Subphylum: Crustacea

Subphylum: Crustacea

1. Body → 5-segmented cephalon (head) + multisegmented trunk

2. Cephalon → bearing: cephalic shield (carapace), 1st antennae (antennules), 2nd antennae, mandibles, maxillules & maxillae

3. Trunk → usually divided into thorax & abdomen

4. Antennal or maxillary glands → excretory nephridia

5. Both simple ocelli & compound eyes (often stalked) in most groups

6. Nauplius + additional larva stages (cypris, zoea, megalopa etc.)

7. Diversity → 5 classes, 46 orders, 68 000 sps

8. Classification

   • Class 1: Remipedia → 12 known living sps (in caves), small size (< 30 mm length), worm-shaped with body subdivided into: 1) cephalon & 2) long homonomous trunk (max 32 segments → each carrying 1 pair of flattened limbs (paddles)
   • Class 2: Cephalocarida → 10 known living sps, small 2-4 mm length, benthic marine dtritus feeders occurring from intertidal to deep waters (1500 m) Body → head + 8-segment thorax + 11-segment abdomen + telson & caudal rami; thoracopods biramous with epipod
   • Class 3: Branchiopoda → 900 known living sps, 0.5 mm to 10 cm long, mostly in freshwater with drought-resistant cysts
     • Order: Anostraca → fairy shrimps, e.g. Artemia salina
     • Order: Notostraca → tadpole shrimps, e.g. Triops spp. can destroy rice crops by burrowing and dislodging seedlings
     • Order: Diplostraca → clam shrimps (bivalved carapace hinged and completely encosing the body - benthic) & cladocerans (“water fleas”, carapace folded and never covering entire body - pelagic with cyclomorphosis, e.g. Daphnia)
   • Class 4: Malacostraca → 40 000 known living sps, uropods & telson forming a broad & flat tail fan - very diverse group, 14 orders (9 very important)
     • Order: Leptostraca → large carapace covering the whole thorax, 5 mm- 5 cm long, marine & adapted to hypoxic environments (intertidal, hydrothermal vents etc.)
     • Order: Stomatopoda → mantis shrimps, thoracopods 1-5 uniramous & subchelate with 2nd pair massive & raptorial → carnivorous predators; 2-30 cm long; burrowers in shallow tropical & subtropical marine systems
     • Order: Euphausiacea → krill shrimps, 4-15 cm long; pelagic & filter-feeders; often in large swarms → staple food item of baleen whales, marine birds & some fishes, e.g. Euphausia superba (Antarctic krill): 500 M-tons biomass
     • Order: Decapoda → 5 pairs of long uniramous pereopods (= decapods), 1-3 pairs usually chelate; well-developed carapace enclosing a branchial chamber; gills arising as thoracic coxal exites (epipods); complex order including true shrimps, crabs, lobsters & crayfish Sub-order: Dendrobranchiata → penaeid & sergestid shrimps, e.g. Penaeus indicus - important commercial sp
       • Infra-order: Caridea → caridean shrimps (2500 living species), 2nd abdominal pleura enlarged to overlap with 1st & 3rd pleura
       • Infra-order: Brachyura → true crabs (10 500 living species); abdomen highly reduced and flexed beneath the thorax; body hidden under well-developed carapace; 1st pereopods chelate & enlarged
       • Infra-order: Anomura → hermit & mole or sand crabs; abdomen soft and asymetrically twisted or short and flexed beneath the thorax; carapace & chelae not always well-developed
       • Infra-order: Astacidea → crayfish & clawed lobsters; 1st 3 pairs of pereopods always chelate, 1st pair greatly enlarged; mainly freshwater spp. but american lobster (Homarus americanus) is marine and largest crustacean by weight (> 20 Kg)
       • Infra-order: Palinura → spiny & slipper lobsters; all marine; produce sound by rubbing the plectrum (base of antennae) against a “file” on the head
       • Infra-order: Thalassinidea → mud prawns & ghost shrimps; marine burrowers with thin cuticle (why?); often form huge colonies on tidal flats, e.g. Callianassa craussi in SA estuaries
     • Order: Mysida → opossum or mysid shrimps (1000 sp); with flattened thoracic coxal endites (oostegites) forming a ventral brood pouch or marsupium; pereopods biramous; pelagic or demersal & form swarms
     • Order: Cumacea → large bulbous anterior and long, slender posterior part (1000 sp, 0.5-2 cm); benthic macrofaunal deposit feeders - no compound eyes
     • Order: Tanaidacea → 2nd thoracopods with large chelae (gnathopod);  1500 sp, 0.5-2 cm long; mainly part of marine benthos
     • Order: Isopoda → carapace absent, body dorso-ventrally flattened; 10 000 sp. (0.5 mm - 50 cm long); marine, freshwater & terrestrial (pillbugs & sowbugs with air sacs or pseudotracheae)
     • Order: Amphipoda → carapace absent, body laterally flattened; 8 000 sp. (1 mm - 25 cm long); marine, freshwater & semi-terrestrial; pelagic group hyperiidae associated with jellyfish, ctenophores & salps
       • Class 5: Maxillopoda → > 26 000 known living sps, small body and reduction in leg number (particularly on abdomen); compound eye with 3 cups, each with tapetal cells = maxillipodan eye; 7 sub-classes (3 very important) Sub-class: Thecostraca→ barnacles (Infraclass: Cirripedia)
         •  Sessile or parasitic;  Mantle producing calcareous plates;  Use of cirri (feathery thoracopods) in suspension-feeding;  Unique bivalved cypris larva with prehensile antennule for attaching to adult substratum
         • Sub-class: Copepoda → no carapace, but well-developed cephalic shield; 12 000 described species (0.5 mm - 1.5 cm long); body divided into cephalosome (cephalothorax), metasome (rest of thorax) & urosome (abdomen with no limbs); 3 main orders: Calanoida, Harpacticoida & Cyclopoida; dominate zooplankton biomass; mainly filter-feeders
         • Sub-class: Ostracoda → body entirely enclosed within the valves of the carapace (valves without concentric growth rings, unlike clam shrimps), have less limbs than any other crustacean (4-5 head + 1-3 trunk appendages); 13 000 living species (0.1 mm - 32 mm long) + 65 000 fossil species; mainly benthic crawlers, but many planktonic filter-feeders