Z202-Unit 9/10 Chapter 22 Chaetognaths, Echinoderms & Hemichordates

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Edwin Short
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Triploblastic metazoans: divided into 2 large clades: 1. Protostomia include acoelomates, pseudocoelomates, & coelomates 2.

1 Z202-Unit 9/10 Chapter 22 Chaetognaths, Echinoderms & Hemichordates I. Diversity A. Evolutionary Diversity - Cambrian Explosion (535 to 530 mya) radiation in diversity seen in fossil record other explosions occurred including one following Permian Extinction (230 mya) - The Triploblastic metazoans: divided into 2 large clades: 1. Protostomia include acoelomates, pseudocoelomates, & coelomates 2. Deuterostomia - all are coelomates *few phyla have characteristics of each clade*?where to place them? - Other modifications among these Phyla show linkage to more advanced phyla but a metamorphosis to simpler body designs II. Phylum Chaetognatha Arrow worms - evolutionary position is debated, old group (fossils age back 500 mya) species of marine predators with highly specialized planktonic characteristics (nightly vertical migration) - Elongated unsegmented body with head, trunk, and postanal tail covered by thin cuticle 1

- sickle-shaped bristles on each side of mouth used to seize prey - complete digestive tract, welldeveloped coelom (used as a hydroskeleton), simple nerve ring connecting the cerebral ganglion to

2 - sickle-shaped bristles on each side of mouth used to seize prey - complete digestive tract, welldeveloped coelom (used as a hydroskeleton), simple nerve ring connecting the cerebral ganglion to lateral ganglion and a large ventral ganglion - sense organs include eyes, sensory bristles, U-shaped ciliary loop across dorsal (vibrations, water currents, chemosensory possibly) - reproduction = hermaphroditic III. Phyum Echinodermata A. Characteristics - ancient group extending back to the Cambrian period (560 mya) 13,000 fossil species - 6,000 species of slow moving, bottom dwellers in marine habitats - Unique traits seen this phyla: 1. spiny calcareous endoskeleton of plates (Ossicles) 2. water-vascular system (developed from coelom) 3. pedicellariae 4. dermal branchiae 5. bilateral larva pentaradial adult (5 point design) & absence of cephalization 2

3 B. Diversity - Descended from Bilateral ancestors (larvae still bilateral) - Radiality result of adaptation to sessile existence - Lack ability to osmoregulate (restricts them to marine) - No parasites, variety of nutritional modes: Asteriods (sea stars) mostly predators Ophiuroids (brittle stars) scavengers, browsers, commensals Crinoids & Holothurians (feather stars & sea cucumbers) suspension or deposit feeders Echinoids (Urchins/Dollars) detritus C. Ecology - Due to spiny structure, not often preyed upon - Some predators adapted (fish, otters, humans, each other) - Prey on molluscs, crustaceans, other invertebrates - damage oyster beds) - Artificial Parthenogenesis (develop w/out fertilization when subjected to stimuli - hypertonic) Class Asteriodea "Sea Stars" A. General Characters - Common along shores, live in muddy, sandy bottoms, or coral reefs - Range from 1cm to over a meter across - Asterias common on East coast; Pisaster on W. coast B. Form & Function 1. External Features - central disc w/ tapering arms - mouth on underside (oral side) - ambulacrum runs mouth to arm tip 3

gills) soft projections lined w/ peritoneum & serve in respiration - aboral side (madreporite) sieve leading to

4 - usually have 5 arms - ambulacral groove bordered by rows of tube feet - radial nerve center of ea. ambulacrum - under nerve is extension of coelom & radial canal of water-vascular system - papula (dermal branchiae/ skin gills) soft projections lined w/ peritoneum & serve in respiration - aboral side (madreporite) sieve leading to watervascular system 2. Endoskeleton - under epidermis, mesodermal endoskeleton of small plates (ossicles) made of calcium carbonate joined by connective tissue 4

3. Coelom, Excretion, & Respiration - spacious fluid filled coelomic compartment - fluid has moving amebocytes - ciliated

Water-Vascular System - unique to echinoderms (2 nd coelomic compartment) - system of canals, tube feet & dermal ossicles -

connects to ring canal by stone canal - lateral canals connect radial canal to tube feet - ampullae regulates hydraulic pressure

