Chapter 18 - San Diego Mesa College

SAN DIEGO MESA COLLEGE

SCHOOL OF NATRUAL SCIENCES

General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D

.

Chapter 18: Evolution of animals, animal kingdom & Animal life cycles

- Part I -



We humans share the surface of this planet with another highly evolved and mobile form of life we call animals



According to scientific evidence, animals have been on this planet since a long time and we humans share many of the animals features, at the molecular, cellular, physiological and anatomical level



In this chapter we will try to understand the natural history of animals and the important animal features as well as characteristics which will help us understand their unique habitats and distribution on this planet

Evolution of animals and prominent members of the animal kingdom



fossil and biochemical evidence tell us, that the earliest forms of biological organisms, which we call animals , existed already around 700 million years ago during the late, so-called Precambrian era

- the first animal fossils appear at the end of the Proterozoic age (650 – 544 mya), also known as the Vendian period

- the first diversification of soft-bodied organisms, collectively known as the

"Vendian fauna" or "Ediacaran fauna“ happened during that time

- scientist are not sure whether these fossilized creatures (see images below) were algae, lichens, giant protozoans, or even a separate (now extinct) kingdom of life (!)



most of the modern phyla of the animal kingdom (see classification scheme below) existed already during the time of the famous Ediacaran fauna which existed during the Cambrian period approx. 600 million years ago

 the earliest fossils appear around that time

 scientists assume, that all “modern members” and still existing life forms of the animal kingdom arose in the oceans from (a) heterotrophic colony-forming unicellular protist(s) (= protozoan)

- biologists hypothesize, that some of these ancient protist colonies began to fold inward (see “Gastrulation” further below), creating the first gastrula-like protoanimal

- this view is still hypothetical since no fossils of “proto-animals” have been found until today



later in this proto-animal stage, cell specialization must have occurred, paving the way for the evolution of true multi-cellular animals

- the first splitting of functional tasks may have occurred in these early multicellular colonies

- an early type of specialization amongst these cells may have created the first somatic and reproductive cells

1




.

- however, how these proto-animals exactly looked like remains a mystery, since fossilized structures are very unlikely to arise from their fragile, soft-bodied bodies

Images of fossils of early animal life forms on Earth

(Age: Cambrian era - approx. 600 million years ago)

Image of original fossil find

Name

D i i c k i i n s o n i i a

- phylum ??

T r r i i b r r a c h i i d i i u

-

Cnidarian?

- Echinoderm?



scientists believe, that the morphology and features of the very early stages of embryonic development in animals (see:  the typical animal life cycle with

Blastula, Gastrula stages

) may reflect in a certain way the shapes of these “protoanimals”



the ancestral colonial protist that gave rise to the animal kingdom diverged first into two separate lineages (see Graphic below)

1. the Parazoa (Latin for "false animal")



contain only one modern phylum, called Porifera, which contains

the sponges

 they are NOT true animals, because they have no true tissues

(= no ectoderm, endoderm nor mesoderm layers)

2




.

2. the Eumatazoa ("true animals")



the Eumatazoa branch gave rise to all other modern animal phyla

(see Chart of animal phyla below)

 they all have true tissues



the radiation of diversity in the kingdom Animalia proceeded based on the evolution of a number of distinct "hallmark" features or characteristics

Characteristics of animals



animals are living organisms characterized by 7 main features

1. they are made of eukaryotic cells

2. animals are multicellular organisms

3. animals are heterotrophic organisms

 most animals take up complex food and digest it in specially

formed body cavities, called digestive tract

4. cells have no cell wall

 but have characteristic so-called intercellular junctions

(= connection structures)

5. have characteristic stages during their life cycle, called blastula and gastrula

6. they have true tissues , each with unique physiological functions within the animal body

7. animals have the capability of mobility at some stage during their life cycle

3




.

