The Animal Kingdom I:

1
Chapter 25 The Animal Kingdom I Introducing the
Invertebrates
2
The Diversity of Animals

• The unifying characteristic among all animals is
  their mode of nutrition
• In the course of evolution as animals have
  adapted to new or changing environments, the
  basic ways that locomotion the capture of food,
  self-defense, and coordination have been refined,
  resulting in the great diversity of structural
  and functional detail
• Diversification has occurred in reproductive
  systems, providing mechanisms for genetic
  recombination and for dispersal into and
  exploitation of habitats with abundant food
  supplies

3
Diversity of Animals (cont)

• Most animals are diploid, with gametes the only
  haploid stage in the life cycle
• In most simple and primitive form of sexual
  reproduction, sperm and egg cells produced by
  different individuals are shed into water, where
  they unite
• Additional versatility, particularly in feeding
  and dispersal, is provided by larvae

4
The Origin and Classification of Animals

• Animals presumably had their origins among the
  protists
• By Cambrian period, two major diversifications of
  animal life had already occurred, but only one
  would survive
• Fundamental structure of virtually all living
  animals is a tube within a tube, modified and
  elaborated in a variety of ways that maintain a
  high ratio of surface to volume
• This diversification was unsuccessful

5
The Origin and Classification of Animals

• Modern animals are classified in about 30 phyla,
  each of which is thought to be monophyletic
• In classifying an animal, the factors considered
  are the number of tissue layers into which the
  cells are organized, the basic plan of the body
  and the arrangement of its parts, the presence or
  absence of body cavities and the manner in which
  they form, and the pattern of development from
  fertilized egg to adult animal

6
Phylum Porifera Sponges

• Often placed in a subkingdom of their own, the
  Parazoa (beside the animals)
• During their adult life, they are all sessile
  (attached to a substrate)
• Sponges are common on ocean floors
• Can be found at great depths

http//www.christiansburgprinting.com/photoalbum/p
ages/Purple20Tube20Sponge_tif.htm
7
Phylum Porifera Sponges

• A sponge is essentially a water-filtering system
  made up of one or more chambers through which
  water is driven by the action of numerous
  flagellated cells
• Choanocytes-the flagellated cells that line the
  interior of the cavity of the sponge
• Sponge cells are not organized into tissues or
  organs
• If sponge cells are separated into individual
  cells and small clumps of cells, they will
  reaggregate

8
Phylum Porifera Sponges

• The outer surface of a sponge is covered with
  epithelial cells, some of which react to touch or
  chemicals by closing pores and channels
• All cells have a specific function
• Amoebocytes
• play several roles in reproduction
• secrete skeletal materials
• carry food particles from the choanocytes to the
  epithelial and other nonfeeding cells
• Sponges cant consume anything larger than
  microscopic particles

9
Phylum Porifera Sponges

• 5,000 species, grouped into four classes,
  according to skeletal structure, stiffening, and
  support

10
Class Calcarea

• Skeleton consists of individual spicules of
  calcium carbonate

http//www.palaeos.com/Invertebrates/Porifera/Calc
area.htm
11
Class Hexactinellida

• The glass sponges
• Have spicules of silica fused in a continuous
  latticework

http//www.natuurmuseum.org/collectie/Zeedieren/Bi
jzonderezeedieren/overzichtbijzzeedieren.htm
12
Class Demospongiae

• Largest class of sponges
• Has unfused silica spicules, or a tough,
  keratin-like protein called spongin, or a
  combination of the two

http//ucf.tekkom.net/bsc2011/?sortclasslab_numb
er1
13
Class Sclerospongiae

• Have skeletons that contain all three kinds of
  material
• Calcium carbonate
• Silica
• spongin

14
http//www.cyhaus.com/marine/sponges/anatomy.gif
15
Reproduction in Sponges Asexual

• Asexual reproduction by fragments that break off
  from parent animal, or by gemmules (aggregations
  of amoebocytes within a hard, protective outer
  layer)
• Production of such resistant forms occurs mostly
  in freshwater organisms
• Invertebrates that live in freshwater are more
  likely to have protected embryonic forms than
  even closely related marine species

16
Reproduction in Sponges Sexual

• Highly specialized fertilization is internal
• Gametes arise from enlarged amoebocytes, but it
  is now said that choanocytes can also form
  gametes
• The sperm cells are carried by the water currents
  out of the osculum of one sponge and into the
  interior cavity of another
• There they are captured by choanocytes and
  transferred to amoebocytes, which then transfer
  them to ripe eggs

