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

Barnacles

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