Taxonomy of important phyla of the animal kingdom & Body characteristics

- Part I -

Ancestral colonial protozoan

hypothetical

no fossil evidence

P a r r a z o a

“false animals”

E u m e t t a z o a

“true animals”

- have true tissues

P o r r i i f f e r r a

( ( S p o n g e s ) )

- 5000 species

- no true

- no digestive

B o d y s y m m e t t r y

R a d i i o l l a r r i i a

- radial symmetrical animals

B i i l l a t t e r r i i a

- bilateral symmetrical animals

C n i i d a r r i i a

( ( “ J e l l l l y f f i i s h e s ” ) )

- 10,000 species

- no

- gastrovascular cavity

- muscles & nerve fibers

+ / / t t h i i r d b o d y c a v i i t t y

( ( = c o e l l o m ) )

A c o e l o m a t t a

- no third body cavity

P s e u d o c o e l l o m a t t a

- pseudo- coelom

C o e l l o m a t t a

animals with

a true coelom

P l l a t t y h e l l m i i n t t h e s

( ( F l l a t t w o r m s ) )

- 10,000

- pharynx, no anus

- incomplete digestive

- nerve cord

- no vascular system

Graphic©E.Schmid/2000

N e m a t t o d a

( ( R o u n d w o r m s

- > 100,000 species

- mouth & anus

- complete digestive system

- no vascular

- hydrostatic skeleton

- nerve cords & red = animal phylum

M o l l l l u s c a

A n n e l l i i d a

A r r t t h r r o p o d a

C h o r r d a t t a

(see Part II)

4




.

The typical animal life cycle and embryonic development



most of our knowledge about the early stages of the animal life cycle and animal development, we owe the classical studies with sea urchins ( L y t t t e c h i i i n u s v a r r r i i i e g a t t t u s )

 historically, sea urchins were a key model system in answering many

questions regarding the mechanisms of fertilization and egg activation , cleavage , gastrulation and early development of the embryo



animals spend their entire life cycle as diploid cells, with the exception of singlecelled, haploid gametes; therefore, animals are diploid biological organisms ;

- all cells of the animal, with the exception of the gametes, have a double chromosome set within the nucleus of their cells

- this is very different to plants, e.g. mosses and ferns, which have multi-cellular, haploid structures (= gametophyte) which produces haploid gametes

1. the female/male adult animals make haploid cells, i.e. e g g a n d s p e r r r m , by meiosis in the so-called gonads



the gonades are called testis in males and ovary in females

2. one egg (= o o c y t t t e ) and one s p e r r r m fuse in a process called fertilization to form a d i i i p l l l o i i i d z z y g o t t t e ( 2n )

 the zygote starts to divide by mitosis and goes through a

series of characteristic morphological stages

3. the zygote then undergoes mitotic divisions, which first forms a berry-like cell complex called Morula and later leads to a stage of development called the

Blastula



the blastocyst (blastula structure) consists of a single cell layer

around a fluid-filled cavity, called blastocoel

Early embryonic development of a typical animal

1. Early sea urchin (L. variegatus) Blastula

5




.

2. L. variegatus Blastula before onset of gastrulation

(Electronmicroscopic image)

4. the Blastula starts to fold inwards to form the so-called Gastrula

 the gastrula, which consists of an inner (= endoderm) and outer cell layer

(ectoderm), forms by infolding of the blastocyst in a blastopore

3. L. variegatus early and late Gastrula

(both viewed from the oral side)

E a r r r l l l y g a s t t t r r r u l l l a L a t t t e g a s t t t r r r u l l l a

5. the Gastrula develops further and the still vastly enigmatic biological process, called pattern formation , begins to shape the animal embryo with an opening

(the later mouth or anus) at one end

 this process creates outer and inner cell layers



the outer cell layer, called ectoderm , develops into the so-called epidermis , which builds the skin and the animals nervous system

 the inner cell layer (= endoderm ) forms the animal’s digestive tract



in most animals a third, so-called mesoderm , forms later, which

develops into most of the inner organs (e.g. liver, heart, lungs, etc.)

6




.

