Aquatic Mandibulates

1. Aquatic Mandibulates Chapter 19

2. Subphylum Crustacea • Crustaceans, subphylum Crustacea typically have biramous, branched, appendages that are extensively specialized for feeding and locomotion.

3. Subphylum Crustacea • Crustaceans are the only arthropods that have two pairs of antennae. • They also have a pair of mandibles (jaw-like appendages) and two pairs of maxillae on the head. • Each body segment usually has one pair of appendages. • Ancestrally biramous except for the first antennae.

4. Subphylum Crustacea • The ancestral condition in arthropods is to have many body segments. • Fewer segments and increased tagmatization is the derived condition.

5. Class Malacostraca • Malacostracans usually have a head with 5 fused segments, a thorax with 8 segments and an abdomen with 6. • Anterior rostrum • Posterior telson

6. Class Malacostraca • Decapods – order decapoda – are all relatively large crustaceans and include lobsters, crabs, crayfish, and shrimp. • 3 pairs maxillipeds & 5 pairs walking legs. • Harder, heavy plates in larger crustaceans due to calcareous deposits in addition to chitin. • The carapace covers much or all of the cephalothorax.

7. Class Malacostraca • Arthropods have a true coelom, but it is much reduced and the major body space is the blood filled hemocoel (derived from the blastocoel). • Open circulatory system • Gas exchange occurs across thin areas of the cuticle or in gills.

8. Class Malacostraca • Most crustaceans have separate sexes. • Many brood eggs, in special chambers or under their abdomens – carried by abdominal appendages.

9. Class Malacostraca • Crayfishes have direct development. • In most crustaceans, there are larval forms. • Nauplius – ancestral, widely occurring larval form.

10. Class Malacostraca • Krill – order Euphausiacea – planktonic shrimp-like animals. • Most are bioluminescent with a light producing organ called the photophore. • Krill are eaten by whales.

11. Class Malacostraca • Other orders of malacostracans include: • Isopoda – including pill bugs. • Compressed dorsoventrally. • Amphipoda – many marine, terrestrial & freshwater forms. • Compressed laterally.

12. Class Branchiopoda • Includes three orders: • Anostraca – fairy shrimp and brine shrimp, no carapace. • Notostraca – tadpole shrimp, carapace forms a large dorsal shield. • Diplostraca – water fleas – carapace encloses body but not head.

13. Class Branchiopoda • Phyllopodia – legs that serve as respiratory organs. • Legs may be used for filter feeding and locomotion as well. • Mostly freshwater forms.

14. Class Branchiopoda • Water fleas (like Daphnia) produce females parthenogenetically in summer. Males are produced when unfavorable conditions arise and overwintering fertilized eggs are produced that are resistant to cold and desiccation.

15. Class Ostracoda • Ostracods are enclosed in a two part carapace and look a bit like a clam. • Marine or freshwater. • Mostly benthic.

16. Class Maxillopoda • Maxillopods generally have 5 cephalic, 6 thoracic, and 4 abdominal segments plus a telson. • Reductions common. • The nauplius of maxillopods has a maxillopodan eye – unique to this group.

17. Class Maxillopoda • Planktonic crustaceans include many species of copepods (subclass Copepoda) which are among the most numerous of all animals. • They lack a carapace. • Retain the simple maxillopodan eye in adults. • Antennules used in swimming. • Very diverse.

18. Class Maxillopoda • Barnacles – subclass cirripedia – are a group of mostly sessile crustaceans whose cuticle is hardened into a shell. • Their legs are long, many jointed cirri that extend out through the calcareous plates to filter feed.

19. Class Maxillopoda • Barnacles are hermaphroditic. • Most hatch as a nauplius larva then become a cyprid larva (resembles the ostracod Cypris). • Cyprids attach to the substrates and begin secreting calcareous plates.