• Order Dicyemida
• Order Heterocyemida
• Class Orthonectida- Parasites of Ophiuroidea, bivalve
mollusks, polychaeta and nemertean.
• They are formed by a layer of ciliated cells that contains
a mass of gametes. Example of this class: Rhopalura
ophiocomae.
• Most of biologists are in agreement that these
minute animals are primitive or simplified
Platyhelminthes, although some biologists
consider that mesozoans are a phase in the course
of the evolution from protozoan to metazoan.
• Some zoologists claim that mesozoans are
descendants of ciliated protozoan.
• Personally, I consider they are simplified
Platyhelminthes; precisely, because of their
parasitic way of life.
Metazoa
• These are group of multicellular apart from parazoa
and mesozoa
• Members of these group different from parazoa in the
following ways
i. Their bodies consist of many cells that co-operate with
one another
ii. Choanocytes are absent in metazoa
iii. They possess sense organs and nervous system
iv. The principal body opening in metazoans is
inhalant
v. Endoderm cells, not choanocytes line their body
cavity
Level of organisation
There are two level of organisation in metazoans
i. Diploblastic and
ii. Triploblastic
• In diploblastic organisation, the body wall is
composed of two layers: Ectoderm and endoderm,
and a layer of secreted jelly, the
mesoglea/mesogloea, between the two layers
• The diploblastic body is attained by the cnidarians
• In triploblastic organisation, there is a third layer,
the mesoderm between the ectoderm and
endoderm.
• The mesoderm is more extensive and forms most of
the body. Other invertebrate phyla belong to this
group.
Phyla under the group metazoa
• The phyla in the metazoa include
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Cnidaria
Platyhelminthes
Nematoda
Annelida
Mollusca
Arthropoda
Echinodermata
Phylum : Cnidaria
• They are diploblastic animals
• They have tissue grade organisation
• They possess single cavity in the body known as
enteron or gastro vascular cavity, which serves for
ingestion and egestion
• They lack anus
• Their mouth is surrounded by tentacles
• They produce nematocysts which serve for defence and
food capture
• They are radially symmetry
• They are either sedentary (seated) or free swimming
• They exhibit polymorphism (i.e they have different
body form), occurring either as hydroid (polyp) or
medusoid type (medusa).
• The medusoid forms are free swimming and
solitary while the polyp forms are sedentary (not
moving or always attach to a rock) and may be
solitary or colonial
• Their nervous system is an irregular network of
cells
• Asexual reproduction is by budding producing
colonial zooids
• Sexual reproduction produces a ciliated larva
known as the Planula
• Cnidaria is divided into three classes
Classes of Cnidaria
i. Hydrozoa
ii. Scyphozoa
iii. Anthozoa
Hydrozoa
They have the polyp and medusa forms in their life cycle
The polyp is the predominant stage while the medusa is
the simple stage
They reproduce by alternation of asexual and sexual
phases of life cycles
e.g Hydra, Obelia, Physalia (Portuguese man-of-war)
Hydra
Phylum : Cnidaria, Class: Hydrozoa and
Order: Hydroida
Class: Scyphozoa
• In this class the polyp stage may either be reduced
to a small larva or it may be absent, if present, it
gives rise to medusae by transverse fission
• They lack gullet
• Nematocysts are present in the ectoderm
• They are exclusively marine
• E.g Aurelia (jelly fish), Pelagia
Life cycle of Jelly fish (Scyphozoa)
Class: Anthozoa
• They are exclusively marine cnidarians
• They constitute the largest class
• They occur only as polyps
• Nematocysts are present in the endoderm
• E.g Actinia (sea anemone), Astrangia (coral) e.t.c
Sea anemones and clown fish
(symbiotic relationship)
Phylum: Platyhelminthes
• They are flatworms because they are dorsoventrally flattened
• Many of the most important morphological features
found in complex higher animal groups were first
observed in the flatworms. These features include
• Cephalization and bilateral symmetry
• Triploblastic organisation
• Organ-system level of organisation
• They are acoelomates i.e the mesoderm
is solid with no space between the
ectoderm and the gut
• They possess a central nervous system
• They lack blood vascular(circulatory) and
respiratory systems
• Respiration and excretion are mainly by
diffusion through the body surface
• They possess a unique excretory and
osmo-regulatory system of branched
protonephridial tubes that end in flame
cells
• The gut (when present) has only one
opening, the mouth, no anus.