Embryonic development & Environment

Embryonic pattern formatio n in animals is an enormously sensitive, “fragile” biological process and can be negatively influenced (= inhibited) by drugs, medications (e.g.

Thalidomide in human embryos) and environmental toxins, e.g. heavy metals such as cadmium or nickel (see I mage of the sea urchin below)

P a tt t tt t e rr r n ff f o rr r m a tt t ii i o n a n d e m b rr r y o n ii i c d e v e ll l o p m e n tt t ii i n tt t h e s e a u rr r c h ii i n (( ( L ..

.

v a rr r ii i e g a tt t e ss )) )

(both pictures show the bilateral or radial skeletal elements = spikules)

N o r r r m a l l l d e v e l l l o p m e n t t t I I I n t t t h e p r r r e s e n c e o f f f N i i i c k e l l l ( ( ( N i i i ) ) )

 disruption of the normal pattern

formation of the primary mesenchyme

cells in the presence of the heavy metal

6. most animals develop: a.) directly into the adult organism b.) others develop into one or more so-called larval stages (e.g. seastar, most insects)

7. in the latter case, the larvae undergoes a major change in body form and shape in a process called metamorphosis

T a x o n o m y



in the past 300 years, scientists grouped the huge diversity of animals, according to distinct evolutionary and adaptive traits, into so-called taxa ; the scientific process of grouping is called taxonomy



taxonomists established several methods of classification to build a taxonomic system of the animal kingdom



the taxonomic system recognizes the generally accepted grouping of animals in socalled phyla , which are arranged in so-called phylogenetic trees ,

7




.

1. Traditional classification :

- this method of systematics stresses both common ancestry (monophylesis) and he degree of divergence among groups

- e.g. birds have feathers, reptiles have scales, and mammals have hair

- it goes back to the Swedish naturalist C a r r r l l l L i i i n n e

’ ’ ’

, who attempted first to

classify all known species of his time (1753)

 however, evidences of past life forms (= fossil records) are not included in

this method of classification

 Linne’ established a hierarchical classification, which is based on the premise

that the species is the smallest unit , and that each species (or taxon) is

nested within a higher category

The Linnean classification of the animal kingdom

Domain: E U K A R Y O T A

Kingdom: A n i i i m a l l l i i i a

Phylum: Chordata

Class:

Order:

Mammalia

Primates

Family:

Genus:

Hominidae

Species:

Homo sapiens L.

C l l l a s s i i i f f f i i i c a t t t i i i o n t t t r r r a i i i t t t s o f f f t t t h e k i i i n g d o m a n i i i m a l l l s

8




.

2. Cladistic classification:



this type of systematics groups organisms based on shared derived characters , not the overall similarity of potential group members

 e.g. the presence of an amniotic egg is used to unite a group sharing common

ancestry

 this method was developed by W i i i l l l l l l i i i H e n n i i i g , who attempted to develop a

more objective method of classifying organisms

3. Phenetic classification

 species are clustered together based on the number of their similarities (or

differences, depending on the numerical coefficient employed)

 traits are measured and converted into integers or numerical data, which are

then mathematically processed using an algorithm that generates a similarity

or distance as the case

4. Genetic classification

 today more and more scientists use sensitive genetic and molecular

biological methods (= DNA sequencing, RNA sequencing, DNA

hybridization and sequence homology analysis) to examine phylogenetic

ancestry of biological organisms

 this powerful approach which compares different forms of life at the molecular

level (not only morphological level) is more and more supported by the use of

computer programs and algorithms (  Bioinformatics )



these morphologic and (nowadays) genetic studies helped to establish the modern phylogenetic tree for the animal kingdom



today the animal kingdom is grouped into more than 35 phyla , which comprise approx. 1 million species ; nine of these phyla generally comprise the bulk of the kingdom, which are: Porifera, Cnidaria, Platyhelminthes, Nematoda, Mollusca,

Annelida, Arthropoda, Echinodermata and Chordata

The phylogenetic tree of Animalia

A N I I I M A L I I I A

I I I N V E R T E B R A T A V E R T E B R A T A

1. PORIFERA (sponges)

2. CNIDARIA (e.g. medusa)

5. ANNELIDA

(e.g. earthworms)

6. ARTHROPODA

(e.g. insects)

7. PISCES (f ishes)

8. AMPHIBIA (e.g. frog)

3. BILATERIA 9. REPTILIA

(flatworms, roundworms) (e.g. snakes)

4. MOLLUSKA (e.g. snails) 10. AVES (birds)

11. MAMMALIA

(e.g. mouse, man)

9




.

