Animals 4

Ecdysozoans and Deuterostomia

Ecdoysozoa

Animals that shed a cuticle (a tough external coat) as they grow

• Inherit its name from this process (ecdysis or molting)

More phyla than all other species combined

Phylum Nematoda

Most ubiquitous of animals

Found in aquatic habitats, soil, plants, body fluids/tissues of animals

Covered by a cuticle (type of exoskeleton); shed as they grow

Do not have a circulatory system - Hemocoel (hemolymph)

Where do most phylum Nematoda live

Most soil and in decomposing organic matter on the bottoms of lakes and oceans

These free-living worms play an important role in decomposition and nutrient cycling, but little is known about most species

Caenorhabditis elegans

Well-studied model organism in biological research

Have over 100 genes associated with human disease

Can be used to investigate roles of these genes (and potentially developing cures for these human diseases)

Mechanisms involved in aging in humans

Human are host to how many Nematoda

At least 50 species (pinworms and hookworms)

Trichinella spiralis

Causes trichinosis

Obtained by eating raw or undercooked pork/meat

Juvenile worms live inside pork/meat muscle tissue

Within human intestines, the juveniles develop into sexually mature adults

• Bore through the body or travel in lymphatic vessels to other organs, including skeletal muscles, where they encyst

Phylum Arthropoda

Zoologists estimate that about a billion billion arthropods are living on Earth

Ubiquitous

Most successful of all animal phyla

Most are insects

Arthropod

Segmented Ecdysozoan with a hard exoskeleton and jointed appendages

Body plan of Arthropods

Segmented Body

Hard exoskeleton

Jointed appendages

Modidfication of Arthropods

Walking

Feeding

Sensory reception

Reproduction

Defense

Exoskelton of Arthropods

The body is entirely covered by a cuticle made of proteins and chitin

• Can be thick/hard in some areas. think/flexible in others

Exoskeleton provides:

Structure, Support, Protection, Point of attachment for muscles

Impermeable to water - prevents desiccation - first evolved in the sea

First animals to colonize land

Although it does prevent growth…

Ecdysis/molting

Energetically expensive and dangerous (vulnerable)

Organs/Circulatory system

Well-developed sensory organs (eyes, olfactory receptors, antennae) for both touch and smell

They are mostly centralized in the anterior side

Open circulatory systems:

Hemolymph - analogous to human blood

Hemocoel - body cavity that surrounds tissues and organs

Tracheal systems

Branched air ducts leading into the interior of the body from pores in the cuticle

Allow gas exchange despite the exoskeleton

3 major clades of Arthropods

Chelicerates (sea spiders, horseshoe crabs, scorpions, ticks, mites, spiders)

Myriapods (centipedes, millipedes)

Pancrustaceans (some insects, lobsters, shrimp)

Clade Chelicerata

Chelicerae (claw-like feeding appendages that serve as pinchers or fangs)

lack antennae

Simple eyes (single lens)

Earliest species - eurypterids (water scorpions, now extinct)

Surviving species - Sea spiders, Horseshoe crabs

The bulk of species are arachnids (spiders, ticks…etc)

Body plan of Chelicerata

6 pairs of appendages

Chelicerae

Pedipalps - sensing, feeding, defense, reproduction

4 pairs of walking legs

Spiders

Capture

Defense/escape

Cover for eggs (protection)

“gift wrap” for food that males offer females during courtship

Silk made by spinnerets (specialized organs)

They ‘build’ it perfectly on the first try

Millipedes and centipedes

All are terrestrial

Pair of antennae

3 pairs of appendages modified as mouthparts

• Includes jaw-like mandibles

Millipedes

Milli-thousand

Eat decaying leaves and plant matter

One of the earliest animals on land, living on mosses and early vascular plants

Centipedes

Centi - hundred

Carnivores

Each segment of their trunk region has just one pair of legs

Poison claws that paralyze prey

Clade Pancrustacea

Greek pan (“all”)

Includes crustaceans and insects

Terrestrial insects are more closely related to lobsters and other crustaceans than they are to myriapods

