crustaceans pt.2 Flashcards
class Malacostraca body characteristics
- Calcified exoskeleton
- Head (cephalon), thorax, abdomen and telson
- The head and thorax are fused into a cephalothorax - may be difficult to distinguish
- 5 segments in head, 8 in thorax, and 6 in abdomen
- Generally, each segment bears a pair of appendages
- Anterior 1-3 thoracic appendages are modified into maxillipeds (feeding)
- first five abdominal appendages = biramous
- last abdominal appendages, if present, = flattened and form a tail fin (telson)
class Malacostraca physiology
- Highly centralised nervous system
- Large brain is connected to a number of ganglia via a paired ventral nerve cord, which runs the length of the body
- Green glands in the second antennae - serve osmoregulatory + excretory function
- Disposal of nitrogenous wastes occurs across gills or body wall itself
- two-chambered stomach - possesses a grinding structure called the gastric mill
- Digestion occurs throughout gut - waste is expelled through anus on the telson
3 subclasses in class Malacostraca
- Subclass Phyllocarida
Oldest known crustaceans, 1 living group - Subclass Hoplocarida
Only extant members are in the order Stomatopoda (mantis shrimp) - Subclass Eumalacostraca
All others (crabs, lobsters, shrimp)
Order Stomatopoda characteristics
Mantis shrimps
- Fast, efficient predators
- Spearers – soft prey (e.g. fish)
- Clubbers – hard prey (molluscs, crustaceans)
- Complex behaviour (including monogamy in some spp.)
- Extraordinary colour vision – high dynamic range
what are the 3 superorders included in Subclass Eumalacostraca
- Superorder Syncarida
Freshwater - Superorder Peracarida
Isopods and amphipods - Superorder Eucarida
Crabs, shrimps
what are the 2 orders in Superorder Peracarida
order Isopoda (dorso-ventrally compressed)
order amphipoda (laterally compressed)
order Isopoda characteristics
- most successful terrestrial crustaceans
- benthic
- Pleopods used for gaseous exchange (highly developed in terrestrial forms)
- Numerous deep sea spp. (some get very large)
- Can be important parasites
order amphipoda characteristics
- No carapace
- Mostly marine, detritivores/scavengers
- Hyperiids (all planktonic)+ gammarids (90% of all amphipods, include sand hoppers)
- Some hyperiids (e.g. Phronima) live in “barrels” constructed from salps and other zooplankton
what are the 2 orders within Superorder Eucarida
- Order Euphausiacea
Krill - Order Decapoda
Crabs, lobsters, shrimp
Order Euphausiacea characteristics
- make up the greatest animal biomass (along with copepods)
- All marine
- Large exposed gills ventilated by thoracic appendages
- Larval stages may be vertically separated: ontogenetic vertical migration (seperation of different larval stages by death)
- Many have photophores (bioluminescence)
Order Decapoda characteristics
- Largest and most diverse group within Malacostraca
- Cephalothorax always covered by carapace, which forms a branchial chamber, protecting the gills
- Five pairs of pereopods (decapod) - First pair usually with claws (chelae): chelipeds
- crustacean appendages were originally biramous
- gills are the internal rami (ENDOPODITES) of the thoracic limbs
- EXOPODITE = external ramus (bit they walk around on)
explain decapod respiration in a crab
- Internal gills are protected by the carapace
- water enters at base of 1st leg (base of all walking legs in shrimp - looser carapace)
- Gill bailer circulates water around gills
- Water comes out through mouth
- use haemocyanin as respiratory pigment (although most O2 is still carried in solution) - allows animal to carry more O2
- Clogging of gills prevented by:
>setae on limbs act as filters
>cleaning of gills
>periodically gill-bailer reverses flow
explain reproduction in decapods
- Mating generally occurs after moulting
- Sexes attracted by pheromones
- Fertilisation internal in brachyurans (true crabs)
- Naupilus larval stage occurs in the egg in decapods
- Most other species, eggs are fertilised when laid
- Spermatophore deposited on sternal surface
- Marine species – hatch at protozoea and zoea stages
how to tell the difference between male and female crabs
Female crab = abdomen tucked under bellies – uses broad abdomen to carry eggs
Male crab = narrow and thinner telson (triangle shape)
Male lobster = hard between last pair of walking legs (transfer sperm)
Female lobster = soft and feathery between last pair of walking legs
explain chromatophores in Malacostraca
Chromatophore = branched but non-contractile pigment granules of several colours
1. Morphological colour change
- Long-term
- Loss or formation of pigments or chromatophores
2. Physiological colour change
- Rapid change in colour caused by changes in concentration or dispersion of granule
