Phylogeny of Arthropods

Arthropoda

Worm-likeAncestor

Trilobites(extinct)

Annelids(worms)

Onychophorans(worms w/legs)

Chelicerates(spiders)

Crustaceans(lobsters)

Insects(butterflies)

General Characteristics

• metamerism (segmented body)

• jointed appendages

• bilateral symmetry

• secreted exoskeleton

• ecdysis (molting)

• open circulatory system

• ventral nerve cord and brain

                                                                                 

DIVERSITY Numbers

• about 80% of all animals are arthropods • estimated to be over 30 million arthropods • far more of them than all other metazoan species

combined • in virtually every conceivable environment:

marine, terrestrial, freshwater, and aerial habitats.

Phylum ArthropodaSubphylum Trilobita (extinct)Subphylum ChelicerataSubphylum CrustaceaSubphylum Uniramia (insects)

Phylum ArthropodaSubphylum Trilobita (extinct)Subphylum ChelicerataSubphylum CrustaceaSubphylum Uniramia (insects)

NERVOUS SYSTEM

Open Circulatory System

• Doral heart surrounded by pericardial sinus

• Blood (hemolymph) enters heart through ostia (openings) pumped through arteries

• Hemolymph- colorless; contains hemocyanin

• Hemocoel- blood cavity

Open Circulatory System

Compound Eye

Facet

LensCrystalline conePigment cells

Visual cells

Nerve fibers from visual cells

Optic nerveOmmatidia

1. General • most arthropods are gonochoric • fertilization may be external or internal in

aquatic arthropods • always internal in terrestrial species

2. Sperm Transfer • sperm transfer usually by mating or

copulation • females usually store the sperm in a

seminal receptacle

REPRODUCTION

Subphylum Trilobita

521-250 mya

Earliest arthropod

Trilobite

eye

Subphylum Chelicerata • xiphosurans (horseshoe crabs),

arachnids, sea spiders • mostly terrestrial • cephalothorax-abdomen • 6 pairs cephalothoracic

appendages • chelicerae, pedipalps, 4 pairs legs • no antennae

a. Xiphosura (horseshoe crab, Limulus polyphemus)

b. Arachnida •most chelicerates are arachnids •several taxa (orders), many are common and familiar

SCORPIONES (scorpions )ARANAE (spiders )OPILIONES (harvestmen, daddy longlegs )PSEUDOSCORPIONES (pseudoscorpions)ACARINI (mites and ticks )

c. Pycnogonida (the giant sea spider, Colossendeis australis)

Subphylum Chelicerata

                                                                

• Limulus is a benthic scavenger and predator. • Prey include clams and other invertebrates that it digs for in

the sand.• The tail spine is used as a self-righting mechanism if the

animal is overturned accidentally. Lives up to 19 years• Reaches sexual maturity at about 9 to 12 years old

Horseshoe CrabLimulus polyphemus, Carcinoscorpius rotunda, and Tachypleus gigas.

• Mates during spring and summer full and new moons, onto ocean beaches.

• Females lay up to 30 thousand eggs, which males fertilize before burying them in the sand

Horseshoe Crab

Horseshoe Crab

Horseshoe Crab

Arachnid

• a heterogeneous taxon with many subtaxa

• two pairs antennae • marine, freshwater, and terrestrial • Primarily aquatic • Free-floating larval stage • 26,000+ known species

Subphylum Crustacea

ANOSTRACA

• fairy shrimp and brine shrimp

PHYLLOPODA

• tadpole shrimps, ostracod, water fleas

MALACOSTRACA

• the largest, most heterogeneous, and diverse crustacean taxon

• shrimps, crabs, lobsters, mantis shrimps, pillbugs, crayfishes

COPEPODA

• copepods

• enormous ecological importance as planktonic herbivores

CIRRIPEDIA

• barnacles

Subphylum Crustacea

Arthropod Development

Zoea MegalopsNauplius

Gills a. General

• gills are evaginations • typical of aquatic animals • blood is oxygenated by gills • oxygen delivered to tissues by blood

b. Crustacean Gills • crustacean gills are usually associated with

appendages • blood circulates through the gill and is oxygenated

c. Book Lungs • present in many arachnid orders • similar to book gills of horseshoe crabs • oxygen transport from the lungs to the tissues is by

blood

Respiration

Subphylum Uniramia

Decorator Crab

Sponge crab

Camouflage

Camouflage: anemone crab

coral guard crabs and pocilloporid corals

coral guard crabs and pocilloporid corals

gall crabs and pocilloporid corals

gall crabs and pocilloporid corals

scarlet cleaner shrimp

scarlet cleaner shrimp

sea cucumber crab and sea cucumberssea cucumber crab and sea cucumbers

pompom crabs and sea

anemones

pompom crabs and sea

anemones