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Home , Appendage, Branchiopoda, Cephalocarida, Chelicerata, Form (botany), Malacostraca

Arthropoda - Lec. 4

Phylum Arthropoda today’s lecture • Characteristics –

• – phylogeny • Crustacea – richness – subclasses

Arthropod Nervous System Phylum Arthropoda Subphylum Trilobitomorpha √ Ventral, paired Class Trilobita √ nerve cord Subphylum √ Class Merostomata √ Dorsal “” of Class Pycnogonida √ 3 ganglia Class Arachnida √ Mandibulata Subphylum Mandibulata 2 ganglia Class Crustacea Class Chelicerata Class Insecta

1 Arthropod Nervous System Arthropod Nervous System

Cerebral Ganglia Deutocerebrum not in Protocerebrum - eyes Chelicerata - why? Deutocerebrum - antennae Tritocerebrum surrounds Tritocerebrum - 2nd antennae, esophagus mouth, locomotion

Arthropod Nervous System Arthropod Nervous System

• Paired • Strikingly similar to nervous segmental system ganglia – 3 lobes (cerebral ganglia) connected by – Circumesophogeal transverse – Paired, ladder-like ventral nerve cords commissures – Evidence for “Articulata”

• Fusion of • share many traits as well! ganglia in many – Evidence for groups

Subphylum Mandibulata Subphylum Mandibulata

Concept of Snodgrass 1930-1950s Three classes • Crustacea – , , etc. 45,000 spp. • Myriapoda Mandibulata is not universally accepted – , , ~13,000 spp • Insecta () – , 1,000,000+ spp.

2 Subphylum Mandibulata Subphylum Mandibulata

Crust. Myria. Insec. Myria. Crust. Insec. Crust. Myria. Insec. Myria. Crust. Insec.

Not clear how the mandibulates are related Atelocerata vs

No marine record for Myriapoda & Insecta vs DNA appear ~ 100 million years after Crustacea & Morphology

Subphylum Mandibulata Giribet et al. 2001

Nature Crustacea + Myriapoda + Insecta

8 + morphology Apomorphies Monophyletic • Mandibles (biting jaws) Mandibulata –Shared development & genetics

& • Ommatidia with retinula of 8 cells

Pancrustacea –Pg. 335 & 345 fig 14.7

Subphylum Mandibulata Subphylum Mandibulata expression - Distal-less (Dll)

Specifies distal part of

Confirmed all mandibulates use the gnathobase of the appendage

Mandibles - developed from limbs Supports hypothesis of Popadiac et al. Dev Genes & Evol. 1998

3 Comparison of heads Class Crustacea

Head segment Chelicerata Crustacea Insecta

I acron acron acron

II antennae1 antennae

III antennae2 hypopharynx?

IV mandible mandible

V legs1 maxillae1 maxillae

VI legs2 maxillae2 labium

Class Crustacea Class Crustacea

Apomorphies ? Nauplius - 3 pair single eye • Two pairs of antennae (2nd . lost in terrestrial lineages)

• Nauplius larva

Class Crustacea Class Crustacea

~ 45,000 species, mostly marine 3/4 of earth surface is covered by freshwater & damp terrestrial Greater morphological diversity than insects but far fewer species But only 15% of the Metazoan species (10 vs 2 subclasses) so far named are marine (275,000)

Seems contradictory - why? (This could be due to lack of study)

4 Class Crustacea Class Crustacea

Aquatic - body less constrained by Time - had ~ 150 million gravity and air = greater body form diversity year head-start on insects

Ecological niches - most of the ocean compare # phyla in ocean to land volume is not complex ecologically compare ratio of species to genera between islands and mainland

Distant island analogy Class Crustacea

Mainland Free-living, predators, Many genera with few species each e.g. 50 genera of 1-5 species Sessile, filter-feeders

Islands Parasites (including terrestrial) Few genera with many species each e.g. 4 genera of 20-50 species

Class Crustacea Biramous limbs seem to be associated with being aquatic & seem to be ancestral for Three tagmata head, thorax, Reduced to uniramous in Insecta & (head+thorax) under Myriapoda & terrestrial (Crustacea) or, head + trunk Biramous limbs

5 Class Crustacea Class Crustacea

Classification (text) Classification Subclass - 75% of spp 2 basal, evolutionary relic groups Subclass - few spp., freshwater Subclass - 9 spp Subclass Ostracoda - seed Subclass - 8 spp. Subclass Copepoda - Subclass - tongue worms 3 main, large groups Subclass Cirripedia - Subclass Branchiopoda - few spp., freshwater Subclass - copepods, barnacles = Maxillopoda Subclass Malacostraca - 75% of spp

Class Crustacea

Subclass Cephalocarida Thought to be sister to rest of Crustacea

< 4 mm, detritivores

9 species, discovered in 1955

Class Crustacea Gnathobases groove

Cross sec. Cephalocarid

6 Class Crustacea Class Crustacea

Subclass Remipedia Subclass Branchiopoda Described in 1981, cavern in Caribbean diverse, small, mostly freshwater, zooplankton homonomous body, primitive? often in temporary ponds < 3 cm, predators fairy, tadpole, & clam shrimp 8 species water , 800 species

Branchiopoda: Tadpole shrimp Class Crustacea

Subclass Maxillopoda Sessile, parasitic, planktonic

Extremely diverse

mostly marine

~ 15,000 species

Class Crustacea Class Crustacea

Subclass Maxillopoda Copepods Copepods -no abdominal limbs -8,500 species lice -most planktonic,

Ostracods marine -25% parasitic Barnacles -huge biomass - base of food chain

Tongue worms -most with single eye

7 Fish Louse, Branchiurans - 130 species, “” Class Crustacea

Ostracods - seed shrimp -carapace encloses body -2000 species, most marine -benthic & planktonic

Class Crustacea

Barnacles - Cirripedes -secret calcareous shell -sessile -some parasites -1,000 species

Class Crustacea Tongue worms Tongue worms -parasites of -in lungs or nasal passages -95 species -4 + mouth -annelid-like, odd -larva & DNA =Crustacean

8 You should be able to (at a minimum): Terms

Paired Nauplius larva • Describe the arthropod nervous system, Protocerebrum Subclass Cephalocarida compare chelicerates to mandibulates Deutocerebrum Subclass Remipedia Tritocerebrum Subclass Branchiopoda Transverse commisures Subclass Maxillopoda • Describe the Mandibulata Fused ganglia Subclass Malacostraca Circumesophogeal Fairy, tadpole & Class Crustacea Water fleas • Contrast the species & subclass diversity of Class Myriapoda Copepods Crustacea to Insecta & explain why Class Insecta (Hexapoda) Barnacles Subphylum Mandibulata Fish lice • Describe the Crustacea Atelocerata Seed shrimp –Characteristics Pancrustacea Tongue worms –Groups, styles, habitat, etc. Mandibles retinula

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