Phylum Arthropoda - largest assemblage in the Animal Kingdom = 80% of
all known species; 800,000 have been described;
estimated total number of species is about 6 million
Characteristics of Phylum Arthropoda:
Metamerism
Exoskeleton
Bilateral symmetry
Paired jointed appendages
Open & dorsal circulatory System
Ventral nervous system
Metamerism – body is segmented, arranged into
regions called tagmata (head, thorax, abdomen)
Exoskeleton – chitinous covering (hard) that must be
shed at intervals (ecdysis) or during growth (molting)
Hypothetical Evolution of Insect
Segmented, legless,
wormlike annelids
Paired, bilateral, lobe-like appendages on the somite, with a pair of
simple eye and antenna
Bilateral appendages on
each body segment becomes jointed, and with typical primitive mandibulate
Differentiation of head,
thorax and abdomen, with modified genitalia
Crustacea – e.g., lobsters, crabs, copepods
Crustacea - mostly aquatic gill-breathers
Crustacea - with 2 well-defined body regions: cephalothorax and abdomen
Crustacea - possess 2 pairs of cephalic appendages, antennae, and several pairs of branching appendages on remaining cephalothoracic segments, with few abdominal appendages
Crustacea - calcium salts impregnate the exoskeleton = rigidity
Arachnida - with 2 well-defined body regions: cephalothorax and abdomen
Arachnida - lack antennae with 6 pairs of
appendages: 1
st pair – chelicerae
(jawlike or fangs), 2nd pair –
pedipalps (not leglike), remaining
4 pairs – legs
Myriapoda - with 2 body regions: head & trunk
Myriapoda - elongated, worm-like bodies, with
9 or more pairs of appendages
Diplopoda (milliepedes) - cylindrical or slightly flattened bodies
Diplopoda (millipedes) - with more than 30 pairs
of legs, typically 2 pair of legs per body segment,
and short antennae
Chilopoda (centipedes) - fewer legs than
millipedes usually
more than 15, with 1 pair per
body segment
Insecta - contains the vast majority of medically important arthropods
Insecta - with 3 body regions (head, thorax and abdomen), 3 pairs of thoracic appendages, compound eyes and simple eyes (ocelli)
Phylum Arthropoda Members of Medical Importance:
Crustacea
Arachnida
Myriapoda
Insecta
Class Insecta: Integument/Exoskeleton
Body covering, made up of hardened/sclerotized plates (sclerites) separated by flexible ("membranous") regions, conjunctivae, or by grooves(sutures) = allows flexibility and protection
Class Insecta: Integument/Exoskeleton
Epidermis – single layer of cells that synthesizes and deposits the cuticle
Class Insecta: Integument/Exoskeleton
Dermal glands – interspersed among the
epidermal cells, secreting the outermost
layer of cuticle including substances and
various pheromones
Class Insecta: Integument/Exoskeleton
Apodemes – infoldings of the body wall
(structural support) and attachment of
muscle fibers
Class Insecta: Integument/Exoskeleton
Setae – multicellular, hairlike, one
cell forming the projected portion
(hair) and another cell forming the socket, pigmented and connected
to a neuron and acting as sensory structures
Class Insecta: Integument/Exoskeleton
Spines – multicellular, the cuticle of
which is continuous with the
integument
Class Insecta: Integument/Exoskeleton
Microtrichia – subcellular, tiny cuticular hairs that cover the cuticle
Class Insecta: General Insect Form
3 regions: head, thorax & abdomen
Class Insecta: General Insect Form
Head – bears the mouthparts (ingestion) &
sensory organs = a pair of compound eyes, simple eyes (dorsal ocelli), and a pair of
antennae
Class Insecta: General Insect Form
Thorax (prothorax, mesothorax, & metathorax) – each thoracic segment bears pair of legs, when wings are present are borne on meso- and/or metathorax
Class Insecta: General Insect Form
Abdomen – composed of 11 segments: last
segment is divided into a dorsal epiproct and
lateroventralparaprocts and cerci/cercus, 8
and/or 9 segments bear the external genitalia
Class Insecta: Head
Head capsule – provides rigid points of attachment
for mouthpart musculature
Class Insecta: Head
Cervix – joined the head capsule with the
prothorax
Class Insecta: Head
Cervical sclerites – small plates in the cervix
that provide articular points for both the
posterior head capsule and the anterior edge
of the prothorax
Class Insecta: Head
Foramen magnum – opening at the back of
the head capsule where skeletal muscles,
alimentary canal, aorta, and nerves enter
Class Insecta: Head
Frons - region between the compound eyes
Class Insecta: Head
Gena - lateral regions between the compound eyes
Class Insecta: Head
Vertex - located between the compound eyes at the dorsal of the head