UT Arlington BIOL 3454 - chaetognaths, echinoderms and hemichordates (4 pages)

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chaetognaths, echinoderms and hemichordates

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chaetognaths, echinoderms and hemichordates


Lecture number:
Lecture Note
University of Texas at Arlington
Biol 3454 - General Zoology
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BIOL 3454 1nd Edition Lecture 26 Lecture 11 19 I II III IV V VI Chaetognaths Echinoderms Hermichordates Mixed characteristics a Not all taxa are protostome or deuterostome features b Chateognaths mixed Chinoderms have a strange body plan a Bilateral ancestor and radial as adults b Coelom modified into a water vascular system for movement c Free moving but radial Phylum Chaetognatha a Arrow worms b Roots Greek chaite long flowing hair gnathos jaw c All marine d Swim to surface at night and descend during the day e Predatory f Form and function i Unsegmented ii Body plan head trunk and postanal tail iii Vestibule depression beneath the head iv Dorsally located eyes v Only invertebrates with a many layer epidermis vi Highly mobile and nearly transparent can have significant ecological impact vii Complete digestive system and well developed coelom viii U shaped ciliary loop over neck and from back of head mechanoreceptive or chemosensory ix No respiratory or excretory systems x Hermaphroditic self or reciprocal cross fertilization xi Deuterostomes but share characteristics with both groups of phyla Phylum Xenoturbellida a Hard to place taxonomy b Deuterostomes c Single genus with 2 species d Live in N sea mud e Feed on bivalves and bivalve eggs f Sexual reproduction with no structured gonads Phylum Echinodermata a Water vascular system of coelomic origin that doubles as part of respiratory system b Unsegemented with pentraradial symmetry c Triploblastic and coelom extensive d Endoskeleton of dermal calcareous ossicles These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute e f g h i j k l m n o p q r Digestive system usually complete axial or coiled Bo brain but extensive nerve ring Regeneration prominent Asexual reproduction by fragmentation Separate sexes free swimming bilateral larval stages Excretory organs absent Blood vascular system very reduced Circulation by peritoneal cilia Fossil record to Cambrian Bilateral ancestor but evolved radiality slow and sessile Most have no ability to osmoregulate Virtually all bottom dwellers a few pelagic Important to knowledge of evolution and development Class Asteroidea i Starfish ii 1500 species iii Predatory iv Central discs with tapering arms v Covered with ciliatd pigemented epidermis vi Mouth that is surrounded by a soft membrane with a canal running from the mouth to the end of each arm vii Form and function 1 Aboral surface usually rough and spiny 2 Bases around spines have pincer like pedicellariae 3 Papulae soft delicate gill structures 4 Madreporite tiny pore on the aboral side leading to the water cascular system 5 Endoskeleton made of small calcareous plates called ossicles bound together with connective tissue 6 Collagen is called catch collagen and under neural control and can change from a liquid to solid state 7 Ossicles have a meshwork between them called stereom unique to echinoderms viii Water vascular system 1 Primary functions locomotion and food gathering 2 Operates hydraulically 3 Madreporite to stone canal to ring canal to several radial canals to many lateral canals to tube feet with end in an external sucker ix Digestive system 1 Mouth on oral side leads to a short esophagus to a large stomach in central disc lower part of stomach can be everted during feeding 2 Upper pyloric part of stomach is smaller and connects to pyloric ceca in each arm 3 Short intestine leads to small intestinal ceca anus inconspicuous may be absent 4 Like to eat other echinoderms and molluscs and bivalves 5 Few feed on plankton x Nervous system made of 3 units 1 Oral or ectoneural nerve ring around mouth and a redaila nerve in each arm 2 Deep or hyponeural lies aboral to ectoneural system ring around anus and radial nerves along roof of each ray 3 Epidermal nerve plexus or nerve net connects the two systems along with bodywall 4 Sense organs are not well developed 5 Ocellus at end of each arm xi Reproductive system 1 Separate sexes 2 Fertilization external eggs and sperm shed into water 3 Can regenerate lost parts 4 Many require lest part of central discs to regenerate 5 Larvae bipinarria 6 Then brachiolaria as they start to mature xii Sea daisies 1 Highly modified asteroids 2 Pentaradial but no arms 3 One species with no digestive tract just a membranous velum that absorbs nutrients s Class Ophiuroidea i Brittle stars ii 2 000 species very abundant iii Arms slender and don t really taper iv No peicellariae or papulae v No suckers on tube feet vi Madreporite on oral surface vii Ampullae absent from podia force for motion exerted by muscles viii Form and function 1 Each arm a column of articulated ossicles connected by muscles and covered by plates 2 5 movable plates surrounding mouth act as jaws 3 No anus stomach saclike no intestine 4 Organs mostly confined to disc 5 5 bursea or inpocketings serves as site for gas exchange also contain gonads that discharge mature gametes into bursae 6 Separate sexes but a few hermaphroditic some brood young bursae 7 Most have a free swimming larvae called a ophiopluteus 8 Water vascular system similar to Asteroids ix Natural history 1 Secretive nocturanal usually live in rock cracks 2 Strongly light sensitive bc of special nerve structure son aboral side 3 Many filter feeders some highly predatory 4 Very good at regeneration will release arms to placate an attacker t Class Echinoidea i ii iii iv v 950 species Sea urchins Distributed everywhere marine Almost all have a complete body with an endoskeleton called a test Most hermispherical radially symmetrical medium to long spines move by tube feet vi Some sand dollars are secondarily bilateral small spines that are used for locomotion vii Form and function 1 Test is generally 10 double rows pf plates 2 5 plates of ambulacral rows that are homologous to those in asteroids have pores where tube feet extend 3 Spines move by small muscles at base 4 Several kinds of pedicellariae usually 3 jawed forms on long stalks keep body clean some bear venom glands 5 Inside test is a specialized digestive structure 6 Aristotles lantern is where teeth are attached for rasping 7 Ciliated siphon connectes espphagus directly to intestine to concerntrate food 8 Hemal and NS similar to Asteroids 9 Have small gills but most gas exchange through water vascular system respiratory feet arranged in fields called peraloids 10 Separate sexes 11 Larvae echinopluteus u Class Holothuroidea i

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