1. Phylum Arthropoda

2. Arthropod Taxonomy: Overview
The arthropods evolved along four main lines, which most zoologists recognize as 4 distinct subphyla
1. Trilobita - extinct trilobites
2. Chelicerata - horseshoe crabs, spiders, ticks, mites, and some extinct groups
3. Crustacea - crabs, lobsters, shrimps, barnacles
4. Uniramia - insects, centipedes, millipedes

3. Arthropod Respiratory Advances
Special respiratory structures allow the arthropods to metabolize more efficiently and thus move rapidly
High metabolic rates require rapid oxygen delivery, and arthropods can accomplish this with respiratory organs that have a large surface area for collecting oxygen quickly

4. Structure of the Exoskeleton
Composed of the polysaccharide chitin and protein – glycoprotein
Secreted by the Hypodermis
Outer surface called the epicuticle; contains waxes
The thicker portion is called the procuticle:
exocuticle
endocuticle

5. The Arthropod Exoskeleton

6. Molting
In order to grow the arthropod must shed its exoskeleton, and secrete a new and larger one - molting or ecdysis.

7. Jointed Appendages
Exoskeleton divided into a number of plates and cylinders
At the junction point between plates and cylinders, the exoskeleton remains thin and flexible; these are the joints
Jointed appendages allows arthropods to move efficiently and quickly
Muscles are integral to arthropod movement; they attach to the inner side of the exoskeleton; they often function as a lever system
Arthropod joint
Vertebrate joint

8. Specialized Arthropod Segments: Reduction in Metamerism
The evolution of the arthropods witnessed a reduction in metamerism
The arthropods evolved modified groups of segments (e.g., segments became lost, some fused together
The fusion of groups of segments into functional groups is called tagmatization
In so doing, various appendages on segments became specialized for functions other than locomotion, e.g. prey capture, filter feeding, sensing various kinds of stimuli, gas exchange, copulation, etc.

9. Tracheae
Gas exchange organs among terrestrial arthropods is usually internal; invaginations of the integument
Insects have tracheae, branching networks of hollow air conducting tubes such that air is sent to every cell in every tissue

10. Acute Senses
Arthropods have a well-developed nervous system that is of the same overall design as the annelids; anterior brain and a double, ventral hollow nerve cord.
The sensory receptors of arthropods are usually associated with modifications of the chitinous exoskeleton
The head usually bears various kinds of sense organs (e.g. antennae) with extreme sensitivity

11. Acute Senses cont.
Many arthropods have compound eyes - eyes that are composed of many visual units called facets (ommatidia); capable of color vision and detecting the slightest movements of prey or predators
Some eyes are simple eyes with only a few photoreceptors; however, they are capable of forming crude images

12. Reproduction Circulatory System
Dioecious; fertilization is external in aquatic forms, internal among the terrestrial forms. Most are oviparous (external development of young from eggs)
Circulatory System
Open circulatory system

13. Arthropod Diversity

14. Subphylum Trilobita A group of extinct marine arthropods.
Ranged in size from a few millimeters up to 75 centimeters.
Body divided into three longitudinal regions:
Compound eye, composed of radially arranged visual units
They would have curled up like a woodlouse for protection against predators.
Two-lobed appendages

15. Subphylum Chelicerata
Lack antennae
Body is usually composed of two regions: cephalothorax (prosoma) and abdomen
Cephalothorax is usually covered dorsally by the carapace
Six pairs of appendages: first pair are modified feeding structures - chelicerae
Second pair are called pedipalps
Four additional pairs of appendages are walking legs
No abdominal appendages
Some have compound eyes, usually have simple eyes capable of forming crude images.

