13Mollusca

▢ Introduction:
❖ Meaning: Term 'Mollusca' means Soft body. Wow great.
❖ CoinedBy: Term 'Mollusca' was coined by Johnston.
❖ Study:
◉ Malacology: Study of Mollusca is called Malacology. What is the study of other things called then.
◉ Conchology:
  1. Study of Shells of Mollusca is called Conchology. Okay you mean to say other things are not called this.
◉ This is the new value:
❖ Habitat:
◉ Marine: Most members are Marine.
◉ Freshwater: Some are found in Freshwater.
◉ Terrestrial: Few are Terrestrial.
▢ General Characters:
❖ Body Plan:
  1. Triploblastic body plan
  2. Bilateral symmetrical (except Gastropods, which are asymmetrical due to torsion)
  3. Unsegmented body (except Neopilina)
  4. Haemocoelomate
❖ Circulatory System: Open circulatory system (except Sepia, which shows tendency to become closed)
▢ Mantle or Pallial Cavity:
❖ MantleFeatures:
◉ Description: Body covered by a skin fold called mantle with shell glands.
◉ Secretes:
  1. Calcareous spicules
  2. Shell plates
  3. Shells
◉ Shell Types:
◈ External: Generally external shells
◈ Internal: Sepia, Slug, Loligo
◈ Absent: Octopus
◉ Shell Composition: Shell made up of Calcium carbonate – protects and supports soft tissues.
◉ Shell Features:
◈ Umbo: In Unio, the oldest and thickest part of shell is called Umbo.
◈ Layers:
  1. Periostracum
  2. Prismatic layer
  3. Nacreous layer
  4. Mantle
❖ Cavity Structures: Mantle cavity contains a pair of pulmonary sacs.
❖ Yes i liked this:
❖ What about this one.:
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❖ this feel goodat firts:
◉ Key:
❖ What about this one:
◉ Key:
◈ sdf: sthis is newsdf
◈ you: Then this is one
◈ I like: This is the next one
◈ then what:
▢ Body Wall:
❖ Epidermis: Single layered ciliated epidermis
▢ Body Regions:
❖ Head: Head bears the mouth and sense organs.
❖ Foot:
◉ Description: Ventral part used for locomotion.
◉ Functions:
  1. Locomotion
  2. Crawling in snails
  3. Modified into tentacles in squid for capturing prey
❖ VisceralHump: Contains digestive tract and other visceral organs.
▢ Digestive System:
❖ Structure:
  1. Complete digestive tract
  2. Digestive gland or liver (hepatopancreas)
❖ BuccalCavity:
◉ Radula:
◈ Description: Rasping organ present in buccal cavity
◈ Structure:
  1. Transverse rows of chitinous teeth
  2. Each row contains 7 teeth
  3. Radula supported by Odontophore (used for straining food)
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◈ Example: Present in Pila
◉ Feeding: Cilia of gills in bivalves help in feeding
❖ GreenGland:
◉ Presence: Present in Unio
◉ Function: Analogous to liver of vertebrates
▢ Circulatory System:
❖ Blood:
◉ Contents:
  1. Amoebocytes
  2. Respiratory pigment: Haemocyanin (copper containing, dissolved in plasma)
◉ Color: Blood is blue due to Haemocyanin
▢ Respiratory System:
❖ Organs:
◉ Gills: Aquatic Molluscs (e.g., Monopectinate in Pila)
◉ Pulmonary Sacs: Aerial Molluscs
◉ Direct: Sometimes occurs
▢ Excretory System:
❖ Organs:
  1. Pair of kidneys (Organ of Bojanus)
  2. Pericardial gland (Keber's gland)
▢ Reproductive System:
❖ Type: Sexual reproduction
❖ Sexes: Dioecious or Monoecious
❖ Fertilization: Generally external
❖ Reproduction: Mostly oviparous, few viviparous
❖ Development:
◉ Mode: Direct or via larval forms
◉ Larvae:
  1. Trochophore
  2. Veliger (larva of marine pelecypods)
  3. Glochidium (ectoparasite, metamorphoses in gills of fish)
▢ Nervous System:
❖ Structure:
  1. Paired ganglia
  2. Commissures
  3. Connectives
❖ Type: Complete ladder-like nervous system
❖ Sense Organs:
◉ Eyes: Includes ommatophores (stalks bearing eyes)
◉ Statocysts: Used for maintaining equilibrium
◉ Tentacles: Sensory structures
◉ Osphradia: Chemoreceptors for testing water quality
◉ Lithocysts: Sensory structures
▢ Classification:
S.N.