• They are hermaphrodites
Classes of Platyhelminthes
i. Turbellaria
ii. Monogenea
iii. Trematoda
iv. Cestoidea
Class: Turbellaria
• They are free-living platyhelminthes, found in
aquatic habitat
• They have a ciliated cellular outer covering to the
body
• They lack cuticle
• Suckers are rarely present
• They possess rhabdites (mucus producing organ)
• E.g Dugesia (Planaria)
Class: Monogenea
• They are mostly ectoparasites of fish, turtles and amphibians
• A few are endoparasitic
• They have simple life cycles and have only one host
• Possess hooked attachment structures
• The large posterior attachment structure is called the haptor
• E.g Polystoma sp., Macrogyrodactylus sp., Dactylogyrus sp.,
Diplozoon sp e.t.c
Class: Trematoda
• They are parasitic
• Their body is covered by a complex tegument
• Adults lack cilia
• They have one or more suckers by which they
attach to their hosts
• They have complex life cycle involving intermediate
hosts
Subclasses of Trematoda
a. Aspidogastrea
b. Digenea
Subclass: Aspidogastrea
• They lack an oral sucker
• They lack a large ventral suckers or several alveoli
• The holdfast is always make up of many suckers or
several alveoli
• They have one host, which may be a mollusc or a
cold blooded vertebrate
• E.g. Aspidogaster conchicola, a parasite of
freshwater clams, Rohdella, Rugogaster and
Cotylogaster spp
Subclass: Digena
• They are endoparasitic in all groups of vertebrates
• Suckers are usually two: Oral and ventral suckers
• They have two or more hosts in their life cycles
• E.g. Fasciola hepatica, Fasciola gigantica,
Fasciolopsis buski, Schistosoma mansoni, Clonorchis
sinensis, Transversotrema e.t.c
Class: Cestoidea (Cestoda)
• Commonly called tapeworms
• They are endoparasitic and their adults live in the
gut of vertebrates
• Body is typically elongated, tape-like and
segmented, each segment is called a
proglottis/proglottid
• They have a head region known as scolex, which
mostly bears hooks and suckers for attachment to
the host
• The anterior proglottides close to the scolex are
young without complement of the reproductive
system
• The middle proglottides are matured and have full
complement of the reproductive system, while the
posterior segments are gravid and contain ripe eggs
• Each proglottis contains a complete set of male and
female reproductive organs
• They have no mouth and no digestive system
• They absorb digested food from the intestine of
their host through the body surface
• Their bodies are covered by a thick cuticle
• No cilia in adults
• Life cycle is complex and involves intermediate
hosts
• E.g Taenia solium, Taenia saginata, Echinococcus
granulosus, Hymenolepsis nana, Diphyllobothrium
latum e.t.c
Phylum : Nematoda
• Features
• Commonly called roundworm
• They are cosmopolitan and occur in the sea,
freshwater, moist soil or as parasites in plants and
animals
• They are elongated cylindrical and unsegmented
• They are triploblastic, pseudocoelomate and bilaterally
symmetrical
• Body is covered by an elastic cuticle
• They have only longitudinal muscles, no circular
muscles
• They are unique in that they have no cilia in any part of
their body
• Sexes are separate i.e dioecious
• They exhibit sexual dimorphism, the males being
smaller than the females
• Alimentary canal is straight tube from mouth to anus
• Some are free living and many are important plant and
animal parasites and are of great medical and
economical importance
Classes of Nematoda
• The phylum nematoda is divided into two classes
• Class 1: Adenophorea (Aphasmidia)
• Class 2: Secernentea (Phasmidia)
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Class 1 : Adenophorea (Aphasmidia)
They lack phasmids (caudal sensory organs)
Excretory system is rudimentary or poorly developed
Males have no spicules
E.g Trichuris sp
Class 2: Secernentea (Phasmidia)
• They have phasmids, excretory system is present
and well developed
• Males have two spicules
• E.g Rhabditis, Wuchereria spp, Onchocerca spp e.t.c
Phylum: Annelida
• In latin annellus means little ring
• They are triploblastics, segmented, coelomate metazoans
• They are bilaterally symmetrical
• They have varying degrees of cephalisation
• They possess a perivisceral coelom (a coelom is a fluid filled
cavity lying between two layer of mesoderm)
• Their body wall consists of a thin cover of cuticle, underneath
which is a single layer of epidermis and a muscular layer
made up of an outer layer of circular muscles and an inner
layer of longitudinal muscles
• They have a blood system in which the blood is
confined to blood vessels (closed system)
• Excretory organs called nephridia are segmented and
ciliated
• Possess chitinous chaetae arranged segmentally
• Cleavage of egg is spiral
• They have a typical trochophore larva
• The central nervous system(CNS) comprises a solid
double ventral ganglionated nerve cord and paired
dorsal cerebral ganglia
Trochophore larva
Classes of Annelids
• Class 1: Polychaeta
• Class 2: Oligochaeta (earthworm)
• Class 3: Hirudinae (leeches)
• Class 1 : Polychaeta
• They are commonly called marine bristle worms
• They have a distinct head, which bears number of
appendages (tentacles, palps, eyes and jaws)
• They have numerous chaetae (bristles composed of
chitin) arranged segmentally
• They usually have biramous segmented parapodia
• They have no suckers
• They are dioecious (separate sexes)
• The gonads are localised but extend throughout the
body
• Fertilization is external
• Zygote produces free swimming trochophore larva
• E.g Nereis, Sabella, Arenicolla, Aphrodite, Eunice,
Glycera e.t.c
Class : Oligochaeta
• These are the earthworms
• The head is not very distinct
• The head is reduced and lacks sensory appendages
• They possess fewer chaetae than the polychaetes
• The chaetae occur singly or in pairs and they lack parapodia
• They are hermaphrodites
• Reproduction is by copulation and cross fertilisation
• They lack suckers
• E.g Lumbricus terrestris, Tubifex tubifex e.t.c
Class: Hirudinea (Leeches)
• They are highly specialised annelids
• Many are ectoparasites of vertebrates, while some
are free predators or scavengers
• They occur mostly in freshwater with a few on land
and in the sea.