16. Class Meristomata (e.g., Horeshoe crabs)
Marine chelicerates, common off of the Atlantic and Gulf coasts
Large dorsal carapace bearing compound eyes
Possess chelicerae, pedipalps, and 4 pair of walking legs (all but the last pair are chelate
Abdomen terminates in a long tail called the telson; used to turn the animal right side up
Possess a series of gill plates called book gills

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18. Class Arachnida
Respiration is accomplished via book lungs, tracheae, or both
Most are harmless or very beneficial to humans
Usually have 8 simple eyes; at the very least they detect motion; for some of the predatory forms, they are capable of forming crude images
Many species have evolved poison glands associated with the chelicerae
Usually food is PREDIGESTED
Black widow
Brown recluse

19. ORDER SCORPIONIDA (Scorpions)
About 2000 species worldwide. Nocturnal animals, all relatively large. Associated with deserts, but also common in tropics.
Fluoresce under UV light.
Small chelicera
Two segments, prosoma and opisthosoma
Most stings are harmless, similar to a wasp

21. Reproduction Courtship rituals; “scorpion waltz” Most are Oviviparous
Sometimes young are “piggybacked”

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23. ORDER Araneae (Spiders)
Largest Group of Arachnids. Eight-eyed!
Prosoma have chelicerae with large fangs and poison glands
Pedipalps are leg-like; in males modified for sperm transfer
Cephalothorax and abdomen shows no external segmentation; tagma are joined by a narrow pedicel

24. Malphigian Tubules

25. Respiration and Circulation
Arachnids have book lungs, chambers with leaf-like plates for exchanging gases; air flows over the plates and blood flows through them
Blood contains hemocyanin and has ameoboid cells that are similar to human immune cells and platelets

26. Prey capture among the spiders
Some species are cursorial predators, those that stalk and ambush their prey; they usually have well-developed eyes
Jumping spider
Others are web building spiders, those that construct various kinds of webs made of silk to trap their prey
Eyes are not as well developed as cursorial predators, but they have a battery of sensory hairs for detecting vibrations
Grass spider

27. Sensory Structures
Most spiders are predaceous and have all kinds of sensory hairs and relatively well-developed eyes for motion detection; chemoreceptors are also used

29. Reproduction Can use chemical, tactile or visual signals
Females use pheromones to attract males
Courtship behavior, like “web-plucking” is common
Male pedipalps have penislike “embolus”

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32. Other Relatives Class Acarina – Ticks and Mites
Herbivores, scavengers or ectoparasites
Can transmit disease
Class Pycnogonida – Sea Spiders
Males protect the young, “stuck together”

33. Class Malacostraca
Possess 2 pair of antennae: First pair is homologous to those of insects; second pair is unique to the crustaceans
Second antennae have various functions, including sensory, locomotion or feeding.
The head bears a pair of compound eyes and 3 pairs of mouthparts: a pair of mandibles (chewing/grinding) and 2 pairs of maxillae (food handling)
Primitively, the first three pairs of thoracic segments are maxillipeds; (handling food/sensory)
Also, there are usually 5 pairs of appendages strengthened for walking (walking legs) and protection (chelipeds, pincer-like claws)

34. Abdomen is also highly variable, but it is primitively large
SubPhylum Crustacea cont.
Abdomen is also highly variable, but it is primitively large
Groups with a well-developed abdomen usually possess six pairs of appendages: Five pairs of structures called swimmerets (=pleopods); one pair of structures called uropods,
Uropods together with the terminal telson form a tail fan than can serve as rudders during locomotion

35. Gills
Many aquatic arthropods (crabs and lobsters) have gills, which are typically modifications of appendages or outgrowths of the body wall - folds of tissue with a large surface area

36. Sensory Structures
Compound eyes on moveable eyestalks
Crayfish have statocysts present for balance
Tactile receptors on the appendages and at joints
Mouthparts and Antennae lined with chemoreceptors (setae)
Reproduction
Male turns female on back and deposits sperm; after fertilization, eggs are shed; they are sticky and attach to the pleopods

37. SubPhylum Crustacea cont.
Primitively many of the appendages of the crustaceans are biramous: there is an outer exopod and an inner endopod
They usually have an extremely hardened exoskeleton, which is impregnated with calcium carbonate - carapace

38. The primitive larva of the crustaceans is called the nauplius larva
SubPhylum Crustacea cont.
The primitive larva of the crustaceans is called the nauplius larva
It has an unsegmented body, a frontal eye, and 3 pairs of appendages, representing the 2 pairs of antennae and the mandibles
Crabs and their relatives have a second larval stage called a zoea. They have Postlarva is a sexually immature miniadult.

39. Crustacean Diversity Ostracod Water flea Copepod Fairy shrimp
Fish louse

40. Barnacles are Crustaceans!
The only members of this class that are monoecious