1. CLASS: MEROSTOMATA CLASS: CRUSTACEA CLASS: PYCNOGONIDA
PHYLUM ARTHROPODA
CLASS: MEROSTOMATA
CLASS: CRUSTACEA
CLASS: PYCNOGONIDA

2. General Characteristics
Jointed appendages – increases mobility
Segmented body (2 or 3)
Gills – gas exchange
Feeding mechanism – filter feed, eat detritus
Separate sexes
Exoskeleton of chitin – protection, muscle attachment, support, reduce water loss.
Must molt to grow
Limits size of organism

3. Nervous system Compound eyes – a mosaic pattern for vision
Smell – very sensitive, detects small amounts of chemical changes
Communication behaviors – mating, defense & territorial displays (waving of claws to opponent)
Well-developed nervous system

4. Class Merostomata “Middle stomach” - Horseshoe Crab
Atlantic Ocean & Gulf of Mexico
Horseshoe shaped carapace (exoskeleton-back)
5 pairs of legs
Shallow water
Collected off coast of Maine for chemical in blood that makes an antibacterial agent

6. Class Pycnogonida
Sea spiders - Most have 4 pairs of legs and some may have 5 or 6 pairs
Legs are twice as long as land spiders
Live in cooler water

7. Sea Spiders
Has proboscis (extension tube) with mouth on end to suck juices out of mollusks, cnidarians, sponges and worms
Abdomen is reduced
May have 2 pairs of eyes
Most are separate sexes. Males care for eggs and young.

8. Class Crustacea Exoskeleton made of calcium carbonate
2 Pairs of antennae
Appendages specialized for life habits: crawling, swimming, feeding & reproduction
Small size
Examples: Copepods, Barnacles & Krill

9. Crustacea Examples

10. Class Decapoda Larger size crustaceans & largest group
Have 10 legs (deca)
Chelipeds – 1st pair legs are large claws
Maxillipeds (3 pairs) sort food & push in food
Feeding - scavengers
Body segments - 2
Cephalothorax – head & thorax covered by carapace
Abdomen – walking legs attached

11. Class Decapoda

12. Examples Lobster: fanlike tail to move quickly
1 large claw for crushing, 1 small claw for biting
Nocturnal scavengers
Crabs: broad cephalothorax & reduced abdomen curved under body
Males – V-shaped abdomen, Females – U-shaped abdomen
Move sideways, burrow or swim for defense
Largest decapod group

13. Examples Hermit Crab – live in abandoned shells
Soft body twists to shape of shell
Must relocate to larger shells for growth
1 claw is larger & is used to close off shell for defense

14. Hermit crab