crustaceans Flashcards
what are the the 6 classes in subphylum crustacea
Class Branchiopoda
Class Cephalocarida
Class Remipedia
Class Cirripedia
Class Copepoda
Class Malacostraca
crustacean characteristics
- Eucoelomic (true coelom)
- Segmentation - usually 16-20 body segments
- Most crustacean possess a cephalothorax + muscular abdomen
- Ancestrally biramous appendages
- chitinous body wall and reinforced with calcium carbonate to form a rigid exoskeleton
- Carapace = shell covering the cephalothorax
- Well-developed head and sensory organs
- Two pairs of antennae (distinguishes them from all other arthropods)
- Three pairs of mouth-part appendages
what is specialised segmentation
head is fused to the thorax = cephalothorax
explain reproduction in crustaceans
- gonochoristic (except the sessile Cirripedia)
- Nauplius larvae (characteristic feature of Crustacea)
- Succession of specialised instars then follows
explain internal transport in crustaceans
- Open circulatory system (no true blood vessels) – haemolymph
- O2 transported in a simple solution or bound to a respiratory pigment (haemoglobin or haemocyanin)
explain gas exchange in crustaceans
- Gas exchange organs usually gills - vary in form, location and derivation
- Respiratory water current provided by appendages
what are the 2 different types of eyes crustaceans can have
- median eye
- compound eye
explain the median eye
- Characteristic of some larval stages (often called a nauplius eye)
- May degenerate in the adult stage
- Persists in adults of some species that are small (e.g. copepods)
- Probably used for orientation
explain the compound eye
- Two, either side of head
- Image cruder than human eye
- Some ability to distinguish form and size
- Colour discrimination (e.g. stomatopods)
what is ecdysis
moulting
explain ecdysis in crustaceans
- To grow, arthropods must periodically moult their exoskeleton
- In crustaceans, this forces hormone-controlled resorption of calcium salts and their redeposition in the new outer chitinous skeleton
- Moult frequency decreases with age and body
size in many crustaceans (especially
malacostracans)
Class Branchiopoda characteristics
Fairy shrimps – mostly small freshwater forms, including Artemia salina
what’s the order within Class Branchiopoda
Order Cladocera
- Water fleas
- Show cyclical parthenogenesis - don’t need to mate when conditions are good – just produce female clones
what’s the 3 superorders within Class Cirripedia (barnacles) and what are they
- Acrothoracica (burrow into calcareous material, e.g shells, corals) - use this as their shells
- Rhizocephala (all parasitic)
- Thoracica (acorn and stalked barnacles)
class Thoracica characteristics
- Order Sessilia: acorn barnacles
- Order Pedunculata: goose barnacles
- Morphology of adults = shrimp that has cemented its head to a rock and grown plates around itself
- Sessile suspension feeders that use modified legs (cirri) to generate a feeding current
- Ecologically very important, especially on rocky shores
- Very important biofouling organisms
- Pollicipes pollicipes is a delicacy in Spain and Portugal