Summary of important body (= morphological) features nine animal phyla

1 .

.

.

P O R I I I F E R A ( ( ( S P O N G E S ) ) )



about 5000 species are known, most of which are marine



among them are the most simple animals



sponges are believed to have evolved from a colonial protozoan



there are no true tissues in sponges and only merely specialized cell layers

(therefore: “false animals”)



they don’t have a digestive tract

and digest intracellularly (= inside the cell body)

 lack a nervous system and muscles



most sponges feed from bacteria by drawing water into the body through a network of pores (hence the name porifera = pore-bearer) and passing it out through the large opening ( osculum ) at one end of the body

S t t t a g e s o f f f t t t h e l l l i i i f f f e c y c l l l e o f f f a s p o n g e

1. a mature sponge produces h a p l l l o i i i d e g g s a n d s p e r r r m that are released into the central cavity

2. after fertilization, the d i i i p l l l o i i i d z z y g o t t t e develops into a ciliated larva without a Gastrula stage ( no Gastrula appears)

10




.

3. the larval stage is mobile and able to move around, while the adult (= sponge) is stationary the lack a of development



sponges are able to reproduce asexually by so-called fragmentation

 a released fragment develops into a new sponge



2 types of sponges are known

1 .

.

.

V a s e s h a p e d o r r r c y l l l i i i n d r r r i i i c a l l l s p o n g e s



have a radial symmetry = the body parts are oriented around a

central axis

 e.g. S c y p h a

 consists of 3 cell types

1. outside and pore-forming cells

 have protective function and regulate the incoming water flow

2. motile amoebocytes with skeletal components

 have delivery and carrier function

 carry the nutrients and metabolites to other cells

3. choanocytes or collar cells

 are flagellated cells which engulf trapped bacteria by a process

called phagocytosis

2 .

.

.

C h o a n o f f f l l l a g e l l l l l l a t t t e s

 is a cluster of flagellated collar cells attached to a stalk, which has

soil contact

 ancestors lived already in the Precambrian seas

 it is assumed that sponges and all animals arose from a

choanoflagellate ancestor

11




.

I I I m a g e o f f f a t t t y p i i i c a l l l s p o n g e a n d c h o a n o f f f l l l a g e l l l l l l a t t t e

2 .

.

.

C N I I I D A R I I I A



the phylum Cnidaria contains 10,000 species, e.g. Hydras , sea anemones , jellies

(‘jelly fish’) and corals , which are characterized by adult bodies having radial symmetry



Cnidarians are aquatic, mostly all marine



they have true tissues and are therefore also called tissue animals ; but they lack the mesoderm , and only show ectoderm and endoderm tissue layers



Cnidaria are carnivores and capture small animals and protists with the help of stinging cells called cnidocytes



these unique and specialized cells each contain a nematocyst , which

is a fluid-filled capsule with a long, spirally coiled hollow thread

 on contact with a prey, this barbed thread, together with a toxin is

ejected to trap and kill the victim



the prey is put in their mouths which leads into a digestive compartment, the socalled gastrovascular cavity

 since they do not have an anus , the undigested food and

other nutritional waste exits through the mouth again



Cnidarians have both, muscle fibers and nerve fibers

 these animals are capable of directional movement and of

transmission of messages in more than one direction

12




.

