Phylum Arthropoda

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