Exam II Rescheduled

• Exam II will be given on Thursday, April 27, instead of Thursday, April 20.
• Format will be the same as in Exam I.
• I will announce exactly what readings and lectures you will be responsible for as we approach the date.

Today's topic: Kings of the Sea Today

The Rise and Diversification of the Crustacea

• Mandibulate specializations:
• Specialization of appendages
• Tagmosis
• Evolution of Mandibles (Crustacea, Uniramia)
• Mandibulate synapomorphies
• Biramous appendages (Crustacea, Trilobites)

Kings of the Sea Today - The Rise and Diversification of the Crustacea

• Crustacea - Insects of the Sea
• Crustacean Synapomorphies
• 5 great evolutionary radiations in the early Paleozoic:
• Class Remipedia
• Class Cephalocarida
• Class Branchiopoda
• Class Maxillopoda
• Class Malacostraca

Phylum Arthropoda

• Synapomorphies
• Arthropod eyes
• Hard cuticle (>> must molt)
• Jointed appendages

Phylum Arthropoda

• In addition to this basic plan, the mandibulates (Crustacea, Uniramia) exhibit
• More specialization of serially homologous parts
• More extensive tagmosis

Mandibulate synapomorphies

• Include:
• Mandibles
• Maxillae on segments 4, 5

The Mandibulate hypothesis

• Evolution of mandibles
• Shared by Crustacea and Uniramia
• Derived from same segment
• Some differences in detail
• Monophyly of the Mandibulata widely accepted
• Relationships of Trilobites and Chelicerates are debated.

A closer look at mandibles

• Shared by Crustacea and Uniramia
• Derived from third segment
• Differ in details
• Crustacea - "Gnathobase jaws" (similar to chelicerates)
• Multiarticulate (several joints)
• Chew with bottom of Y
• Uniramia - "Whole arm jaws"
• Jaw a single element
• Chew with end

But biramous appendages ...

• Evolution of biramous appendages
• Y- shaped
• Shared by trilobites and crustaceans
• Lost or modified on some segments of crustaceans -- some appendages uniramous, some biramous, some triramous in certain groups

Crustacea - Insects of the Sea

• Crustacean synapomorphies:
• Gnathobasic mandibles
• Biramous 2nd antennae
  • Only Arthropod subphylum with two pairs of antennae
• Nauplius larvae

Crustacea - Insects of the Sea

• 5 great evolutionary radiations of Crustacea -- origins go back at least to Cambrian
• *Remipedia
• *Cephalacarida
• *Branchiopoda
• Maxillopoda
• Malacostraca
  *persist only in marginal refugia today

Crustacean Relationships

"Primitive" features of Crustacea (Classes Remepedia, Cephalocarida, some Branchiopoda)

• Elongate
• Many segments
• Morphologically similar structures repeated down length of body
• Many appendages:
• Swimming - Remipedes
• Suspension feeding - Cephalocarida, Branchiopoda

"Primitive" Crustaceans

• Class Remipedia
• Described in 1981
• 11 species
• Many trunk segments
• Repeated, biramous appendages along entire length of body
• Tropical island caves (Bahamas, Azores)

"Primitive" Crustaceans

• Class Cephalocarida
• Described in 1953
• 9 species
• < 0.5 cm
• 20 trunk segments, first eight bear appendages
• Buried compound eyes

"More advanced" Crustaceans

• Class Branchiopoda (intermediate -- also considered "primitive" in several features)
• Class Maxillopoda
• Class Malacostraca
• United by:
• Carapace
• Reduction in number of segments -- variously fused and lost
• Appendages reduced or lost on various tagmata

Class Branchiopoda

• About 800 species
• Mostly fresh water
• Gills on protopod
• Hence the name
• Flat leafy trunk appendages
• Suspension feeding
• Locomotion
• Gas exchange

Class Branchiopoda

• Carapace in most
• Includes:
• Sea Monkeys, fairy shrimp, brine shrimp
• Tadpole shrimp
• Cladocera (Daphnia)
• Ephemeral habitats or permanent fresh water (ponds, lakes)

Class Maxillopoda

• Very heterogeneous group
• Generally small in size
• Includes:
• Ostracods - seed shrimp
• Copepods
• Barnacles

Class Maxillopoda; Subclass Ostracoda

• 2000 species
• Body enclosed in carapace
• Mostly marine (bioluminescent!)
• Wide variety of habitats
• Mostly along bottom
• Some terrestrial in moss
• Up to 3 cm - Gigantocypris
• Fossils back to Cambrian

Class Maxillopoda; Subclass Copepoda

• 9000 spp.
• Small - usually < 5 mm
• Diversity of lifestyles
• Mostly marine plankton -- predators, herbivores
• Some parasitic, may be extremely modified
• Some damp terrestrial
• Ecologically important!

