Aquatic Mandibulates - Subphylum Crustacea (crusta = shell)

both Crustaceans and Uniramians share:

pair of antennae (sensory), pair of mandibles (mastication), pair of maxillae (food handling) - all on the head

Crustaceans and Uniramians used to be the Subphylum Mandibulata

General characteristics of subphylum

1. Appendages only arthropods with two pairs of antennae

also have appendages on thorax and abdomen

all appendages are primitively biramous

Appendages show serial homology

2. Body plan is variable - largest group have head, thorax, and abdomen rostrum and telson

3. Cuticle is hard protective covering -

4. Coelom -

5. Respiration over thin areas of cuticle or gills.

6. Open circulatory system - no veins.

A. hemolymph (colorless blood) enters heart from surrounding percardial sinus through paired ostia

B. travels out of heart through arteries

C. enters small arteries that empty into tissue sinuses which empty into larger sinus

D. afferent sinus channels carry hemolymph to gills for gas exchange

E. hemolymph returns to pericardial sinus by efferent channels.

7. Excretory System

antennal glands or maxillary glands (green glands)

no malpighian tubules

8. Nervous System

Supraesophageal ganglia - eyes and antennae

Subesophageal ganglia - mouth, appendages, esophagus and antennal glands.

Ventral nerve cord - each of somites

Better developed sense organs than annelids. - some with compound; statocysts found on basal segment of first antenna; tactile hairs.

9. Reproduction

most dioecious brood sacs

Some with direct development others with indirect (larval forms)

10. Digestive System

Stomach (gastric mill and filter) ----- >> intestine (chemical digestion).

Class Branchiopoda

fairy shrimp, brine shrimp, tadpole shrimp, water fleas .....

Daphnia


Branchiopod - legs flattened and leaflike - swimming and respiration




Class Maxillopoda

Ecological importance = Copepods - often dominate primary consumer level.


Cirripedia - barnacles


Class Malacostraca

Largest Class of Crustacea

Isopods or pill bugs -

Decapods - crayfish, lobsters, crabs, shrimp