5 3. Coelom, Excretion, & Respiration - spacious fluid filled coelomic compartment - fluid has moving amebocytes - ciliated peritoneum circulates fluid, moving gases & waste (ammonia) to diffuse across dermal branchiae (or skin gills) & tube feet 4. Water-Vascular System - unique to echinoderms (2 nd coelomic compartment) - system of canals, tube feet & dermal ossicles - functions in locomotion (hydraulic), food gathering, respiration & excretion - opens to outside at madreporite on aboral side connects to ring canal by stone canal - lateral canals connect radial canal to tube feet - ampullae regulates hydraulic pressure for tube feet movement 5. Feeding & Digestion - complete system (mouth esophagus - cardiac stomach ducts connect w/ pyloric ceca pyloric stomach intestine - anus) 5

- anus on aboral end - regurgitate larger indigestible parts - lower cardiac

Nervous System - nerve ring w/ radial nerves to coordinate tube feet - epidermal

chem & light intensity) - mainly active at night 7.

oral surface of each arm - external fertilization (broadcasting) so release

6 - anus on aboral end - regurgitate larger indigestible parts - lower cardiac stomach can be everted thru mouth (insert into molluscs) 6. Nervous System - nerve ring w/ radial nerves to coordinate tube feet - epidermal nerve plexus coordinate tactile stimulation & response (react to touch, temp, chem & light intensity) - mainly active at night 7. Reproduction, Regeneration & Autonomy - Dioecious, pair of gonads along interior oral surface of each arm - external fertilization (broadcasting) so release timed in early summer) larvae = bipinnaria - regenerate arms lost or damaged - arm can regenerate new star if 1/5 of central disc present 6

7 Class Ophiuroidea "Brittle stars" A. General Characters - largest in # of species & probably in abundance - found benthic marine to abyssal plane - more pronounced regeneration since fragile - secretive & live on hard or sandy bottom where little light (often under rocks or in kelp holdfast) - arms slender & distinct from central disc - lack papulae & ambulacral groove closed & coated w/ ossicles - tube feet lack suckers & ampullae - madreporite on oral surface - arms moved in pairs for locomotion - 5 movable plates for mouth, no anus - skin leathery & surface cilia mostly lacking - all organs in central disc (arms too slender) - incomplete digestive system (sac-like stomach); no intestines, no anus (eat small particles browsers & suspension) 7

- Dioecious, few hermaphroditic - Larvae = ophiopluteus Class Echinoidea "Urchins & Sand Dollars" A.

arm to the central disc - Irregular Echinoids (dollars & heart urchins oval or heart shaped) are bilateral w/ short

"ball & socket" joints moved by small muscles at base - some have pedicellariae w/ poison glands to paralyze small prey -

8 - Dioecious, few hermaphroditic - Larvae = ophiopluteus Class Echinoidea "Urchins & Sand Dollars" A. General Characters - lack arms but test in 5-part symmetry - up-folding brings ambulacral area up to anus and fuses the arm to the central disc - Irregular Echinoids (dollars & heart urchins oval or heart shaped) are bilateral w/ short spines & move using spines - Regular Echinoids (urchins) are radial w/ long spines & move using tube feet - spines on "ball & socket" joints moved by small muscles at base - some have pedicellariae w/ poison glands to paralyze small prey - anus, genital pore & madreporite aboral side - irregular echinoids shift anus to posterior = bilateral w/ chewing structure inside = Aristotle's lantern 8

- irregular urchins, respiratory podia arranged in fields = Petaloids on aboral surface - Dioecious w/ external fertilization - Some brood young in depressions between spines (pencil urchins) - Larva

9 - irregular urchins, respiratory podia arranged in fields = Petaloids on aboral surface - Dioecious w/ external fertilization - Some brood young in depressions between spines (pencil urchins) - Larva = echinopluteus Class Holothuroidae "Sea Cucumbers" A. General Characters - greatly elongated in oral-aboral axis - tiny ossicles reduced & buried, body soft w/ leathery wall (few have dermal armor) = shift to a hydroskeleton - some species crawl, others burrow - tube feet (locomotion) distributed to ambulacral (ventral) that face substrate = 2 o Bilateral - both ventral tube feet & muscular body waves move animal - oral tentacles are tube mouth - digestive system opens into cloaca, respiratory tree also empties into the chamber 9

