PRESICE AND SHORT NOTES TO BE ABLE TO CRACK NEET EXAM COMING FROM AN MBBS STUDENT. CAN BE USEFUL IN BOARD EXAMS AS WELL. INFORMATION FROM AAKASH COACHING CENTRES AND NCERT TEXTBOOKS HAVE BEEN ADDED.
CH 4 - Animal kingdom :
Metazoans : multicellular eukaryotic organisms - holozoic mode of nutrition (ingest internally)
● Parazoa : sponges - cells loosely aggregated - no tissue or organs
● Eumetazoa : rest of animals - organs, organ systems, tissues
Organisation levels :
● Cellular level - sponges - loose aggregate cells
● Tissue level - coelenterata (cnidaria) and ctenophores
● Organ level - platyhelminthes onlyy
● Organ system level - aschelminthes, annelida, arthropoda, mollusca, echinodermata, hemichordata,
chordata
○ Digestive sys - incomplete - single hole for mouth and anus - platyhelminthes
○ Circulatory sys - open type (blood pumped out of heart and cells directly bathed) closed type
(blood circulated through series of vessels - veins, capillaries)
Symmetry :
● Asymmetrical - sponges (porifera)
● Radial - ctenophores, colenerates (cnidaria), echinoderms
○ Simple radial - hydra
○ Biradial - adamsia (sea anemone)
○ Pentamerous radial - starfish
● Bilateral - all others - platyhelminthes, aschelminthes, annelida, arthropoda, molluscs, echinoderms,
hemichordata, chordata.
Germ layers :
● Diploblastic : 2 embryonic layers - ectoderm and endoderm - mesoglea in between
○ Ex: coelenterata (hydra), ctenophora
● Triploblastic - ecto, meso, endoderm - ex: platyhelminthes to chordata
Coelom :
● Acoelomate : body cavity absent - porifera to platyhelminthes (flatworms) - space between 2 germ
layers filled with parenchyma.
● Pseudocoelomate : mesoderm present as scattered pouches - roundworm (aschelminthes) -
nematodes.
● Eucoelomate : true coelom - annelids to chordates.
○ Schizocoelom : split in mesoderm - annelid, arthropods, mollusc.
○ Enterocoelom : mesoderm arise from a wall of embryonic gut (enteron) as hollow outgrowth -
echinoderms, hemichordates, chordates.
Segmentation :
● Annelids, arthropods, chordates - externally / internally divided - repetition of organs - earthworm
(annelids) - metameric segmentation (metamerism)
Notochord :
● Mesodermally derived - dorsal side
● Chordates - has notochord
● Non chordates - no notochord - porifera to echinodermata
Exclusively marine : ctenophores, echinoderms, hemichordates
Phylum porifera :
● Habitat : mostly marine - some freshwater - spongilla
● Habit (locomotive) : Sessile - attached - substratum
● Body plan : cellular level - some asymmetry, mostly radial symmetry - acoelomate - no germ layers
(ONLY PHYLUM WITH NO NERVE CELLS)
● Body form : mesohyl between pinacoderm (flattened cells) and choanoderm (flagellate cell -
choanocytes)
○ Choanocytes / collar cells - line spongocoel (body cavity)
, ○ Canal system present : water enters through OSTIA (minute pores) then into (central cavity)
OSTOCOEL then out of OSCULUM - helps in food gathering, respiration, removal of waste.
● Systems :
○ Digestive : intracellular in food vacuoles, holozoic nutrition, filter feeding
○ Respiratory : canal sys
○ Circulatory : canal sys
○ Excretory : ammonia, canal sys
○ Skeletal : spicules and spongin fibres - internal skeleton. (euspongia - only spongin fibres)
○ Nervous : absent
○ Reproductive : sexuality - hermaphrodite (not seperate)
■ Fertilisation - internal - sperm carried in water current to other sponge reach ova
■ Asexual - fragmentation
■ Indirect devp - has larvae stage (distinct from adult)
● Ex : sycon (scypha), euspongia (bath sponge), spongilla (freshwater sponge)
Phylum Coelenterata (cnidaria) :
● Habitat : mostly marine - few freshwater - ex : Hydra
● Habit (locomotive) : tentacles (6-10) or sessile - solitary (hydra) and colonial (obelia)
● Body plan : tissue level - radial symmetry - acoelomate - diploblastic (endoderm, ectoderm,
mesoglea)
● Body form : has cnidoblasts / cnidocytes (stinging capsules - nematocysts) on tentacles - used
for anchorage defence and capturing prey.
○ Blind sac - one opening to alimentary canal - mouth(stome) on hypostome
○ Polyp : cylindrical - sluggish, sessile - hydra, adamsia
○ Medusa :umbrella shaped - free swimming - aurelia, jellyfish
○ Alternation generation - metagenesis - polyps produce medusa asecually - medusa produce
polyps sexually - eg : obelia [PAMS]
● Systems :
○ Digestive : incomplete gut - only one opening - intracellular and extracellular digestion
○ Respiratory :
○ Circulatory :
○ Excretory :
○ Skeletal : CaCO3 - great australian reef (ex : corals)
○ Nervous : (nerve net - mesoglea) - neurons non polar
○ Reproductive : fertilisation is external, cross - indirect devp.
● Ex : physalia (portuguese man of war), adamsia (sea anemone), pennatula (sea pen), gorgonia
(sea fan), meandrina (brain coral).
Phylum ctenophora : comb jellies - sea walnut - comb plates.
● Habitat : exclusively marine
● Habit (locomotive) : eight rows of ciliated comb plates, free swimming, tentacles (2)
● Body plan : tissue level - radial symmetry - acoelomate - diploblastic
● Body form : bioluminescence (emit light - glow)
● Systems :
○ Digestive : incomplete gut - one opening (mouth and anus) - intracellular and extracellular.
○ Respiratory, Circulatory, Excretory, Skeletal : absent
○ Nervous : sensory cells and nerve cells
○ Reproductive : only sexual means - hermaphrodite (not seperate) - fertilisation is external,
cross - indirect devp (cydippid larva)
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