Phylum Arthropoda

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Phylum Arthropoda

• BIOL 102

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• Know the five subphyla of arthropods and the key
  characteristics of each subphylum.
• Identify the external features of a preserved
  crayfish. Remove the appendages
• one side of the preserved crayfish and lay them
  out on p. 217. The instructor will
• initial the page after the correct
  identification of the removed appendages.
• Remove the carapace and observe a gill utilizing
  a microscope. Draw a picture of
• the gill.
• D. Observe the live crayfish specimens (if
  available).
• E. Observe the external anatomy of the preserved
  grasshopper.
• F. Observe the slide of spiracle and trachea and
  prepare a labeled drawing of the slide.
• Prepare a list of the different types of
  metamorphosis as seen in this phylum. Refer
• to p.201.
• H. Prepare a list contrasting the characteristics
  of annelids and arthropods.

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Arthropods segmented bodies with segmented
appendages

• The phylum Arthropoda contains animals with
  segmented appendages on their body segments.
  Arthropods occupy every habitat, and are in many
  respects the most successful animal group on
  Earth. There are conservatively over 1 million
  species of living arthropods. Biologist E.O.
  Wilson estimates there are 10 million species, 9
  million of which are arthropods. Certain groups
  of arthropods have extremely complete fossil
  records.

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Characteristics that led to success!

• A hard exoskeleton, a strong but flexible outer
  covering composed primarily of the carbohydrate
  chitin. This functions in protection, attachment
  for muscles, locomotion, and prevention of
  desiccation.
• Presence of jointed appendages. Modern arthropod
  appendages are specialized for walking, swimming,
  reproduction, etc.
• 3. A complex nervous system with a brain
  connected to a ventral solid nerve cord.
• 4. A unique respiratory system that employs a
  variety of respiratory organs. Marine arthropods
  utilize gills. Terrestrial forms have book lungs
  (e.g., spiders) or tracheae. (e.g., insects).
  Book lungs are invaginations to serve in gas
  exchange between air and blood. Tracheae are air
  tubes that serve as ways to deliver oxygen
  directly to cells.
• 5. A complex, yet adaptable, life cycle

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Benefits of Metamorphosis

• Metamorphosis is a drastic change in form and
  physiology that occurs as an immature stage
  becomes an adult. Metamorphosis contributes to
  the success of arthropods because the larval
  stage eats food and lives in environments
  different from the adult reducing competition
  between immature and adults of a species.
  Reduction in competition thus allows more members
  of the species to exist at one time.

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Characteristics of the Sub-phyla

• The arthropod body consists of three major
  collections or zones of body segments
• head
• thorax
• abdomen
• The Subphylum Crustacea
• The Subphylum Crustacea contains 30,000 mostly
  marine species. A few species live in freshwater.
  Lobsters, crabs, crayfish, shrimp, barnacles, and
  several other groups of organisms belong to this
  subphylum. All crustaceans possess two pairs of
  antennae, a pair of mandibles, a pair of compound
  eyes (usually on stalks), and two pair of
  maxillae on their heads, followed by a pair of
  appendages on each body segment. Crustacean
  bodies usually have a head, thorax, and abdomen.
  Crustaceans utilize gills for gas exchange.
• Most crustaceans are free-living, but some are
  sessile and a few are even parasitic. Some
  crustaceans filter tiny plankton or bacteria from
  the water, while others are active predators. A
  few crustaceans scavenge nutrients from detritus.
  
• Many species, including lobsters, crayfish,
  barnacles, and crabs are economically important
  (yum, yum).

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Characteristics of the Sub-phyla

• The Subphylum Chelicerata
• The subphylum Chelicerata includes spiders,
  scorpions, ticks, mites, horseshoe crabs, etc.
  The first pair of appendages are chelicerae,
  second pair are pedipalps, and the next four
  pairs are walking legs. Chelicerae are appendages
  that function as feeding organs. Pedipalps are
  feeding or sensory in function although in
  scorpions, they are large pincers. All appendages
  attach to a cephalothorax, a fusion of the head
  and thoracic regions. The head lacks antennae,
  mandibles, or maxillae appendages.

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Characteristics of the Sub-phyla

• Subphylum Myriapoda
• This subphylum contains arthropods that have
  unbranched appendages. The uniramian body has two
  or three tagmata, and an abdomen that has many
  segments. Appendages in the head region include
  paired antennae and mandibles, and also two pairs
  of maxillae. Gas exchange is by means of tracheae
  and spiracles. This subphylum include millipedes
  and centipedes.

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Subphylum Hexapoda

• The Class Insecta
• Insects are the largest group, with probably over
  one million identified and named species. Insects
  live in almost all terrestrial and freshwater
  habitats, with a few species living in the
  oceans.
• Many insects have some thoracic appendages
  modified for flight. Insects are important as
  pollinators for flowering plants, as well as for
  the damage they do annually to crops, and the
  diseases they transmit (malaria, some forms of
  encephalitis, etc.).
• Insects display a wide huge variation in body
  styles, although there seems to be a size limit
  on the insect-style of body organization.

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Insect Characteristics

• body composed of three tagmata
• one pair of relatively large compound eyes
• usually three ocelli located on the head
• one pair of antennae on the head
• mouthparts
• two pairs of wings derived from outgrowths of the
  body wall
• three pairs of walking legs
• Insects have a complete, complex digestive
  system.
• They exchange gases through a tracheal system,
  with external openings called spiracles dividing
  into finely branched tubules that carry gases
  directly to metabolizing tissues. Aquatic forms
  may exchange gases through the body wall or may
  have various kinds of gills.
• Excretion of nitrogenous waste takes place via
  Malpighian tubules.
• The nervous system of insects is complex,
  including a number of ganglia and a ventral,
  double nerve cord. Sense organs are complex and
  acute. In addition to ocelli and compound eyes,
  some insects are quite sensitive to sounds, and
  their chemoreceptive abilities are excellent.

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Insects cont.

• Growth patterns are quite variable.
• Some insects hatch from eggs as miniature adults,
  which in turn shed their exoskeleton.
• Most insect species have newly hatched young that
  are completely different in appearance from
  adults. These larval forms usually live in
  different habitats, eat different foods, and look
  completely different from their adult stages.
  When larval growth is completed, the larva stops
  feeding and builds a case or cocoon around
  itself. In this non-feeding condition (pupa or
  chrysalis) the larva undergoes a complete
  transformation or "metamorphosis" of its body
  form, eventually emerging as a fully-formed
  adult.

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Benefits!

• Insects are very valuable to us. While insects
  eat our food, feed on our blood and skin,
  contaminate our dwellings, and transmit diseases,
  we could not exist if thety were not here.
  Insects are a vital part of our ecosystem,
  functioning in
• pollination of many flowering plants
• decomposition of organic materials
• recycling of carbon, nitrogen, and other
  essential nutrients
• control of populations of harmful invertebrate
  species (including other insects)
• direct production of certain foods like honey
• manufacture of useful products such as silk and
  shellac