17
Reproduction in Sponges Sexual

• The embryonic stage develops into a flagellated,
  free-swimming larvae that develops into an adult
  sponge
• Most kinds of sponges are hermaphrodites the
  same individual has both male and female
  reproductive structures and produces both sperm
  and egg cells
• Great advantage for animals with no motility

18
Phylum Mesozoa Mesozoans

• About 50 species are known
• Simple wormlike animals that live as parasites
  inside a variety of marine invertebrates
• The cells are organized in a mass of reproductive
  cells surrounded by a single layer of ciliated
  cells
• No organs or cavities

19
Radially Symmetrical Animals

• Phylums Cnidaria and Ctenophora consist of
  gelatinous animals in which the adult form is
  generally radially symmetrical
• Radial symmetry body parts are arranged around a
  central axis
• Characterized by a gastrovascular cavity
• Enzymes are released that break down food,
  partially digesting it extracellularly
• Food particles then taken up by cells lining the
  cavity
• Water circulating through the cavity supplies
  dissolved oxygen to the lining cells and carries
  carbon dioxide, other waste products, and the
  inedible remains of food particles out the single
  opening

20
Phylum Cnidaria

• Carnivorous
• Cells are organized into distinct tissues
• Activities coordinated by nervous system
• Basic body plan
• Polyp vase-shaped
• Medusa bowl-shaped
• Polyp usually sessile, medusa usually motile
• Consist of two layers of tissue epidermis and
  gastrodermis

http//www.cityhillmiddleschool.com/jellyfish.htm
21
Phylum Cnidaria

• The Mesoglea, middle jelly, is between the two
  layers of tissue
• Made of collagenlike material
• Cnidarians have two embryonic tissue layers the
  ectoderm and the endoderm
• Said to be diploblastic
• Capture prey using tentacles, armed with
  cnidocytes, special cells that contain
  nematocytes (thread capsules)
• Nematocyst threads, often poisonous or barbed,
  can lasso prey, harpoon it, or paralyze it

22
http//www.csulb.edu/zedmason/emprojects/charlie/
moffet.html
23
Class Hydrozoa

• Epidermis is composed largely of
  epitheliomuscular cells, which perform a
  covering, protective function and also serve as
  muscle cells
• Each cell has contractile fivers, myonemes, at
  its base
• Contractile run lengthwise in the animal and the
  fibrils of the gastrodermis run circularly

24
Class Hydrozoa

• Contain two types of nerve cells
• Sensory receptor cells
• Nerve net, a loose connection of nerve cells
  lying at the base of the epidermal layer
• When stimulated, sensory receptor cells transmit
  their impulses to an adjacent cell
• The nerve net links an entire organism into a
  functional whole
• Coordinate muscular contractions of Hydra
• No center of operations

25
Class Hydrozoa

• Hydra lives as a solitary polyp and has no medusa
  stage
• Most hydrozoans are colonial marine animals and
  have both hydroid (polyp) and medusoid forms at
  different times in their life cycles
• Genus Obelia
• Colony arises from a single polyp, which
  multiplies by budding
• Within colony, there are two types of polyps
  feeding polyps with tentacles and cnidocytes, and
  reproductive polyps from which tiny medusas bud
  off
• Medusas produce sperm or eggs that are released
  into the water and fuse to form zygotes

26
Class Scyphozoa- cup animals

• The medusa form is dominant
• Commonly known as jellyfishes
• The epitheliomuscular cells underlie the
  epidermis, contracting rhythmically to propel the
  medusa through the water
• The contractions are coordinated by
  concentrations of nerve cells in the margin of
  the bell
• Statocysts are specialized receptor organs that
  provide information by which an animal can orient
  itself with respect to gravity
• Ocelli are groups of pigment cells and
  photoreceptor cells
• Located at the bases of the tentacles

27
Class Anthozoa- flower animals

• Sea anemones and corals
• Have no medusa stage
• Reproduce asexually by budding, division, or
  fragmentation sexually by production of gametes

http//www.ucsc.edu/opers/scuba/images/anemone.jpg
28
Class Anthozoa- flower animals

• Gastrovascular cavity is divided by vertical
  partitions
• In most corals, epidermal cells secrete
  protective outer walls, usually of calcium
  carbonate, into which the delicate polyp can
  retreat