• They have anterior and posterior suckers
• They lack a distinct head
• Their body is somewhat shortened, all members of
this class have 33/34 segments
• They lack chaetae or parapodia
• They are hermaphrodites
• Reproduction is by cross fertilisation
• E.g Hirudo medicinallis e.t.c
leech
The Phylum: Mollusca
• Characteristics
• They are soft-bodied, triploblastic, typically
unsegmented coelomate animals, which are bilaterally
symmetrical
• Their body is divided into head, a ventral muscular foot
and a dorsal visceral hump
• The skin covering the visceral hump is the mantle and it
secretes the shell
• They possess a radula which is a toothed belt/ribbon
used for feeding
• Their blood system consists of a heart, arterial and
venous systems which expand into an extensive
haemocoel
• They possess haemocyanin as respiratory pigment
• The coelom is reduced to the cavity of the gonad,
the kidneys and perivisceral cavity
• They are oviparous
• The zygote typically develops into a trochophore
larva and then into a veliger larva
Mollusc Anatomy
Classification of the Mollusca
• The classification of mollusca is based on the
characteristics of the foot, mantle, shell, radula and
respiratory organs, based on this, there are seven
classes as follows
• A. Aplacophora
• B. Monoplacophora
• C.Polyplacophora
• D. Scaphopoda
• E. Gastropoda
• F. Bivalvia
G.Cephalopoda
The Molluscs
Class: Aplacophora
• They are worm like in morphology
• Commonly known as solenogasters
• Lack foot, mantle and shell (spicules in place of shell)
• Head is poorly developed
• They have a radula and style sac
• E.g Neomenia sp., Chaetoderma sp., e.t.c.
Class: Monoplacophora(single plate)
• They are circular in shape and bilaterally
symmetrical
• They resemble limpet but the shell is tipped
forward
• The shell is made from one unit with definite
growth rings
• The foot is well developed, broad, flat and disc
shaped
• They have an internal metamerism (the only
segmented molluscs)
• Their nervous system lack ganglia
• E.g Neopilina
Class: Polyplacophora(bearer of many
plates)
• Their body is oval, bilaterally symmetrical and
dorso-ventrally flattened
• The foot is flat and occupies most of the ventral
surface of the body
• The mantle form a thick girdle around the foot
• The shell is made up of many units
• There are ctenidia in two rows, one on either side
of the body
• The eye is reduced without eyes or tentacles
• Sexes are separate
• Fertilisation is external
• The trochophore larva develops to adult without
passing through the veliger stage
• E.g chiton
Class: scaphopoda(tooth-shells, tuskshells)
• The body is elongated nearly cylindrical and
bilaterally symmetrical
• The shell is tubular, tusk-shaped and open at both
ends
• They have a short foot
• They lack a heart
• The head is reduced with no eyes but has bundles
of ciliated prehensile tentacles called captacula
used for feeding
• E.g Cadulus sp, Dentalium sp e.t.c
Class: Bivalvia(Lamellibranchiata)
• They are all aquatic and are found in freshwater and
the sea
• They are bilaterally symmetrical
• Their body is laterally compressed and enclosed in a
shell that develops as two large plate-like valves hence
the name Bivalvia
• The head is rudimentary (greatly reduced)
• They lack tentacles, eyes and radula
• The foot is wedged/hatchet/tongue-shaped and can be
protuded for ploughing into soft deposits
• They are mainly filter-feeders
• Fertilisation is external
• E.g Mytilus (mussel), Ostrea (oyster), Pecten, Anodonta,
Ensis, Teredo e.t.c
Class: Gastropoda
• This is the largest class of molluscs
• They are mainly marine but some occur in the
freshwater and terrestrial habitats
• Possess distinct and well developed head bearing
tentacles and eyes
• They have a well developed radula
• They have a flat muscular ventral foot used for creeping
• They may or may not possess a shell and if the shell is
present, it is only one piece
• Fertilisation is internal
• E.g The giant West African land snail, Archachatina,
Patella (limpet), Limax (slug), hallotis (abalone) e.t.c.
