ARTHROPODS

Arthropods Most diverse phylum - > 85% of all species All habitats – esp. extremes Segmented body w jointed appendages Chitin (polysaccharide) exoskeleton good protection requires molting prohibits large size

Phylum Arthropoda Subphylum Trilobitomorpha – Trilobites (Camb-Perm) Subphylum Chelicerata – Arachnids, Horseshoe crabs, Eurypterids (Ord-R) Subphylum Crustacea – Lobsters, crabs, shrimp, barnacles, ostracodes (Camb–R) Subphylum Tracheata (Unirama) – Insects (Dev–R)

Trilobites Cranidium = cephalon missing free cheeks

Sutures Opisthoparian Proparian Gonatoparian underside

Biramous legs

A. compound (holochroal) eyes B. schizochroal eyes Trilobite eyes A. compound (holochroal) eyes B. schizochroal eyes Huygens lens corrects spherical aberration

Subphylum Trilobitomorpha Class Trilobita Order Agnostida (Camb-O) Phylum Arthropoda Subphylum Trilobitomorpha Class Trilobita Order Agnostida (Camb-O) Order Redlichiida (Camb) Order Corynexochida (Camb) Order Ptychopariida (Camb-O) Order Asaphida (Camb-O) Order Illaenida (O-D) Order Trinucleida (O-S) Order Harpida (Camb-D) Order Phacopida (O-D) Order Lichida (O-D) Order Odontopleurida (O-D) Order Proetida (Camb-P)

Agnostid – Peronopsis small, isopygous, 2-3 thoracic segs, most blind Redlichiida – Olenellus & Paradoxides v. primitive, pygidium may not be fused, long genal spines, telson, O. sutures

Corynexochid – Basidechenella O. sutures, 7-8 thorax, Ptychoparid – Elrathia diverse, glabella tapers forward, straight g. furrows, many thorax., small pygidium

Asaphid – Isotelus snowplow shape, 6-9 thorax Illaenid – Illaenus smooth ceph & pyg, isopygous

Trinulceid – Cryptolithus small pyg and thorax, broad ornamented ceph brim, long genal spines (burrowing? Pelagic?) Harpid – Harpes broad smooth ceph, eyes on stems, many thoracic segs

Phacopids – Flexicalymene & Phacops P sutures, prominent eyes, enroll

Lichid – Amphilichas glabella to front of ceph, large pyg w 3 pairs spiny pleurae Odontopleurid – Dicranurus spines everywhere

Proetid – Anisopyge & Kaskia O. suture, large holochroal eyes, conservative

Trilobite ontogeny proaspid – A, B meraspid – C,D holaspid - E

Marine – swimmers, crawlers, burrowers, probably ate detritus Trilobite Ecology Marine – swimmers, crawlers, burrowers, probably ate detritus Trilobite Evolution Responded to most extinctions, conservative forms, burrowers survive best Late Ordovician extinctions wiped out many groups. Frasnian-Fammenian almost ended them, rare afterwards Good examples of iterative evolution

Phylum Arthropoda Subphylum Chelicerata Class Merostomata Subclass Eurypterida “Sea Scorpions” – largest known early Paleozoic predators (up to 2.5m) Subclass Xiphosura Horseshoe crabs

Varied forms compound eyes, telson Name refers to paddle legs swim and walk marine to brackish (fresh?)

Xiphosurans – “living fossil” Limulus Larvae called “trilobite larvae”

Phylum Arthropoda Subphylum Crustacea Class Malacostraca Order Decapoda – crabs, lobsters, crayfish, shrimp Class Maxillopoda Subclass Cirripeda – barnacles Subclass Ostracoda - ostracodes

Malacostraca - Decapods

Maxillopoda - Barnacles

Ostracodes – most small (Leperditids get up to several cm’s) Most benthic, v small planktonic Good environmental info