animal diversity iiØ kingdom animalia consists of organisms ranging from the simplest of animal...
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B.Sc. II Semester
ANIMAL DIVERSITY II
UNIT I
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KINGDOM ANIMALIA
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Ø Kingdom Animalia consists of organisms ranging from the simplest of animal forms to the most complex.
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Kingdom Animalia
Non-chordates Chordates
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Phylum Chordata Created by Balfour in 1880
Chorde = string or cord; ata = bearing
On the basis of ‘notochord’
Noton = back; chorda = cord
Thus, Chordata are animals having a cord i.e. notochord
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• The chordates form a large heterogenous group of members differing widely from one another.
• They are largest deuterostome phyla
• highest and most important, including vast variety of living and extinct animals, (including man)
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FUNDAMENTAL CHORDATE CHARACTERS
1. A longitudinal supporting rod-like notochord
2. A dorsal hollow or tubular nerve cord
3. A series of pharyngeal gill slits
4. A postanal tail.
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Cephalochordata VertebrataUrochordata
PHYLUMCHORDATA
Acrania or
(Lower chordata) (Higher chordata)
Craniata or Euchordata Protochordata
3 subphylums
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Subphylum Cephalochordata • Gr. Cephale = head; L. chorda = string or cord
Notochord from head to tail.
• The organisms in this subphylum are called Lancelets, as body shape matches with lancet.
• All fundamental chordate characters present.
• Exclusively Marine, widely distributed, found in shallow waters.
• Mostly sedentary and burried in sand with anterior side (mouth) outside during filter feeding.
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• Body small 5-8 cm long, laterally flattened, slender, elongate, fish-like, metameric and transparent.
• Body lacks head and is divisible into trunk and tail.
• Paired appendages lacking. Median fins present.
• Exoskeleton is absent and epidermis is single layered.
• Muscles dorsolateral segmented into myotomes.
• Muscle cells present on sides of notochord; contraction and relaxation of muscle fibres creates movement in notochord, thus helps in moving body.
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• Coelom entrocoelous reduced in the pharyngeal region by development of atrial cavity (only gill bars).
• Notochord is persistent through out the life, extending from rostrum to tail.
• Nerve cord is dorsal, tubular and hollow, without ganglion and brain. Dorsal and ventral roots are separate.
• Two pairs of cerebral and several pairs of spinal nerves are present.
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• Digestive tract complete; Mouth leads to pharynx, (posterior part of mouth is attached to pharynx which is large sac-like) perforated by numerous persistent gill-slits for filtration in the atrium.
• All are filter feeders.
• Respiration through general body surface i.e., no specialized respiratory structure found.
• Circulatory system is closed type, without true heart and respiratory pigments. Walls of blood vessels contract producing movement in blood for circulation.
• Hepatic portal system is developed.
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• Excretory system shows paired protonephridia with solenocytes.
• Diocieous; sexes are separate. Gonads are metamerically arranged and without gonoducts. No asexual reproduction.
• Gametes released in atrium, exit through atriopore in sea water. Fertilization external.
• Development indirect, including a free-swimming larva.
• Larva before metamorphosis attaches to substrate.
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Classification: SubphylumCephalochordata
Leptocardii family
Branchiostomidae
class
Branchiostoma (Amphioxus)
Asymmetron
genus
Unpaired gonads, lie only on the right side of body
paired gonads, lie on each side of body
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Primitive, degenerate and specialized characters of Branchiostoma (Cephalochordata)
– Primitive characters:
Branchiostomaisregardedtobeaprimi4vechordate.itdiffersfromvertebratebecauseitretainsseveralprimi4vechordatecharactersinmosttypicalorunmodifiedform.
Theseprimi0vecharactersare:
– Asymmetricalbodyasinechinodermswhichareregardedtohavecommonancestrywithchordates.
– Absenceofaspecializedheadorcephaliza4on
– Absenceofpairedlimbsorfins.
– Epidermisone-cellthick.Dermisabsent.
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– Coelomenterocelous,arisingaslateralpouchesofLavalarchenteron.
– Metamericallyarrangedmusclesormyotomes.
– Notochordpersistentthroughoutlife.Vertebralcolumnoranyotherendoskeletonnotdeveloped.
– Jawsabsent.Alimentarycanalstraight.
– Pharynxlarge,perforatedbypersistentgillslitsandspecializedforciliarymodeoffeedingbydrawingawater-foodcurrent.Endostylepresentwithoutmodifica4on.
– Liverrepresentedbyamidgutdiver4culum.
– Bloodvascularsystemissimple,withoutaheartandanydis4nc4onbetweenarteriesandveins.Hepa4cportalsystemisprimi4ve.
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– Nospecialreportrespiratoryorgansandrespiratorypigment
– Excre4onbysegmentallyarrangedprotonephridiawhicharenotcoelomoducts.
– Neural tube hollow lying dorsally above notochord.Specialised brain lacking. Dorsal and ventral roots of spinalnervesseparate.Dorsalrootswithoutgangliasothatimpulsespassdirectlyfromskintoneuraltube.
– Sensoryorganssimpleandpaired.
– Gonadsseveralpairs,alikesegmentallyarrangedandwithoutgonoducts.
– Eggaresmall,almostyolkless.Blastulaissperical,hollowandone-layered
– Gastrula4onembolic.
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Degenerate characters:
Branchiostoma was once more developed but underwentspecializa4on and degenera4on during evolu4on due to semisedentarymodeoflife.
Thesecharactersare:– Poorlydevelopedbrain(cerebralvesicle)andsimplesensoryorgans.
– Lackofanycar4laginousorbonyendoskeleton.– Lackofgonoducts.
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Specialized, peculiar or secondary characters: Changesdevelopedduetospecialmodeoflife(becauseoftheirdegenerateandspecialcharacterstheyarenotconsideredindirectlineofevolu4onofchordatesbutassideoffshoots).
Theseare:– Peculiarasymmetryofadultandearlyestagesofdevelopment.
– Anterior projec4on of notochord into rostrum making itstrongerforburrowing.Overdevelopmentofnotochordmayberesponsibleforthelackofbrain.
– Mouthsurroundedbyoralhood,withsensoryoralcirri,meantforfilteringandconcentra4ngfoodpar4clesfromwater.
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– Elaboratevelumwithsensorytentaclestopermitonlysmallfoodpar4clestoenterpharynx.
– Large,spaciousandelaboratepharynx,withciliatedgill-cleSswhicharemorenumerousthanactualbodysegments,toenablesufficientfoodcollec4on.
– WheelorganandHatschek’sgrooveandpitdevelopedtohelpinciliaryfeeding.
– Delicatepharynxsurroundedbyaprotec4veatrialcavityopeningtooutsidethroughatriopore.
– Coelomdisplacedandreducedduetodevelopmentofatrium.