M13 Arthrapoda

Question 1

Arthropoda

Answer 1

21.04% of Kingdom Animalia. One of most diverse and old phyla (originated 541 mya). Shared characteristics are a segmented body, chitinous exoskeleton and jointed appendages.

Question 2

Subphyla

Answer 2

Success lie in adaptability, diverse forms, and niche occupancy
-Chelicerata (spiders, scorpions)
-Myriapoda (millipedes, centipedes)
-Hexapoda (insects, basically terrestrial crustaceans)
-Crustacea (crabs, lobsters)

Question 3

Crustaceans

Answer 3

-Hard but flexible exoskeleton, grown by molting. Before this Ca is reabsorbed and deposited in the new cuticle.
-Segmented = head is 6 fused segments, thorax, abdomen, no. of segments varies and there can be more complex combinations. Each segment has set of limbs.
-Appendages are branched (biramous), can be modified.
-Gas exchange via general body surface and/or the gills.

Question 4

Subphylum Crustacea, Superclass Allotriocarida: Class Remipedia 12 species

(Malacostraca, Copepoda, Ostracoda, Thecostraca, Pycnogonida)

Answer 4

(Horsehsoe shrimp)
-Large head, no eyes
-Sediment, intertidal and up to 1.5km deep
-Similar limbs, no carapace or abdominal appendages
-True hermaphrodites, unique discharching eggs and sperm through same duct
-Thought to still have primitive features from ancestral group

Question 5

Class Malacostraca: 29000 species

Answer 5

-Well-developed segmented body with distinct head, thorax (8 segments), abdomen (6 segments).
-Body form diversity.

Question 6

Class Copepoda: 9000 species

Answer 6

-Free-living, dominant members of plankton, many parasitic
-Two swimming speeds (slow with mouthparts, or jumps separated by stillness via appendages on thorax)
-Some feed on phytoplankton using maxillae

Question 7

Class Ostracoda

Answer 7

-Bilaterally symmetrical body in bivalve-like carapace, small <1mm
-Big head, body is reduced (sac-like and segmentation unclear)
-Two pairs of antennae, well developed and used for swimming. First thoracic limb for walking
-Marine, planktonic or benthic

Question 8

Class Thecostraca

Answer 8

(barnacles)
-Sessile adults with calcified shells, specialised cirri for feeing, anchored to substrates
-Head reduced, 1st antennae reduced 2nd absent, abdomen reduced
-Larval stages include nauplius and cypris. Undergo complex metamorphosis to settle as sessile adults
-Filter feeds via cirri fans, generate water currents to capture plankton

Question 9

Genus Xiphosura

Answer 9

-Class Merostomata (horsehoe crabs, only 4 living species, nocturnal, benthic in shallow waters)

Question 10

Class Pycnogonida: 1300 species

Answer 10

(sea spiders)
-Marine, benthic, part of Chelicerata, few mm to 100cm leg span
-Body divided into front part (cephalosoma) and trunk segments, with 4 pairs of legs. Front part has eyes, straw-like mouth and limb pairs, and the first pair of legs
-Carnivorous (feed on sponges, cnidarians and bryozoans)
-During mating, fertilised eggs are transferred from female to the ovigers of the male, where they are glued into packages with secretions of cement glands located in males segmented legs