Body shapes of a typical polyp and medusa (Phylum: Cnidaria)

Stages of the life cycle of a typical Cnidarian

The life cycle of a typical Cnidarian



The typical Cnidarian life cycle involves both sexual and asexual reproduction



Cnidarians show "alternation of generations" between the sessile p o l l l y p p h a s e and the mobile m e d u s a p h a s e

 but unlike plants, both phases are diploid



after fertilization of an egg cell by free-swimming sperm, a bilaterally symmetrical larva known as a planula , develops from the zygote; the larva development shows a clear Gastrula stage

13




.



the planula settles in an appropriate location and grows into an adult polyp



a polyp is a mostly stationary, cylindrical body with tentacles on top

 it has so-called stinger cells (= Cnidocytes ) on the surface of the

polyps tentacles



the polyp reproduces asexually to form a stage called medusa

 a medusa is a free-swimming, umbrella-shaped body with fringes of

tentacles



have a soft, glassy-transparent body

 some of the medusas show so-called bioluminescence due to the

activity of a special protein called aquorin (e.g. Aquoria species)



many medusa produce and release biologically highly active

compounds ( toxins ), which are able to paralyze or kill their prey

 some of these toxins are strong irritants to humans and can cause

severe rashes and burns



each medusa develops gonads which start to form gametes (= egg and sperm) by meiosis



some species, e.g. the sea nettle, exist only as a medusa while others, such as

Hydra or the sea anemones, exits only as polyps

3 .

.

.

B I I I L A T E R I I I A



an important "fork in the road" of evolution, occurred with the divergence of bilaterally symmetric animals from the irregularly-shaped Porifera (=sponges) and the radially symmetric Cnidarians



Bilaterally symmetric animals tend to swim or move in a head-first direction; they are marked by a distinct posterior and anterior end (= head and tail), as well as by dorsal and ventral surfaces

3.1. Flatworms (= Phylum: PLATYHELMINTHES)



the Phylum Platyhelminthes contains about 13,000 species of flatworms



they have a so-called bilateral symmetry of their body

 the animals body has two mirror-image left and right sides

 have an anterior head region and a posterior end part of the body



they have three tissue layers : ectoderm , mesoderm and endoderm

 the mesoderm layer gives rise to muscles and reproductive organs

 The presence of three muscle layers facilitates varied movement



gland cells secrete a mucous material upon which the animal slides

or glides

14




.



their body plan is acoelomate ; they have only one interior space (= the digestive tract) and no third body cavity (see roundworms!)



their body shape is sac-like with a single opening , called pharynx



they capture food by wrapping itself around prey and entangling it in slime



flatworms have (like the Cnidarians) an incomplete digestive tract (= no anus!); the gastrovascular cavity is highly branched

 it distributes nutrients throughout the body and is the site of extracellular digestion



flatworms have two light-sensitive eyespots that have pigmentation (



primitive form of bright/dark vision for sense of orientation)



they have muscles, a nerve cord, and digestive organs, but have no respiratory or circulatory system

 gas exchange occurs by diffusion through the skin



the length of different species varies from 1mm to (in the case of tape worms) up to

20 meter (!!)

T h e t t t y p i i i c a l l l l l l i i i f f f e c y c l l l e o f f f f f f l l l a t t t w o r r r m s

 flatworms, such as Planaria, can reproduce sexually and asexually



in asexual reproduction , the body constricts beneath the pharynx and each half will grow into a whole animal by a biological process called regeneration



since Planaria are so-called hermaphroditic animals , i.e. they possess both male and female sex organs , it comes to cross-fertilization during sexual reproduction



after fertilization, the zygotes (= fertilized eggs) are enclosed in a cocoon and hatch in two to three weeks

15




.

Typical anatomy of a flatworm (Phyla: Platyhelminthes)



3 types of flatworms are known

1 .

.

.

F r r r e e l l l i i i v i i i n g f f f l l l a t t t w o r r r m s ( ( ( C l l l a s s : : : T u r r r b e l l l l l l a r r r i i i a ) ) )



the class Turbellaria includes the 5-10 mm long freshwater planaria, such as

D u g e s i i i a



have a nervous system with a simple brain, nervous cords and eyespots



have tissue clusters and a single mouth opening (= pharynx)



the mouth leads into a highly branched digestive tract



live under rocks in freshwater ponds and streams, where they crawl on ventral cilia in search for food

2 .

