6 Arthropods Armored Achievers Crabs Lobster Shrimp Barnacles

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

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

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.

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.

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 food • Crustacean larvae that swim and attach before metamorphosing into adults

B a r n a c l e s

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

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

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

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

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

Arthropods: Subphylum Crustacea • Crabs – Abdomen small and tucked under large cephalothorax • V shaped abdomen = male • U shaped abdomen = female – Highly mobile and walk sideways

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

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

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

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

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

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

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

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