Phylum Arthropoda Phylum Arthropoda Most “successful” lineage on Earth greatest biomass (>750 kg per person) numbers of species numbers of individuals number of ecological niches Phylum Arthropoda Subphylum Trilobitomorpha Class Trilobita Subphylum Chelicerata Class Merostomata Class Pycnogonida Class Arachnida Subphylum Mandibulata Class Crustacea Class Myriapoda Class Hexapoda From: Briggs & Fortey (2005) Wonderful strife: Systematics, stem groups, and the phylogenetic signal of the Cambrian radiation. Paleobiology supplement to Vol 31(2): 94-112 ARTHROPODA Why so successful? 1. Exoskeleton -allowed invasion of land & flight 2. Metamerism & limbs -allowed incredible limb modifications 3. Short life span & high fecundity -allows higher rates of evolution 1 Subphylum Chelicerata Subphylum Chelicerata Apomorphies • No antennae (lost) • Chelicerae • Two tagmata – Prosoma & Opisthosoma (no distinct head) Subphylum Chelicerata Subphylum Chelicerata Chelicerae Chelicerae first two appendages modified for chelate (pinching) feeding, clawed - not mandibles or venomous fangs or piercing stylets (for sucking body or plant juices) Sun scorpion Subphylum Chelicerata Pedipalps - 2nd pair of appendages modified for sensory perception communication catching prey conveying sperm (spiders) 2 Subphylum Chelicerata Pedipalps Subphylum Chelicerata Subphylum Chelicerata 12 appendages Three classes 1 pair of chelicerae • Merostomata 1 pair of pedipalps – relic, 4 species left 4 pair of walking /swimming legs • Pycnogonida (3 pair in immature mites & Ricinulei) (1st pair sensory in many groups = 3 pair for walking) – marine “sea spiders”, 1,000 spp. Most species are predators • Arachnida Most are liquid feeders (don’t chew) – spiders, scorpions, etc. 70,000 Gnathobases - grind prior to ingestion spp. Subphylum Chelicerata Subclass Xiphosura Class Merostomata Horseshoe crabs not crabs (not Crustaceans) Order Xiphosura - Horseshoe crabs closest extant relatives of • 4 species left (3 genera: NA, se Asia, Malaysia) eurypterids & trilobites – “living fossil” “evolutionary relic” “trilobite larva” • all marine, shallow (but oviposit on shoreline) • only chelicerates with compound eyes • primitive ! simple! 3 Class Arachnida 4 Class Arachnida Class Arachnida • primarily terrestrial (marine origin) Among the earliest animals on land – few mites & spiders secondarily aquatic – Tracks 460-500 mya ? (some mites parasitize marine animals & – Most activity from the Devonian (410- some live in deep ocean trenches) 360 mya) – Fossil mites, scorpions, spiders • ~ 93,000 species – 1 m long aquatic /amphibious scorpions • Most are spiders (37,000 spp) & mites (45,200 spp) Class Arachnida • Respiration via 2-4 pairs of book lungs and / or rudimentary tracheae - open via spiracles • Tracheae not homologous with those of other terrestrial arthropods (& not as efficient = lower metabolic rates) • Usually “sit & wait” predators Class Arachnida Class Arachnida Pumping stomach Species with tracheae rely less on blood for gas exchange (insects do not use blood for gas exchange) Book lung 5 Spermatophore Class Arachnida ~93,000 species Orders No. described spp. 1. Aranae ~37,000 2. Acari ~45,200 (~500,000 new?) 3. (Solifugae) Solpugida 1,065 4. Uropygi 101 5. Amblypygi 126 6. Opiliones ~4,500 7. Pseudoscopriones 3,100 8. Scorpiones 1,260 9. Schizomida 195 10. Rincinulei 53 11. Palpigradi 80 Life in the undergrowth Data from: Coddington, J. A. & Colwell, R. K. 2001. Arachnids, pp. We will focus on those indicated in bold 199-219 in Encyclopedia of Biodiversity vol. 1 Academic Press. Ricinulei Class Arachnida Order Araneae - 7th largest animal order • Spiders – Spinnerets, silk glands – Chelicerae modified into fangs - venom tubes – A few species dangerous to humans • Black widow, brown recluse, hobo(?) • Most spider “bites” are not – All predators, (on insects) SEM of Spider spinnerete & silk Gasteracantha sp. Silk proteins - Spider silk used for: prey capture safety lines egg sacks aerial dispersal lines air bags for diving One of the strongest & 5 times stronger than steel of toughest natural fibers same weight & more elastic Crab spider: known than nylon Thomisidae 6 Jumping spiders Salticidae . Orb-weavers Araneidae: Gasteracantha sp. Courtship dances by jumping spiders (Salticidae) Class Arachnida by Dr. W. Maddison (UBC) Order Acari • Mites & ticks – Hyperdiverse – ~ 1 million undescribed species – rival nematodes & beetles in species # – Many parasitic – Herbivores & predators 7 Class Arachnida Order Acari • Prosoma & opisthosoma ~ fused • Ticks - vector pathogens, e.g. • Lyme disease (Spirochaete bacteria) • Some plant pests • “Chiggers” & mange • Some aquatic spp. Class Arachnida Order Acari • Demodex folliculorum -the eyebrow mite -harmless, usually -cosmopolitan - < 0.4 mm Ixodidae: Amblyomma komodoense 8 Class Arachnida Phalangium opilo L. Order Opiliones – “Daddy long-legs,” “Harvestmen” – No venom – 4,500 spp – Tagma fused – Trachea only – Have penis – Can eat solids Class Arachnida Order Pseudoscorpiones – ~ 3,100 species – Predaceous, in leaf litter & crevices – Often phoretic on flying insects – 7mm or less, usually 5 or less – Pedipalps large, pincerlike, no tail – Poison glands in pedipalps 9 Class Arachnida Order Scorpiones – Terrestrial, largest bodied arachnid – Large, chelate pedipalps – 1,260 species – Poison gland in tail – Aquatic 425 mya – Terrestrial 400 mya – Nocturnal Phylum Arthropoda Subphylum Mandibulata Good with curry! 