SUBPHYLUM CRUSTACEAGeneral Characteristics:•The Crustacea are a large group (~52,000 spp. described) of ecdysozoanswhose members are primarily aquatic (they moult, or undergo ecdysisas they grow).•Most are marine, some freshwater, but only a few have radiated into terrestrial habitats.•Diversity of crustacean anatomy is huge! Typically comprise 3 body segments: head, thorax andabdomen.4
Main Characteristics of Crustacea•Crustacea possess 2 pairs of antennae(which are jointed in some species, e.g. in lobsters) – this feature separates them from the phylum Chelicerata (which have 1 pair of antennae).•Crustacea have biramousappendages, which separates them from the Insecta (which have uniramous appendages).5In many crustaceans, the cuticle is thickened and strengthened with deposits of calcium carbonate, i.e. the cuticle is calcified.Alaskan king crab
Crustacea: body organization of a shrimpBody is divided into functional units (= tagmata): head, thorax – which are fused to form the cephalothorax, covered by the carapace, and abdomen6
Comparing the structure of different types of appendagesPhyllopodousStenopodousGeneralised function: locomotion, feeding, respiration, sensation, etc.More specialisedfunctions, fewer
Crustacean Classes1. Class Branchiopoda2. Class Ostracoda3. Class Copepoda4. Class Branchiura5. Infraclass Cirripedia(in Thecostraca)6. Class MalacostracaMalacostraca contains ~75% of known crustacean species, including most that are of direct economic benefit to humans, e.g. shrimps and crabs.Tree of Life
Recapitulation: trends in evolution of crustacean appendages•From phyllopodous to stenopodous•From biramous to (predominately) uniramous•From many to few•From generalism to specialism•From similarity to diversity (between species & within individuals)13
PHYLUM ARTHROPODASUBPHYLUM HEXAPODABIOL1309 Evolutionary DiversityMoriaki YasuharaPhoto by C. Yau: Common hedge blue butterfly
17SUBPHYLUM HEXAPODAFrom Greek meaning ‘six legs’.!Composed of Class Insecta(insects) and Class Entognatha.
181. Class Entognatha!Formerly “Wingless insects” are grouped as the class Apterygota within Insecta.!But, recent research revealed Apterygota is paraphyletic.!Then some of “Wingless insects” are grouped as the class Entognatha (outside of Insecta) under Hexapoda.