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Phylum Echinodermata and Phylum Chordata

Objectives: Differentiate between protostome and deuterostome characteristics.

Identify traits of echinoderms.

Differentiate between the different Chordate subphyla.

Perform a Sea Star dissection.

All Animals Are: • heterotrophs

• multicellular

• eukaryotes

• are mobile at some stage of life

• store carbohydrates as glycogen, not starch, as in plants

• have an early developmental stage called a blastula

• have RNA (extracellular matrix)

Protostomate and Deuterostomate Lineages:

Figure 1 Protostome and Deuterostome

The names protostome and deuterostome derive from the differing fate of the initial opening of the

primitive digestive tract (the archenteron) in an embryo. As illustrated in the following picture, in

protostomes, this initial opening develops into the mouth, and an opening that develops later

becomes the anus. In deuterostomes, it develops into the anus, and an opening that develops later

becomes the mouth.

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Figure 2 (Images from the University of Tennessee at Martin Biology pages)

Determinate cleavage is characteristic of protostomes. After the initial cell division the fate of the

resulting daughter cells is determined -- these cells can only develop into specific tissues, not the

whole organisms. Indeterminate cleavage is characteristics of deuterostomes. After the initial cell

division the fate of the resulting daughter cells is not determined -- each has the potential to develop

into an entire organism. Sometimes this occurs; resulting individuals are genetically identical (in

humans, they are called identical twins).

Figure 3 Protostome and deuterostome cleavage differs in other ways

too.

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Figure 4 (Images from the University of Tennessee at Martin Biology pages)

Coelom Development: A coelom is a body cavity completely surrounded by mesoderm. The coelom can be used as a

hydrostatic skeleton, i.e., for support. It provides an avenue for release of, for example, gametes and

excretory waste. It also provides a place for internal organ placement.

The coelom can develop via two pathways: In protostomes: blocks of mesoderm hollow out to form

the coelom. Deuterostomes; pockets of mesoderm pinch off to form the coelom.

Phylum Echinodermata: Starfish, Sea Urchins

Tissues: Three distinct tissue layers in embryo, leading to multiple tissue types in

adult.

Symmetry: Bilateral in the larva, but adults are more or less radially symmetrical

(pentaradial, since they have five arms).

Body cavity: Coelom

Proto/deutero: Deuterostome

Digestive tract: Complete digestive tract (mouth at one end and anus at the other).

Other features: Body not clearly segmented. Calcareous endoskeleton. Hydrostatic

skeleton (water vascular system). Water vascular system. Planktonic

larvae.

You might not guess it from looking, but the echinoderms are probably our closest relatives

outside our own phylum.

Key echinoderm features include:

Endoskeleton: Much like our own skeleton, the echinoderm skeleton consists of

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numerous calcified structures joined by more flexible tissues.

Water- vascular system: A system of water-filled tubes running throughout the animal’s

body, the water-vascular system functions as an elaborate and

flexible hydrostatic skeleton. (Echinoderms therefore have two

skeletons: the hard plates of the endoskeleton and the flexible

hydrostatic skeleton.) The water-vascular system includes tube

feet, which are used by sea stars and other echinoderms to walk

and to grab prey items.

Coelom: The coelom in echinoderms is large, filling much of the body.

The coelom is just a big, fluid-filled space. It’s not the water

vascular system, which contains water in a closed system of

vessels, and it’s not the gut, which is smaller and also enclosed.

The coelom is the space where the other organs (water vascular

system, gut, gonads, etc.) form.

Examples: sea urchins, starfish, sea cucumbers:

Figure 5: Sea Cucumber Figure 6: Starfish Figure 7 Sea Urchin

• Water vascular system - system unique to this phylum. Functions in movement, support,

respiration, digestion.

• Decentralized nervous system.

• Rapid regeneration.

• Secondary radial symmetry -

Larvae are bilaterally symmetrical. Adults are radially symmetrical.

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A tube foot, an extension of the water

vascular system of a starfish. The tube feet

act like little suction cups which enable to

starfish to grasp onto the sediment

for movement or to break into bivalves

for food. Note that since this is not a

muscular system, they will not tire.

Major Classes of Echinoderms

Sea urchins; class Echinoidea: No arms; spiny body. Detritivores.

Sea stars (starfish); class Asteroidea: Five or more arms. Predators.

Sea cucumbers; class Holothuroidea: No arms; body often soft. Detritivores

Brittle stars; class Ophiuroidea: Five arms with central disk;

delicate and thin. Detritivores.

Figure 8: Tube Foot

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Phylum Chordata:

This is your phylum. The phylum Chordata includes humans and other vertebrates

Examples: Sea squirts, lancelets, vertebrates

• Notochord

• Pharyngeal Gill Slits

• Dorsal Hollow Nerve Cord

• Post Anal Tail

Chordate Characteristics

Tissues: Three well-defined tissue layers in embryo.

Symmetry: Bilateral, with cephalization.

Body Cavity: Coelom

Proto/deuterostome: Deuterostome: the blastopore formed during gastrulation eventually

becomes the anus; the mouth forms later.

Digestive Tract: Complete digestive tract.

Circulatory System: Closed in vertebrates; open in a few others.

