Chapter 23The Animal Kingdom

General Features of Animals• All animals are multicellular heterotrophs• They are diverse in form– Invertebrates are animal species that lack a

backbone– Vertebrates have a backbone (about 1% of

Kingdom Animalia)

• No cell walls• Active Movement• Sexual Reproduction• Embryonic Development

Evolution

• The first multicellular animals evolved about 600 million years ago.

• From humble beginnings, they diversified into many habitats.

Evolutionary Innovations

• We will learn about animal diversity by examining a series of nine key evolutionary innovations, each exemplified by a major phylum.

The Simplest Animals

• The simplest animals, members of the phylum Porifera

• Members of phylum Porifera include sponges

• Characteristics of sponges– Lack symmetry– Not organized into

tissues

Sponges

• Sponges are perforated by tiny holes (where name of phylum comes from

• They have unique flagellated cells that line the body cavity of the sponge

• The flagella on the cells will draw water through the sponge and throughout the body cavity

• Any food particles in the water will be trapped and later ingested

Phylum Cnidaria• Phylum Cnidaria consists of jellyfish, sea anemones, sea coral

and hyroids• Unlike sponges, they have symmetry and tissues• Able to undergo extracellular digestion, where digestion takes

place inside a body cavity• Cnidarians have two true tissue layers: ectoderm and

endoderm• They have radial symmetry and a nerve net to provide

sensory input.

Symmetry• Symmetrical objects have similar parts that are

arranged in a similar manner• Three types of symmetry– Asymmetry – no pattern in parts– Radial Symmetry – when a body is constructed

around a central axis– Bilateral symmetry – is when an animal is constructed

with equivalent parts on both sides of a plane, includes a definite head end, known as cephalization

Phylum Platyhelminthes• In phylum Platyhelminthes (flatworms), they have

bilateral symmetry, so they have cephalization• Also have three embryonic layers, the outer ectoderm,

the inner endoderm, and a third layer, the mesoderm, which forms between the ectoderm and the endoderm– The ectoderm forms into the outer covering of the body

and the nervous system– The digestive and intestines develop from the endoderm– The skeleton and muscle form from the mesoderm

• They do not have a body cavity, making them acoelomates

Flatworms• Have a simple body design, but do have a definite

head and organs• Most species are parasitic, occurring within the

bodies of many other kinds of animals• Have an incomplete gut, with only one opening– They cannot feed, digest, and eliminate waste

simultaneously• Lack a circulatory system– Undergo diffusion of oxygen

• Many are hermaphroditic, with each individual containing both male and female parts

Body Cavity• A key transition in the evolution of the animal

body was that of a body cavity.– All bilaterally symmetrical animals other than solid

worms have a cavity within their body• Important for body design for:– Circulation – fluids can move within the body cavity,

permitting the rapid passage of materials from one part of body to another

– Movement – Fluid in cavity makes animal’s body rigid, making it harder for muscle contractions

– Organ Function – Body organs can function without body being deformed by surrounding muscles

Body Cavities• Three basic kinds of body

plans found in bilaterally symmetrical animals– Acoelomates – have no body

cavity– Pseudocoelomates – have a

body cavity called the pseudocoel located between the mesoderm and endoderm develops entirely

– Coelomates – has a fluid-filled body cavity not between the endoderm and mesoderm, but rather entirely within the mesoderm, coelom• Gut is suspended, along with

other organ systems

Phylum Nematoda• In phylum Nematoda, they are pseudocoelomates, the

first evolutionary phylum to have an internal body cavity.– Includes nematodes, ellworms and rotifers

• Nematodes mouth is often equipped with piercing organs, and the food will pass through the mouth as a result of the sucking action of a muscular chamber, known as the pharynx. After passing the pharynx food continues through the digestive tract and is eliminated through the anus

Phylum Mollusca

• Phylum Mollusca have a coelom, which is more functional than animals without coeloms. – This is because of primary induction, where one of the

three primary tissues (endoderm, mesoderm, and ectoderm) interact with one another

• Only coelomate without a segmented body• Most have a radula, a rasping, tongue-like organ– Used to scrape algae off rocks

Phylum Mollusca• Mollusks are divided into with outwardly

different body plans• The three different classes of mollusks– Gastropods – include snails and slugs, use a muscular

foot to crawl, their mantle secretes a single, hard protective shell

– Bivalves – include clams, oysters and scallops, secrete a two-part shell, with a hinge

