Arthropods

Arthropods: Most Successful Group Ever!• Insects cause huge economic losses (but a lot of benefits, as

well) each year– Negatives– Compete for humans for food supplies– Spread serious diseases– Positives– Pollinate flowers– Food, yield drugs and dyes, create silk, honey and beeswax

• They are the dominant group of animals on the earth today• The diversity of insects is far greater than all other taxa

combined• There are an estimated _____ million insects alive for

every human today

Locust Outbreaks in Africa (still today)

• Contain 40-80 million insects per sq. kilometer• Can cover up to 20% of earth’s surface at peak

times

Phylum Arthropoda• Arthropods includes spiders, scorpions, ticks, mites,

crustaceans, millipedes, centipedes, insects, and some smaller groups as well

• There is a rich fossil record extending back to the mid-______________________ period

Ecological Relationships• They are found in all environments and

virtually all altitudes and latitudes• Species are adapted to land and to fresh,

brackish, and marine water• Most species fly to their favored habitats• All modes of feeding occur among arthropods

though the majority are ________________• Nothing else matches their diversity

General Characteristics: Arthropods

Characteristics:

Arthropods are invertebrates that have jointed appendages. There are over a million known species making them the largest group of animals. Why so diverse and abundant???

- Jointed __________________**jointed appendage

- Bilateral symmetry (cephalization**)

bilateral symmetry

- Segmented bodies**- Exo_________________**

Exoskeleton (made of chitin)

- Coelom and Triploblastic- Body Systems**- Complex behavior patterns**- Separate sexes (most)

Evolutionary Milestone: _______________Arthropods have various appendages. They are differentiated and specialized for walking swimming, flying, or eating. Typically each segment has a pair of jointed appendages (may be reduced though). They can also be equipped with sensory hairs for sensory functions.

Segmented BodiesThe bodies of arthropods are divided into segments similar to those of segmented worms. However, two things: Unlike annelids, arthropods have various patterns of segmentation. And segmentation in these two groups evolved independently!!!

- Some arthropod have many segments

- Others have fused segments or somites that form body regions (tagma or tagmata)

Segmented Bodies

Exoskeleton

- Covers, supports, and protects the arthropod, without sacrificing mobility

- Made of CHITIN (tough polysaccharide) and the protein resilin- Many land-dwelling arthropods have a waxy layer to prevent water loss.

- The exoskeleton cannot grow as the animal grows, thus many species molt (or ecdysis)

All arthropods have a hard, outer covering called an _______________________.

ExoskeletonCuticle (exoskeletion) consists of:• Epicuticle: outer, thin layer

• Procuticle: inner, thicker layer that is flexible and prevents water loss

Divided into two parts:

Exocuticle-secreted before a molt

Endocuticle-secreted after molting

Cuticle may be soft or like a coat of armor.

Other functions: ingrowth for muscle attachment, support tracheae

• Respiration – marine arthropods have GILLS; land arthropods have a series of tubes inside (trachea) and spiracles (pores) on body surface. Oxygen pumped directly to tissues.

• Cephalization- have large heads, slender necks, intricate eyes and other sensory organs, important for arthropod success. Dragonfly eyes

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Other Body Systems….

• COMPLETE Digestive System:– With adapted

mouthparts– Specialized gut

• Complex Muscular System:– Exoskeleton for attachment– Striated muscles for rapid

action– Smooth muscles for visceral

organs

More Body Systems…..• Nervous system

– Similar to annelids– Dorsal brain– Double nerve cord

connecting ventral ganglia

• Circulatory System– OPEN system– Dorsal pumping heart

• Reproduction– Sexes usually Separate– Usually Internal

fertilization

Phylum Arthropoda

Subphylum TrilobitaSubphylum Chelicerata

Class Merisomata (horseshoe crabs)Class Pycnogonida (sea spiders)Class Arachnida (spiders, mites, ticks, scorpions)

MandibulataSubphylum Myriopoda (centipedes, millipedes)

Class Diplopoda (millipedes)Class Chilopoda (centipedes)

Subphylum CrustaceaClass Branchiopoda (water fleas, sea-monkeys)Class Ostracoda (seed shrimps)Class Cirripedia (barnacles)Class Peracarida (Isopoda, slaters, woodlice)Class Malacostraca (shrimps, prawns, crabs, lobsters, crayfish, yabbies)

Subphylum Insecta (Hexapoda)Class Apterygota (wingless insects e.g. earwigs)Class Pterygota (winged insects)

Taxonomy

• Subphylum Uniramia used to exist– Recently divided into two subphyla

• Myriapoda• Hexapoda

Arthropods are classified based on types of appendages present and number of tagmata (body regions)

Subphylum Trilobita• Trilobita arose before the Cambrian, flourished, and

then became extinct 250 million years ago• They have a trilobed body shape due to a pair of

longitudinal grooves• They were bottom dwellers and probably were

scavengers• They ranged from an inch to 20 inches or more and

could roll up like pill bugs

Subphylum Chelicerata• Include the horseshoe crabs, spiders,

ticks, mites, scorpions, and sea spiders• Chelicerates have SIX pairs of

appendages including chelicerae, pedipalps and FOUR pairs of legs (how classified!)