Crustaceans

Crabs, lobsters, barnacles

Marine, freshwater, terrestrial

Highly specialized appendages

Antennae - crustaceans are the only arthropods with 2 pairs

Mouthparts - Including the hard mandibles

Walking legs on the thorax

Tail

How do crustaceans exchange gas

Small crustaceans exchange gases across a thin area of the cuticle

Larger species have gilles

Isopods

One of the largest groups of crustaceans

Terrestrial, freshwater, and marine species

• Pill bugs and woods lice

Decapods

Lobsters, crayfish, crabs, and shrimps (relatively large crustaceans)

Cuticle made of calcium carbonate

Deca - ten

Most are marine - some live on land

Plankton community

Many of them are important members of the plankton communities

Planktonic crustaceans include many species of copepods (one of the most numerous of all animals)

• Some are grazers (algae)

• Some are predators of small animals

Major food source for several whales

Barnacles

Sessile

The cuticle is hardened into a shell containing calcium carbonate

Anchor themselves to rocks, boat hulls, pilings, and other submerged surfaces

Feed by extending appendages from their shell to strain food from water

Insects

Form an enormous clade (hexapoda) with other 6-legged terrestrial relatives

terrestrial, freshwater, air

Rare in marine habitats (although not completely absent)

1 or 2 pairs of wings that emerge from the dorsal (top) side of the thorax

Insects can fly without sacrificing any walking legs

Grasshoppers

Go through an incomplete metamorphosis

The young (nymphs) resemble adults but are smaller, have different body proportions, and lack wings

Multiple molts until it reaches full, adult size and become sexually mature

Complete metemorphosis

Ex: Caterpillars —> Butterflies

Larval stages are specialized for eating and growing

Larval stage looks completely different from adult stage (specialized for dispersal and reproduction)

Metamorphosis from larval —> adult stage occurs in the pupal stage

Why should we care about Insects?

Consume LOTS of plant matter

Predators, parasites, decomposers

An essential source of food for larger animals

Pollination

Edible for protein

Carriers for many diseases

• African sleeping sickness (tsete flies carry protist trpanosome)

• Malaria

Compete with humans for food

Deuterostomia

Clade of bilaterian animals

“Mouth second”

Anus forms from the blastopore

Clade Deuterostomia is defined by DNA similarities and not developmental similarities

Have both vertebrates and invertebrates***** specifically chordates

3 phyla of Deuterostomia

Echniodermata (“Spiny skin”)

Hemichordata (“Half chordate”)

Chordata (“Chordate”)

Echinoderms

Spiny skin

Includes sea stars, brittle stars, sea urchins, sand dollars

Divided into 5 clades

Slow-moving and/or sessile

Have a coelom

Water vascular system

Unique to echinoderms, a network of hydraulic canals branches into extensions called tube feet that function in locomotion and feeding

Madreporite

Water can flow in or out of the water vascular system into the surrounding water through the madreporite

Clade Asteroidea

Sea stars

Arms extend from a central disk

Undersurfaces bear tube feet

gripping action is due to adhesive chemicals, not by suction

• Also use tube feet to grasp prey

Can regenerate their arms

Can turn parts of its stomach inside out for feeding

Sea Daisies

Armless

Only 3 known species

Live on submerged wood

The body is disk-shaped

Less than a cm in diameter

The edge of body is ringed with small spines

• Absorbs nutrients through a membrane that surrounds their body

Brittle Stars

Central Disk

Long, flexible arms

Lash their arms in serpentine movements

Don’t have flattened discs at the end of their tube feet (like sea stars and sea urchins do)

Use adhesive chemicals

Can be suspension feeders, predators, or scavengers

Sea urchins/ sand dollars

Mouth located on the underside

Ringed by highly complex, jaw-like structures well adapted to eating seaweed

Roughly spherical in shape

Skeleton is called a test

SD- Mostly flat

Both - No arms, 5 radially arranged groups of tube feet

Sea lillies

Attached to a substrate by a stalk

Suspension feeders

Fossilized specimens, very similar to present members

Feather stars

Crawl by using long, flexible arms

Suspension feeders

Sea cucumbers

lack spines

reduced exoskeletons

Elongated shape

5 radially arranged sections of tube feet

Some tube feet around the mouth are adapted as feeding tentacles