Advanced Invertebrates Have Complex Bodies and Internal Systems

• Arthropoda • Most successful phylum on Earth- phylum with largest number of species: , , spiders, etc. • Exoskeleton – chitin • Striated muscle • Articulation

What is an ? • Exoskeleton- • Tough outer covering • Protection and support • three layers excreted from the epidermis: • composed of Chitin and proteins, often hardened with calcium carbonate • Segmented body • Body often divided into head, thorax, and abdomen (segmentation) • Head and thorax can be fused in a cephalothorax • Fewer body segments • Highly specialized for feeding, movement, etc. • Different body plans for different environments What is an Arthropod? • Jointed appendages • is a structure that extends from body wall • Example: legs and antennae • True coelom • Cephalization • Divided into Subphyla Subphylum Trilobitomorpha-Triolobites-extinct

Subphylum -, horseshoe crabs, and sea spiders

Subphylum -, , etc.

Subphylum Crustacea-shrimp, lobsters, crabs

Subphylum -insects Form and Function in the • Feeding: • Arthropods can be: • herbivores, carnivores, parasites, etc. • Mouth parts vary from groups of arthropods. • Respiration • 2 ways aquatic arthropods respire: • Featherlike gills -Found in crabs and other aquatic arthropods. • Book gills -Found in Horseshoe crab. • Circulation: All have an Open Circulatory system • Process: • 1) Heart pumps blood through arteries into tissue. • 2) Blood leaves vessel and moves through sinuses. • 3) Blood then collects in large sinus around heart. • 4) Reenters blood. Form and Function in the Arthropods • Response:

• All arthropods have a brain • Also a ventral nerve cord • Ganglia are found along this chord. • Compound eye – multiple lens each w/ light detectors

• Movement:

• Arthropods use muscles to move. • Muscles generate force by Contracting and pulling • Muscles flex (bend) or Extend (straighten) at the joint causing movement. Growth and Development in Arthropods

• Aquatic arthropods • External fertilization and internal fertilization • Molting • Exoskeleton does not grow with body. • When exoskeleton is outgrown arthropods molt • Molting – the removing and replacement of arthropod exoskeleton • Molting is controlled by Endocrine system and hormones Crustaceans • Dominant marine arthropods: , , isopods, amphipods, shrimps, lobsters, crabs • The form and function of the crustaceans 1st three appendages: • 1st and 2nd antennae – sensory hairs. • 3rd mandibles – chewing mouthpart. • Some are filter feeders, others scavengers, parasites, carnivores • Appendages specialized for different functions: feeding, swimming, carrying eggs, etc. • Male transfers sperm directly to female to ensure reproductive success. Arthropods: Subphylum Crustacea • Basic characteristics: • The parts of a ’s body:

• Cephalothorax – fusion of head and thorax

• Thorax – body segment that houses most internal organs • Carapace – part of the exoskeleton that covers the cephalothorax • Abdomen – posterior part of body Crustaceans • Decopods-Order Decapoda • Examples: Crayfish, Lobster, and crabs • 5 pairs of legs • first pair called Chelipeds • Modified in to Claws • rest of the pair of legs for Walking legs • Along the abdomen Swimmerets • Final abdominal segment fused into Paddle like appendage called the • Most have Larva stage called Nauplius • Copepods- ”oar-feet” • Barnacles- Class Cirripedia-"curl-footed“ • Horseshoe Crabs-Class Merostomata • Sea Spiders -Class Pycnogonida Copepods-”oar-feet” Found in the sea and nearly every freshwater habitat. Some species are planktonic (drifting in sea waters), some are benthic (living on the ocean floor) Eggs hatch into larval form (Nauplius), with a head and a tail but no true thorax or abdomen. The larva molts several times until it resembles the adult. The Nauplius form is so different from the adult form that it was once thought to be a separate species. Lobster Body Structure

(bkgd)Comstock Images/PictureQuest Barnacles- Cirripedia-"curl-footed". Exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings.

Related to crabs and lobsters Sessile suspension feeders 2 nektonic (active swimming) larval stages Around 1,220 species are currently known. Horseshoe Crabs (Class Merostomata): Among the oldest creatures on Earth, having remained virtually unchanged for millions of years

• Horse-shaped carapace that encloses a body with five pairs of legs • They live and burrow in soft sediments, normally near shore, where they scavenge and feed on other invertebrates

• Mating pairs come onto beaches each spring to breed and lay their eggs in wet sand Sea Spiders (Class Pycnogonida):

• Four or more pairs of jointed legs

• Proboscis for feeding on soft invertebrates like sea anemones and hydrozoans

- More common in cold water, but found worldwide http://www.serc.si.edu/education/resources/bluecrab/molting.jsp

MOLTING- Periodic shedding of exoskeleton to allow growth •Growth puts pressure on old shell •Stimulating molting hormones to digest old exoskeleton and make new one underneath •Shell cracks open and animal backs out •Animal pumps up with water and expands •New shell hardens in few days •While waiting for new exoskeleton to harden = particularly vulnerable to predators “soft shelled crabs”