BIO 102: GENERAL BIOLOGY IIUNIT: 4

INVERTEBRATESCOURSE 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 FRIDAYSVENUES: 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• They possess pseudopodia (false feet) as locomotory organelles and can be withdrawn into the body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 metazoansi. 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

• 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 Cnidariai. Hydrozoaii. Scyphozoaiii. Anthozoa

HydrozoaThey have the polyp and medusa forms in their life cycleThe polyp is the predominant stage while the medusa is

the simple stageThey reproduce by alternation of asexual and sexual

phases of life cycles e.g Hydra, Obelia, Physalia (Portuguese man-of-war)

HydraPhylum : 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 dorso-

ventrally 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)

• 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, tusk-shells)

• 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.

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• 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 water-breathers 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 habitats6. 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 Insects1. Some are source of food for humans e.g honey

from honeybee, termites, caterpillars, grubs e.t.c2. They pollinate flowers and consequently aid in

fruit formation3. They produce important raw materials for

industries e.g silk from silkworm4. 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 mosquitoes7.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 parasite-borne 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