Untitled Quiz

Arthropods

• 85% of all metazoans are Arthropods.
• Defining characteristics:
  • Segmented, jointed, and sclerotized chitinous exoskeleton with musculature between individual joints of appendages
  • Loss of cilia in adults & larvae
  • Metameric (segmented) development, new segments arising from a zone at the rear of the animal
  • Tagmatization: regions of the body modified from fused segments
  • Cuticle made of chitin, secreted over the whole body by epidermal cells, water-impermeable, highly resistant to dehydration, thin and flexible in some regions
• Exoskeleton shedding (ecdysis): process of shedding and regrowing, under hormonal and neural control, increasing animal size
• Striated muscles, contracting faster than smooth muscles due to the rate nerve impulses are delivered to fibers
• Open circulatory system with a heart and ostia
• Vision through ocelli (light-sensitive, non-image forming), and compound eyes (image-forming, ommatidia, wide visual range)

Major Arthropod Groups

• Subphylum Trilobitomorpha:
  • Class Trilobita (trilobites), extinct, 2 anterior furrows dividing the body (2 lateral, 1 central), flattened dorsoventrally, covered by a carapace, biramous appendages, compound eyes with ommatidia
• Subphylum Chelicerata:
  • Lack antennae
  • Body divided (prosoma and opisthosoma), no distinct head,
  • First pair of appendages are chelicerae (feeding),
  • Includes classes: merostomata (horseshoe crabs), arachnida (spiders, mites, ticks, scorpions) and pycnogonida (sea spiders),
  • Chelicerae for biting and shredding
  • Lack mandibles
• Class Merostomata (Horseshoe Crabs):
  • Flattened appendages on opisthosoma modified into book gills
  • Telson with elongated spike
  • Prosoma (cephalothorax) covered with a carapace, composed of chelicerae, 5 pairs of walking legs, first pair=pedipalps, last pair=chiliaria,
  • Opisthosoma with 6 pairs of appendages & book gills
• Class Pycnogonida (Sea Spiders):
  • Body without tagmata
  • Proboscis with an opening
  • Varied number of walking legs
  • Ovigers for grooming and carrying eggs
  • Parasitic larvae
• Class Arachnida (spiders, mites, ticks, scorpions):
  • Prosoma & opisthosoma are the tagmata
  • Appendages: chelicerae, pedipalps, maxilla, walking legs
  • Book lungs with spiracles and tracheae
  • Spinnerets in spiders

Mandibulata vs. Pancrustacea

• Mandibulata:
  • Mandibles on third head segment for chewing/grinding food
  • Retinula of compound eyes: 8 cells
  • Includes subphyla myriapoda, insecta, and crustacea
• Pancrustacea:
  • Recent molecular data showing close relationship to myriapoda and chelicerates
  • Morphological characteristics

New Organization

• Hexapods are a subgroup of Pancrustacea.
• Old Crustacea are paraphyletic
• Many traits in hexapods and myriapods are convergent
• Single pair of antennae
• Tracheal system
• Mandibulates are a group distinguished by mandibles vs. chelicerate mouthparts

Myriapoda

• Includes chilopoda (centipedes) & diplopoda (millipedes)
• Unwaxed cuticle
• Lack compound eyes, have ocelli
• Chilopoda (centipedes): carnivorous, tracheae with open spiracles, nocturnal for water conservation, repugnatorial glands
• Diplopoda (millipedes): detritivores, pairs of segments fuse, 2 pairs of legs per diplosegment, calcium salts to discourage predation

Crustacea

• Defining characteristics:
  • Head bearing 5 pairs of appendages (including 2 pairs of antennae),
  • Larval form (nauplius) bearing 3 pairs of appendages & medial eye
  • Includes classes: malacostraca, branchiopoda, ostracoda, copepoda, pentastomida, cirripeda

Branchiopoda

• Coxa of leg modified to make flattened paddle for gas exchange & locomotion
• Filter feeders
• Some lack a carapace

Cirripeda (Barnacles)

• Highly modified to attach to hard substrate or other organisms,
• Thoracic limbs (cirri) modified as filtering structures
• Lack abdomen, shell (carina, rostrum, scutum, terga), cirri for feeding, lack abdominal segments, and heart, reduced head
• Non-motile

Malacostraca

• Thorax with 8 segments, abdomen with 6–7 segments plus a telson
• Appendages on 6th abdominal segment flattened to form uropods
• Includes orders: decapods, euphausiids, stomatopods, isopods, and amphipods
• Rostrum (beaklike projection on head), compound eyes.
• Antennae, mandibles, maxillae, maxillipeds, walking legs, uropods, and chromatophores