Spectrum Biology - September 2016

INVERTEBRA

CONCEP

Revi

your

Phylum–Annelida

Polychaeta Oligochaeta Hirudinea

Three classes

Marine, fossorial

or tubicolous.

Distinct head

bearing tentacles,

palps and eyes.

Bristle-like setae

and parapodia

for locomotion.

Clitellum is absent.

Unisexual, e.g.

Aphrodite and

Chaetopterus.

Mostly

freshwater,

few marine.

No cephalisation.

Locomotion by

anterior and

posterior suckers.

Clitellum appears

during breeding

season.

Bisexual, e.g.

Hirudinaria and

Acanthobdella.

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Terrestrial, freshwater

Distinct head with

eyes (palps and

tentacles are absent).

Locomotion by

peristalies, parapodia

is absent.

Permanent clitellum

is present.

Bisexual, e.g.

Pheretima and

Tubifex.

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Phylum–Arthropoda

Chelicerata Trilobitomorpha Mandibulata

Three sub-phyla

Body is divided into

cephalothorax (prosoma)

and abdomen (opisthosoma),

cephalothorax is covered by a carapace.

Antennae are absent.

Mandible absent.

Body is divided into

cephalothorax and

abdomen.

One or two pair of

antennae are present.

One pair of mandible

present.

Extinct group •

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Three classes

Mesostomata

Aquatic (marine)

Abdomen ends into

a spike-like telson,

e.g. Limulus and

Eurypterus.

Arachnida

Mostly terrestrial,

some parasitic.

Abdomen lacks

locomotory appendages.

e.g., Araneae, Palamnaeus.

Pycnogonida

Marine

Abdomen is

reduced.

Crustacea

Mostly aquatic,

few are terrestrial

or parasitic.

Body is divisible

into two parts–

cephalothorax

and abdomen.

Exoskeleton is

calcified.

Excretion by

green glands,

e.g. Cyclops

and Sacculina.

Chilopoda

Terrestrial

Body is divisible

into two parts, i.e.

head and trunk.

Exoskeleton is

uncalcified.

One pair of

Malpighian

tubule is present.

e.g. Scolopendra

and Lithobius.

Diplopoda

Terrestrial

Body is divisible

into three parts–head,

thorax and abdomen.

Calcified

Two pair of

Malpighian

tubules are

present.

e.g. Julus and

Glomeris.

Insecta

Found in all habitats.

Body is divisible

into three parts, i.e.,

head, thorax and

abdomen.

Uncalcified

Two to many

pairs of Malpighian

tubules are present.

e.g. Mantis and

Lepisma.

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Four classes

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Ampulla

Pores

Grooves

Madreporite

Madreporic

canal

Calcareous

rings

Ring canal

Tiedmann’s

body

Tube root

Lateral canal

Radial canal

Ampulla

Podium

Sucker

A. Water vascular system of star fish; B. Ped

C. Pedicellaria with

A

Tentacles

Introvert

Locomotory

ventral podia

Anus

Holothuria

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Shell

opening

Shell

Captacula

Foot

Dentalium

u PHYLUM–ANNELIDA

THE SEGMENTED ANIMALS

(Gk. Annulus–ring; lidos–form)

A HABITAT

• Annelids occur in freshwater, sea water or

moist soil. Some are free-living, some are

burrowing and a few are parasitic.

B GENERAL CHARACTERISTICS

• Annelids are characterised by metameric

segmentation. The body is externally

divided by ring-like grooves called annuli

and internally by transverse septa. The

segments are called metameres.

• The first segment is called peristomium from

which an outgrowth prostomium arises.

• Unjointed chitinous setae are often present

(except leeches). Some annelids like Nereis

have unjointed, locomotory structures the

parapodia.

• The body wall

consists of thin,

moist, non-cellular

cuticle, single

layered epidermis

and circular and

longitudinal

muscles.

• They have a true

schizocoelic coelom

filled with coelomic

fluid. The coelomic

fluid serves as a

hydroskeleton.

Digestive tract is

complete.

• Usually show

cutaneous

respiration. Some

possess gills and

show branchial

respiration, e.g.

Terebella.

• Blood vascular

system is of closed type. Blood is red due to

the presence of haemoglobin or erythro-

cruorin found dissolved in blood plasma.

• They lack red blood corpuscles, instead of it

amoeboid blood corpuscles are present.

Leeches lack true vascular system. They possess

haemocoelomic system and red coelomic fluid

is called haemocoelomic fluid.

• Excretory system consists of a coiled tubular

structure, called nephridia. The chief

excretory waste is ammonia.

• The nervous system consists of a nerve ring

and a solid, double, mid-ventral nerve cord

with ganglia. Tactile receptors (for touch),

gustatoreceptors (for taste) and photore-

ceptors (for light) are usually found. Some

possess statocysts (balancing organs) also.

• Development is mostly direct. Indirect

development (e.g. Nereis) includes a

trocophore larva.

v PHYLUM–ARTHROPODA

THE ANIMALS WITH JOINTED FEET OR

APPENDAGES

(Gk. Arthron–joint; podos–foot)

A HABITAT

• They occur on land in the soil in freshwater

in the bodies of animals and plants as

parasites.

B GENERAL CHARACTERISTICS

• They have jointed legs. The body is segmented
  externally and consists of head, thorax and
  abdomen. The body is covered with a thick,
  tough and non-living chitinous cuticle which
  forms the exoskeleton.


• The true coelom is greatly reduced. The body

cavity is a haemocoel. Digestive tract is

complete. The alimentary canal consists of

stomodaeum (foregut), mesenteron

(midgut) and proctodaeum (hindgut).

• Blood vascular system is of open type. There are

present irregular spaces, known as lacunae or

sinuses, filled with blood.

• Respiratory organs are gills or book gills in

aquatic forms and tracheae or book lungs in

terrestrial forms. Excretory organs are either

green glands or Malpighian tubules. Some

have coxal glands.

• Nervous system consists of a nerve ring and a

solid double ventral nerve cord with ganglia.

• Sensory organs like antennae and eyes are

present. Some arthropods have compound eyes

in which mosaic vision is developed. Some

possess statocysts.

• Cilia are completely lacking.


• Striped muscles are usually found. Unstriped

muscles are also present.

• Endocrine glands secrete hormones. Some
  secrete pheromones (sex attractants). They are
  dioecius and show sexual dimorphism.


• Fertilisation is usually internal. They are usually

oviparous. Development is direct or indirect.

• Parental care is often seen in many arthropods.


• Parthenogenesis is also seen in some
  arthropods, e.g. honeybee.

Feelers

Compound eye

CarapaceAbdominal

terga

Antenna

Walking legs

Uropod

Pleopods

Telson

Palaemon

Median eye

Lateral eye

Carapace

Mesosoma

Metasoma

Telson

Immovable

spines of

mesosoma

Limulus

Prosoma

Rostrum

Tentacle

Palp

Cirr i

Prostomium

Perist omium

Body segments

Parapodia

Intersegmental

grooves

Eye

Anal cirr i

Anus

Anal

segment

Nereis