Biology chapter 29 echinoderms and invertebrate chordates
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Biology - Chapter 29 “Echinoderms and Invertebrate Chordates” Charles Page High School Stephen L. Cotton Section 29-1 Echinoderms OBJECTIVES: Relate the structure of echinoderms to essential life functions. Section 29-1 Echinoderms OBJECTIVES:

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Biology chapter 29 echinoderms and invertebrate chordates l.jpg

Biology - Chapter 29“Echinoderms and Invertebrate Chordates”

Charles Page High School

Stephen L. Cotton

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Section 29-1Echinoderms


    • Relate the structure of echinoderms to essential life functions.

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Section 29-1Echinoderms


    • Describe the characteristics of the classes of echinoderms.

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Section 29-1Echinoderms

  • Phylum Echinodermata- starfish, sea urchins, sand dollars, etc.

    • echino- means spiny; dermis means skin

    • these are spiny-skinned animals

    • Cambrian period; 580 million yr.

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Section 29-1Echinoderms

  • In addition to having spiny skin, they are characterized by:

    • 5 part radial symmetry

    • internal skeleton

    • water vascular system

    • suction-cuplike structures called “tube feet”

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Section 29-1Echinoderms

  • The internal skeleton (or endoskeleton) is made up of hardened plates of calcium carbonate; often bumpy or spiny

  • water vascular system consists of an internal network of fluid-filled canals connected to the external appendages called tube feet

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Section 29-1Echinoderms

  • The water vascular system is essential for:

    • feeding; respiration; internal transport; elimination of wastes; and movement

  • Echinoderms have an internal skeleton like Chordates, and some similar development

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Section 29-1Echinoderms

  • Thus, some biologists feel that among invertebrates, echinoderms are most closely related to humans!

  • Echinoderms are somewhat “ugly”- however, they are very well adapted to life in the sea; have changed very little

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Section 29-1Echinoderms

  • Adult echinoderms have a body plan with five parts organized symmetrically around a center

    • neither anterior nor posterior end; no brain

    • but, they are two-sided

    • mouth side is the oral surface

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Section 29-1Echinoderms

  • Side opposite the mouth is the aboral surface

  • they have a unique system of internal tubes called a water vascular system

    • opens to the outside through a sieve-like structure called the madreporite

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Section 29-1Echinoderms

  • In starfish, the madreporite connects to a tube called the ring canal that forms a circle around the animal’s digestive system

    • Figure 29-3, page 639

    • from the ring canal, five radial canals extend into each body segment

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Section 29-1Echinoderms

  • Attached to each radial canal are hundreds of movable tube feet

    • this entire system acts like a series of living hydraulic pumps that can propel water in or out of the tube feet

    • can create a partial vacuum to hold on to what it is touching

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Section 29-1Echinoderms

  • Feeding-

    • carnivores, such as starfish, use their tube feet to pry open the shells of bivalve mollusks

      • then flips the stomach out of it’s mouth, pours out enzymes, and digests it’s prey in its own shell; then pulls the stomach back, leaving an empty shell

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Section 29-1Echinoderms

  • Herbivores, such as sea urchins, scrape algae from rocks by using their 5-part jaw

  • Filter feeders, such as sea lilies, basket stars, and some brittle stars, use tube feet on flexible arms to capture plankton that float by on ocean currents

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Section 29-1Echinoderms

  • Detritus feeders, such as sea cucumbers, move much like a bulldozer- taking in a mixture of sand and detritus

    • much like an earthworm, they digest the organic material and pass the sand grains out in their feces

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Section 29-1Echinoderms

  • Respiration- in most species, the thin-walled tissue of the tube feet forms the main respiratory surface

    • in some species, small outgrowths called skin gills also function in gas exchange

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Section 29-1Echinoderms

  • Internal transport- the functions of transporting oxygen, food, and wastes- which is normally done by a circulatory system, are shared by different systems in echinoderms

    • don’t really need a system for gases, because of gills and skin

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Section 29-1Echinoderms

  • The distribution of nutrients is performed primarily by the digestive glands and the fluid within the body cavity

