The document summarizes key characteristics of the phylum Mollusca. It includes 80,000 living species of soft-bodied animals found in terrestrial, freshwater, and marine environments. They have a head, muscular foot, and visceral hump. Respiration occurs via gills and circulation is open, except in cephalopods. Molluscs exhibit bilateral symmetry and have torsion in gastropods. Their classification divides them into two subphyla - one with a single shell and the other with multiple shell plates.

2. Subphylum: Chelicerata
General characters:
Body: Prosoma (6) and Opisthosoma (12)
A pair of chelicerae on the 1st prosomal
segment
 One pair of pedipalps + 4 pairsof walking
legs
 Three classes:
1.Arachnida
2. Merostomata
3. Pycnogonida

5. SP: Chelicerata, Class Merostomata
Limulus limus – horseshoe crab

6. SP Chelicerata, Class Merostomata

7. SP: Chelicerata, Class Pycnogonida

8. SP Chelicerata, Class Arachnida, Order Araneae

10. General characters:
Includes: scorpions, spiders, ticks and mites
All areterresterial
 No antennae or true jaws
 Head is not distinct
 The body: prosoma (6) + opisthosoma
 Respiration by:
1. lung books or tracheae in terresterial forms
2. through skin in parasitic forms
3. gill books in aquatic forms
 Excretion by Malpighian tubules or coxal glands
 Open Circulatory system
 Separate sexes. Viviparous or Oviparous
 Mostly carnivorous but some are ectoparasites
Class: Arachnida

11. Classification
of
Arachnida
O:
Scorpionidea

12. O: Scorpionidea
 Terrestarial
 Body: pro-, meso- and meta- soma
 Prosoma: one pair of chelicera,
one pair of pedipalps,
4 pairs of walking legs
 Mesosoma: 6 segments
 A pair of pectins on the 2nd segment of mesosoma
 Respiration: by 4 pairs of lung books
 Viviparous
 eg Buthus quinquestriatus (scorpion)

14. Lethally Poisonous Scorpions
Centruroides exilicauda
Leiurus quinquestriatus

15. Class Arachnida, Order Scorpionida
Paninus imperator (Emperor scorpion)

18. O: Araneida
 Terrestarial
 Body: pro-, and opistho- soma
 Prosoma: one pair of chelicera (non-chelate),
one pair of pedipalps (non-chelate),
4 pairs of walking legs
 Opisthosoma: 12 segments
 Spinnerets: 2-4 pairs
 Respiration: by lung books
 Oviparous
 eg Lycosa ferox (wolf spider)

19. SP Chelicerata, Class Arachnida, Order Araneae

20. Spinnerets

22. Anatomy of spider

26. Regional Poisonous Spiders
Lactrodectus mactans
Loxosceles reclusa

27. Brown Recluse Bite Victom

28. Tan Tarantula
Argiope aurantia
Aphonopelma anax
Golden Orb Spider/Garden Spider

29. Class Arachnida, Order Opiliones

30. Class Arachnida, Order Solifugae
Eremobates sp

31. Class Arachnida: Ticks and mites
• No external division or segmentation
• Found almost everywhere
• Chiggers: feed on dermal tissues of
humans
• Dust mites: can cause allergies
• Hair follicle mites: infect most of
us, but we are unaware of it
• Ticks spread disease: Rocky mountain
fever and Lyme’s disease

35. Class Arachnida, Order Acari
Dermacentor variabilis American dog tick
Rhipicephalus sanguineus Brown dog tick
Rocky mountain spotted fever

36. Class Arachnida, Order Acari
Ixodes scapularis Deer tick
Lyme disease

37. Class Arachnida, Order Acari

38. Class Arachnida, Order Acari
Eutrombicula alfreddugesi Chigger
Sarcoptes scabiei scabies mite

39. Class Arachnida, Order AcariDermatophagoides spp
Dust mite

40. Class Arachnida, Order Amblypygi

43. CHARACTERISTICS
Second largest phylum in the animal kingdom
(80000 living species and 40000 fossil species)
Soft bodied animals
Body: head, foot and visceral hump
Microscopic to macroscopic
They include
chitons, snails, slugs, clams, oysters, cuttlefish,
squids, octopods, scaphopods, …….
Slow to active organisms
Coelomate, triploplastic, unsegmented

44. Terrestrial, freshwater, or marine
environments
Occur in a wide variety of environments
Have different modes of nutrition
Bilateral symmetry, torsion and coiling in
gastropods
True coelom is reduced
Skin is soft and often secrets the exoskeleton or
the shell
Respiration by one to many gills (ctenidia)
Radula in most molluscs
Circulatory system of open type (except
cephalopods)

45. Blood contains haemocyanin and amoebocytes
The nervous system is composed of a nerve
ring around the oesophagus and two pairs of
nerve cords
Sense organs include tentacles, eye
spots, statocysts in foot and osphradia beside gills
Excretion by a pair of u- shaped metanephridia
Molluscs are unisexual (dioecious) but some
are hermaphrodite (monoecious)
Fertilization is mostly external and rarely
internal
Development is direct (no larva) or indirect
through free swimming trochophore and/or
veliger larvae

46. GENERAL BODY PLAN
Head
Ventrally located muscular foot
Dorsally located visceral mass
Mantle / pallium – for shell/spicule secretion
Radula (except for bivalves)
Complete digestive tract
Gonads in visceral mass
Monoecious or dioecious

47. • Subphylum Conchifera: with 1 shell; (-)
spicules
1. Class Gastropoda
2. Class Bivalvia
3. Class Cephalopoda
4. Class Scaphopoda
5. Class Monoplacophora
• Subphylum Aculifera: with multiple shell
plates; (+) spicules
1. Class Polyplacophora
2. Class Aplacophora
CLASSIFICATION