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Revision Notes Deuterostomes REVISION NOTES 0 N . Sea daisies (Concentricycloidea), disk shaped DEUTEROSTOMES animals with no arms, mouth or anus. PHYLUM CHAETOGNATHA Animals in which the mouth originates from an .Arrow worms, possess bristles around their opening in the embryo other than the blastopore. mou,ths and enables these planktonic animals to Characterized by radial and determinate cleavage prey on other organisms. Their relationships during embryological development. Includes the to other deuterostomes is unclear. following four animal phyla: Echinodermata, Chaetognatha, Hemichordata and Chordata. Possess transparent, elongated bodies with Lateral and caudal fins. PHYLUM ECHINODERMATA Two simple eyes and a nervous system consisting Spiny skinned animals with internal skeletons . of a ventral ganglia in the trunk and a dorsal of calcareous ossicles typified by the ganglia in the head region. starfish. ALL forms are marine and penta- syrrmetrical (sometimes synmnetry is in multiples Hermaphroditic, with ovaries in trunk and of five). Most forms have an upper aboral . testes near the caudal fin. surface with the anal opening and a Lower oral surface with a central mouth. ALL echinoderms PHYLUM HEMICHORDATA are characterized by a water vascular system and tube feet which functions for Locomotion, Two groups, the acorn worms such as obtaining food, respiration and excretion. Balanoglossus (class Enteropneusta) and the others belong to the class Pterobranchia which .A water vascular system is a division of the may include the fossil animals called coelom to form a hollow interconnected tube graptolites which were numerous in the system filled with water. The water vascular Ordovician Period. system comnunicates to the outside via a madreporite and terminates in tube feet which Similar to Chordates since they possess have suckers. pharyngeal gill slits and a dorsal tubular nerve cord. There is no brain; the nervous system consists of a circun oral nerve ring and radial nerves Dissimilar to Chordates since there is no in each arm. Simple eyes are found at the tip . notochord. The buccal diverticulwn was once of the starfish's arms. thought to be a notochord. Sexes are separate, fertilization external, and v Acorn worms have bodies divided into an there is a free-living bilaterally symnetrical anterior proboscis, a collar and a slimy trunk Larvae call the bipinnaria which develops into characterized by a genital fold. They are the branchiolaria followed by metamorphosis colonial or solitary, and either Live in U- into the pentasyrrmetrical adults. shaped burrows, or burrow through marine sediment. They extract detritus using cilia on .Starfish (Asteroidea) is characterized by five their proboscis. Food particles are bound on to arms or multiples of. They use tube feet to mucous strings which are then swallowed. collect small food particles and take them by ambulacral grooves to the mouth. They are also Pterobranchia: tiny degenerate hemichordates carnivorous on bivalves, which they open with . that Live in colonies, the individuals have their tube feet, invert their stomachs, release tentacles that project out of their tubes. digestive juices which dissolves them. PHYLUM CHORDATA v Brittle stars (Ophiuroidea) are similar to starfish except their arms are much thinner. DEFINITION: the phylum Chordata relates to a They have no anus (= incomplete digestive diverse grqup of deuterostomes, classified system). They are not carnivorous. together since they share the following structures: a notochord, a dorsal hollow nerve . Sea urchins (Echinoidea) have a rigid test of chord, pharyngeal slits, a postanal tail, and calcareous plates. Pentasymnetry is only body segmentation. These structures have became obvious when examining the test. They graze on variously modified and even lost in the various algae and have "jawedH mouthparts called an chordate taxa, but all possessed these aristotlels Lantern. characteristics in the early stages of their development (embryology). Sea cucumbers (Holothuroidea). Have an elongated form with Little evidence of Three subphylun exist; the Cephalochordata pentasyrrmetry except by examining the pattern . which includes amphioxus (Lancelet), the of tube feet. They have specialized tube feet Urochordata which includes marine filter- around the mouth (called tentacles) and mucous feeding tunicates, or sea squirts (e.g. Pyura) secretions entraps detritus on the tentacles and the Vertebrata. from where it is passed onto the mouth. SUBPHYLUM CEPHALOCHORDATA . Sea Lilies and feather stars (Crinoidea) are sessile and free-living respectively. Their Cephalochordate is an amphioxus or Lancelet pentasymnetry is complicated by Lateral . (Branchiostoma) which are small fish-like branching of the arms. These are highly