• They lack mandibles and antennae• Most suck liquid food from prey

Chelicerata: Class Merostomata• Includes the modern horeshoe crab; Limulus

polyphemus• This species is nearly unchanged from its

Cambrian ancestor (Eurypterids; lived 200-500 mya)

• Five species survive today

Class Merostomata: The Horseshoe Crab• Most live in shallow water (North American

Atlantic coast)• They have an unsegmented carapace that covers

the body in front of a broad abdomen• A TELSON or spinelike tail• Book gills are exposed on some of the abdominal

appendages• They walk with their walking legs and swim with

abdominal plates• They feed at NIGHT on worms and small molluscs• Mating: Male clings to Female’s back

Horseshoe Crabs

Chelicerata: Class Pycnogonid- Sea Spiders• They vary from a few millimeters to centimeters; all

have small, thin bodies• Some males use legs to carry developing eggs• The mouth at the tip of a proboscis, drinks juices

from cnidarians (hydroids) and soft-bodied animals• They have a greatly reduced abdomen attached to an

elongated cephalothorax (tagmata)

Chelicerata: Class Arachnida-Spiders, etc.• Consists of a great diversity among scorpions,

mites, ticks, daddy longlegs and others• Of 80,000 species, most are free living and

more common in warm, dry regions• Arachnids are divided into a cephalothorax

and abdomen (tagmata)

Order Araneae: JUST Spiders• About 40,000 species of spiders are known• The body consists of an unsegmented

cephalothorax and abdomen joined by a slender pedicel (waistline!)

Order Araneae: The Spiders

• The anterior appendages are a pair of chelicerae with terminal fangs

• All spiders are Predators, mostly on insects, which are killed by poison

• The injected __________ liquefies and digests the tissues which are then sucked into the spider’s stomach

• Spiders breath by book lungs and/or trachae

Characteristics of the spiders• Book lungs are found only in the spiders; parallel air

pockets extend into a blood-filled chamber• Air enters the chamber through a slit in the body wall

• The tracheae system is less extensive than in insects; it carries air directly to tissues

• Spiracles are openings to the trachea

• Most spiders have ______ simple eyes, each with a lens, optic rods and a retina

• They detect movement and may for images• Sensory Setae detect air currents, web vibrations, and

other stimuli

Web-spinning Habits

• Spinning Silk is a critical ability for spiders and some other arachnids

• Two or three pairs Spinnerets contain microscopic tubes that run to silk glands

• A liquid protein secretion hardens as it is extruded from the spinnerets

• Silk threads are very strong and will stretch considerably before breaking

• Spiders are often camouflaged or cryptic

Web-spinning Habits• Jumping spiders (Salticidae) have excellent vision and stalk their prey• Silk is used for orb webs, lining burrows, forming egg sacs, and wrapping

prey• Wolf spiders, jumping spiders, and fisher spiders chase and catch their

prey

Spider Diversity

Reproduction in spiders• ______________ court ____________ before mating• The male spins a small web, deposits a drop of sperm

on it, and then stores the package in his pedipalp• Mating involves inserting the pedipalps into the

female genital openings and depositing the spermatophore

• Sperm are stored in a seminal receptacle for weeks or months until the eggs are ready

• Eggs may develop in a cocoon in the web or may be carried by the female

• The young hatch in a few weeks and may molt before leaving the cocoon

Venomous spiders• Most are feared for no reason at all!!• Spiders help to control the populations of insects• American tarantulas rarely bite and the bite is not

dangerous• The black widow (Lactrodectus mactans)

however, can be fatal– The venom is neurotoxic (attacks nervous system)

• The brown recluse spider, Loxosceles recluse, has hemolytic venom that destroys tissue around the bite

• Some Australian and South American Spiders are the most dangerous and aggressive

Black Widow

Brown Recluse

Order Scorpionida: Scorpions

• More common in tropical and subtropical (such as Florida!) zones but do occur in temperate areas

• They are eat at NIGHT and feed largely on insects and spiders

• The short cephalothorax has the appendages and 1 to 6 pair of eyes

• The postabdomen has the long slender tail of five segments that end in a Stinger

• Scorpions bear live young carried on the mothers back

Scorpions

Order Opiliones: Harvestmen

• Harvestmen or DADDY LONG LEGS are common, especially in tropical areas

• Unlike spiders, their abdomen and cephalothorax join broadly without a narrow pedicel

