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

Arthropods Largest phylum (3/4 of all species on earth)Largest phylum (3/4 of all species on earth) Insects – largest groupInsects – largest group Majority of marine arthropods are crustaceans (subphlyum Crustacea)Majority of marine arthropods are crustaceans (subphlyum Crustacea) Flexible, segmented, bilateral symmetryFlexible, segmented, bilateral symmetry Jointed appendages moved by sets of attached musclesJointed 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 exchangeMost marine with gills for gas exchange Appendages specialized for swimming, crawling, attaching to other animals, mating, and feedingAppendages specialized for swimming, crawling, attaching to other animals, mating, and feeding Two pairs of antennae involved in sensing surrounding.Two pairs of antennae involved in sensing surrounding.

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

BarnaclesBarnaclesBarnaclesBarnacles

Arthropods: Subphylum Crustacea Small CrustaceansSmall Crustaceans –Amphipods Curved, flattened bodies (sideways)Curved, flattened bodies (sideways) Beach hopers, common in shore debris, seaweed, burrowing in whales, or planktonicBeach hopers, common in shore debris, seaweed, burrowing in whales, or planktonic –Isopods Parasitic fish lice that are dorsoventrally flattenedParasitic fish lice that are dorsoventrally flattened Marine pill bugMarine pill bug

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

Arthropods: Subphylum Crustacea Small CrustaceansSmall Crustaceans –Euphausiids (yoo-fa-ze-id) (Krill) Planktonic, shrimp-like, filter feedersPlanktonic, shrimp-like, filter feeders Common in polar waters in giant schoolsCommon in polar waters in giant schools Most exclusive food source for whales, penguins and fishMost exclusive food source for whales, penguins and fish

Arthropods: Subphylum Crustacea Shrimps, Lobsters, and CrabsShrimps, Lobsters, and Crabs –Decapods (10 legs) Largest in size, great commercial importanceLargest in size, great commercial importance 5 pairs of legs w/ first pair being claws used for feeding and defense5 pairs of legs w/ first pair being claws used for feeding and defense Well developed carapace encloses cephalothoraxWell developed carapace encloses cephalothorax Rest of body called abdomenRest of body called abdomen

Arthropods: Subphylum Crustacea Shrimps and LobstersShrimps and Lobsters –Laterally compressed –Shrimp - scavengers feeding on detritus Some may remove parasites from skin of fishSome 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 CrabsCrabs –Abdomen small and tucked under large cephalothorax V shaped abdomen = maleV shaped abdomen = male U shaped abdomen = femaleU shaped abdomen = female –Highly mobile and walk sideways

Arthropods: Subphylum Crustacea CrabsCrabs –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 DigestionFeeding and Digestion –Filter feeding common among small crustaceans Bristles on some appendages used to gather foodBristles on some appendages used to gather food Other appendages move food from bristles to mouthOther appendages move food from bristles to mouth Some may use appendages to pierce or suck (parasitic)Some may use appendages to pierce or suck (parasitic) Bristles sift, chitinous teeth in stomach grindsBristles sift, chitinous teeth in stomach grinds

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

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

Biology of Crustaceans Reproduction and Life HistoryReproduction 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)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- daSea 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)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