Arthropoda: Pancrustacea (Cirripedia)

Question 1

Cirripedia General Characteristics

Answer 1

Sessile lifestyle (unusual in arthropods)
Carapace as calcified plates (not moulted)
Suspension feeding
Free-living and symbiotic forms

Question 2

Body Plan

Answer 2

No 2nd pair of antennae 
1 pair of mandibles 
2 pair of maxillae 
6 pair thoracopods (cirri)
NO abdomen

Question 3

Acorn barnacles

Answer 3

Calcified wall plates
Ventral opercular plates allow for opening
Cirri extend out ventrally to feed

Question 4

Stalked barnacles

Answer 4

Fleshy stalk on the bottom attaches barnacle to rocks
Also has hardened shell plates
Cirri extend out ventrally for feeding (thoracic appendage)
This stalk is called the peduncle (formed from the 1st pair of antennae)
Peduncle has a very narrow band of growth zone where the new cuticle is added (calcareous spicules contained within)
The peduncle is also muscular so it can match the water flow direction
The cuticle around the peduncle is not moulted

Question 5

Feeding

Answer 5

Suspension feeding by filtering
These are biramous and setose
Acorn barnacles rake these through the water to overcome the low Reynolds number
Gooseneck barnacles cannot rake their cirri, so they are restricted to high flow environments
The cirri exoskeleton is moulted

Question 6

Reproduction

Answer 6

Most are hermaphroditic (unusual among arthropods)
Very long penis (internal fertilization)
Gregarious settlement & metamorphosis
Important that they live in close proximity

Question 7

Larvae

Answer 7

Nauplius larva: has a naupliar eye, feed on phytoplankton and this moults
Cypris Larva (unique to Cirripedia): non-feeding, the sole purpose is to find substrate to metamorphose into adult
Uses 1st pair of antennae to walk over the substrate
Metamorphosis is induced by glycoproteins in the cuticle of adult barnacles

Question 8

Cement Glands

Answer 8

The cement gland has 2 different secretory cells
One secretes lipid and the other is a phosphoprotein
Lipids are secreted first to push water away, then the phosphoprotein forms attachment plaque in a non-aqueous environment

Question 9

Rhizocephalan Barnacles (dioecious)

Answer 9

Parasites on decapod malacostracans
Highly derived adult morphology
Manipulation of hosts behaviour
Female cypris injects cells into decapod host - grows through the body and absorbs nutrients from digestive tract and gonads
Forms an external that the decapod grooms much like an egg mass
Externa is fertilized by male cypris in the water column