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Class: Cephalopoda
Cephalopods are marine animals
They are bilaterally symmetrical
The long axis of the body is dorso-ventral
They are the largest in size and the most advance
group of invertebrates
• The cephalopods especially squids have evolved
many similarities to vertebrate e.g the squids have a
cartilagenous support analogous to the vertebrate
skeleton, they also have a cartilagenous brain case
• Their head is well developed and is surrounded by
tentacles
• They have a well developed eyes
• They have a closed blood circulatory system
• The shell may be massive and external, reduced and
internal or completely absent
• The radula is well developed and in addition there is
a pair of horny mandibles that form a beak
• The nervous system is well developed with a large
and complex brain
• E.g Octopus, Argonauta, Sepia (cuttle fish), Loligo
(Squid), Nautilus e.t.c
Cuttle fish
Octopus vulgaris
Octopus eye (Camera- type)
Octopus injecting ink as a defensive
mechanism
Nautilus
Giant African Snail
Phylum: Arthropoda
• This is the largest phylum in the animal kingdom
and contains about 80% of all animal species
• Arthropods exhibit a great diversity of structure and
mode of life
• The are triploblastic, bilaterally symmetrical,
metamerically segmented coelomates
• They possess more than one pre-oral segment, they
typically have three
• They have a stout chitinous cuticle secreted by the
epidermis, this is the exoskeleton
• The cuticle is flexible at some points on the trunk and
limbs to provide joints
• Growth occurs after shedding of the cuticle, a process
called moulting or ecdysis
• Possess jointed appendages on some or all the body
segments.
• Appendages are structures joined to the main body and
limbs e.g mouthparts, antennae, wings, styles, cerci
e.t.c
• Muscles are in discrete bundles
• Coelom is reduced to the cavity of the
gonads and pericardial spaces
• They have an open vascular system
• They possess compound eyes
• Their sexes are almost always separate
• They have different types of larvae but
never a trochophore
• E.g crayfishes, crabs, spiders, ticks,
millipedes
Classification of arthropods
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Arthropods are divided into the following classes
1. Trilobita
2. Onychophora
3. Crustacea
4. Diplopoda (myriapoda)
5. Chilopoda (myriapoda)
6. Symphyla (myriapoda)
7. Pauropoda (myriapoda)
8. Arachnida
9. Pycnogona
10. Insecta (Hexapoda)
Arthropod representatives
Moulting in crab
Class: Trilobita
• An extinct group of arthropods now represented by
fossils in which the body was moulded
longitudinally into three lobes
• They had a pair of antennae and all the appendages
on the post- antennal somites (body segments) are
of a common type
• They were marine arthropods and were numerous
in the Cambrian and Silurian but became extinct by
the secondary period (about 250 million years ago)
• E.g Olenus
Fossilized trilobite
Class: Onychophora (Velvet worm)
• These are terrestrial caterpillar-like
animals
• They possess a combination of arthropod
and annelid characters
• They occur in damp forests beneath logs
of wood, leaves and beneath the bark of
rotten logs
• They are largely nocturnal and avoid light
e.g peripatus
Velvet worm (onychophoran)e.g. Paripatus
Annelid-like characters of onychophora
• Thin flexible and permeable cuticle
• Muscles occur in layers
• Body wall made of circular and longitudinal muscle
layers
• Nephridia are segmentally arranged
• Appendages are non- jointed
Arthropod-like characters of onychophora
• Chitinous cuticle with tanned outer layer as in
insects
• Undergo moulting as in arthropods
• Reduced coelom with haemocoelic body cavity
• One pair of appendages modified as jaws
• Presence of claws on the legs
• Respiration by means of trachea as in insects
Class: Crustacea
• Primarily aquatic arthropods, occurring in the sea
and freshwater
• Body consists of head, thorax and abdomen
• The head and thorax fused to form cephalothorax
• There are six segments on the head and it bears
three pairs of post -oral appendages that act as jaws
• They possess a pair of compound eyes
• They possess biramous (forked like or Y shaped)
appendages on every segment of the thorax and
abdomen
• The biramous appendage is Y-shaped consisting of a
basal protopodite and two arms, the expodite and
endodite
• Gaseous exchange is by gills
• Excretion is by means of green gland
• E.g. Astacus (crayfish), Penaeus, Daphnia (water flea),
Artenia (fairy shrimp) e.t.c
Fairy shrimps
Murray river crayfish
Japanese Spider Crab
Subphylum: Myriapoda
• These are terrestrial arthropods with one pair of
antennae and many walking legs
• Myriapoda means many footed
• Their bodies consist of a head and a long trunk
• They lack a waxy epicuticle in their exoskeleton and
are therefore prone to desiccation, for this reason
they live in humid environments
• True compound eyes are present, simple eyes are
often present
