class malacostraca - crabs, shrimps, lobsters class maxillopoda - ostracods, barnacles, copepods...
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Class Malacostraca - crabs, shrimps, lobsters
Class Maxillopoda - ostracods, barnacles, copepods
Class Branchiopoda - brine shrimp, tadpole shrimp
Class Remipedia - small cave-dwellers; basal lineage
Class Cephalocarida - small benthic detritivores; basal
SubPhylum Crustacea
Class Malacostraca SuperOrder Peracarida
- carapace reduced in size
- unique endites called oostegites (brood pouch, or marsupium)
- direct development, which helped colonize land: bypass a planktonic larval stage, mother broods young & releases fully developed juveniles
Order Mysida (opossum shrimp)
Order Isopoda (isopods) made it onto land
Order Amphipoda (amphipods)
Class Malacostraca SuperOrder Peracarida
Order Mysida (opposum shrimp)
- well developed carapace covering head+thorax segments
- pelagic, intertidal, or burrowing
- often form benthic “swarms,” which are small clouds of tiny shrimp that hide among urchin spines for protection
brood pouch where young develop
Class Malacostraca SuperOrder Peracarida
Order Isopoda >10,000 species
- no carapace: you can see each segment from above- one lineage successfully colonized dry land: the pill bugs- pereopods are very structurally variable- pleopods used in gas exchange
Cirolana
rock lousekelp isopod
Class Malacostraca SuperOrder Peracarida
Order Amphipoda 8,000 species
- no carapace
- includes semi-terrestrial “beach hoppers”
- thoracic gills are epipods, extensions of pereopods
Decapods typically brood their larvae to a well developed, large-eyed zoea larva capable of fast swimming and active behaviors, which can help larvae migrate in & out of estuaries
After several molts, the final megalopa larva is produced, which looks very much like the adult - except in crabs, the abdomen is not yet tucked under the thorax
Decapod Larvae
crabzoea
stomatopod(mantis shrimp)megalopa
Class Malacostraca - crabs, shrimps, lobsters
Class Maxillopoda - ostracods, barnacles, copepods
Class Branchiopoda - brine shrimp, tadpole shrimp
Class Remipedia - small cave-dwellers; basal lineage
Class Cephalocarida - small benthic detritivores; basal
SubPhylum Crustacea
barnacles, copepods, ostracods
Class Maxillopoda
Head (5 segments)Thorax (6)Abdomen (4)
- usually biramous limbs; no abdominal appendages
- mostly small; reduced abdomen, missing some legs
Subclasses: Thecostraca (barnacles) Copepoda Ostracoda
26,000 spp.
free-living (acorn, gooseneck)
parasitic on crustaceans
Class Maxillopoda: SubClass Thecostraca
Free-living barnacles Parasitic Rhizocephalans- hermaphrodites - separate sexes- carapace produces shell - carapace lost- suspension feeders - endoparasites w/ interna
and externa
Capitulum
Cirri
Peduncle
ScutumTergum
ExternaRootlets oframifying body
- in adult barnacles, the appendages on the thorax (= thoracic legs, or cirri) are similar in appearance to tentacles of filter-feeding worms and crinoids (to come later)
- used to filter feed: scutum and tergum plates open in response to water current, cirri extended up into water, then rapidly retracted inside shell over and over again
Antennule
Antenna
Mandible
Naupliareye
Nauplius Larval Stage
antennules, antennae, mandibles; no segmentation; single eye- successive molts: remaining head, thoracic appendages
Unique feature of barnacles: non-feeding cyprid larval stage which follows the nauplius stage
- has a bivalved shell, and swims using antennae
- in free-living barnacles, cyprid glues its head onto the first suitable hard surface it encounters
Cyprid Larvae
Cyprid attaching, cementing itself head-first to substrate
become cirri of adult
- cephalic “shield”- keep single naupliar eye- primary consumer of phytoplankton- tiny; swim by flicking antennae
Class Maxillopoda: SubClass Copepoda - 8,500 spp.
Caudal rami
Ovisac(clump of embryos)
articulation point(attachment of thorax to abdomen)
Antennule
Antenna
Naupliar eye
Class Maxillopoda: SubClass Copepoda - 8,500 spp.
In males, 1st antennae and 5th thorax limb may be specially modified for “mate guarding” behaviors
- males locate, grab and ride around holding a virgin female before her terminal (final) molt
- this way, they ensure they are the male who will fertilize her eggs when she molts, and is then ready to mate
Class Maxillopoda: SubClass Ostracoda - 6,600 spp.
- bivalved carapace (how many independent origins of a bivalved shell have we seen now??..)
- reduced segmentation; body not split into thorax + abdomen
- 5 head appendages + 1-3 thoracic appendages, including male copulatory limb-- fewest limbs of any crustacean
- many are bioluminescent, using light flashes in complex mating rituals
- swim using antennae
Class Malacostraca - Crabs, shrimps, lobsters
Class Maxillopoda - Ostracods, barnacles, copepods
Class Branchiopoda - Brine shrimp, tadpole shrimp
Class Remipedia - small cave-dwellers; basal lineage
Class Cephalocarida - small benthic detritivores; basal
SubPhylum Crustacea
Class Branchiopoda
Notostracans: tadpole shrimp Anostracans: fairy shrimp
Artemia,brine shrimp
no carapace
telson
carapace
caudalramus
often inhabit freshwater vernal pools (temporary)
Sow bugs (terrestrial isopods) are most successful group
- direct development cut ties to the sea
Crustaceans on Land
Land crabs must still return to the ocean to spawn
1. 2.