29
Phylum Ctenophora- comb bearers

• About 90 species
• Comb jellies and sea walnuts
• Bioluminescent
• Characterized by gastrovascular cavity and two
  tissue layers, epidermis and gastrodermis, with
  mesoglea between
• Reproduction is sexual
• All individuals are hermaphrodites

http//www.njscuba.net/biology/sw_jellies.html
30
Bilaterally Symmetrical Animals An Introduction

• In bilaterally symmetrical animals, the body is
  organized along a longitudinal axis with the
  right half an approximate mirror image of the
  left half
• Makes possible more efficient locomotion
• Has dorsal (back), ventral (front), anterior
  (head), and posterior (tail) surfaces
• Many of the sensory cells are collected into the
  anterior end
• Structures useful in capturing and consuming prey
  are generally located in anterior region of the
  animal
• Digestive, excretory, and reproductive structures
  usually located towards posterior

31
Bilaterally Symmetrical Animals An Introduction

• Cephalization concentration of sensory and nerve
  cells and of structures associated with feeling
  at the anterior end of an animal
• All bilateral animals are triploblastic three
  embryonic layers (collectively known as germ
  layers)
• Mesoderm layer of cells located between the
  ectoderm and the endoderm
• Covering and lining tissues and nerve tissues are
  derived from ectoderm
• Digestive structures from endoderm
• Muscles and most other parts of body from mesoderm

32
Bilaterally Symmetrical Animals An Introduction

• Triploblastic animals can be grouped in three
  categories, according to presence or absence of a
  body cavity
• Acoelomates animals with tissues derived from
  the three germ layers packed together with no
  body cavity other than the digestive cavity
• Pseudocoelomates animals with an additional
  cavity that develops between the endoderm and
  mesoderm
• Coelomates animals with a fluid-filled cavity
  that develops within the mesoderm

33
Phylum Platyhelminthes Flatworms

• Their tissues are specialized for various
  functions two or more types of tissue cells may
  combine to form an organ
• Have a digestive cavity with one opening
• Food cannot be processed continuously
• Acoelomates with solid bodies no circulatory
  system for the transport of oxygen and food
  molecules

http//struggle.net/history/images/flatworm.gif
34
Phylum Platyhelminthes Flatworms

• All cells must be within diffusion distance of
  sources of oxygen and of food
• Flatworms do this by either
• Flattening the body, which keeps the cells close
  to the external oxygen supply
• The digestive cavity is branched, carrying food
  particles to all regions of the body
• About 13,000 species, all placed in three classes
• Class Turbellaria contains free-living form
  Classes Trematoda (flukes) and Cestoda
  (tapeworms) are parasitic

35
Class Turbellaria

• Free-living, carnivorous
• Ectoderm of a freshwater planarian gives rise to
  cuboidal epithelial cells
• Ventral epithelial cells secrete mucus, which
  provides traction for the planarian as it moves
  using cilia along its own slime trail

http//www.rzuser.uni-heidelberg.de/bu6/sou_gall0
4.html
36
Class Turbellaria

• Eats dead meat or other slow-moving animals
• Feeds by means of a muscular organ, the pharynx
• Muscular contractions in the tubular pharynx
  cause strong sucking movements
• Excretory system in planarian, system is a
  network of fine tubules that runs the length of
  the animals body
• Side branches of the tubules contain flame cells,
  each of which has a hollow center in which a tuft
  of cilia beats
• Regulates water balance
• Fertilization is internal for all turbellarians
• Planarians are hermaphrodites

37
The Planarian Nervous System

• Neurons are condensed into longitudinal cords
• In planarians, there are two main conducting
  channels, one on each side of the body
• The channels carry impulses to and from the
  aggregation of nerve cells in the anterior end of
  the body
• Known as ganglia
• Ocelli are usually inverted pigment cups
• Planarians are photonegative they move away from
  light sources
• The heard region of a planarian is rich in
  chemoreceptors
• The animal locates the food source by repeatedly
  turning toward the side on which it receives the
  stimulus more strongly until the stimulus is
  equal on both sides of its head

38
Classes Trematoda and Cestoda

• Trematodes (flukes) and tapeworms (class Cestoda)
• Parasitic can cause fatal diseases among
  vertebrates
• Have tough outer layer of cells resistant to the
  body fluids of their hosts, particularly
  digestive fluids
• Most have suckers or hooks on their anterior end
  to fasten on to their hosts

http//www.teachnet.ie/farmnet/Animal_classificati
on.htm
39
Classes Trematoda and Cestoda