• Respiration is by means of trachea
• Excretion is by means of Malpighian tubules
• Sexes are separate
• Young resemble adults but possess fewer segments
Class: Diplopoda
• Commonly known as millipedes
• Each apparent segment bears two pairs of legs,
hence the name Diplopoda (double feet)
• The first four segments represent the thorax, which
bear one pair of legs each
• No appendages on the first trunk segment
• The genital pore is in the third thoracic segment
• They are sluggish and sensitive, often coiling up when
disturbed, they also do this for protection
• They are cosmopolitan in the tropics hiding under
leaves, stones, logs e.t.c
• They generally keep away from light
• They are herbivorous
• E.g Julus, Polydesmus, Ophyiulus
Millipede
Millipede
Class: Chilopoda
• They are commonly known as the centipedes
• The body is dorso-ventrally flattened
• The trunk segments are numerous
• Each trunk segment except the last two bears a
single pair of legs
• The first trunk segment bears poison claws or
maxillipeds, which cover the other mouth parts
• The cuticle is elastic and not strengthened
• The genital pore is located at the posterior end of
the body
• They are carnivores
• They are fast moving and do not coil but also live
under leaves, bark of trees, beneath stones and
around the house
• E.g Lithobius, Scolopendra, Scutigera
Peruvian centipede
centipede
• They have a single pair of tracheae that open
through spiracles on the head
• They are blind
• They are herbivorous
• E.g Scolopendrella, Scutigerella immaculata
Class: Symphyla (symphyla means growing
together)
• They are small less than 8mm long
• They are morphologically similar to the centipedes
• The leg bearing segments are not more than 12
• They have a single pair of legs per leg- bearing
segment
Class: Pauropoda
• They are minute less than 2mm long
• They live in the same habitats as symphylans and
millipedes
• They feed on fungal hyphae
• They are morphologically similar to the millipedes
• The head bears two maxillae
• The first two and last two trunk have no legs
• They have no heart
• They have no tracheae
• They have branched antennae
• They are blind and colourless
• They all belong to one order
• E.g Pauropus
Class: Arachnida
• They are terrestrial arthropods
• Body divided into two, an anterior prosoma that is
not divided into head and thorax but is made of six
segments,
• the posterior opisthosoma consists of 13 segments
• The first body segment bears a pair of prehensile
appendages called chelicerae
• The second body segment bears a pair of sensory or
prehensile pedipalps
• There is a pair of segments on segments on each of
segments 4-7 (making a total of 4 pairs of walking
legs)
• Respiration is by internal air spaces which may be
lungbooks or tracheae
• E.g Scorpions, spiders, ticks, mites e.t.c
Brown Recluse Spider
• The brown recluse spider builds a loose, irregular
web in sheltered outdoor or indoor corners.
• It sometimes hides in folds of cloth, and it may bite
if disturbed.
• The bite of the brown recluse spider is poisonous to
humans and can cause death.
Brown recluse spider
General Anatomy of Spider
African Wolf Spider
Young Garden Spiders hatching
Scorpion raising its tail up
United state scorpion
Sheep tick
chigger
Project topics
• Group 1 : The Biology and adaptation of Scorpion
• 1.Joseph Adeiza,2. Orifunmishe Jacinta, 3.Amlabu
Sokolayam, 4.Oni Folake Maria, 5.Abadi Ndutimi
Rufus, 6. Ohikere Anavami Grace, 7. Ekele Faith
• Group 2: The Biology and adaptation of Octopus
• 1.Jonah Itohowo, 2. Eme Ihuoma, 3.Adeoye
Aderonke, 4. Ukwedeh Esther, 5. Idih Favour
• 6. Adamu Deborah 7. Olugbemi Titilope
Class: Insecta (Hexapoda)
• They are mainly terrestrial arthropods but a
considerably number are aquatic
• Body is divided into head, thorax and abdomen
• Head bears a pair of antennae and a pair of
compound eyes
• The thorax is divided into prothorax, mesothorax
and metathorax, each has a pair of walking legs
ventrally
• The mesothorax bears a pair of wings dorsally, which
are nonmembraneous and not used in flight, these
wings are called elytra
• The metathorax has a pair of membraneous wings
dorsally that are used for flight
• The abdomen consists of eleven segments with no
walking legs
• Respiration is by means of trachea
• Excretion is by means of malpighian tubules
• Insects undergo metamorphosis, which involves abrupt
changes of form
Classification of insects
• Insects may be grouped based on the presence or
absence of wings and/or metamorphosis
• A. Based on the presence or absence of wings,
there are two subclasses
• Subclass 1: Apterygota
• These are primitive wingless insects
• They do not undergo metamorphosis
Orders of Apterygota
• There are four orders in this subclass: These are:
• Order 1: Collembola (springtails)
• Order 2: Protura
• Order 3: Diplura
• Order 4: Thysanura
Order: Collembola
• They have six abdominal segments
• Their antennae have 3-6 joints
• No metamorphosis
• No malpighian tubules
• E.g. Podura, Sminthurus, e.t.c
