Crustaceans

Question 1

Primitive condition body form

Answer 1

Predominantly marine, some FW, some terrestrial
-head and trunk region
-has lots of appendages that are the same
-has 2 pairs of antennae (like most)
Segments undifferentiated and are used for both food and respiration (primitive)
See lots of modification of this form among crustaceans
Hox genes have led to Tagmatisation and adaptive radiation of appendages

Question 2

Biramous appendages

Answer 2

2 branches - like trilobites
Filamentous branch, gill-like structure
Walking leg
In some the differences are less obvious, but should still be able to see 2 parts
In more rounded and stumpy appendages, both parts are involved in gas exchange and swimming
Filamentous branch can be enclosed in a chamber (seen in crabs)

Question 3

Crayfish example - Malacostraca morphology

Answer 3

Head and thorax - joined to form cephalothorax
-covered in carapace
Appendages change dependent on where they are
-head = antennae + compound eyes
-thoracic = claw and walking legs
-pleopods used for swimming on abdomen or holding onto eggs
-tail used for swimming too
Mandibles are used as grinding surface for feeding
-1st and 2nd maxilla used for food processing
-thoracic legs become maxillipeds in processes food

Question 4

Daphnia structure

Answer 4

Tiny abdomen
Mainly composed of thorax
Whole animal enclosed in carapace - see-through and splits down middle
Can open carapace to let water in
-legs on thorax for food gathering and respiration
-legs pass food to mouth
2 pairs of antennae - 2nd well-developed and huge, used for swimming (1st pair reduced)
Single compound eye caused by fusion of eyes in the past

Question 5

Daphnia reproduction

Answer 5

Gives birth to offspring which are genetically identical to mother - parthenogenesis
(when conditions are favourable)
Reproduce sexually when conditions are changing/unfavourable (ponds freezing or drying out)
-forms eggs that drop to bottom of pond
-stay resting till conditions improve

Question 6

Barnacle features

Answer 6

Sits on back, head cemented down into shell enclosure of calcium salts
Mainly thorax
6 thoracic appendages -3 long and gather food and respiration
-3 short and get passed food to pass to mouth
No abdomen, hox gene Abdominal-A lost
Hermaphrodites
Internal fertilisation
Trade-off with legs and penis, for length for reaching and wave action

Question 7

DR - barnacle penises

Answer 7

Diverse penis form that varies according to tidal patterns of environment
Display phenotypic plasticity and vary widely from group-to-group
Those in more wave exposed coasts will have shorter, thicker penises - enabling them to control in harsh water flow
Variability down to constraints in needing to control it but needing to reach enough mates
-risk of it just varying due to leg length though

Question 8

Examples of barnacles

Answer 8

Goose barnacles - stalked version
Darwins barnacles - looking at larval stage discovered they weren’t molluscs
Parasitic barnacles - latches onto crabs and grows into crabs body
-goes for reproductive system, attacking adrenal glands and will feminise the crab (if M)
-changes behaviour acting as if it had its own young - aiding in dispersal of barnacles eggs

Question 9

Crustacean reproduction examples

Answer 9

Gammarus - shrimps mate guard (precopulatory mate guarding)
-carries F in precopulam can only mate when she moults and is soft
-F give off certain smell before moulting triggering behaviour in M
-M fight to access F
Crabs with enlarged claws - F more attracted if big and can move quick
-stays next to and protects smaller Ms = looks good