– Cephalopods – include octopuses and squids, have a modified mantle cavity to create a jet propulsion system to propel them through water

Phylum Annelida

• In this phylum, their key evolutionary trait is segmentation, where the building of a body is from a series of similar segments

• Includes: Earthworms, brittle worms• In phylum Annelida, there segmentation are

nearly identical segments– The advantage of segmentation is hat segments

are able to have different functions, such as reproduction, feeding

Phylum Annelida

• Annelida organization is simply basic body structure of Annelida: is a tube within a tube; the digestive tract is a tube suspended within the coelom

1. Repeated segments: each segment has digestive, excretory, and locomotor organs

2. Specialized segments: sensory organs that are sensitive to light

3. Connections: circulatory and nervous connections to each segment

Phylum Arthropoda

• This phylum includes insects, crabs, shrimp lobsters, crayfish, water fleas

• Their evolutionary adaption include jointed appendages and exoskeleton

• Their exoskeleton is a rigid external skeleton made of chitin and provides places for muscle attachment– Helps protect against predators and slow water

loss

Phylum Arthropoda

• Arthropods that lack jaws, also known as mandibles are called chelicerates. – These include spiders, mites, scorpions

• Those with mandibles that were formed through the modification of anterior appendages are known as mandibulates.– This group includes crustaceans, insects,

centipedes and millipedes

Mandibulates

• Crustaceans – large, diverse group of primary aquatic animals.– Most have two pair of antennae, three pairs of chewing

appendages, and various number of legs– Have compound eyes

• Millipedes and Centipedes – Centipedes have one pair of legs on each segment– Millipedes have two pairs of legs on each segment

Mandibulates• Insects are the largest group of arthropods• They have three body sections– Head – very elaborate, with one pair of antennae

and elaborate mouthparts and compound eyes– Thorax – has three segments as well, each of

which have one pair of legs; most insects have two pairs of wings attached to the thorax

– Abdomen – digestion takes place, and have excretion organ called Malpighian tubes

Embryonic Development

• In coelomates, there are two different types of embryonic development

• In mollusks, annelids, and arthropods, the mouth near the blastopore making it a protostome

• Protostomes form in a cleave radially and are tightly packed

Embryonic Development

• In echinoderms and chordates,the anus forms near the blastopore, making it a deuterostome

• It forms through spiral cleavage

Phylum Echinodermata• In phylum Echinodermata include sea stars, sea

urchins, sand dollars and sea cucumbers• Their key evolutionary developments include

deuterostome development and endoskeleton• The endoskeleton is composed of hard calcium-rich

plates just beneath a delicate skin• They have pentamerous (5-way) symmetry.• All members have a water vascular system which

acts like a line of suction cups along radial canals to tube feet.

Phylum Chordata• Lancets, terrestrial vertebrates are included in

this group• The major evolutionary innovation in this group

is the notochord• In all of the 50 thousand species, there are four

principal features– Notochord– Nerve Cord– Pharyngeal slits– Postanal Tail

Phylum Chordata• Notochord is a stiff, but flexible rod that forms

beneath the nerve cord that acts to anchor internal muscles, permitting rapid body movements

• Nerve cord is a single dorsal hollow nerve cord, which the nerves that reach the different parts of the body are attached

• Pharyngeal slits are a series of slits behind the mouth into the pharynx ,which is a muscular tube the mouth to the digestive tract and windpipe

• Postanal Tail is a tail that extends beyond the anus

Amniotic Egg• While amphibians were the first land

animals, they are still largely tied to the water for reproduction and resupply body fluids.

• One key step was the development of a waterproof skin.

• The evolution of the amniotic egg expanded the success of vertebrates on land by allowing reproduction on land.

• A series of specialized membranes function in gas exchange, waste storage, and energy storage for the developing embryo

Mammals• Hair traps body heat. • All mammal females supply nourishment to

their offspring in the form of milk.– It is produced in special glands.

• The Monotremes (platypus and echidna) actually lay eggs.

• Marsupials begin development internally, but young are born are a very early stage and do most of their development in a pouch.

• In placental mammals, embryos complete far more of their development in a special support structure, the placenta.

Phylum Innovative Evolutionary Traits

Includes

Porifera

Cnidaria

Platyhelminthes

Nematoda

Mollusca

Annelids

Arthropoda

Echinodermata

Chordata