Arthropods and Crustacea

Question 1

Crustacea

Answer 1

Paraphyletic group (i.e.
pan-crustacea without the hexapods)~84,000 species
● Incredibly diverse morphology & ecology
● Overall accounts for by far the largest animal biomass on earth (copepods and krill), critical to all marine food webs and carbon capture

Question 2

General Crustacea characteristics

Answer 2

● Two pairs of antennae (a distinguishing feature)
● Three or more pairs of mouth parts
● Walking/swimming legs on thorax and abdomen (as opposed to thorax/cephalothroax
based legs in hexapods and chelicerates)
● Biramous appendages (sometimes highly
specialised in some groups, and vary along the body)

Question 3

Crustacean Cuticle

Answer 3

● The cuticle is calcified (in contrast to most arthropods) but also
made of protein & chitin
● The epicuticle and procuticle contain deposits of Calcium Carbonate salts
● The outer layer of procuticle is also pigmented and contains
tanned proteins

Question 4

Crustacean trunk anatomy

Answer 4

● The trunk is composed of distinct and similar segments and a telson
● This basic design is often modified by the fusion of segments
● The thorax or anterior trunk segments is covered by a dorsal carapace (with a pointed rostrum in the Malacotraca)

Question 5

Biramous appendages

Answer 5

Biramous appendages are ones that break into two, and typically have multiple functions (walking, swimming, sperm transmission feeding, gas exchange), and are ancestral in Crustacea (loads of shrimp-like things with loads of generalised appendages)

Question 6

Crustacea blood vascular systems

Answer 6

Crustacea, like other arthropods have a reduced coelom called the haemocoel
● Blood (hemolymph) is pumped through an open circulatory system, with gas-exchange across gills
● Blood contains respiratory proteins normally called hemocyanins, which are copper-containing (and blue-green, rather than iron-containing hemoglobin)
● Large Crustacea have more extensive arterial systems

Question 7

Crustacean Phylogeny

Answer 7

Oligostraca:
● Fish lice & tongue worms (Ichthyostracans, ~300
species)
● Seed shrimp (Ostracods, ~13,000 extant species)

Thecostraca:
~2,200 species, typically have marine planktonic larvae followed by a sessile adult stage
The largest sub-clade are the barnacles (Cirripedia, ~2,100 species)

Branchiopoda (translates as gill-foot):
● ~1,800 species

Copepoda: (translates as oar-foot)
● ~15,000 species

Question 8

Malacostracan Phylogeny

Answer 8

Malacostraca: (translates as soft-shell)
● ~46,500 species

Decapoda: (translates as ten-footed) & includes crabs, lobsters, crayfish, shrimp, & prawns
● ~15,000 species

Isopods: (translates as same-foot)
● ~11,000 species

Stomatopoda: (mantis shrimp, translates as mouth-foot)
● ~520 species

Question 9

The Caridoid escape reaction

Answer 9

The Caridoid escape reaction is a fast-start
response found only in Malacostraca that
has been intensively researched in
neuroethology and neurophysiology