Phylum Arthropoda

Terrestrial Mandibulates: Spiders and Insects

Characteristics– Segmented bodies – Jointed appendages • Specialized for eating, sensing, reproduction, defense

and movement

– Exoskeleton• Hard covering on the outside of the animal• Limits the growth of the organism (must shed)• Muscles are attached to this layer• Secreted by underlying epidermis • Shed (molted) at intervals

– Bilateral symmetry – Muscular system • Complex • Contains two types of muscles

– Body cavity • Coelom is smaller in size • Most of body cavity consists of hemocoel (sinuses, or

spaces, in the tissues) • Filled with blood

Characteristics

–Digestion • Complete digestive system – Esophagus, crop, gizzard, midgut, hindgut and anus

• Mouthparts modified from appendages and adapted for different methods of feeding

–Circulatory System• Open system• Dorsal contractile heart, arteries

Characteristics

–Respiration• Obtain oxygen through:

– 1) body surface (diffusion), – 2) gills, – 3) tracheal (air tubes) – carry oxygen to muscles– 4) book lungs

• Spiracles—small openings in the exoskeleton through which air opens

Characteristics

–Water retention—3 structures • 1) Malpighian tubules—– excretory structures that remove metabolic wastes

from blood and return water to the cells

• 2) Exoskeleton—– prevents water evaporation

• 3) Book Lungs—– gas exchange without water loss (also used in

respiration)

Characteristics

– Excretory system• Paired excretory glands in some • Same as the nephridial system of annelids • Some with other excretory organs, called

Malpighian tubules

Characteristics

–Nervous system• Contains same system of annelid (with dorsal

brain connected by a double nerve chain)• Fusion of ganglia in some species • Well-developed sensory organs – Compounds eyes with many lenses (can see motion

and color)

Characteristics

–Reproduction• Sexes usually separate, • Paired reproductive organs and ducts; • Usually internal fertilization; • often go through metamorphosis (change in

body form larva to adult)

Characteristics

Classification• Phylum Arthropoda (most diverse phylum)– Subgroups of Terrestrial Arthropods: • Subphylum Chelicerata –

– Characteristics of all:» six pairs of appendages that include » a pair of chelicerae, » a pair of pedipalps, and » 4 pairs of walking legs » No mandibles and no antennae. » Suck up liquid food from their prey.» Two body segments (abdomen and cephalothorax)

– Class Merostomata – • Horseshoe crabs are practically

unchanged • Have an unsegmented, horseshoe-

shaped carapace, and a broad abdomen, which has a long spine like telson.• Book gills are exposed. • They feed at night on worms and

small mollusks and are harmless to humans.• Include horseshoe crabs

Classification

– Class Arachnida – • over 50,000 species • Body organization: cephalothorax,

abdomen• Examples: Spiders (35,000 species),

scorpions, ticks, mites

Classification

–Spiders: » hunt using strong legs and good eyes; weave silk

for web (hunt and reproduction); fangs are modified chelicerae (liquefy prey with venom)

–Scorpions:» long, segmented abdomen with a stinger;

–Mites and Ticks: »mites have one body segment, eat bacteria or

skin cells of humans; ticks are mostly parasitic, require blood before molting and can cause Rocky Mtn spotted fever

Classification

• Subphylum Uniramia – – Characteristics:» Appendages are unbranched. » Includes the insects and the myriapods

(centipedes and millipedes). » Heads resemble the crustacean head but have

only one pair of antennae, instead of two. • Also have a tympanic membrane for sound

» Have mandibles and two pairs of maxillae» Respiration is by body surface and tracheal

systems, • Although juveniles, if aquatic, may have gills.

Classification

• Class Chilopoda - – They are active predators with a preference for

moist places such as under logs or stones, where they feed on earthworms, insects, etc. – Each segment (they have between 10 and 70),

except the one behind the head and the last two, bears one pair of appendages. – Include: centipedes

Classification

• Class Diplopoda – – Include Millipedes – Have cylindrical bodies made up of 25 to 100

segments. – Abdominal segments each have two pairs.–Millipedes are less active than centipedes – Generally herbivorous, living on decayed plant and

animal matter

Classification

• Class Insecta – –Most numerous and diverse of all arthropods. » (There are more species of insects than species

in all the other classes of animals combined!!)– Have three pairs of legs – Usually have two pairs of wings (although some

have one pair of wings, or none) – Body organization: head, thorax, and abdomen.» The head usually bears a pair of large

compound eyes, a pair of antennae, and usually three ocelli.

Classification