6. Arthropods: Armored Achievers Crabs, Lobster, Shrimp, Barnacles

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6. Arthropods Armored AchieversCrabs, Lobster,
Shrimp, Barnacles
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Arthropods

• Largest phylum (3/4 of all species on earth)
• Insects largest group
• Majority of marine arthropods are crustaceans
  (subphlyum Crustacea)
• Flexible, segmented, bilateral symmetry
• Jointed appendages moved by sets of attached
  muscles

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Arthropods exhibit bilateral symmetry and a
chitinous exoskeleton. Provides support,
protection, and increased surface area for muscle
attachment.
To grow they must molt the exoskeleton and absorb
water to expand before the new exoskeleton
hardens.
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Arthropods Subphylum Crustacea

• Most marine with gills for gas exchange
• Appendages specialized for swimming, crawling,
  attaching to other animals, mating, and feeding
• Two pairs of antennae involved in sensing
  surrounding.

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Arthropods Subphylum Crustacea

• Small Crustaceans
• Copepods (cope-a-pod)
• Planktonic, use mouthparts to filter feed, some
  may swim, many are parasitic
• Barnacles
• Filter feeders that usually live attached to
  surfaces, even living organisms
• Cirri (sear-I) (feathery legs) sweep water for
  food
• Crustacean larvae that swim and attach before
  metamorphosing into adults

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Barnacles
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Arthropods Subphylum Crustacea

• Small Crustaceans
• Amphipods
• Curved, flattened bodies (sideways)
• Beach hopers, common in shore debris, seaweed,
  burrowing in whales, or planktonic
• Isopods
• Parasitic fish lice that are dorsoventrally
  flattened
• Marine pill bug

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Amphipods and Isopods
Orchestoidea, a beach hopper are often found on
marine mammals.
Sea louse a marine pill bug
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Arthropods Subphylum Crustacea

• Small Crustaceans
• Euphausiids (yoo-fa-ze-id) (Krill)
• Planktonic, shrimp-like, filter feeders
• Common in polar waters in giant schools
• Most exclusive food source for whales, penguins
  and fish

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Arthropods Subphylum Crustacea

• Shrimps, Lobsters, and Crabs
• Decapods (10 legs)
• Largest in size, great commercial importance
• 5 pairs of legs w/ first pair being claws used
  for feeding and defense
• Well developed carapace encloses cephalothorax
• Rest of body called abdomen

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Arthropods Subphylum Crustacea

• Shrimps and Lobsters
• Laterally compressed
• Shrimp - scavengers feeding on detritus
• Some may remove parasites from skin of fish
• Lobsters Marine scavengers and predators that
  crush molluscs and sea urchins
• Hermit crabs not true crabs that hide soft body
  in empty shells

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Arthropods Subphylum Crustacea

• Crabs
• Abdomen small and tucked under large
  cephalothorax
• V shaped abdomen male
• U shaped abdomen female
• Highly mobile and walk sideways

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Arthropods Subphylum Crustacea

• Crabs
• Scavengers/predators
• Some have specialized diets of seaweeds, organic
  matter, or coral mucus
• Live along rocky shores or sandy beaches
• Land crabs live most of life on land but may
  return to ocean to release eggs

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Biology of Crustaceans

• Feeding and Digestion
• Filter feeding common among small crustaceans
• Bristles on some appendages used to gather food
• Other appendages move food from bristles to mouth
• Some may use appendages to pierce or suck
  (parasitic)
• Bristles sift, chitinous teeth in stomach grinds

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Biology of Crustaceans

• Feeding and Digestion
• Decapods have 2 chambered stomach connected to
  digestive gland that secretes enzymes and absorbs
  nutrients (extracellular)
• Intestine ends in an anus
• Open circulatory system distributes nutrients

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Biology of Crustaceans

• Nervous System and Behavior
• Small, simple brains but well-developed sensory
  organs
• Compound eyes
• Keen sense of smell (chemical sensitivity)
• Have statocysts for balance
• Most behaviorally complex of all invertebrates
• Have special body posture and movement of legs
  and antennae
• Helps settle disputes between neighbors and
  courtship

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Biology of Crustaceans

• Reproduction and Life History
• Separate sexes in most crustaceans
• Males use specialized appendages to transfer
  sperm directly to female
• Decapods - takes place after molting and females
  can store sperm to use on different batch of eggs
• Most have planktonic larvae type and number of
  larval stages vary widely

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Other Marine Arthropods

• Horseshoe Crabs (class Merostomata)
• Only surviving members
• Widely represented by fossil records
• 5 living species and not true crabs
• Live on soft bottoms of shallow waters on
  Atlantic and Gulf coasts of North America and
  Southeast Asia
• Emerge on beaches to reproduce

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Other Marine Arthropods

• Sea Spiders (class Pycnogonida) Pic no ga-
  ni- da
• Superficially resemble spiders
• Four or more pairs of legs
• Large proboscis with mouth at tip used to feed on
  soft invertebrates such as sea anemones and
  hydrozoans
• More common in cold water but do not occur
  throughout oceans

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Other Marine Arthropods

• Insects (class Insecta)
• 3 pairs of legs as adults
• Rare in the sea
• Live at waters edge scavenging for seaweeds,
  barnacles, and rocks
• Inhabit decaying seaweed that accumulates at high
  tide