Biology - Chapter 29

1
Biology - Chapter 29Echinoderms and
Invertebrate Chordates

• Charles Page High School
• Stephen L. Cotton

2
Section 29-1Echinoderms

• OBJECTIVES
• Relate the structure of echinoderms to essential
  life functions.

3
Section 29-1Echinoderms

• OBJECTIVES
• Describe the characteristics of the classes of
  echinoderms.

4
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.

5
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

6
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

7
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

8
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

9
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

10
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

11
Section 29-1Echinoderms

• In starfish, the madreporite connects to a tube
  called the ring canal that forms a circle around
  the animals digestive system
• Figure 29-3, page 639
• from the ring canal, five radial canals extend
  into each body segment

12
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

13
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 its mouth, pours
  out enzymes, and digests its prey in its own
  shell then pulls the stomach back, leaving an
  empty shell

14
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

15
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

16
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

17
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
• dont really need a system for gases, because of
  gills and skin

18
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

19
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

20
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

21
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

22
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

23
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 animals internal organs

24
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

25
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

26
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

27
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

28
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

29
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

30
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

31
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

32
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

33
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

34
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

35
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

36
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

37
Section 29-2Invertebrate Chordates

• OBJECTIVES
• Name and discuss the three distinguishing
  characteristics of chordates.

38
Section 29-2Invertebrate Chordates

• OBJECTIVES
• Describe the two subphyla of invertebrate
  chordates.

39
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

40
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

41
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

42
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

43
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

44
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 its
  internal organs, muscles, and sense organs

45
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

46
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

47
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

48
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

49
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

50
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

51
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

52
Section 29-2Invertebrate Chordates

• Lancelets 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

53
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