Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Advanced Biology Chapter 40 Echinoderms and Invertebrate Chordates Brittle Star Focus Concept - Evolution • Although Echinoderms are radially symmetrical as adults, they are bilaterally symmetrical as larvae suggesting that they evolved from bilaterally symmetrical ancestors • Because both echinoderms and chordates are deuterostomes, it is likely that they have a common ancestor. Chapter 40 Echinoderms and Invertebrate Chordates • 40-1 Echinoderms • 40-2 Invertebrate Chordates Characteristics of Phylum Echinodermata • Group of invertebrates that includes sea stars, sand dollars, sea urchins, and sea cucumbers • Inhabit many marine environments from shallow coastal waters to deep ocean trenches • Vary in diameter from 1cm – 1m • Often brilliantly colored • Adults have radial symmetry (like cnidarians and ctenophores) • Larvae have bilateral symmetry (unlike cnidarians and ctenophores) which indicates that echinoderms evolved from bilaterally symmetrical ancestors • No head or any other sign of cephalization This one has 6 arms instead of the normal 5 Echinoderm larva • Fossil Record of Echinoderms – Dates back to Cambrian period more than 500 million years ago – Early echinoderms were sessile. Radial symmetry is an adaptation to a sessile existence – Later evolved ability to move from place to place. Most slow crawling on ocean floor. (80 species sessile) • Deuterostomes (different from all other invertebrates studied so far) – Coelomates whose embryos have radial cleavage. Anus forms near the blastopore and mesoderm arises from outpockets of the endoderm – More closely related to chordates than to other invertebrates • Characteristics NOT shared by any other phylum – Pentaradial symmetry (most): body parts extend from center along 5 spokes – Endoskeleton composed of calcium carbonate plates known as ossicles. May have spines or spicules that protrude through the skin. Echinoderm= “spiny skin” – Water Vascular System: network of water-filled canals used in movement – Tube Feet: small, movable extensions of the watervascular system which aid on movement, feeding, respiration, and excretion Sea Urchin Classification Feather Star • 7,000 species in 6 classes – Class Crinoidea – Class Ophiuroidea – Class Echinoidea – Class Holothuroidea – Class Concentricycloidea – Class Asteroidea Sea Cucumber Brittle Star Class Crinoidea (Crinoids) • Sea lilies, feather stars • Crinoids = “lily-like” • Sea lilies: most closely resemble fossils of ancestral echinoderms from Cambrian period. Sessile as adults. Attach to rocks or sea bottom by long stalk • Feather stars: can swim or crawl as adults, may stay in one place for long periods. Feather Star Feather Star Fossil Sea Lily Sea Lilies • Both types have 5 arms that extend from body and branch to form many more arms (up to 200) • Tube feet at the end of each arm filter small organisms from the water. Also serve as respiratory surface for O2/CO2 exchange with the water. • Cilia on arms transport trapped food to the crinoids mouth at the base of the arms • Mouth faces up (in most echinoderms the mouth faces toward sea bottom) A fossil of an ancient sealily, which probably lived 90 million years ago. Class Ophiuroidea • 2000 species of basket stars and brittle stars • Ophiuroidea = “snake tail” • Long narrow arms – move more quickly • Flexible arms branch repeatedly to form numerous coils that look like tentacles • Brittle stars: parts of arms break off easily and can regenerate Basket Star Brittle Star • Live on ocean bottom - beneath stones, crevices, holes in coral reefs • So numerous – cover sea floor in some locations • Some feed by raking in food with arms or gather it from ocean bottom with tube feet or with numerous mucous strands located between spines Class Echinoidea • 900 species of sea urchins and sand dollars • Echinoidea = “spine-like” • Test: compact, rigid endoskeleton that encloses the internal organs of an echinoderm • Spherical sea urchin: well adapted to life of hard sea bottoms. – Tube feet for locomotion. – Feed by scraping algae from hard surface with 5 teeth surrounding mouth – Aristotle’s lantern: complex jaw-like mechanism of teeth and muscles – Spines protrude from the test. Short and flat or long and thin or wedge shaped depending on the species. Some barbed others hollow with venom (dangerous to predators as well as swimmers) Sea Urchin Pencil Sea Urchin • Sand dollars – Live along sea coasts, sandy areas. – Flat round shape adapted for shallow burrowing – Short spines used in locomotion, burrowing, and cleaning body surface – Use tube feet to capture food that settles on or passes over their body Sand dollar Sand dollar Mouthparts Class Holothuroidea • • • • Sea cucumbers Holothuroidea = “water polyp” Armless echinoderms Live on sea bottom. Crawl or burrow into soft sediment • Ossicles that make up their endoskeleton are very small and not connected. Body soft Sea Cucumber Orange Sea Cucumber • Modified tube feet form fringe of tentacles around mouth. When extended – resembles polyp form of some cnidarians • Uses tentacles to sweep up sediment and water. Stuff tentacles into mouth and cleans food off them. When threatened many species squirt out noxious and sticky