Terrestrial Mandibulates: Spiders and Insects
Phylum Arthropoda
Characteristics
– Segmented bodies
– Jointed appendages
• Specialized for eating, sensing, reproduction, defense
and movement
– Exoskeleton
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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
Characteristics
– 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:
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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)
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)
Classification
– Class Merostomata –
• Horseshoe crabs are practically
unchanged
• Have an unsegmented, horseshoeshaped 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.