Hemichordata and Invertebrate Chordates

Phylum HemichordataAll live marine environments.

Bilaterally symmetrical.

Body divided into three sections, a proboscis, a collar and a trunk. Characteristics of Hemichordata:-

Body cavity a truecoelom divided intothree cavities.Complete digestive tract, feeds on fine particles in the water. Dorsal, sometimes tubular, nerve cord.

Class EnteropneustaBurrow in sandy and muddy substrates

Ciliated epidermis and glandscover acorn worms

Marine wormsCommon name acorn worms

Maintenance FunctionsVentral MouthLateral Pharyngeal slits,few to several hundredCilia and mucus assist acorn worms in feedingCiliary tracts converge near the mouth and form a mucoid string that enters the mouth

Enteropneusta extends its posterior end out of the burrow during defecation.Eww!!!

Nervous systemEctodermal in originLies at the base of the ciliated epidermisConsist of dorsal and ventral nerve tractsNo major gangliaSensory receptors are unspecialized

RespirationSimple diffusion of metabolic wasteCilia associated with Pharyngeal slits circulate water into mouth and out of bodyGas exchange as water passes through pharyngeal slits

Circulatory systemColorless blood moves nutrients and wastesDorsal and ventral contractile vesselBlood moves anteriorly in dorsalPosteriorly in ventral vesselBranches from theses vessels lead to open sinuses (Partially open circulatory system)Anterior flowing blood moves through glomerulus (excretory organ)Waste filtered into proboscis coelom and out through pores found in wall of proboscis

Reproduction and DevelopmentDioecious!!External Fertilization pheromones

Evolutionary ties b/w hemichordatres and echinodermsCiliated larvae

Class Pterobranchiapteron- wing branchia- gill

Deep marine waterSome live in shallow waters

Body divided into three regionsSize 0.1 - 5mm

Individuals called zooids

Most live in secreted tubes in asexually produced colonies

Maintenance FunctionsFilter feedersCilia on tentacles trap and transportFood to mouthRespiration and excretory exchange by diffusion

Reproduction and DevelopmentAsexual budding is common and responsible for colony formation

Also some posses one or two gonads

Most species are dioeciousExternal fertilizationPlanula-like larva (cnidarian) Settles to a substrate, forms cocoon and metamorphoses into an adult

Phylum ChordataCharacteristic of the chordatesDeuterostome embryo development Notochord, phayngeal slits or pouches, dorsal tubular nerve cord, and postanal tailCoelomate animalsBilateral symmetryEndoskeletonTwo major groups: nonvertebrate chordates and vertebrates

Subphylum UrochordataUro, tail and chorda, cordClass ascidians Tunicates or sea squirts

Solitaire or colonialSessile adultsAttach to solid substratestwo siphons that permit seawater to circulate through the body Oral siphon also the mouthAtrial siphon

Body wallTunic- gownConnective tissue like coveringTough secreted by the epidermisComposed of proteinsSalts, celluloseStolons extensions of tunic help root

Maintenance FunctionsLongitudinal and circular muscles below the body wall epitheliumNervous system largely confined to body wallForms nerve plexus with a single ganglion between oral and atrial openingSensitive to mechanical and chemical stimuli around siphon but no complex sensory organs

Reproduction and DevelopmentTadpole larvaAttaches to substrate by adhesive papillae located below the mouthDuring development internal structures rotate 1800 bending the digestive tract into a U-shape

Reproduction and DevelopmentMonoeciousSelf fertilization and cross fertilization

Subphylum CephalochordataElongated laterally flattened nearly transparent LanceletsSize up to 5 cm tadpole like animalsAll four chordate characteristics persist throughout lifeShallow watersgenera Branchiostoma (Amphioxus)

Reproduction and DevelopmentDioeciousGonads shed gametes into the atrium Leave the body through the atrioporeExternal fertilization Bilaterally symmetrical larvaLarva free swimmingLarva Settle to substrate then metamorph into adults

Maintenance FunctionFilter feedersBuried in sandy substrateMouth pointed upward

Cilia on lateral surfaces of gill sweep water into mouth Food sorted in the cirri Edible particles move along cilia to the gut

No true heartContractile waves in the walls of major vessels propel bloodBlood contains amoeboid cells and bathes tissues in open spaces

Excretory tubules are modified coelomic cells closely associated with blood vessels.

Coelom reduced- restricted to canals near the gill bars, endostyle and the gonads