Crustaceans

Question 1

crustacea

Answer 1

primarily aquatic - most marine, some fw, terrestrial

Question 2

Hard, but flexible, exoskeleton

Answer 2

grows by molting. prior to molting Ca reabsorbed - deposited in new cuticle

Question 3

Segmented (tagmatization)

Answer 3

(total number varies)
- head (6 segments fused)
- paired eyes
- Thorax (may be fused with head = cephalothorax
(those with cephalothorax often have carapace)
- abdomen
- post segmental telson
- each segment has a set of limbs

Question 4

Appendages primitively
branched (biramous)

Answer 4

May be modified but adults always have some
biramous appendages
- Gas exchange via general body surface and/or gills
(‘lung’ in terrestrial crabs)

Question 5

crustacea - overview

Answer 5

Some species highly developed osmoregulation and ion regulation

Nitrogenous excretion – ammonia (although terrestrial crabs can produce uric acid (like insects)

Fertilization mainly internal

Sexes separate (some hermaphrodism)

Question 6

Arthropoda systematics

Answer 6

Crustacea are paraphyletic

Single common crustacean ancestor which gave rise to Hexapoda (insects).

If true, insects are terrestrial crustaceans!

Millipedes and centipedes (Myriapoda) more closely related to the crustaceans than to Chelicerata.

Question 7

Xenocarida

Answer 7

Remipedia
not a primitive crustacean. Just retained a lot of primitive characteristics – 20+ species.
Little specialization in appendages
Described 1981: Central America Canaries, Caribbean, Australia). All found in caves connected to the sea.

Cephalocarida (horseshoe shrimp)
12 species – large head – no eyes
Sediment – intertidal to 1.5 km deep
Similar limbs and 2nd maxilla
No carapace or abdominal appendages
True hermaphrodites – unique in discharging eggs and sperm through same duct

Question 8

vericrustacea

Answer 8

Body form- extremely diverse
Internal anatomy relatively uniform

Class Malacostraca (29 k species)
Head/8 segmented thorax/6 segmented abdomen - each
segment with appendages - but also greatest diversity of
body forms in any one class!
Retention of basic
pattern,e.g. Hoplocarida
or mantis shrimps

Class Copepoda
(9 k species)
Most small (<2 mm).
3 of 10 groups free-living Dominant members of the plankton (calanoids and cyclopoids)
Herbivores e.g. Calanus
Carnivores e.g. Euchaeta

Two swimming speeds.
1. Slow, steady using mouthparts.
2. Succession of jumps separated by stillness. - appendages on thorax.