• They can lose one or more LEGS of their eight without ill effect

• Their chelicerae are pincer-like and they feed more as scavengers than do spiders

Harvestmen

Order Acari: Ticks and Mites

• They are medically and economically the most important arachnids

• Their mouthparts are on the tip of the anterior capitulum

• They are both aquatic and terrestrial; some parasitize vertebrates and invertebrates

• About 40,000 species have been described; many more are estimated to exist

Diversity of mites and ticks• House mites are free-living and cause ALLERGIES• Spider mites are one of the many important

agricultural pest mites that suck out plant nutrients• Chiggers are larval Trombicula mites; they feed on

dermal tissues and cause ITCHY RASHES• The hair follicle mite Demodex is harmless but related

species cause mange in domestic animals• Ticks are usually larger than mites• Tick species of Ixodes carry LYME Disease (#1 Disease!)• Tick species of Dermacentor transmit Rocky Mountain

Spotted Fever• The cattle tick transmits Texas cattle fever

Subphylum Myriapoda

• Includes the centipedes, millipedes, pauropods and symphylans

• Several classes have _____tagmata – a head and trunk with paired appendages on the trunk

• Myriapods only have one pair of antennae, mandibles, and maxillae

• Legs are always uniramous (NOT __________)• Respiration occurs through the body surface,

trachea, or gills in juveniles

Class Chilopoda: Centipedes• Centipedes are terrestrial carnivorous PREDATORS found

under logs, bark and stones eating earthworms, cockroaches and other insects

• Their flattened bodies have up to 177 segments

Class Chilopoda: Centipedes• Each segment, except the one behind the head and the

last two, bears 1 pair of appendages• Appendages of the first body segment form venom claws• The head has a pair of eyes on either side of the head that

consist of groups of ocelli• A pair of spiracles in each segment allows air to diffuse

through branched air tubes of the trachae• The sexes ar separate; all are oviparous and the young

resemble the adults• One genus of house centipede has 15 pairs of legs and

another has 21 pairs• Most are harmless to humans but a few large,

tropical centipedes are dangerous

Class Diplopoda• Millipedes have many legs, but not a thousand as they

are sometimes called• Their cylindrical bodies have from 25 to 100 segments• Two pairs of legs are present per segment, probably

from the fusion of two segments• Each abdominal segment has two pair of spiracles

opening into air chambers and tracheal air tubes• Most eat decayed plants but a few eat living plant

tissue so they are HERBIVORES• After copulation, the female lays eggs in a nest and

guards them• Larvae have only one pair of legs to each segment

Millipedes

Subpylum Crustacea• Crustaceans include lobsters, crayfish, shrimp,

crabs, and copepods• Most are aquatic, and free living, many are

sessile, commensal, or parasitic• The main distinguishing characteristic of

crustaceans is that they have _____ pairs of antennae

• The head also has a pair of mandibles and two pair of maxillae

Typical Body Plan

Life Cycle of Gulf Shrimp

Types of Crustaceans• Ostracods are enclosed in a bivalve carapace and

resemble tiny clams and are less than 1/16 inch long• Most live in marine or freshwater sediments but

some scavenge or feed on detritus

Copepods

• Copepods have numerous species• They lack a carapace and retain the simple,

median eye in the adult• They have four pairs of flattened, biramous,

thoracic swimming appendages• Free-living copepods may be the dominant

primary consumer in aquatic communities• Parasitic forms are highly modified and

reduced, often unrecognizable as arthropods

Cirripedia – the barnacles• Barnacles as adults are sessile and attach

directly or by a stalk to the substrate• The carapace surrounds the body and secretes

a set of calcareous plates• The head is reduced, the abdomen is absent

and the thoracic legs are long with hair-like setae

• The many-jointed cirri that bear the setae are extended from the plates to feed on small particles

Isopods

• Isopods are dorsoventrally flattened, lack a carapace and have sessile compound eyes

• The abdominal appendages bear gills• Common land forms include the sow bugs and pill bugs• Some isopods are highly modified as parasites of fish or

crustaceans

Amphipods

• Amphipods resemble isopods except they are somewhat compressed laterally

• They lack a carapace and have sessile compound eyes

• Many are marine, others are beach-dwelling, freshwater or parasitic

Krill

• Euphausiacids or “Krill” has only 90 species but includes the important ocean plankton called krill

• They form a major component of the diet of baleen whales and of many fishes.

• Some are over 2 inches long

Decapods

• Decapods have five pairs of walking legs, the first forming pincers or chelae

• They range from a few millimeters to the larges arthropod, a Japanese crab with a 12 foot leg-span

• They are true crabs with a broader cephalothorax and reduce abdomen, compared to crayfish or lobsters

• Fiddler crabs have a reduced abdomen and burrow in the sand

• Hermit crabs are adapted to live in snail shells

Variety of Decapods