latex-like threads which harden on contact with sea water, and entangle or irritate the potential predator. These are extremely difficult to remove. If this fails, they will eject their entire digestive system (gut) in an attempt to scare the enemy and hence escape. The gut can then be regenerated. Some individuals may harbour commensals inside their gut or respiratory system. Two prominent ones are the eel-like pearl fish (Carapus) and the pea crab (Pinnotheres). Pentacta (length 6-8cm) is common on sandy/muddy areas. Phyllophorus (up to 10crn) (both F. Cucumariidae), which prefers muddier substrates, has been reported to be used to make a virtual "panacea" called "Air Gamat". The animals are slit, their body fluids collected and then left to stand for several weeks before sale. Most famous of all is H. scabra, the Beche-deMer or Trepang (F. Holothuridae) (length 1520cm), a much sought after delicacy. Degutted, cleaned and dried, they fetch good market prices. They prefer sandy areas. The reef cucumbers (mostly F. Holothuridae) grow to larger sizes (length up to 43cm). Their colours vary between brown and black, and are often seen in large numbers in the lower littoral zone, usually, among Sargassum covered rocks. Some of the reef species have been reported to contain a poison called holothurin and should not be eaten Class Concentricycloidea • Sea daisies (two species discovered in 1986 New Zealand) • Deep waters • Flat, disk-shaped. Less than 1cm in diameter • Tube feet around edge of disk (instead of along radial lines) Class Asteroidea • • • • • Asteroidea = “star-like” Sea stars (starfish) Live in coastal waters all over the world Variety of colors and shapes Economically important: prey on oysters, clams, other organisms that humans use as food Bat Star Short-spined Star Ochre star (Pisaster ochraceus) eating a chiton Sunflower star (Pycnopodia helianthoides) Structure and Function of Echinoderms Acanthaster planci, or the crown-ofthorns starfish External Structure • Flattened body composed of several arms extending from a central region (pentaradial symmetry). Typically 5 arms, some as many as 24 • 2 rows of tube feet run along the underside of each arm • Oral surface: the side of the body where the mouth is located (sea stars – underside) • Aboral surface: side of the body that is opposite the mouth • Body usually covered with short spines. Rough texture • Pedicellariae: numerous tiny pincers surrounding each spine. Help keep the body surface free of foreign objects including algae and small animals. *Not found in other echinoderm classes Water-Vascular System • A network of water-filled canals that are connected to the tube feet. • Water Pathway: – Madreporite: water enters system through small pores. Sieve-like plate on the aboral surface – Stone Canal: tube that connects the madreporite to ring canal – Ring Canal: tube that encircles the mouth – Radial Canal: tube extends from ring canal to end of each arm. Carries water to hundreds of hollow tube feet – Tube feet: valves prevent backflow into radial canals from tube feet • Ampulla: bulb-like sac on upper end of each tube foot. Ampulla(latin)=“flask”. Surrounded by muscles • Sea stars use water pressure and muscle contraction to extend and withdraw tube feet • Many species have small muscles that raise the center of tube foot’s disk-like end creating suction cup for climbing slippery rocks and capturing prey. Tube feet Feeding • Most are carnivorous: feed on mollusks, worms, other slow-moving animals • When captures bivalve (ex. Clam) – Attaches tube feet to both halves of shell and exerts steady pull. – Clam’s muscles tire and shell opens slightly. – Sea star inserts cardiac stomach and digests clam’s soft tissues while still in shell. – Then withdrawals stomach containing partially digested food back into body to complete the digestive process. Sea star eating mussels Digestion • Mouth • Esophagus • Cardiac Stomach: turns inside out through mouth when it feeds. Breaks down food with enzymes • Pyloric Stomach: Connects to a pair of digestive glands in each arm. Breaks down food with help of enzymes. Nutrients absorbed into coelom through walls of digestive glands • Anus: undigested material expelled. On aboral surface Other Body Systems • No circulatory, excretory, or respiratory systems – Fluid in coelom bathes the organs and distributes nutrients and O2 – Gas exchange and waste excretion take place by diffusion through thin walls of tube feet and through skin gills, which are hollow tubes that project from the coelom lining to the exterior Primitive Nervous System • No head, no brain • Nerve ring circles the mouth • Radial nerves run from nerve ring down length of each arm • Coordinate movements of the tube feet. If radial nerve cut, tube feet in that arm lose coordination. If nerve ring cut, all arms lose coordination • Also nerve net near body surface that controls the movements of spines, pedicellariae and skin gills • Eyespot on end of each arm responds to light • Several tentacles on end of each arm respond to touch. Tube feet also responsive to touch • Touch-sensitive and chemical sensitive cells scattered over surface of sea star’s body Reproduction and Development • Most species have separate sexes (same as most echinoderms) • Each arm contains a pair of ovaries or testes. Females produce 200 million eggs/year • Fertilization occurs externally – eggs and sperm are shed into water • Bipinnaria: bilaterally symmetrical free-swimming larvae that develops from the fertilized egg • After 2 months, larva settles to bottom – metamorphosis begins and it develops into pentaradially symmetrical adult Regeneration • Can regenerate arms from central region of their body even of all arms are lost • Process very slow – takes as long as 1 yr. • Use regenerative ability as defensive mechanism – automatically shedding arm at base when arm captured by predator • Some can even regenerate a complete new individual from a detached arm if it contains a portion of the central region • Certain species reproduce asexually by splitting body through central region. Two parts then regenerate missing structures. Linckia regenerating five rays from a single surviving ray. Specimens like this are often called "comets." 40-2 Invertebrate Chordates 40-2 Invertebrate Chordates • Phylum Chordata includes vertebrates (animals with a backbone) and 2 groups of invertebrates (animals that lack a backbone) • Early development of chordates is similar to development of echinoderms which suggests that they descended from a common ancestor. Characteristics of Phylum Chordata • Notochord: stiff, but flexible rod of cells that runs the length of the body near the dorsal surface – Stiffness provides resistance against which the body muscles can exert force when they contract – Flexibility allows body to bend from side to side and up and down – Some chordates retain notochord throughout life – [In most vertebrate, notochord present in embryos but becomes greatly reduced when vertebral column or backbone develops. In adult mammals, the notochord persists only as small patches of tissue between the bones of the vertebral column • Dorsal Nerve Cord: (unlike ventral nerve cord of other invertebrates) – Hollow tube with anterior end that enlarges during development to form the brain – Posterior end forms spinal cord – Brain receives info from a variety of complex sensory organs concentrated at anterior end • Pharyngeal Pouches – Out-pockets in the pharynx (portion of digestive tract between the mouth and esophagus) – In aquatic chordates: pharyngeal pouches became perforated by slits and evolved first into filter-feeding structures and later into gill chambers – Terrestrial chordates: pouches evolved into a variety of structures including jaws, inner ear, tonsils Link to facial development • Postanal Tail – Muscles in tail can cause it to bend – Provides propulsion in many aquatic chordates. (Invertebrates in other phyla lack this form of propulsion because anus is located at end of body) Cat and human embryos in the tailbud stage. A cat embryo is shown on left, a human embryo right. Note the post-anal tail in both, positioned at the lower left below the head of each. The human embryo is about 32 days old. Evolution and Classification • Chordates are deuterostomes (like echinoderms) – provides evidence that they likely evolved from a common ancestor • Phylum Chordata divided into 3 subphyla – Vertebrata (vertebrates) 95% of all chordate species (Ch 41-45) – Cephalochordata – Urochorata • Both subphylum live only in the ocean. Closest living relatives to the early animals from which all chordates evolved Subphylum Cephalochordata • 2 dozen species of blade-shaped animals known as lancets • Look much like idealized chordate in Figure 4010p788 • Retain notochord, dorsal nerve cord, pharyngeal pouches, and postanal tail throughout life • Live in warm, shallow water. Use muscular tail to wriggle backward into sand. Only anterior end protrudes from sand Amphioxus • Use cilia to draw water into pharynx through mouth. Food particles in water are trapped as it passes through numerous slits in the pharynx. Food enters intestine to be digested. Water leaves body through opening called the atriopore • Can swim weakly. Powered by coordinated contraction of muscles that run length of body. Muscles arranged as a series of repeating segments. – Body segmentation is another common feature of chordates. Annelids and arthropods are also segmented although it probably evolved independently from chordates. Subphylum Urochordata • 2,000 species commonly called tunicates – Body covered by a tough covering or “tunic” – Also called sea squirts – squirt out a stream of water when touched • As adults, most are sessile, barrel-shaped animals. Live on sea bottom • May be solitary or colonial Belize Painted Tunicate Tunicate – Sea squirt • Adapted for filter-feeding. Beating cilia draw water in through incurrent siphon, passes through slits in pharynx, exits through excurrent siphon – Food filtered by pharynx moves into stomach. Undigested material leaves via anus which empties into excurrent siphon • Hermaphrodites: sperm and eggs released through excurrent siphon into water where external fertilization occurs • Larval tunicates posses all 4 chordate characteristics but lose most during metamorphosis • Adults bear little resemblance to idealized chordate. Do have pouch-like pharynx with slits, but no notochord, dorsal nerve cord or postanal tail.