Order: Protura
• They possess twelve abdominal segments
• Rudimentary malpighian tubules
• No antennae, no eyes
• E.g Acerentomon
Order: Diplura
• Possess eleven segments
• Segmented antennae
• Malpighian tubules rudimentary or absent
• E.g Campodea, Japyx
Order: Thysanura(Bristle tail, silverfish)
• They have eleven abdominal segments
• Antennae have many joints but the segment are not
capable of independent movement
• Malpighian tubules present
• E.g Petrobius, Lepisma, Silver fish or sugar mite e.t.c
Silver fish or sugar mite
Subclass: Pterygota
• These are the winged insects
• They lack abdominal locomotory appendages
• Show simple metamorphosis
• Malpighian tubules are present
Divisions of Pterygota
• The pterygota are divided into two groups, based on
the mode of development of the wings
• 1. Endopterygota
• 2. Exopterygota
• Endopterygota: They possess wings that develop
internally e.g the order Diptera (beetles) and
lepidoptera (moths and butterflies)
• Exopterygota: They have wings that developed
externally e.g the order Odonata (dragon flies)
Based on the types of metamorphosis
• The insects are divided into
• 1. Holometabola : This group of insects undergo
complete metamorphosis e.g
• order Coleoptera (beetles, bean weevil),
• order Lepidoptera (butterflies and moths),
• Order Hymenoptera (ants, bees, wasps e.t.c)
• Hemimetabola : Winged or secondarily wingless
insects, they undergo incomplete metamorphosis
• They have compound eyes
• They have externally developed wing pads and genital
appendages
• E.g order : Odonata (Dragonfly)
• Order :Dictyoptera (Mantids and cockroaches)
• Order: Orthoptera (locusts, grasshopper and crickets)
Reproduction and development
• A few arthropods, such as barnacles, are hermaphroditic, that
is, each can have the organs of both sexes. However,
individuals of most species remain of one sex all their lives.
• A few species of insects and crustaceans can reproduce by
parthenogenesis, for example, without mating, especially if
conditions favour a "population explosion".
• However most arthropods rely on sexual reproduction, and
parthenogenetic species often revert to sexual reproduction
when conditions become less favourable.
• Aquatic arthropods may breed by external fertilization, as for
example frogs also do, or by internal fertilization, where the
ova remain in the female's body and the sperm must
somehow be inserted.
• All known terrestrial arthropods use internal fertilization, as
unprotected sperm and ova would not survive long in these
environments.
• In a few cases the sperm transfer is direct from the male's
genital tract to the female's oviduct, but it is more often
indirect.
• Some crustaceans and spiders use modified appendages to
transfer the sperm to the female. On the other hand, many
male terrestrial arthropods produce spermatophores,
waterproof packets of sperm, which the females take into
their bodies.
• A few such species rely on females to find spermatophores
that have already been deposited on the ground, but in most
cases males only deposit spermatophores when complex
courtship rituals look likely to be successful.
• Most arthropods lay eggs,but scorpions are
viviparous: they produce live young after the eggs
have hatched inside the mother, and are noted for
prolonged maternal care.
• Newly born arthropods have diverse forms, and
insects alone cover the range of extremes.
• Some hatch as apparently miniature adults (direct
development), and in some cases, such as
silverfish, the hatchlings do not feed and may be
helpless until after their first moult.
• Many insects hatch as grubs or caterpillars, which
do not have segmented limbs or hardened cuticles,
and metamorphose into adult forms by entering an
inactive phase in which the larval tissues are broken
down and re-used to build the adult body.
• Dragonfly larvae have the typical cuticles and
jointed limbs of arthropods but are flightless waterbreathers with extendable jaws.
• Crustaceans commonly hatch as tiny nauplius
larvae that have only three segments and pairs of
appendages.
Reproduction in scorpion
The nauplius larva
of prawn
Economic importance of Arthropods
• Crustaceans such as crabs, lobsters, crayfish,
shrimps and prawns have long been part of human
delicacy, and are now farmed on a large commercial
scale.
• Insects and their grubs are at least as nutritious as
meat, and are eaten both raw and cooked in many
non-European cultures.
• Cooked tarantulas (wolf spiders) are considered a
delicacy in Cambodia, and by the Piaroa Indians of
southern Venezuela, after the highly irritant hairs –
the spider's main defense system – are removed.
• Humans also unintentionally eat arthropods in
other foods, and food safety regulations lay down
acceptable contamination levels for different kinds
of food material.
• The intentional cultivation of arthropods and other
small animals for human food, referred to as
minilivestock, is now emerging in animal husbandry
as an ecologically sound concept.
