the deuterostomes

Download The  Deuterostomes

Post on 24-Feb-2016




0 download

Embed Size (px)


The Deuterostomes. Echinoderms and Chordates. Developmental Variations. During embryonic development, the process of gastrulation forms the digestive cavity. Gastrulation varies in the animal kingdom No gastrulation ( placozoans ) Incomplete gastrulation - PowerPoint PPT Presentation


The Deuterostomes

The DeuterostomesEchinoderms and ChordatesDevelopmental VariationsDuring embryonic development, the process of gastrulation forms the digestive cavity.Gastrulation varies in the animal kingdomNo gastrulation (placozoans)Incomplete gastrulation Forms a gastrovascular cavity with one openingComplete gastrulation Forms a digestive tract with 2 openingsAnimals with Complete GastrulationComplete gastrulation forms a true digestive tract with 2 openings, the mouth and the anusIn protostome animals, the first opening of the gastrula forms the mouthIn deuterostome animals, the second opening of the gastrula forms the mouthDeuterostome PhylaThere are 3 phyla characterized by deuterostome developmentEchinodermsSea Cucumbers, Crinoids, Sea Stars, Brittle Stars and Sea UrchinsHemichordatesAcorn Worms and PterobranchsChordatesTunicates, Lancelets, Jawless fish and VertebratesPhylum EchinodermataThe echinoderms are unusual in the animal kingdom in that they have a great deal in common with the chordates and hemichordates, but also differ in ways that do not appear anywhere else in the animal kingdomIt seems unlikely that their similarities with other deuterostomes are the result of convergent evolution, so it seems that through the course of evolution the echinoerms have lost a number of ancestral characters retained in the other phylaCharacters retained:Embryonic development & GastrulationTriploblasticComplete digestive tractBody CavityEucoelomateSymmetryBilateral during larval stages

Characters lost or diminished:SegmentationCephalizationNo head, brain or specialized sense organsSensory apparatus are not centralizedBilateral symmetry in the adult formThe bilateral symmetry in the larvae goes through a dramatic metamorphosis, reorganizing the body into a Pentaradially Symmetrical adultMetamorphosisThe coelom forms as a U shape, which pinches off into 3 distinct cavities, 2 of which will become diminishedThe digestive tract becomes reorganized, with the formation of new mouth and anal openings and a new orientation (mouth on the left and anus on the right)The left and right sides of the larvae undergo differential development, with the left side forming the oral surface and the right side forming the aboral surface

Derived characters special to the EchinodermsWater-vascular systemConsisting of a madroporite, a system of canals (stone canal, ring canal, radial canals and lateral canals) and sucker tipped tube feetDermal endoskeletonConsisting of calcified plates called ossicles and a variety of spines and pedicellariaHemal systemPoorly understood, it appears to function for distribution of materialsPentaradial symmetryOrgans radiate from a central disc, characteristically in a pattern of fivesWater Vascular System

Tube Feet

Crinoids (Sea Lilies) Stars Brittle Stars Cucumbers

Sea Urchins

Echinoderms - VideoSea Stars Urchins Dollars

Phylum HemichordataHemichordates are deuterostomes, a characteristic they share with both echinoderms and chordatesAs the name suggests, hemichordates have some derived characteristics that are ancestral to the phylum chordataDorsal, hollow nerve cordGill slits in the pharynxThese traits are shared with all chordates, but are absent in the echinoderms

Hemichordate DiversityThe phylum Hemichordata consists of two classesThe Acorn Worms (Enteropneusta)The PterobranchsThe Acorn Worms and the Pterobranchs are similar in body form, but vary with regard to feeding structuresFeeding structures in both are ciliated to collect food particles and direct them to the mouthAcorn Worms Feeding The acorn worms have a muscular proboscis used for food gathering located anterior to the mouth openingThe mouth is ventrally locatedA collar is associated with the mouth, and is used both to direct food into the mouth and to redirect particles too large to ingestAcorn worms are free living and burrow actively to search for food

