Phylum Arthropoda

Subphylum Crustacea

General Characteristics

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

 

Internal Structures

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 Isopoda - terrestrial, freshwater, and marine spp.; most common and familiar type are the pill bugs (terrestrial; aka roly-polies).

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

 

Form

External

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.

3) Appendages:

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

 

Internal

1) Excretory system

a) green glands: uropods only: flood control device

1) bladder

2) tubule

3) labrynth

4) end sac

2) Nervous system

a) brain: one pair supraesophageal ganglia

b) subesophageal ganglia

c) Possibly a sympathetic system with digestive tract