Class Maxillopoda; Subclass Cirrepedia

• Includes Barnacles (Cirrepedia)
• 900 spp.
• Usually small (some reach moderately large sizes)
• Sessile, aberrant: have lost head and abdomen (penis is all that remains)
• Previously viewed as molluscs (Darwin studied, recognized nauplius and unique cyprid larva)

Barnacle Reproduction

• Usually hermaphroditic, but copulate
• Tough for sessile organism
• Bisexual individuals with penis long enough to reach neighbors

Barnacle Development

• Usually brood eggs in "mantle" cavity
• Nauplius larva develops into unique "cyprid" larva
• Cyprid samples substrate and settles - cement glands at the base of the first antennae
• Deposits calcified carapace, molts chitin exokeleton (mantle cavity, legs) to grow

Barnacle Feeding

• "Nothing more than a little shrimp-like animal, standing on its head in a limestone house and kicking food into its mouth", L. Agassiz
• Well developed thoracic appendages = "cirri" = suspension feeders = filter feeders

Barnacles as commensals and parasites

• Attach to other organisms
• free ride
• free food
• Invade other organisms
• "Parasitic castrator"-- injects itself inside another crustacean, may manipulate host’s hormones, host cares for its eggs

Class Malacostraca

• Most successful crustaceans - diverse body sizes and life styles
• Long evolutionary history
• Much evolutionary experimentation in early Paleozoic; many earliest forms were scavengers/filter feeders; many Orders went extinct
• Several main groups (below) made it through the end-Paleozoic mass extinction and under-went reradiation in Mesozoic and again in Coenozoic (especially Eocene); several other Orders persist as thin threads in marginal refugia (ground water, caves, ephemeral fresh water)

Class Malacostraca

• Very diverse, but basic plan pretty conservative
• Five fused head segments
• Eight segments in thorax
• Abdomen usually six
• Rostrum, telson, uropods

Order Isopoda

• About 10,000 species
• 5000 aquatic, mostly marine, some fresh water
• 5000 terrestrial
• Group currently undergoing active diversification
• Dorsoventrally flattened
• No carapace
• Thoracic appendages: 1 pair maxillopeds, 7 pairs walking legs
• Brood pouch, no pelagic larva
• Varied lifestyles, many scavengers, some parasitic

Order Isopoda

• Terrestrial Isopods
• Pillbugs, sowbugs, etc.
• A pseudotracheal system
• Eat detritus, decomposers
• Brood and hatch live young
• Some (common garden varieties) have been introduced into North America

Order Isopoda

• Aquatic Isopods
• Both marine and fresh water
• Can be large - 0.5 m! in deep or cold environments
• Variously carnivorous, herbivorous, parasitic

Order Isopoda

• Parasitic Isopods

Order Amphipoda

• Similar to isopods
• No carapace
• Thoracic appendages: 1 pair maxiilipeds, 7 pairs legs, posterior ones used for walking
• Brood young, no pelagic larva
• But
• Laterally flattened
• Marine, fresh water,
  semi-terrestrial groups ("beach hoppers")
• Group currently undergoing active diversification

Order Amphipoda

• Often scavenging
• Can be parasitic
• Some bore into wood ("gribbles") with aid of symbiotic bacteria
• Some pelagic
• Some deep sea
• large size

Order Decapoda

• Includes:
• Shrimps
• Lobsters
• Crabs
• About 10,000 species
• Highly diverse
• Group currently undergoing active diversification
• Thorax: Three pairs of maxillopeds,
  Five pairs of walking legs (hence "Decapoda"),
  gills on bases of thoracic legs enclosed in carapace

Order Decapoda

• General Decapod trends:
• Laterally to Dorsoventrally flattened
• Pelagic to benthic
• Exoskeleton thin to thick
• Small to large (up to 4 m)
  • Most species are small, as in all other animals!

Order Decapoda

• Decapods display:
• Strong tagmosis
• Extensive specialization of appendages
  • Locomotion
  • Feeding
  • Defense/escape
  • Reproduction

Order Stomatopoda - mantis shrimps

• All marine, about 500 species; currently undergoing active diversification
• All strict carnivores
• An ancient group (one of early Malacostracan experiments -- lineage goes back to Devonian)
• Triramous antennules
• Carapace covers only first 5 segments
• Moveable rostrum
• Thoracic appendages:
• Five pairs maxillopeds --
  • Second pair enlarged into clubs or spears: Raptorial appendages
• 3 pairs walking legs
• Small gills on bases of thoracic legs (as in Decapods) but largest, most functional gills are on pleopods
• Large abdomen (important fishery in Japan, Mediterranean, South Pacific)
• Armored telson, roll up in ball for defense (like trilobite)

Order Stomatopoda - mantis shrimps

• Extremely active and extremely aggressive
• Reef species are highly colorful, have extremely elaborate, ritualized displays (mud and sand-dwelling species excavate U-shaped burrows that they can expand, are less colorful and less aggressive)
• Highly mobile compound eyes -- can detect more colors than humans can see, including UV
• Use club-like maxilloped claw to smash hard bodied prey (crabs, clams, snails) like a hammer, and fight to the death over holes in coral (territorial)
• Species that live in sand and mud habitats have spear-like maxilloped claw -- spear fish, worms, eels, other crustaceans

Why have crustaceans been so successful?

• Relative to trilobites and chelicerates, crustaceans (especially malacostracans) show:
• Extensive tagmosis
• Reduction of body segments
• Specialized appendages
• Especially mouthparts
• Diverse ways of feeding
• Highly efficient respiratory systems