• Trematodes feed through their mouths
• Tapeworms hang on and absorb predigested food
  molecules through their skin
• Tapeworms cause illness by encroaching on the
  food supply, producing wastes, and obstructing
  the intestinal tract
• All parasites are believed to have originated as
  free-living forms and to have lost certain
  tissues and organs

40
Other Acoelomates Phylum Gnathostomulida

• About 80 species of tiny marine worms
• Have a unique pair of hard jaws
• Abundant along coastal shorelines live in the
  spaces between particles of sand and slit
• Have no coelom or pseudocoelom
• Digestive cavity only has one opening
• Use jaws to scrape bacteria and fungi from sand
  and slit particles

41
Phylum Rhynchocoela

• 650 species
• Acoelomate worms, commonly called ribbon worms or
  nemertines
• Have long, retractile, slime-covered hollow tube
  (proboscis)

http//shop.uwphoto.no/detail.asp?PRODUCT_IDesv06
2cd17
42
Phylum Rhynchocoela

• Have one-way digestive tract beginning with a
  mouth and ending with an anus
• Advantages
• Eating can be continuous
• Various segments of the tract can become
  specialized for different stages of digestion
• Have a circulatory system, typically consisting
  of one dorsal and two lateral blood vessels that
  carry the colorless blood
• Reproduction sexes are separate, fertilization
  is external
• Asexual reproduction by fragmentation of the body
  and regeneration of whole worms from the parts

43
Pseudocoelomates

• Pseudocoelom a body cavity that develops between
  the endoderm and the mesoderm
• Pseudocoelom is a sealed, fluid-filled tube
• It increases the efectiveness of the animals
  muscular contractions
• Functions as a hydrostatic skeleton causes the
  body to return to its original shape after the
  muscles have contracted
• Have one-way digestive tract, but lack
  circulatory system
• Movement of fluids within the pseudocoelom
  enhanced by muscular contractions of the body wall

44
Phylum Nematoda-roundworms

• Most are free-living microscopic forms
• Some are parasites
• nematodes lack circular muscles
• Moves by contracting the longitudinal muscles
  against both the tough, elastic cuticle and the
  internal hydrostatic skeleton
• Mouth has a muscular pharynx, often equipped with
  piercing stylets
• Reproduction is sexual, sexes usually separate

http//cas.bellarmine.edu/tietjen/images/phylum_ne
matoda.htm
45
Phylum Nematoda-roundworms

• Humans are hosts to about 50 species of parasitic
  nematodes
• Most common parasitic nematodes in North America
  are pinworm (Enterobius), whipworm (Trichuris),
  hookworm (Ancylostoma), intestinal roundworm
  (Ascaris), and Trichinella
• Trichinella causes trichinosis injection of only
  a few hundred of these cysts can be fatal
• Caused by eating uncooked/undercooked pork

46
Other Pseudocoelomate Phyla

• Members of seven other phyla have body plans
  based upon the pseudocoelom
• Phylum Nematomorpha horsehair worms adults are
  free-living and reproduce in water juveniles are
  parasites of arthropods
• Phylum Acanthocephala spiny-headed worms
  parasitic throughout life cycle adults live and
  reproduce in intestines of vertebrates adult
  worms lack digestive tract and have a proboscis
• Phylum Loricifera larvae are free-swimming
  adults are sedentary

47

• Phylum Kinorhyncha marine worms feed on
  diatoms have spiny, retractile proboscis sexes
  are separate adults are motile
• Phylum Gastrotricha hermaphrodites feed on
  protists and dead organic matter adults are
  motile
• Phylum Rotifera found in fresh water called
  wheel animalcules have muscular pharynx with
  hard jaws feed on protists, bits of vegetation,
  and other smaller animals sexes are separate,
  but in some groups, the females produce eggs that
  can develop without fertilization (called
  parthenogenesis)

48

• Phylum Entoprocta resemble hydrozoans and
  bryozoans usually sessile have U-shaped
  digestive tract, and both the mouth and anus are
  located within a circle of tentacles some
  species have separate sexes, some are
  simultaneous hermphrodites, and in others, a
  phenomenon known as sequential hermaphroditism
• A single reproductive organ produces sperm at one
  stage in the life cycle and eggs at a later stage