filter-feeding marine animals. They possess a calcareous animals, which filter feed detritus dorsal, caudal and ventral fin strengthened from the water. with dense connective tissue. The begirmings of a head region can be seen. ORIGIN OF THE VERTEBRATES . Have protruding mouth (no jaws) surrounded by Original theory was that the vertebrates arose an oral hood form which project oral tentacles. during the early Cambrian period from filter- feeding cephalochordate- 1i ke ancestors (Pikaia). They filter-feed, using 180 pairs of gill slits It is now considered more likely that the to sieve the food from the water. A ventral vertebrates arose from an ancestor resembling a ciliated groove, the endostyle secretes mucous. tunicate Larva (which in turn was derived either Cilia conveys the mucous with entrapped from an ancestor to the hemichordates or detritus to the stomach. echinoderms or a comnon ancestor to all three forms). It is postulated that this Larva became A notochord and dorsal tubular nerve cord are sexually mature before metamorphosis, a distinct, as is the muscle segmentation. phenomenon called paedogenesis. SUBPHYLUM UROCHORDATA VERTEBRATE CHARACTERISTICS .There are three classes, Larvace, Thaliacea and .Vertebrate development is characterized by an Ascidiacea. increasing degree of cephalization (development of increasingly specialized brains capable of ,The class Ascidiacea is referred to as the processing increasingly extensive sensory tunicates (possessing a tunic or coating), an inputs). example is seasquirt Pyura (red bait). .Most vertebrates possess a colunn of vertebrae .Ascidians have very different Larval and adult that enclose the nerve cord. The skull and the stages. The larval stage has a full complement vertebral colunn are part of a carti laginous or of chordate features whereas the adult has lost bony endoskeleton. some chordate characteristics. .The vertebrate heart punps blood containing Adult ascidians such as the Pyura are sessile, haemoglobin through a closed system to gills, filter-feeding animals, which are designed to skin or Lungs where it is oxygenated. Wastes circulate water through their pharynx. These in the blood are removed by kidneys. animals are covered in a thick protective test, there are two dorsal teat-like structures, one .Reproduction is almost always sexual, with is an inhalant syphon in which water is drawn separate sexes. Fertilization is either in, the other is the exhalant siphon (atrial external or internal. pore) in which the water passes out. The pharynx acts as a sieve which collects .Of the seven classes of vertebrates with Living suspended food items. representatives, three are fishes; members of the other four classes generally have two pairs . The adult tunicate has degenerated from the of limbs and are called tetrapods. Larval stage and is without a notochord, the dorsal tubular nerve cord is reduced to a CLASS AGNATHA (Fishes without jaws) ganglia. .The oldest vertebrate fossils are jawless . The free-swimning ascidian Larvae possesses agnathans, a group with round or slit-like both a notochord and dorsal tubular nerve mouths, which include the extinct armoured chord. ostracoderms (bone-skinned) which first appeared in the Ordovician Period. The class ORIGIN OF THE CHORDATES Agnatha is now represented by only lampreys (Order Petromyzontida) and hagfish (Order Annelids, arthropods and arachnids have been Myxinida). proposed. This theory assumes the animal's dorsal and ventral surfaces are turned around, w Lampreys and hagfish have Long, slender changing the ventral nerve into a dorsal nerve. cylindrical bodies with median dorsal and Problems with this theory are the positioning of caudal fins supported by cartilaginous fin- the mouth (in the chordates it would mean that a rays. Both forms are extremely slimy. dorsal mouth would have to be closed and a new ventral mouth formed, a change in the nerve cord . Lampreys have suctorial mouths held open by from being solid to being hollow and finally a cartilage by which they adhere to host fish. change in development from spiral cleavage and a They use a horny tongue to rasp the flesh of determinate embryotogy to radial cleavage and the host. The hagfish has a biting mouth, with indeterminate embryology. Other theories include which it scavenges on dead and dying animals. a comnon ancestry with phyla echinodermata and hemichordata. Both embryological and biochemical .Olfactory organs are paired but there is a similarities between these groups and the single dorsal nostril. They have paired lateral chordates exists. eyes as well as a pineal eye on the dorsal surface. The brain is differentiated with 10 cranial nerves, and each "ear" consists of two SUMMARY OF THE VERTEBRATES and one semicircular canals for Lampreys and hagfish
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