.

.

F l l l u k e s ( ( ( C l l l a s s : : : T r r r e m a t t t o d a ) ) )



the Class T r r r e m a t t t o d a includes flukes



all flukes are parasitic and are named after the organs they inhabit, e.g. blood flukes, liver flukes or lung flukes



the fluke bodies tend to be oval and elongate



flukes lack a definite head, but have an oral sucker surrounded by sensory papillae



flukes have reduced digestive, nervous, and excretory systems, but the reproductive systems are well developed



they are usually hermaphrodites



a prominent example of a fluke is S c h i i i s t t t o s o m a ;

 it’s larvae infect and invade humans, where they attach to the blood

vessels near the intestines, after uptake of infectious water

 there they reproduce sexually and the fertilized eggs pass out via the

feces

 the hatched eggs infect a water snail and they asexually reproduce in

this host organism into an infectious larvae again;



Schistosoma causes a persistent disease in humans, called

16




.

Schistosomiasis , which is accompanied by anemia and abdominal

pains

3 .

.

.

T a p e w o r r r m s ( ( ( C l l l a s s : : : C e s t t t o d a ) ) )



the Class C e s t t t o d a consists of the tapeworms



tapeworms are like flukes also parasitic organisms



they inhabit the digestive tracts of vertebrate animals, reptiles, birds and mammals, where they directly absorb the already digested food of their hosts; therefore they do not have an own digestive tract



they have very long, ribbon-like bodies with repeating segments

 the tapeworm’s head or also called the scolex has typical hooks and suckers that allow the organism to attach to the host's intestinal wall



behind the head is a short neck and then a long string of so-called proglottids

 each proglottid segment contains a full set of both male and female

sex organs and very little other structure



following fertilization, ripe eggs appear in the last, posterior proglottid, which breaks off and leaves the host via it’s feces



when the released tapeworm eggs are ingested by pigs or cattle, the larvae burrow through the intestinal wall and travel by bloodstream to the muscles where it becomes encysted

 a cyst is a hard-walled structure sheltering a larval worm



if humans eat under-cooked meat of infected pigs or cattle they become infected, too

 e.g. T a e n i i i a r r r y n c h u s ; can reach up to 20 meters (!!) in the human

intestine if not medically treated

3.2. Roundworms (= Phylum: NEMATODA)



the phylum Nematoda comprises several hundred thousand species of roundworms



most are free-living , although some parasitic species are known



pinworms are thought to infect 30% of all US children



its numerous species inhabit virtually every place on Earth

 some live on rotten organic matter and are organic decomposers



some live in soil or on ocean floors



roundworms have a cylindrical body shape with finely tapered tail and a more blunted head region



developed a skin = a layer of non-living cells which have protective function

17




.



have a complete digestive tract with mouth and anus

 food travels one way through the gastrointestinal system



anterior part breaks down (= digests) food with the help of digestive

enzymes

 the posterior part absorbs the food components and nutrients



nematodes lack a circulatory system , but do have a well developed digestive system



nematoda is the first phylus of animals which developed a third body compartment, called body cavity ; adult nematodes have a typical

“tube-within-a-tube” body structure , which is also called a pseudo-coelom

 a pseudo-coelom is a closed, fluid-filled space that acts as a hydrostatic skeleton , aids in circulation and dispersal of nutrients

Coelom-less animals (Acoelomates)

(e.g. flatworms, flukes)

18




.