10 Phylum Arthropoda Subphylum Mandibulata Subphylum Trilobitomorpha ! Concept of Snodgrass 1930-1950s Class Trilobita ! Three classes Subphylum Chelicerata ! Class Merostomata ! • Myriapoda Class Pycnogonida ! – centipedes, millipedes, ~13,000 spp Class Arachnida ! • Crustacea Subphylum Mandibulata – shrimps, lobsters, etc. 45,000 spp. Class Myriapoda Class Crustacea • Hexapoda Class Hexapoda – insects, 1,000,000+ spp. Subphylum Mandibulata Subphylum Mandibulata Crustacea + Myriapoda + Insecta Apomorphy • Mandibles (biting jaws) –Shared development & genetics Crustacea Hexapoda (Diplura) Hexapoda (Thysanura) Mandibles - developed from limbs 11 Class Myriapoda Class Myriapoda Class Myriapoda Centipedes & Millipedes Centipedes - Chilopoda • 2,800 species (8,000 total?) Largely homonomous body • Terrestrial (some marine?) Direct development (no larvae) • Unwaxed cuticle & un-closable spiracles = moist habitats, nocturnal • Genital opening posterior <1 - 30 cm Class Myriapoda Geophilomorpha Centipedes - Chilopoda Soil Centipedes • Predators Common Defensively • Poison fangs (1st limbs on trunk) produce HCN gas No. body • One pair of legs per segments not body segment constant even in a species 12 Scolopendromorpha Scutigeromorpha Dorsal spiracles! Class Myriapoda Class Myriapoda Millipedes - Diplopoda Millipedes - Diplopoda • 7,000 species (80,000 total?) • No venom • Terrestrial • Trunk of diplosegments (2 segments fused) = 2 pair of legs per segment • Detritivores, herbivores • Many with calcium hardened cuticle (tough! • Genital opening anterior But also rare in acidic habitats) 13 Hexapods Phylum Arthropoda Subphylum Trilobitomorpha ! Class Trilobita ! Subphylum Chelicerata ! Class Merostomata ! Class Pycnogonida ! Class Arachnida ! Subphylum Mandibulata ! Class Crustacea ! Class Myriapoda ! Class Hexapoda Tagmosis & limb loss CLASS HEXAPODA in the Insecta Characteristics From hypothetical worm-like & myriapod- • 6 walking legs (each of up to 6 segments) like ancestors • 3 tagmata Note loss of limbs on • Cuticle tanned with sclerotin (a lightweight abdomen protein) Note incorporation of limbs as mouthparts • Abdomen originally of 11 segments CLASS HEXAPODA Reconstruction of Fossil History Rhyniella praecursor Among the oldest No marine fossil hexapods? (Crustaceans?) terrestrial animals Devonian (400 mya) Oldest fossil hexapods ~ 400 mya (Devonian) order Collembola - Rhynie chert of Scotland Rhyniella praecursor 14 Family richness In fossil record Order Collembola - Springtails Labandeira & Sepkoski 1993 Fossil record Phylogeny of the Hexapoda Collembola & Archeognatha Earliest Hexapods Fig. 8.1 Fig. 7.2 Phylogeny of basal Hexapoda Insecta Fig. 7.3 © Dave Walter 15 Ectognathy! Subclass & Order Protura • No antennae, wings, or eyes see. p.230-231 – (pseudoculus) • Entognathous mouth – (mouthparts inside cavity) • 400-600 species, 8 families ~ 48 species in North America © Dave Walter Subclass & Order Protura Subclass & Order Protura • Small (0.6-1.5 mm) • Inhabit soil, decaying vegetation, and rotting see. p.230-231 wood • Prolegs modified for sensory • Associated with fungus (thought to purposes feed on mycorrhizal fungi) • Tracheal system reduced • Rare in collections, no? specialist • Anamorphosis - autapomorphic. in North America Immature has few segments & more are added posteriorly during • Rarely seen alive - collected with development Berlese funnels (as are Diplurans) Functionally a tetrapod Subclass & Order Collembola • Abdomen reduced to 6 or fewer segments – Tracheal system reduced / absent • Entognathous mouth ( & no palps) – (mouthparts inside cavity) • 6,000-9,000 species, 700 in North America • Many undescribed spp. © Dave Walter 16 Subclass & Order Collembola Subclass & Order Collembola • Abdominal seg 1 has collophore • Ubiquity similar to Acari & nematodes – Used for many purposes, incl. osmoregulation – but not as many species • Furca - “spring tail” a forked jumping organ • Ubiquitous & abundant (100,000+ / m3 of surface soil & most common insect on Antarctica, -20m in fresh & marine habitats, •