  • Excretion- in almost all echinoderms, solid wastes are released through the anus (on the aboral surface) as feces

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Section 29-1Echinoderms

  • The nitrogen-containing cellular wastes are excreted primarily as ammonia

    • wastes seem to be excreted in many of the same places around the body in which gas exchange takes place- the tube feet and the skin gills

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Section 29-1Echinoderms

  • Response- since they have no head, they have primitive nervous systems

    • they do have scattered sensory cells to detect food

    • starfish also have up to 200 light-sensitive cells clustered in eyespots at the tip of each arm

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Section 29-1Echinoderms

  • However, they can do little more than tell whether it is light or dark

    • also may have statocysts for balance, telling them whether it is right side up

  • the spiny surface is not very good protection; good in some such as the crown-of-thorns starfish

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Section 29-1Echinoderms

  • Many predators have learned that if they turn these animals over, they can attack them through their unprotected underside

    • thus, many echinoderms hide during the day; active at night when most predators sleep

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Section 29-1Echinoderms

  • Movement- use tube feet and thin layers of muscle fibers attached to the plates of the endoskeleton to move

    • in sand dollars and sea urchins, the plates are fused together to form a rigid box that encloses the animal’s internal organs

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Section 29-1Echinoderms

  • In sea cucumbers, the plates are reduced to tiny vestiges inside a soft, muscular body wall. The loss of the plates makes the body of sea cucumbers very flexible

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Section 29-1Echinoderms

  • Reproduction- most echinoderms are either male or female, some are hermaphrodites

    • place the eggs and sperms in the water where fertilization takes place

    • the larvae have bilateral symmetry- very advanced

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Section 29-1Echinoderms

  • When the larvae mature and metamorphose into adults, they have radial symmetry

  • many starfish have incredible powers of regeneration

    • each piece can grow into a new animal as long as it contains a portion of the central part

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Section 29-1Echinoderms

  • Echinoderm Classes- 5 classes, although exact names not given

  • almost 6,000 species found in almost every ocean (salt water) in the world

    • no echinoderms have ever entered fresh water, and they cannot survive for long on land

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Section 29-1Echinoderms

  • 1. Starfish- this class contains the common starfish, which are also known as sea stars

    • some have more than 5 arms

    • Figure 29-7, page 642

    • carnivorous, preying upon the bivalves they encounter

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Section 29-1Echinoderms

  • 2. Brittle Stars- live in tropical seas, especially on coral reefs

    • look like common starfish, but longer more flexible arms- thus able to move much more rapid

    • protection by shedding one or more arms when attacked; are filter and detritus feeders

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Section 29-1Echinoderms

  • 3. Sea Urchins and Sand Dollars- includes disk-shaped sand dollars, oval heart urchins, and round sea urchins Fig. 29-8, p. 643

    • are grazers that eat large quantities of algae; may burrow into the sand or mud; may protect by long sharp spines

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Section 29-1Echinoderms

  • 4. Sea Cucumbers- look like warty moving pickles, with a mouth at one end and an anus at the other

    • Figure 29-9, page 644 top

    • most are detritus feeders

    • some produce a sticky material to “glue” a predator helpless

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Section 29-1Echinoderms

  • 5. Sea Lilies and Feather Stars- filter feeders, have 50 or more long feathery arms

    • the most ancient class of echinoderms; not common today, but once were widely distributed

    • sea lilies: sessile animals-p.644

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Section 29-1Echinoderms

  • How Do Echinoderms Fit Into the World?

    • Starfish are important carnivores, controlling other animal populations; a rise or fall in numbers affects other populations

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Section 29-1Echinoderms

  • For example, several years ago the coral-eating crown-of-thorns starfish suddenly appeared in great numbers in the Pacific Ocean

    • within a short period of time, they caused extensive damage to many coral reefs

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Section 29-1Echinoderms

  • In many coastal areas, sea urchins are important because they control distribution of algae

  • in various parts of the world, sea urchin eggs and sea cucumbers are considered delicacies by some people

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Section 29-1Echinoderms

  • Several chemicals from starfish and sea cucumbers are currently being studied as potential anti-cancer and anti-viral drugs

  • sea urchins have been helpful in embryolgy study, since they produce large eggs; fertilize externally; develop in sea water

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Section 29-2Invertebrate Chordates


    • Name and discuss the three distinguishing characteristics of chordates.