• However, the greatest contribution of arthropods to
human food supply is by pollination
• Besides pollinating, bees produce honey, which is the
basis of a rapidly growing industry and international
trade.
• The blood of horseshoe crabs contains a clotting agent
Limulus Amebocyte Lysate which is now used to test
that antibiotics and kidney machines are free of
dangerous bacteria, and to detect spinal meningitis and
some cancers.
• Forensic entomology uses evidence provided by
arthropods to establish the time and sometimes the
place of death of a human, and in some cases the cause
• The relative simplicity of the arthropods' body plan,
allowing them to move on a variety of surfaces both
on land and in water, have made them useful as
models for robotics.
• The redundancy provided by segments allows
arthropods and biomimetic robots to move
normally even with damaged or lost appendages.
Female mosquito sucking blood
Tsetse fly
Success of insects
• In terms of diversity and abundance, insects are the
most successful group of animals and constitute
about 75% of the known species of animals. Their
success is attributed to :
1. Their small size, which enables them to escape
from enemies and go undetected by predators
2. Ability to fly in some, to enable them escape from
danger
3. Possession of chitinous exoskeleton that is
resistant to water loss thus preventing
dessicccation
4. Possession of efficient nervous system with numerous
sensory organs like antennae, eyes, setae e.t.c for
detecting changes in their immediate environment
5. They are well adapted to all habitats
6. They are adapted to eating a wide range of food items
(minimises interspecific competition for food): even
within a species, the larval stage and adult have
mouthparts that are adapted to feeding on different
food materials.
7. Their reproductive efficiency allow them to produce
large numbers of eggs and offspring within a short time
8. They produce resistant eggs that can be carried by air,
water currents, animals e.t.c
Economic Importance of Insects
1. Some are source of food for humans e.g honey
from honeybee, termites, caterpillars, grubs e.t.c
2. They pollinate flowers and consequently aid in
fruit formation
3. They produce important raw materials for
industries e.g silk from silkworm
4. They constitute food for other animals in the
biosphere e.g lizards, toads and fish, all feed on
insects
5. They help in the decomposition of dead organic
matters by scavenging
6.They form important research tools e.g mosquitoes
7.They are used in biological control of some pest e.g
Toxorhynchite brevipalpis that predates on other
mosquito larvae
8. Some are vectors of parasitic diseases of humans
and animals e.g tsetseflies, houseflies, mosquitoes,
sandflies e.t.c.
9. They are parasites of humans and plants e.g lice,
fleas, bedbugs e.t.c
10. Some insects attack stored food items and
produce e.g bean weevil, rice weevil e.t.c
11. They destroy wooden structures in furniture,
buildings e.t.c., e.g termites, wood lice, carpenter
bees e.t.c
Diseases transmitted by insects
Disease
Insect
Cases per year
Deaths per year
Malaria
Anopheles mosquito
267 M
1 to 2 M
Yellow fever
Aedes mosquito
4,432
1,177
Filariasis
Culex mosquito
250 M
unknown
• Although arthropods are the most numerous
phylum on Earth, and thousands of arthropod
species are venomous, they inflict relatively few
serious bites and stings on humans.
• Far more serious are the effects on humans of
diseases carried by blood-sucking insects.
• Other blood-sucking insects infect livestock with
diseases that kill many animals and greatly reduce
the usefulness of others.
• Ticks can cause tick paralysis and several parasiteborne diseases in humans.
• A few of the closely related mites also infest humans,
causing intense itching, and others cause allergic
diseases, including hay fever, asthma and eczema.
• Many species of arthropods, principally insects but also
mites, are agricultural and forest pests.
• The mite Varroa destructor has become the largest
single problem faced by beekeepers worldwide.
• Efforts to control arthropod pests by large-scale use
of pesticides have caused long term effects on
human health and on biodiversity.
• Increasing arthropod resistance to pesticides has
led to the development of integrated pest
management using a wide range of measures
including biological control.
• Predatory mites may be useful in controlling some
mite pests.
Phylum : Echinodermata
• They are said to be a link between the invertebrates
and the chordates because of certain similarities
that the two phyla share
• The echinoderms and chordates are known as
deuterostomes because in both groups, the
blastopore of the embryo develops into mouth and
the anus forms at the opposite end
• In protostomes (annelids, molluscs, arthropods and
their allies), on the other hand, the blastopore of
the embryo gives rise to the mouth of the adult.
• Echinoderms are typically pentamerous i.e having
five arms as seen in the star fish and the sand dollar
Pentamerous limbs
The echinoderms differ from all other
invertebrates in the following ways
• They begin as bilaterally symmetrical larvae and
later change into radially symmetrical adults
• They have an internal skeleton of calcium
carbonate. This calcium carbonate is obtained from
the sea
• They have spiny skin
• They have larvae, which are planktonic, bilaterally
symmetrical and ciliated
Characteristics of Echinoderms
• They are pentaradially symmetrical coelomate
animals
• The early larva shows evidence of metameric
segmentation, adults are unsegmented
• Adult is secondarily radially symmetrical
• There are two main types of body form among
adults; radiate and globular
• They are not cephalized but have oral-aboral axis
• Their body surface consists of five field with podia
(ambulacra) alternating with five that have no podia
(interambulacra)
• There are various forms of the gut and it might not
have an anus
• Their nervous system is well developed but
uncentralized.