Development of a body cavity (= pseudo-coelom) in nematods



the body cavity does not develop from splitting of the mesoderm



with the exception of C a e n o r r r h a b d i i i t t t i i i s e l l l e g a n s , little is known about the life cycles of roundworms and their metabolism



some roundworms are serious agricultural pests and attack the roots of plants



some live as parasites in animals or the human body; humans are host to about 50 species of roundworms

 e.g. h o o k w o r r r m s ; attach to the intestinal wall and suck blood

E x a m p l l l e s o f f f r r r o u n d w o r r r m s : : :

1. C a e n o r r r h a b d i i i t t t i i i s e l l l e g a n s



C. elegans is a small roundworm and an important so-called model organism in

Biology



it consists of only about 1000 cells

 for comparison: the human body is made of 60 trillion cells !!!)



C. elegans has only 1000 genes in its genome; it therefore serves an important organism in biological research, where it is used as a model to study eukaryotic gene expression, aging and the role of genes in animal development and heredity

- especially aging research with C. elegans lead to the discovery of several

“aging genes” which are involved in the aging process in this organism



it has been extensively studied as part of the human genome project, and the DNA of it’s complete genome has been successfully sequenced

19




.

2 .

.

.

T r r r i i i c h i i i n e l l l l l l a s p i i i r r r a l l l i i i s



T. spiralis migrates into muscle tissues where it reproduces



this roundworm causes trichinosis in affected mammals and humans; causes nausea and in, case the worm enters the heart tissue, sometimes leads to death

 worms are acquired by people who eat undercooked pork meat

3 .

.

.

A s c a r r r i i i s



Ascaris is a parasitic roundworm , which thrives in warmer climate zones



these worms are un-segmented and have a smooth outside wall



after mating and fertilization the eggs mature in the soil; when these eggs are swallowed, the ingested larvae burrow through the intestinal wall and move to the liver, heart and/or lungs



within the lungs, the larvae molt and, after 10 days, migrate up the windpipe to the throat where they are swallowed



in the intestine, the mature worms mate and the female deposits the fertilized eggs that are lost with the feces; this feces must reach the mouth of the next host to complete the life cycle



therefore, proper sanitation is advised to prevent Ascaris infections

Anatomy of a typical roundworm (Phylum: Nematoda)

20




.

Trichinella sp. larvae in muscle tissue

T h e e v o l l l u t t t i i i o n ( ( (

“ “ i i i n v e n t t t i i i o n

” ” ) ) ) o f f f a b o d y c a v i i i t t t y b r r r o u g h t t t a n i i i m a l l l s m a n y a d v a n t t t a g e s

1. increases the animals flexibility and motility

2. it suspends the organs from the surrounding mesentary tissue

3. the enclosed fluids in the body cavity cushion the internal organs and structures from impact and prevent injury

4. it improves the circulation of nutrients and oxygen through the body and assists in waste disposal

5. it enabled the appearance of larger animals



during the Cambrian-Ordovician era of Earth history, a huge diversity of animals with a series of new “invention” appeared on the scene of life; due to the sudden appearance of almost all major animal phyla during that ear, scientists tend to speak of the “Cambrian explosion” in animal evolution

 during that time animals evolved which had for the first time “real” internal body cavities, called coeloms and external skeletons



today, all highly developed animals are coelomates ; they have real body cavities formed by the embryonic mesoderm layer

 we humans are coelomates, too; we have an abdominal (digestive

21




. organs, some of the excretory and reproductive organs) and a

thoracic cavity (heart and lungs).

4 .

.

.

M o l l l l l l u s k s ( ( ( = P h y l l l u m : : : M O L L U S C A ) ) )



the phylum Mollusca contains over 100,000 species with a variety of body forms and lifestyles, e.g. snails, clams



most have a soft body protected by a hard, calcified shell



mollusca have two typical body features

1. a foot

 a muscular tissue which extends from the main body

 serves for locomotion or penetration

2. a mantle

 is an outgrowth of the body surface

 in clams and snails the mantle produces the shell

 functions in respiration, waste disposal and sensory

reception

 the so-called mantle cavity harbors gills or lungs ; these organs enable the uptake and exchange of gases, i.e.

oxygen, from water or air, respectively



most mollusks have a so-called radula in their mouth region



it is a rasping organ with which help mollusks scrape and

chop their plant food (e.g. algae, plant leaves)



have a real coelom , which is reduced and limited to the region around the heart



it consists of three cavities which enclose the heart, kidney and the

reproductive organs



mollusks developed already a primitive circulatory system which branches out from the heart into the body parts



the heart of this so-called

“open circulatory system”

pumps hemolymph through vessels into a hemocoel

 the blood diffuses back to the heart and is pumped out to the body

again



they have a developed nervous system which consists of several so-called ganglia connected by nerve cords

22




.