3. Insects – molecular evidence indicates the most successful animal lineage evolved from a crustacean ancestor
Regier et al. 2010, Nature
Analysis of 62 genes redefined arthropod relationships
(1) Insects are nested within the“Crustacea”, which is therefore a paraphyletic group!
New name, “Pancrustacea”, refers to crustaceans + insects
Regier et al. 2010, Nature
(1) Insects are nested within the“Crustacea”, which is therefore a paraphyletic group!
2) Maxillopoda not a true group
- barnacles, copepods & ostracods do not form a clade
- despite sharing the same “formula” for body segments, these are all unrelated groups
Regier et al. 2010, Nature
Insects are nested within the“crustacea”, which is therefore a paraphyletic group!
2) Maxillopoda not a true group
2a – barnacles are sister to Malacostraca (crabs, etc)
2b – copepods are sister to (Malacostraca + barnacles)
2c – ostracods are basal to rest of Crustacea
Tardigrades
Onychophorans
Arthropods
Ecdysozoa
Priapulids
Kinorhynchs
Loriciferans
Nematodes
Nematomorphs
- clade Ecdysozoa was named in 1997 from an analysis of 18S ribosomal RNA gene
- members all molt to grow, controlled by hormone ecdysone
- microscopic 8-legged “water bears” from semi-aquatic habitats prone to drying out (e.g. moss)
- display extreme cryptobiosis when environments dry out: the ability to enter a state of suspended animation, with no metabolism or apparent ageing, until conditions improve
- 4 pairs of unjointed legs
- uncalcified cuticle lines parts of gut
- main cavity = hemocoel; no gills, respire across wet body wall
Phylum Tardigrada - “water bears”3 Orders, 10 Families ~ 800 species
Cryptobiosis in Tardigrades
During environmental stress, legs are pulled and body coated in a double-walled cuticular envelope, forming a cyst
Then, a single-walled tun state develops, where metabolism is undetectable and individuals can survive long periods of dessication (= dryness)
Tuns have survived… - up to 10 years without water - complete vacuum, long periods with no oxygen - temperatures near absolute zero: 8 hr at -272°C !! - toxic liquids (ether, 100% alcohol)
Allows tardigrades to persist in an unstable ecological niche
styletused topunchholesin plantsor algae;then tardigrade sucks out cytoplsm
mostly feed on plants, algae
convergent evolution: very similar to the single tooth and method of feeding in sacoglossan sea slugs (my group, the herbivores)
Tardigrades
Onychophorans
Arthropods
Ecdysozoa
Priapulids
Kinorhynchs
Loriciferans
Nematodes
Nematomorphs
clade Cycloneuralia– brain forms a loop around esophagus– anterior end = introvert, which can be withdrawn into body
Cycloneuralia
Tardigrades
Onychophorans
Arthropods
Ecdysozoa
Priapulids
Kinorhynchs
Loriciferans
Nematodes
Nematomorphs
clade Cephalorhyncha
– spiny collar of scalids around the introvert
Cephalorhyncha
Phylum Nematoda ~25,000species
- body round in cross-section, but no circular muscles; longitudinal muscles let them thrash around to move
- covered in cuticle, shed in 4 molts during juvenile growth allows survival in hostile environments
- extensions of muscles called muscle arms branch out to contact neurons, instead of other way ‘round like most animals
- unique excretory system featuring renette cells; no circulatory structures
Includes model organism for developmental biology, C. elegans
Phylum Nematoda
Ecological importance:
- tremendously abundant decomposers - 200 per ml of coastal mud - 90,000 per rotting apple - 9 billion per acre of soil
Medical importance: - cuticle allows them to resist immune system, function as endoparasites (endo = living inside the host’s body)
- parasitic forms cause diseases including river blindness, elephantiasis, trichinosis
Nematomorphs – “horsehair worms”
- long thin body encased in well-developed cuticle
- over 1 meter long, less than 1 mm wide
- no apparent segmentation
- all growth accomplished by larvae, which are parasites in
arthropod hosts
- gut, but no mouth; nutrients are
absorbed from insect host across
body wall, taken up by gut tissue
~320species
Priapulids - benthic marine “worms”
- introvert with hooked spines
- complete gut, protonephridia for excretion
- no circulatory system
- thin cuticle surrounds body
- loricate larva has special cuticle that’s
shed at metamorphosis
18 species
Introvert
Trunkrings
Caudal appendages
Phylum Kinorhyncha- all marine; interstitial = live between grains of mud or sand
- body with 13 segments: head, neck, and 11-segment trunk
- no cilia; crawl by extending head, locking spines in place
- head = introvert; can retract into neck
- ring of backward-facing spines (scalids) used to lock body in
place when crawling
convergent evolution with how annelids use chetae to dig
- well-developed cuticle
- no larval stage!
~ 180 species
Phylum Kinorhyncha
Phylum Loricifera- all marine; only discovered in 1983!
- body tiny (< 0.5 mm) but complex (>10,000 cells)
- head with piercing stylets around mouth
- head, neck + thorax retract into abdomen
- 9 rings of spines called scalids
- complete gut, but no circulatory system
or nephridia
~ 100 species
Phylum Loricifera
Head
Thorax
Abdomen