Invertebrate chordates

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what are the invertebrate chordates?

• invertebrate - animals without backbone

• chordates - animals with nerve cord

what is the notochord?

• longitudinal flexible rod between gut and nerve cord

• provides structural support

• key for swimming in chordate ancestors 

• replaced by vertebrae in vertebrates

what is the dorsal hollow nerve cord?

• lies dorsal to the notochord

• develops from rolled ectodermal tissue

• develops into the central nervous system

what are the pharyngeal slits?

• slits that open to the outside of the body

• develop from grooves in the pharynx called pharyngeal clefts

functions:

• suspension feeding

• gas exchange in vertebrates

• repurposed - ear structures and tonsils

what is the post anal tail?

• chordates have a tail posterior to the anus

• contains skeletal elements and muscles

• provides propulsion in many aquatic species

• reduced or lost in many species

Why are they not quite vertebrates?

• two invertebrate lineages: tunicata and cephalochordata

• both closer to vertebrates than other invertebrates

differences:

• no vertebrae (backbone)

• no true head

• use of pharyngeal slits for feeding not respiration

What are features of class ascidians?

• common in coastal habitats

• known as sea squirts

• filter feeders

• could be confused with sponges

• bluebell sea squirts: solitary, clumped or colonial growth forms

What is ascidian reproduction like?

• most are hermaphrodites

• gametes released into water collumn

• develop into free swimming tadpole larvae

• larvae last a few minutes to days

• settle and metamorphosise into sessile adult form - losing notochord, dorsal nerve chord and tail

What are the features of thaliacea (salps)?

• similar to adult ascideans

• not as sessile

• free swimming tunicates

• solitary and colonial forms

• morphology adapted for jet propulsion

what is the role of salps?

• salps are food for many marine animals

• they filter large amounts of water

• they produce heavy carbon rich pellets

• much about their ecology still unknown

what are the majestic colonial salps?

• pyrosomes

• long gelatinous colonies

• many zooids embedded in a shared tunic

• zooids orientated in same direction - water pumped into the atrial chamber

• often biolumiscent

what are the features of appendicularia?

• larvaceans

• have a mucus house

• mucus house typically lasts three hours

• larvaceans very common

• mucus house is major pathway for moving carbon and nutrients to deep waters

what are the features of cephalochordates?

• small fish like invertebrate chordates

• bury in shallow marine sediments

• found globally

feeding:

• water enters mouth into pharynx

• mucus from endostyle traps food

• water exits via pharyngeal gill slits

movement:

• myotomes provide swimming movement

• notochord resists compression and prevents body shortening

• tail fin aids propulsion

• some cephalisaion present

what are the risks to invertebrate chordates?

• habitat loss from coastal development and pollution

• impacts of climate change - acidification etc

• bycatch and overfishing

• invasive species altering community structure

What are the invertebrate chordate classes?

• ascidiacea (ascideans)

• thaliacea (salps)

• appendicularia ( larvaceans)

• sub phylum cephalochordata