Other Important Features:

Segmented body; vertebrae, for example.

Endoskeleton

Notochord: a connective-tissue body stiffener.

Dorsal tubular nerve cord – forms the brain and spinal cord.

Pharyngeal pouches and slits – gill related structures that may appear early in development. In

addition to forming gills, these structures also develop into jaw bones and other structures in

vertebrates.

Post anal tail: In many worms, the anus is at the very end of the animal’s body; chordates

typically have a tail beyond the anus.

Figure 9: Chordate Body Plan

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Non- Vertebrate Chordates

Subphylum Urochordata - the sea squirts

• Larval stage possesses all of the chordate characteristics.

• Most of these characteristics are lost when the

larvae undergo metamorphosis and emerge as adults.

Adult stage are primarily sessile filter-feeders.

Subphylum Cephalochordata - the lancelets

• Possesses all of the chordate characteristics throughout life cycle.

• Burrow into sand and use mucous-secreting organs to filter-feed.

• Feeble swimmers

Vertebrates

The vertebrates (phylum Chordata, subphylum Vertebrata) include fish, amphibians, reptiles

(including birds) and mammals. All these animals have the basic characteristics of chordates, with

some added twists:

• The anterior region of the dorsal hollow nerve cord expands to become a brain and is encased

within a skeletal cranium.

• Mesodermal blocks develop not only myotomes, but a segmented vertebral column that

protects the posterior region of the dorsal nerve cord (spinal cord) and replaces the notochord.

The cranium and vertebral column comprise the axial skeleton of vertebrates allowing an

elaborate central nervous system and powerful muscle action with a flexible body.

• The development of a brain has further spurred the development of more sophisticated

cephalic sensory organs, especially eyes, nostrils and ears.

• To support their enhanced homeostasis, vertebrates also have a closed circulatory system with

distinctive types of heart and kidneys, and a greater suite of endocrine organs.

The notochord, one of the unique defining characteristics of chordates, is a semi-stiff rod of

connecting tissue that forms in the embryo and serves to guide the development of the vertebral

Figure 10: Urochordate

Figure 11: Lancelet

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column (backbone) of vertebrates, along with other structures. In your own body, the notochord has

mostly disappeared; the only remnants are the cartilaginous disks between your vertebrae.

Subphylum Vertebrata Bone - reduction of notochord (vertebral disks)

Class Agnatha - the jawless fish (not

monophyletic)

Examples: lamprey, hagfish

• No jaws

• Most are parasitic fish

• Very diverse group in past. Now, only a few

species are still hanging on.

Class Chondrichthyes - the cartilaginous fish

Examples: sharks, rays, skates

• Endoskeleton is composed entirely of cartilage.

• Heterocercal caudal fin

• Two-chambered heart

• Numerous rows of teeth

• Internal fertilization and separate sexes

Figure 14: Stingray

Figure 13: Sand Tiger Shark

Figure 12: Lamprey

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Class Osteichthyes - bony fish (not monophyletic)

Examples: marlin, bass, catfish, angelfish, eels

• Most diverse group of vertebrates.

• Paired fins with fin rays of cartilage or bone.

• Respiration by gills supported by bony gill arches and

covered by a common operculum.

• Swim bladder often present.

• Two-chambered heart.

• Sexes separate and fertilization is usually external.

Ray-finned fish - most fish possess this fin structure

Lobe-finned fish - lung fish, Coelacanth, etc. The lobe-finned fish gave rise to tetrapods

Class Amphibia - amphibians (not

monophyletic)

Examples: frogs, salamanders

• Living skin - must be moist to breathe

• Lay eggs in water

• Outcompeted in water (fish) and land

(reptiles)

Figure 19: Amphibian

Figure 17: Stickleback

Figure 16:

Seahorse

Figure 15: Scaley Head

Figure 18: Coelocanth

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Class Reptilia - reptiles (not monophyletic)

Examples: lizards, snakes, gators

• First truly terrestrial animals

• Amniotic egg

• Scales (lungs now sole respiratory organ)

• Modifications of pectoral and pelvic girdles to

facilitate movement on land

Figure 20: Reptile

Class Aves - birds (monophyletic)

Examples: robin, jays, emu

• Feathers

• Warm-blooded (high metabolic rate)

• Hollow bones

Figure 21: Ave

Class Mammalia - mammals (monophyletic)

Examples: elephant, bats, Al Gore

• Hair

• Mammary glands

• Occlusional teeth

• Warm-blooded (high metabolic rate)

Figure 22: Vampire Bat

Figure 23: Deer Mouse

Figure 24: Elephant

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Lab Exercise:

Observe the preserved specimens for this lab.

View the following prepared slides:

Amphioxus-or lancelet, a fish-like marine chordate in the invertebrate subphylum

Cephalochordata.

Starfish arm-Note the coelom, tube feet and radial canal (parts of the water vascular system), pyloric

ceca (digestive glands), and pedicellaria (pincers on the outer surface of the body).

Starfish development

Starfish, ray

Dissection of a Preserved starfish dissection (separate document)

Sources: http://www.uic.edu/classes/bios/bios100/labs/animaldiversity.htm

http://facultyfiles.deanza.edu/gems/heyerbruce/6AManual15S.pdf