1) Moveable mouth parts (specialized for chewing wide-variety of food).
a) mandibles: specialized moveable mouthpart, structure usually associated with an immovable part(s) called maxillae.
2) Antennae are present. Pair of chemoreceptors & tactile - receptive sensory structures
3) Cephalothorax & abdomen; distinctly segmented abdominal tagma.
4) Gills for aquatic respiration
5) *Biramous appendages - "two-branched" e.g. swimmerets, chelipeds, etc.
Form and Function
External structures & specialization
1) Caridoid facies: referring to arrangement & consistent arrangement of body segments & tagma; key distinguishing body feature of subphylum Crustacea.
2) Rostrum: anterior, non-segmented region or projection at tip of cephalothorax.
3) Telson: posterior, non-segmented region or projection at tip of abdomen
4) Uropod: extension of last abdominal somite; usually ventral to telson.
5) Carapace: armor-like plate-like protective covering; usually on dorsal side.
6) Tergum: dorsal, cuticular plate covering somites that are not enclosed by carapace.
7) Sternum: ventral, transverse bar of cuticular material between segmental appendages.
8) Biramous appendages:
a) Gills sometimes associated with appendages (e.g. crayfish maxilliped)
b) Coxa: major joint of biramous appendage
c) Basis: major joint of biramous appendage
d) Exopod: two-branched portion appendage
e) Endopod: two-branced portion appendage
1) Hemocoel: reduced, blood-filled coelomic sinus cavity
2) Muscular system: extensive specialization
a) extensors: muscles which "straighten out" a specific structure such as tail\appendage.
b) flexors: muscles which "pull in" a specific structure.
3) Respiratory system
a) Some respiration occurs thru thin regions in cuticle (nonspecialized, passive diffusion)
b) Gills: major, specialized, aquatic respiratory organ; found in larger crustacea.
4) Circulatory system: open (no veins). specialized heart made up of cardiac muscle tissues, true arteries, specialized blood pigments for carrying oxygen.
a) Blood pigments
1) Hemolymph: "colorless" blood "pigment" (oxymoron) --> better term: nutrient carrier component of blood. May carry some oxygen. Involved clotting.
2) Hemocyannin: true pigment carries oxygen; uses copper as reactive portion of pigment.
3) Hemoglobin: true pigment uses iron reactive portion.
Classification and Specific Characteristics
Class Branchiopoda - brine shrimp and water fleas (Daphnia spp.. Mostly freshwater spp.; microscopic to nearly microscopic; form a large segment of the freshwater zooplankton; share some similarities with rotifers but are eucoelomic; can reproduce asexually by parthenogenesis.
Class Malacostraca - largest class of crustaceans; very diverse; includes 3 subclasses and 14 orders; most common and familiar class:
Order Decapoda - crayfish, lobsters, crabs, and true shrimp; have 3 pairs of maxillipeds and five pairs of walking legs, of which the first pair is modified into many types of pinchers forming the chelipeds.
1) Pair of antennae: sensory functions
2) Pair of mandibles: food handling and chewing
3) Pair of maxillae: functions in chewing
4) Well defined head, thorax, and abdomen
5) Most contain cephalothorax
6) Majority are free-living, many sessile, commensal, or parasitic
7) Crustacea only contain two pair antennae
1) Exoskeleton: cuticle composed of chitin, somites are covered by tergum sternum lies between segmental appendages telson (tail): not a true somite.
2) Gonopores: reproductive pores. position will vary to class and age.
a) Antennule: touch, taste, and equilibruim.
b) Antennae: touch, taste
c) Mandible: crushing food
d) 1st maxilla: food handling
e) 2nd maxilla: drawing H2O -------> gills
f) 1st maxilliped: touch, taste, and food handling
g) 2nd maxilliped: touch, taste, and food handling
h) 3rd maxilliped: touch taste, and food handling
i) cheliped: offense and defense
j) walking legs: walking and prehension
k) swimmerette: reproduction function in both sexes
l) uropod\telson: swimming and egg protection females
1) Excretory system
a) green glands: uropods only: flood control device
4) end sac
2) Nervous system
a) brain: one pair supraesophageal ganglia
b) subesophageal ganglia
c) Possibly a sympathetic system with digestive tract