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Section 29-2Invertebrate Chordates


    • Describe the two subphyla of invertebrate chordates.

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Section 29-2Invertebrate Chordates

  • The phylum Chordata, to which fishes, frogs, birds, snakes, dogs, cows, and humans belong, will be in future chapters

    • most chordates are vertebrates, which means they have backbones, and are placed in the subphylum Vertebrata

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Section 29-2Invertebrate Chordates

  • But, there are also invertebrate chordates- these are divided into two subphyla:

  • 1. the tunicates

  • 2. the lancelets

  • due to similar structures, the chordate vertebrates and invertebrates may have evolved from a common ancestor

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Section 29-2Invertebrate Chordates

  • Chordates are animals that are characterized by a notochord, a hollow dorsal nerve cord, and pharyngeal (throat) slits

    • some chordates posses these characteristics as adults; others as only embryos; but all have them at some stage of life

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Section 29-2Invertebrate Chordates

  • 1. Notochord- a long, flexible supporting rod that runs through at least part of the body, usually along the dorsal surface just beneath the nerve cord

    • most chordates only have this during the early part of embryonic life

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Section 29-2Invertebrate Chordates

  • Vertebrates will replace the notochord quickly with the backbone

  • 2. The second chordate characteristic- the hollow dorsal nerve cord- runs along the dorsal surface just above the notochord

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Section 29-2Invertebrate Chordates

  • In most chordates, the front end of this nerve cord develops into a large brain

    • nerves leave this cord at regular intervals along the length of the animal, and connect it’s internal organs, muscles, and sense organs

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Section 29-2Invertebrate Chordates

  • 3. The third chordate characteristic- the pharyngeal slits- are paired structures in the pharyngeal (or throat) region of the body

    • in aquatic chordates such as lancelets and fishes, the pharyngeal slits are gill slits that connect with the outside

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Section 29-2Invertebrate Chordates

  • In terrestrial chordates that use lungs for respiration, pharyngeal slits are present for only a brief time during the development of the embryo

    • they soon close up as the embryo develops- page 283

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Section 29-2Invertebrate Chordates

  • In humans, pouches form in the pharyngeal region, but never open up to form slits

    • thus, some scientists consider the pharyngeal pouches, not slits, as the “true” chordate characteristic

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Section 29-2Invertebrate Chordates

  • Tunicates- small marine chordates that eat plankton they filter from the water

    • name from a special body covering called the tunic

    • only the tadpole-shaped larvae have the notochord and dorsal nerve cord

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Section 29-2Invertebrate Chordates

  • Examples of tunicates are the sea squirts Figure 29-11, page 646

    • adults are sessile, living as colonies attached to a solid surface; larvae are free swimming

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Section 29-2Invertebrate Chordates

  • Lancelets- small fishlike creatures; live in sandy bottoms of shallow tropical oceans

    • unlike tunicates, the adult lancelets have a definite head; a mouth that opens into a long pharyngeal region with up to 100 pairs of gills

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Section 29-2Invertebrate Chordates

  • Figure 29-12, page 646

    • feed by passing water through their pharynx, where food particles are caught in a sticky mucus; lack any jaws

    • have a primitive heart pumping blood through closed circulation

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Section 29-2Invertebrate Chordates

  • Lancelet’s muscles are organized into V-shaped units on either side of the body

    • each muscle unit receives a branch from the main nerve cord; lack any appendages

    • similar system found in all living vertebrates

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Section 29-2Invertebrate Chordates

  • How Do Invertebrate Chordates Fit Into the World?

    • By studying the invertebrate chordates, it is like using a time machine to study the ancestors of our own subphylum