Spectrum Biology - September 2016

ATE WORLD-2

PT MAP

ision Tool

Monoplacophora

Limpet shaped shell

formed of single valve.

Head bear tentacles,

but eyes are absent.

Radula is present.

Foot is broad and flat

and has 8 pairs of pedal

retractor muscles.

e.g. Neopilina.

Scaphopoda

Tusk-like shell open at both side.

Head is absent.

Radula is present.

Foot is conical shaped for digging.

e.g. Dentalium. Pelecypoda (Bivalvia)

Two-valved shell.

Head is absent.

Radula is absent.

Foot is wedge shaped

and muscular for

creeping or burrowing.

Absent in sedantary forms.

e.g., Pecten.

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Amphineura

• Shell is formed of 8 plates.


• Head is reduced and lacks
  tentancles and eyes.


• Radula is usually present.


• Foot is large, flat and
  muscular.


• Absent in some forms.
  e.g. Chiton.

Gastropoda

Spirally coiled shell,

but absent in

pulmonates.

Head bear both eyes

and tentancles.

Radula is present.

Foot is large and

flat for creeping

and attachment

e.g. Pila.

Cephalopoda (Siphonopoda)

Externally spiral shell.

Well-developed, internal or

absent.

Head bear a pair of large

complex eyes.

Radula is present.

Foot is partially modified

into 8-10 suckers and

partially into siphon or funnel.

e.g. Octopus.

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  Phylum–Mollusca

  
  

Spine

Dermal branchae

Pedicellariae

Jaws

Basilar plate

Stalk

dillarie spine and dermal branchae and

parallel jaws

B

C

Phylum–Echinodermata

Asteroidea

Star-shaped

body with

pentagonal disc.

5-50 arms

are present.

Bipinnaria larva

e.g. Asterias.

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Ophiuroidea

Star-shaped

body with

rounded disc.

5-7 arms

are present.

Pluteus

larva.

e.g. Ophiothrix.

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Echinoidea

Spherical, oval

or heart-shaped

body.

Arms are

absent.

Echinopluteus

larva.

e.g. Echinus.

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Holothuroidea

Elongated and

cylindrical body.

Arms are absent.

Auricularia larva.

e.g. Holothuria.

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Crinoidea

Contains mostly

extinct forms.

e.g. Antedon.

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Five classes

a

Marginal

spines

Madreporite

Arms

Terminal Tentacle

Anus

Central disc

Aboral surface of Asterias (Star fish)

w PHYLUM–MOLLUSCA

THE SOFT BODIED ANIMALS

(L. Molluscs–soft)

A HABITAT

• They are mostly marine. Some occur in
  freshwater and some in damp soil.

B GENERAL CHARACTERISTICS

• The body is unsegmented with a distinct

head, muscular foot and visceral hump.

(Neopilina is a segmented mollusc).

• They show bilateral symmetry. Some (e.g.

Pila), become asymmetrical due to torsion.

• A shell of calcium carbonate is secreted by

mantle. Shell may be external, internal

(slug, cuttle fish, squid) or absent (Octopus).

• A thin, fleshy fold of dorsal body wall,

mantle (pallium) more or less covers the

body.

• Body wall consists of single layered

ciliated epidermis. Muscles are unstriped

and occur in bundles.

• Coelom is greatly reduced and forms
  haemocoel.


• Digestive tract is complete.


• Blood vascular system is of open type. It

includes heart, arteries and veins.

Blood is of blue colour due to the presence

of a copper containing respiratory

pigment, haemocyanin (Cuttle fish have

closed vascular system).

• Respiration occurs through gills

(ctenidia), mantle and pulmonary sac

(in semi- terrestrial forms).

• Excretion occurs through one or two pairs

of sac-like kidneys. Gills are also excretory

in function. Ammonia is chief excretory

waste.

• The nervous system comprised paired cerebral,

pleural, pedal and visceral ganglia joined by the

nerve connectives and commisures.

• Eyes are present over stalks called

ommatophores. Statocysts may also be present.

Osphradium is used for testing chemical and

physical nature of water.

• Sexes are separate, but some are hermaphrodite.


• They are oviparous. Development may be direct

or indirect (veliger, trochophore or glochidium

larva). Asexual reproduction is absent.

x PHYLUM–ECHINODERMATA

THE SPINY SKINNED ANIMALS

(Gk. Echinos–spines; derma–skin)

A HABITAT

• All existing echinoderms are marine. They
  usually live at sea bottom. Some are pelagic and
  some are sessile.

B GENERAL CHARACTERISTICS

• Body is unsegmented, lacks head. The body could
  be star-shaped, spherical or cylindrical.


• Many echinoderms bear spines (for protection)
  and pincer-like pedicellariae (to keep body surface
  clear of debris).


• Its larvae are bilateral symmetrical while adults
  show pentamerous radial symmetry.


• Epidermis is single layered and ciliated. Many have
  endoskeleton of calcareous plates in the dermis
  which are mesodermal in origin.


• Presence of ambulacral system (water vascular

system) is their characteristic feature. They possess

a perforated plate, madreporite which allows

water into the system.

• Tube feet help in locomotion, capture of food and
  respiration. Water vascular system is of coelomic
  origin.


• Digestive tract is complete. Brittle stars have

incomplete digestive tract.

• Instead of blood vascular system, haemal and
  perihaemal systems (of coelomic origin) are found.


• Circulatory system is of open type. Blood is
  without a respiratory pigment and heart is absent.


• Gaseous exchange occurs by dermal bracnhae or

papulae in star fish, peristomal gills in sea

urchins, genital bursae in brittle stars and cloacal

respiratory trees in holothurians. Tube feet are

also used.

• Specialised excretory organs are absent. Nitrogenous
  wastes are diffused out via gills. Ammonia is chief
  excretory waste.


• Nervous system consists of nerve ring and radial

nerve cords.

• Usually sexes are separate, no sexual dimorphism.
  Fertilisation is usually external.


• Some reproduce asexually by self-division.


• Autotomy and regeneration are well-marked
  phenomena.


• Development is indirect. A ciliated, bilaterally

symmetrical larva changes into a radially

symmetrical adult.

Apex of shell

Sutures

Lines of

growth

Body

whorl

Umbilicus

Inner lip

Penultimate

whorl

Outer

lip

Operculum

Pila

Arms

Suckers

Web

Funnel

Visceral

hump Head

Eye

Hectacotylysised

arm

Octopus