- respiratory tree functions in respiration & excretion; gas exchange also occurs thru skin & tube feet - cloaca &

them - Organs of Cuvier expel sticky mass w/ toxins in direction of enemy - Dioecious; some hermaphroditic - Single

in being attached for most of life - deep water to shallow water - sea lilies, flower shaped body at tip of stalk -

10 - respiratory tree functions in respiration & excretion; gas exchange also occurs thru skin & tube feet - cloaca & respiratory tree used by carapus fish for Shelter - when irritated; cast out part of viscera thru anus then regenerate them - Organs of Cuvier expel sticky mass w/ toxins in direction of enemy - Dioecious; some hermaphroditic - Single gonad (not paired) - External fertilization with larvae known as Auricularia Class Crinoidea "Sea Lilies & Feather Stars" A. General Characters - far more numerous in fossil record (grew to 20m long), average cm length - sessile - unique in being attached for most of life - deep water to shallow water - sea lilies, flower shaped body at tip of stalk - feather star, long many branched arms (some adults free-moving) - body disc (calyx) covered by leathery skin or tegment of calcareous plates - 5 arms branch to more arms - calyx & arms form a crown - madreporite, spines, & pedicellariae absent 10

- complete digestive system (mouth- esophagus- intestine- anus) - feed w/ tube feet & mucous

known as Doliolaria IV. Phyum Hemichordata A.

subphylum Chordata (possess gill slits, dorsal nerve cord, & rudimentary notochord) -

11 - complete digestive system (mouth- esophagus- intestine- anus) - feed w/ tube feet & mucous nets - Water-vascular system, oral ring & radial nerve in each arm - Dioecious with larvae known as Doliolaria IV. Phyum Hemichordata A. Characteristics - 70 species of marine worm-like animals formerly considered part of subphylum Chordata (possess gill slits, dorsal nerve cord, & rudimentary notochord) - hemichord (stomochord) is not homologous to notochord, really a buccal diverticulum - bottom dwellers, sized 20mm-2.5m long, usually living in shallow waters: some colonial, most are sessile - live in secreted tubes, secretive & fragile - 2 classes: 1. Enteropneusta ( intestine breathing ) acorn worms 2. Pterochanchia ( wing gills ) 11

12 V. Phylogeny & Adaptive Radiation A. Phylogeny - extensive fossil record - ancestors bilateral - three-part coelom (Tricoelomate) - Echinoids & Holothuroids are closely related - relationship of Ophiuroids & Asteroids controversial - Hemichordates puzzling (contain both echinoderm & chordate characteristics) B. Adaptive Radiation - Echinoderms - lost brain & sense organs w/ adoption of radial symmetry - body plan limited evolutionary opportunities (no parasites) - only Ophiuroids have any commensals species B. Classification: Phylum Cheatognatha Phylum Echinodermata Subphylum Eleutherozoa Class Asteroidea Class Ophiuroidea Class Echinoidea Class Holothuroidea Class Concentricycloidea (New Zealand sp) Subphylum Pelmatozoa Class Crinoidea Phylum Hemichordata 12

13 Traditional higher-level groupings: Phylum Parazoa P. Porifera P. Placozoa Eumetazoa Grade 1 (Radiata) P. Cnidaria P. Ctenophora Grade 2 (Bilateria) Division A (Protostomia) Acoelomates: P. Platyhelminthes P. Nemertea P. Gnathostomulida Pseudocoelomates: P. Rotifera P. Entoprocta P. Gastrotricha P. Priapulida P. Kinorhyncha P. Loricifera P. Nematoda P. Acanthocephala P. Nematomorpha Eucoelomates: P. Mollusca P. Tardigrada P. Annelida P. Pentastomida P. Arthropoda P. Onychophora P. Echiurida P. Pogonophora P. Sipunculida Deuterostomia: P. Phoronida P. Chaetognatha P. Ectoprocta P. Hemichordata P. Brachiopoda P. Chordata P. Echinodermata 13

CHAPTER 22. Echinoderms 22-1

CHAPTER 22. Echinoderms 22-1 CHAPTER 22 Echinoderms 22-1 Phylum Echinodermata: Diversity and Characteristics Characteristics All members have a calcareous skeleton Spiny endoskeleton consists of plates Unique water-vascular system