2 Evolutionary Perspective Echinoderms, Hemichordates, and Chordates are most likely derived from a common (yet undiscovered) ancestor, since they all share deuterostome characteristics.
3 What characterizes a chordate? A dorsal tubular/hollow nerve cordA notochordPharyngeal slits or pouchesPostanal tail
4 Which are shared by both Chordates and Hemichordates? Pharyngeal slitsMost have a dorsal (sometimes hollow) nerve cord.This shows that evolutionary ties b/w Hemichordates and Chordates are closer than b/w echinoderms and either of these phyla.
6 Hemichordates Hemichordata means “half chord” Includes: Acorn worms and PterobranchsLive in or on marine sediments
7 5 Characteristics of Hemichordates Marine, deuterostomes w/bodies in 3 segements-proboscis, collar, and trunkCiliated pharyngeal slitsOpen circulatory systemComplete digestive tractDorsal (sometimes hollow) nerve cord
8 Class EnteropneustaAcorn worms-named so b/c of the proboscis at the anterior end75 species, cm usuallyMost occupy U-shaped burrows along the sandy shore-lineCilia and a mucous-covered proboscis assist in feeding
9 Class Pterobranchia Name means “wing or feather gills” Around 20 species-RhabdopleuraSmall mm, often living in secreted tubes in asexually produced coloniesProboscis is sheild-like and secretes the tubeFound mostly in deep oceans of the Southern hemisphereUse cilia on arms/tentacles to filter and transport food to mouth
11 Phylum Chordata Bilateral symmetry, deuterostomes Notochord, pharyngeal slits or pouches, dorsal nerve chord, and postanal tail present at some point during developmentPresence of endostyle (produces mucous) or thyroid glandComplete digestive tractVentral, contractile blood vessel (heart)
12 Notochord-a supportive rod extending most of body length Pharyngeal slits-series of openings along pharyngeal region. Invert chordates use for filter feeding. Some chordates for gas exchange.Dorsal hollow nerve cord-runs along length of body, associated w/development of complex sensory systemsPostanal tail- extends posterior to the anus
13 SubPhylum Urochordata Marine animals; some species are solitary, others are colonial.Sessile adults, but motile during the larval stagesPossess all 5 chordate characteristics as larvaeSettle head first on hard substrates and undergo a dramatic metamorphosis (e.g., tail, notochord, muscle segments, and nerve cord disappear)
14 SubPhylum Urochordata cont. Adult body covered by an outer envelope or tunic; composed of proteins, salts, and celluloseTunic encloses a basket-like pharynx, that is perforated by gill slitsTunicates are filter feeders; Oral siphon (mouth)-plankton is trapped in a sheet of mucus and cilia later direct the food-laden mucus to the stomachWater leaves the animal via an excurrent siphon
15 SubPhylum Cephalochordata- 45 species “Head chord”Exclusively marine, tadpole-like animals (up to 5cm)Although they are capable of swimming, they usually are buried in the sand with only their anterior end being exposedWorld’s oceans in shallow waters clean sands
16 All chordate characteristics are present throughout their life history SubPhylum Cephalochordata cont.All chordate characteristics are present throughout their life historyThey are filter feeders: inside of the oral hood is lined with cilia -wheel organThese cilia, plus cilia in the pharynx help generate a water currentWater and suspended food particles pass through the oral hood, equipped with projections called cirri that strain larger particlesFeed by secreting a mucous net across the gill slits to filter out food particles that are present in the water.
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