Phylum Mollusca, Study notes of History

Download Phylum Mollusca and more Study notes History in PDF only on Docsity!

AnnelidaMollusca

EchinodermataArthropoda

Chordata

PlatyhelminthesNematoda acoelomate^ pseudocoelomates

eucoelomates Rotifera

deuterostomes^ Hemichordata

Phylum Hemichordata

•Share characteristics with bothEchinoderms and Chordates•Like chordates they have gillslits and a dorsal nerve cord.•They have a larval form called atornaria that is similar to theEchinoderm bipinnaria

Phylum Hemichordata

•Some species are colonial and livein secreted tubes (superficiallyresemble polychaetes)

AnnelidaMollusca

EchinodermataArthropoda

Chordata

PlatyhelminthesNematoda acoelomate^ pseudocoelomates

eucoelomates Rotifera

deuterostomes^ Hemichordata

Chordata Characteristics All chordates possess these 4 unique characters atsome point in their life:^ • notochord^ • dorsal hollow nerve cord^ • pharyngeal slits^ • postanal tail

anus

mouth^

basic chordate body plan

Chordata Characteristics

Notochord

• a flexible rod-like structure • extends the length of the body • an axis for muscle attachment • in all jawed vertebrates, it is replaced by a series ofcartilaginous or bony vertebrae

Chordata Characteristics

Pharyngeal slits

• perforated slit-like openings that connect thepharyngeal opening and the outside• formed by alternating pharyngeal grooves andpouches• in aquatic chordates, they become the gills• in tetrapod (4 limbed) vertebrates, they becomeparts of the throat and ear cavity

Chordata Characteristics

Postanal tail

• located posterior to the anus • associated with somatic musculature • provides motility in the aquatic environment

segmented myotomesanchored to notochord

Subphylum Urochordatatunicates, ascidians, sea squirts, etc.

Subphylum Urochordata • 3000 species •marine •swimming “tadpole larva”possesses all 4 chordatecharacteristics • sessile adults (mostly) have lost all chordatecharacteristics except pharyngeal gill slits

Subphylum Urochordata

Adult Anatomy

mouth Pharynx/ atrium^ **gill slits ***

buccal siphon^ atrial siphon^ anus^ intestine^ tunic

larvae settled larvae

Metamorphosing•Notochord and nerve cord absorbed•Entire body rotates 180

o •The number of pharyngeal slitsincreases

adult

Feeding and Digestion

transverse vessel^ gill slit^ longitudinal vessel

The ascidian pharynxshows an evolutionarytrend for increasedsurface area

Circulation

gut vessels heart Urochordates have acomplete circulatorysystem with a heart.