Aplacophora
Monoplacophora
Polyplacophora
Scaphopoda
Gastropoda
Pelecypoda/ Bivalvia
Cephalopoda/ Siphonopoda
Common name
Solenogasters animal
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Chitons
Tooth shells or Tusk shells
Shell
Absent
Single cap like
8 pieces
Single piece
Single piece, usually spirally coiled.
Bivalve
  1. May be:
  2. • External (Nautilus)
  3. • Internal (Sepia)
  4. • Absent (Octopus)
Foot
Absent
Flat
Muscular
Adapted for digging
Flat, large and highly muscular
Laterally compressed without shell
Located on the head modified in the form of oral arms
Features
1. Calcareous spicules are found.
Most primitive mollusc having characters of Annelids.
During development, Visceral mass and Mantle rotate 90–180° on foot, a phenomenon called Torsion.
Examples
  1. Neomenia
  2. Chaetoderma
  1. Neoplina
  2. Living fossil and connecting link between annelids and Molluscs
  3. Segmented body
  1. Chiton
  2. Lepidopleurus
  1. Dentallium (Elephant's Tusk shell)
  1. Pila (Apple snail)
  2. Helix (Garden snail)
  3. Limax (Slug)
  4. Turbinella (Shankha)
  5. Cypraea (Cowda)
  6. Aplysia (Sea hare)
  7. Doris (Sea lemon)
  8. 1. Radula is present in it.
  9. 2. Gill is monopectinate.
  10. b. Gill of Pila consists of long ctenidial axis with a single row of a long series of triangular leaflets known as lamellae. Such a gill is called Monopectinate.
  1. Unio (Fresh water mussel)
  2. Mytilus (Sea water mussel)
  3. Teredo (Ship worm)
  4. Pecten (Scallops)
  5. Pinctada vulgaris (Pearl oyster)
  1. Octopus (Devil fish)
  2. Sepia (Cuttle fish)
  3. Loligo (Squid)
  4. Architeuthis (Giant squid)
  5. Nautilus
  6. • Closed circulatory system
  7. • Ink gland in some squids for offence and defence.
Q1.
Molluscs possess
Q2.
Radula is present in
Q3.
Closed circulatory system does not occur in
Q4.
Trochophore is the larva of
Q5.
Which of the following is a freshwater mollusca?
Q6.
Most primitive among the following molluscs is
Q7.
The most remarkable characteristic of Neopilina is
Q8.
Filter feeding occurs in
Q9.
Amoeboid sperms are not found in
Q10.
Which of the following eats its prey?
Q11.
In cephalopod Sepia
Q12.
Members of which phylum exhibit adaptations to widely varied environmental conditions?
Q13.
Which one of the following is not a deuterostome?
Q14.
Which one of the following classes has the maximum economic importance?
Q15.
Doris is commonly known as
Q16.
Which of the following is absent in Mollusca?
Q17.
In mollusca, eye is present over a stalk called
Q18.
The main component of pearl is
Q19.
Pearl is produced by animals of phylum
Q20.
Shell of mollusca is derived from
Q21.
Pericardial gland of Unio is called
Q22.
Octopus belongs to the class
Q23.
Torsion is the characteristic in Pila belonging to class
Q24.
The phylum name Mollusca means
Q25.
The metallic ion contained in the blood of mollusca is
Q26.
Ctenidia in molluscs are
Q27.
A cephalopod without a shell is
Q28.
Many molluscs have a water-testing organ present in the mantle cavity called
Q29.
A devilfish has
Q30.
In mollusca, blastopore gives rise to
Q31.
Sepia and octopus swim swiftly by means of
Q32.
Trochophore is the larva of
Q33.
Pearl is secreted by
Q34.
A wood-boring mollusc is
Q35.
Asymmetry in gastropoda is due to
Q36.
Eye of molluscan group that resembles vertebrate eye is in
Q37.
In cephalopoda