Anatomy of a typical aquatic gastropod (Phylum: Mollusca)

A n a t t t o m y o f f f a t t t y p i i i c a l l l b i i i v a l l l v e ( ( ( P h y l l l u m : : : M o l l l l l l u s c a ) ) )



3 different classes of mollusks are known

1 .

.

.

G a s t t t r r r o p o d a



builds the largest group of mollusks with over 75,000 species

 the only group which comprises land inhabitants

 e.g. the vineyard snail H e l l l i i i x p o m a t t t i i i a , which has lungs instead of gills and breathes air; it has primitive eyes which sit on a pair of antenna-like, retractable body extensions, has one helical shaped shell made of calcified proteins



the class Gastropoda includes the snails , terrestrial slugs , whelks , conchs , periwinkles , sea hares , and sea slugs



most gastropods are marine inhabitants

23




.



most gastropods have a well developed head with eyes and tentacles projecting from a coiled shell that protects the visceral mass



in aquatic gastropods the mantle cavity under the shell harbors the gills ; in terrestrial gastropods , the mantle is richly supplied with blood vessels and functions as a lung when air is moved in and out through respiratory pores

L i i i f f f e c y c l l l e s t t t a g e s o f f f g a s t t t r r r o p o d s

 aquatic but not terrestrial gastropods have a swimming larval stage



terrestrial gastropods are hermaphroditic animals

1. during mating each individual inserts a penis into the vagina for the other to provide sperm for future fertilization of eggs

2. the fertilized eggs are deposited in the soil and the embryo development proceeds without formation of a larval stage



Hermaphroditism assures in slow-moving animals that any two animals that meet can reproduce

2 .

.

.

B i i i v a l l l v e s



this class of mollusks consists of the clams , oysters , mussels , and scallops

 most are marine species which are sedentary and live in mud or sand

on the ocean floor



"Bivalves" are two-part shells that are linked by a hinge-like so-called ligament and usually kept closed by powerful muscles

 the muscular foot is used for digging and anchoring



the presence of shells in this group has yielded an impressive fossil record



the bivalves have no head, no radula, and little cephalization; many have multiple, eye-like sensory organs which are able to detect movement

3 .

.

.

C e p h a l l l o p o d a



the class Cephalopoda (literally "head-footed" ) includes squids , cuttlefish , octopuses , and nautiluses (and extinct relatives, the g o n i i i a t t t i i i t t t e s , a m m o n o i i i d s , and a m m o n i i i t t t e s )



amongst them are successful marine predators



Squids and octopuses are fast animals thanks to a form of

“biological jet propulsion”

 they can squeeze water from their mantle cavity out through a funnel,

which propels them



surrounding their head are tentacles with suckers that can grasp prey

and deliver it to a powerful beak/mouth



cephalopods developed a large, complex brain and highly sophisticated sensory organs



they have eyes (with lenses and retina), which are considered to be the most sensitive in the animal kingdom

24




.

 the eye of the giant squid is the largest known sensory organ on our

planet and the biggest examples measured 30 cm!!



octopuses show learning behavour in laboratory experiments

25

Chapter 18 - San Diego Mesa College

Chapter 18: Evolution of animals, animal kingdom & Animal life cycles

Related documents

Products

Support

Chapter 18 - San Diego Mesa College

Chapter 18: Evolution of animals, animal kingdom & Animal life cycles

Related documents

Add this document to collection(s)

Add this document to saved

Suggest us how to improve StudyLib