• The system is made up of three nerve rings around the
digestive tube with peripheral nerves radiating from
them
• The body wall is made up of a ciliated epidermis
underneath which is a dermis that contains
calcareous ossicles, which give rise to spines
• The musculature of their body wall is poorly
developed
• They have a simple circulatory or haemal system
that runs through a system of coelomic
compartments
• Their coelom is large and is in three distinct
compartments
• A unique water vascular system is formed from one of
the compartments of the coelom.
• This is said to be the most unique feature of the
echinoderms
• The tube feet (podia) are offshoots of the radial canals
of the water vascular system and the suckers at their
ends facilitate attachment to a substrate and are also
used for locomotion
• No special organs of excretion
• Sexes are separate
• They have various forms of free swimming and free
living larvae each associated with the different
classes
Classification of Echinoderms
• There are three subphyla of echinoderms
1. Crinozoa
2. Asterozoa
3. Echinozoa
Subphylum: Crinozoa
• They have stalked and sessile larval and adult stages
• Tube feet, when present, are tentacular
• The anus is usually on the oral surface
• Mouth is directed upwards
• There is a single class in this subphylum
Class : Crinoidea (sea lilies & feather stars)
• They are said to be the most primitive of extant
echinoderms
• Their bodies are roughly hemispherical/star shaped
• They have five arms that are branched
• The arms and the central disc are clearly
dermarcated
• The coelom and gonads extend into the arms
• They have no madreporite (a perforated plate
through which water passes into the water vascular
system)
• The ambulacral grooves are opened
• Tube feet are small and sensory, they have no suckers
• The skeleton is made up of large ossicles
• There are no spines
• The oral surface is directed upwards and bears the
mouth and the anus
• Some of them have stalks for attachment
• The larval stage is the vitellaria
• E.g Antedon, Pentacrinus, Rhizocrinus
Crinoid Structure
Subphylum: Asterozoa
• They are radially symmetrical, free swimming (not
stalked) and their bodies are star shaped
• They have double set of tube feet
• The anus is usually on the aboral surface
• The mouth is directed downwards
There are two classes of Asterozoa
• Class 1: Asteroidea and
• Class 2: Ophiuroidea
Class Asteroidea (Star Fish)
Typically have 5 arms which arise with a central disc
• Mouth is located in the center of oral surface which
is directed downward
• The tube feet end in suckers
• Endoskeletal ossicles are separated by connective
tissue
• The anal opening and madreporite are on the aboral
surface
• The larva is typically a bipinnaria and develops into
a brachiolaria larva.
• E.g Asterias, Astropecten.
Class 2: Ophiuroidea(Brittle-stars and
Basket-stars)
• The body is pentagonal
• The arms are distinctly marked off from the central
disc (This is a definitive feature of the ophiuroids)
• Stomach pouches and gonads do not extend into the
arms as they do in the Asteroidea
• The madreporite is not very distinct but it is on the
oral surface
• The tube feet are sensory and not locomotory-no
suckers
• They have no ambulacra groove
• The skeleton is made up of calcareous plates in the
disc and articulating articulating ossicles in the arms
• They have no anus
• The larva is an ophiopluteus
• E.g Ophiothrix, Gorgonocephalus, Ophiura,
Ophiocomina e.t.c.
Subphylum: Echinozoa
• They are globular in shape
• Arms are never formed
• Ambulacral grooves are closed
• The anus varies in position
• The mouth is directed either downward or forward
Classes of Echinozoa
• Class 1: Echinoidea
• Class 2: Holothuroidea
• Class: Echinoidea (Sea urchins and Sand-dollars)
• Lack arms
• Body is enclosed in a shell or test
• Body surface is usually covered with moveable spines
• They are globular or heart shaped
• The tube feet have suckers and run from oral to aboral
surfaces
• Their bodies are covered in many long movable spines
• The larva is an echinopluteus
• E.g Echinus, Spatangus, Echinocardium
Structure of Echinozoa
Class: Holothuroidea
• Lack arms
• Oral-aboral axis is greatly extended
• Endoskeleton is reduced to a few ossicles scattered
over the surface of the animal making them rather soft
bodied
• Some species crawl along the substrate using podia;
others have peristaltic locomotion via muscle
contractions
• They have no mouth, they possibly feed by absorption
of nutrients through the body surface
• They have a water vascular system
• E.g Xylopax is the only genus in the class
Structure of Holothuroidea