B.Sc. II Semester

ANIMAL DIVERSITY II

UNIT I

KINGDOM ANIMALIA

Ø Kingdom Animalia consists of organisms ranging from the simplest of animal forms to the most complex.

Kingdom Animalia

Non-chordates Chordates

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

• 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)

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.

Cephalochordata VertebrataUrochordata

PHYLUMCHORDATA

Acrania or

(Lower chordata) (Higher chordata)

Craniata or Euchordata Protochordata

3 subphylums

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.

•  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.

•  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.

•  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.

•  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.

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

Primitive, degenerate and specialized characters of Branchiostoma (Cephalochordata)

– Primitive characters:

Branchiostomaisregardedtobeaprimi4vechordate.itdiffersfromvertebratebecauseitretainsseveralprimi4vechordatecharactersinmosttypicalorunmodifiedform.

Theseprimi0vecharactersare:

– Asymmetricalbodyasinechinodermswhichareregardedtohavecommonancestrywithchordates.

– Absenceofaspecializedheadorcephaliza4on

– Absenceofpairedlimbsorfins.

–  Epidermisone-cellthick.Dermisabsent.

– Coelomenterocelous,arisingaslateralpouchesofLavalarchenteron.

– Metamericallyarrangedmusclesormyotomes.

– Notochordpersistentthroughoutlife.Vertebralcolumnoranyotherendoskeletonnotdeveloped.

–  Jawsabsent.Alimentarycanalstraight.

–  Pharynxlarge,perforatedbypersistentgillslitsandspecializedforciliarymodeoffeedingbydrawingawater-foodcurrent.Endostylepresentwithoutmodifica4on.

–  Liverrepresentedbyamidgutdiver4culum.

–  Bloodvascularsystemissimple,withoutaheartandanydis4nc4onbetweenarteriesandveins.Hepa4cportalsystemisprimi4ve.

– 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.

Degenerate characters:

Branchiostoma was once more developed but underwentspecializa4on and degenera4on during evolu4on due to semisedentarymodeoflife.

Thesecharactersare:– Poorlydevelopedbrain(cerebralvesicle)andsimplesensoryorgans.

– Lackofanycar4laginousorbonyendoskeleton.– Lackofgonoducts.

Specialized, peculiar or secondary characters: Changesdevelopedduetospecialmodeoflife(becauseoftheirdegenerateandspecialcharacterstheyarenotconsideredindirectlineofevolu4onofchordatesbutassideoffshoots).

Theseare:– Peculiarasymmetryofadultandearlyestagesofdevelopment.

– Anterior projec4on of notochord into rostrum making itstrongerforburrowing.Overdevelopmentofnotochordmayberesponsibleforthelackofbrain.

– Mouthsurroundedbyoralhood,withsensoryoralcirri,meantforfilteringandconcentra4ngfoodpar4clesfromwater.

–  Elaboratevelumwithsensorytentaclestopermitonlysmallfoodpar4clestoenterpharynx.

–  Large,spaciousandelaboratepharynx,withciliatedgill-cleSswhicharemorenumerousthanactualbodysegments,toenablesufficientfoodcollec4on.

–  WheelorganandHatschek’sgrooveandpitdevelopedtohelpinciliaryfeeding.

–  Delicatepharynxsurroundedbyaprotec4veatrialcavityopeningtooutsidethroughatriopore.

– Coelomdisplacedandreducedduetodevelopmentofatrium.