Pterobranchs - FeedingThe proboscis itself is shield shapedThe base of the proboscis bears several tentacles which extend into the water to create a food gathering surface for filter feedingPterobranchs move freely inside of a collagenous tube, but are sessile in that they are restricted to life within that tubeGill Slits in the PharynxHemichordates have one or more pairs of gill slits that allow water from the pharynx to pass out of the animal, rather than being ingestedCilia maintain water flow through the gill pouchesAside from providing a mechanism for filtering and concentrating food particles, the gill pouches create a surface for gas exchange. Central Nervous SystemA point of emphasis in our discussion of the evolution of the central nervous system has been the presence in many invertebrate phyla of ventral nerve cordsA ventral nerve cord persists in the hemichordates, but is accompanied by a dorsal nerve cordThe dorsal nerve cord is hollow because it is formed by an invagination of ectodermal embryonic tissue, as is the spinal cord associated with the chordatesPhylum ChordataThe chordates are deuterostomes they possess a complete digestive tract with the mouth forming from the 2nd opening of the gastrulaChordates, like the hemichordates, have a dorsal hollow nerve cord. Unlike hemichordates they do not have a persistent ventral nerve cordAll chordates, at some time in their development, have pairs of pharyngeal gill slitsThe NotochordThe distinguishing characteristic of phylum Chordata is an endoskeleton centered around the formation of a notochordThe notochord is a rod of mesodermal tissue located on the dorsal side of the animal that extends almost the full length of the bodyThe notochord lies just ventral to the nerve cord that forms the central nervous systemMore notochord stuffIn the simplest of the chordates, the notochord is a simple rod of tissue with a fibrous sheath that provides some level of longitudinal rigidityIn other chordates, the notochord may exhibit pronounced segmentation, and may or may not become ossified (impregnated with calcium, forming bone)

Ancestral and Derived CharactersAside from the shared ancestral characteristics that Chordates share with their closest relatives (deuterostome development, notochord, dorsal hollow nerve cord & pharyngeal gill slits) the Chordates share 2 derived characteristic only with other Chordates:An endostyle (from which the thyroid gland is derived)A post-anal tailThe EndostyleThe endostyle is a specialized organ associated with the pharynxIn some of the invertebrate chordates the endostyle functions largely as a filter-feeding apparatus, secreting mucus for trapping food particles in the pharynx The endostyle persists in Chordates that do not filter feed. The thyroid gland is derived from the embryonic endostyle, and retains a function related to feeding and metabolismChordate DiversityThe Chordates are a diverse phylum, including both invertebrate and vertebrate classesThe Protochordates are invertebrate filter feeders, and consist of the Urochordates (tunicates) and the Cephalochordates (lancelets)The Agnatha are the jawless fish. They are the simplest bodied vertebrates, with a cranium and a well developed tripartite brain (three regions: forebrain, midbrain, hindbrain)Protochordates: Tunicates

Tunicate AnatomyTunicates are filter feedersWater enters the mouth, filters through the gill slits in the pharynx, and passes out through the atrial siphonFood passes through a complete digestive tract

Protochordates: Lancelets

Lancelet Anatomy

Lancelets are filter feeders like the tunicates, but they have more fully developed musculature, notochord and dorsal nerve cordVertebrates with JawsThe most familiar Chordates are the Vertebrates. Aside from the Agnatha, the remaining vertebrate Chordates have jaws derived from the first 2 pairs of gill archesThe ability to process food has evolved independently in many different phyla. Any level of processing has the potential to improve digestion and thus increase the chances of survival

Vertebrate Diversity - FishAgnatha jawless fish (hagfish and lampreys)Chondrichthyes jawed fish with cartilage skeletons (sharks and rays)The Chondrichthyes lack a swim bladder, and maintain bouyancy through a large, oily liverOsteichthyes jawed fish with bony, calcified skeletons (most familiar fish)The bony fish offset the density of their heavy skeleton with an air filled swim bladder on the dorsal side of their body cavityClass Agnatha Jawless Fish

Chondrichthyes Cartilage Fish

Osteichthyes Bony Fish

Poikilothermy vs. HomeothermyPoikilothermicTemperature variesCold BloodedEctothermicBody temperature is a function of the outside environmentAll invertebrates, as well as f


View more >