CLASS: MEROSTOMATACLASS: CRUSTACEA

CLASS: PYCNOGONIDA

General CharacteristicsJointed appendages – increases mobilitySegmented body (2 or 3)Gills – gas exchangeFeeding mechanism – filter feed, eat detritusSeparate sexesExoskeleton of chitin – protection, muscle

attachment, support, reduce water loss.Must molt to growLimits size of organism

Nervous systemCompound eyes – a mosaic pattern for visionSmell – very sensitive, detects small amounts

of chemical changesCommunication behaviors – mating, defense

& territorial displays (waving of claws to opponent)

Well-developed nervous system

Class Merostomata“Middle stomach” - Horseshoe CrabAtlantic Ocean & Gulf of MexicoHorseshoe shaped carapace (exoskeleton-

back)5 pairs of legsShallow waterCollected off coast of Maine for chemical in

blood that makes an antibacterial agent

Class PycnogonidaSea spiders - Most have 4 pairs of legs and

some may have 5 or 6 pairsLegs are twice as long as land spidersLive in cooler water

Sea SpidersHas proboscis (extension tube) with mouth

on end to suck juices out of mollusks, cnidarians, sponges and worms

Abdomen is reducedMay have 2 pairs of eyesMost are separate sexes. Males care for eggs

and young.

Class CrustaceaExoskeleton made of calcium carbonate2 Pairs of antennaeAppendages specialized for life habits:

crawling, swimming, feeding & reproductionSmall size Examples: Copepods, Barnacles & Krill

Crustacea Examples

Class DecapodaLarger size crustaceans & largest groupHave 10 legs (deca)Chelipeds – 1st pair legs are large clawsMaxillipeds (3 pairs) sort food & push in foodFeeding - scavengersBody segments - 2Cephalothorax – head & thorax covered by

carapaceAbdomen – walking legs attached

Class Decapoda

ExamplesLobster: fanlike tail to move quickly

1 large claw for crushing, 1 small claw for bitingNocturnal scavengers

Crabs: broad cephalothorax & reduced abdomen curved under bodyMales – V-shaped abdomen, Females – U-shaped abdomenMove sideways, burrow or swim for defense

Largest decapod group

ExamplesHermit Crab – live in abandoned shells

Soft body twists to shape of shellMust relocate to larger shells for growth1 claw is larger & is used to close off shell for

defense

Hermit crab