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
explain reproduction in superorder Thoracica
- Adults = hermaphrodites but do not usually self-fertilise
- 6 naupliar stages followed by a cypris larvae
- These cyprids are non-feeding and fast moving, they follow physical and chemical cues to locate a suitable settlement site
what are the 2 ways copepods can live
- parasitic / associative (Both endo- and exo- parasitic forms)
- free-living
name a parasitic copepod
sea lice : Lepeophtheirus salmonis (Siphonostomatoida)
- The most damaging parasite to the salmon farming industry + Northern hemispheres, replaced by Caligus species in Southern hemisphere
- Use rasping mouthparts to graze host and remove mucus, skin and underlying tissues
explain free-living copepods
- Median nauplius eye even in adults
- Cephalothorax (head and first thoracic segment fused) contains both antennae and mouthparts
- 5 thoracic segments each with a pair of swimming legs = cephalosome or prosome
- Abdomen up to 5 segments and no appendages = Urosome
- Believed to be the most abundant metazoans
what is the thorax called in free-living copepods
cephalosome or prosome
what is the abdomen called in free-living copepods
Urosome
what are the 3 main areas Kiørboe (2011) attributes the competitive success of pelagic copepods to
- Surviving: body form allows rapid detection and escape from predators
- Feeding: Extremely efficient prey detection
- Mating: Efficient mate selection allowing sexual reproduction
planktonic copepod characteristics
calanoids and cyclopoids
- Very abundant
- Key grazers of phytoplankton
- Key food source for juvenile fish
explain the Development of calanoid copepods
- Normally 12 developmental stages, each separated by a moult:
6 nauplius stages (NI – NVI)
6 copepodite stages (CI – CVI) - Sexually mature adult is the last stage CVI
- Live 6-12 months
- Rate of development = variable between species (weeks – year)
- Reflects metabolic rate
- Ontogenetic vertical migration
explain feeding in calanoid + cyclopoids copepods
- Most species = omnivores
- Two main ways: ambush feeding + feeding-current feeding
- All pelagic cyclopoid copepods = ambush feeders
- Most pelagic calanoid copepods generate feeding currents - although some species (e.g. Acartia spp., Calanus pacificus) can switch between feeding modes
- Feeding appendages (and sometimes swimming legs) vibrate
- Feeding current is not passed through a filter but is instead a scanning current - prey in that feeding current are captured by the maxillae
