BIO 385 — Invertebrate Zoology
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Invertebrate Diversity
Arthropod Relatives & Trilobites

(Click on any image for larger version)

Phylum Onychophora — Velvet Worms

Characteristics

  • Caterpillar-like, 5 mm - 15 cm long
  • Numerous paired, unjointed lobopods (legs)
  • Head appendages: antennae, jaws, oral papillae
  • Thin, chitinous cuticle is molted
  • Covered in fine tubercles (sensory papillae), giving velvet-like appearance
  • Produce sticky slime to capture prey
  • Terrestrial in moist tropical forests
Velvet Worm
Closeup of head of a preserved velvet worm, Peripatoides sp.
See also labeled photo.
Velvet Worm
Velvet Worm, Peripatoides sp., preserved specimen
Extinct
Possible Onychophorans (lobopods) from the Cambrian Period (labeled in larger image; not to scale)

Phylum Tardigrada — Water Bears

Characteristics

  • Small (< 0.5mm), stubby-bodied
  • 8 short, clawed legs
  • Have a slow, lumbering gait
  • Chitinous cuticle that is molted
  • Oral stylets for piercing plants
  • Most in moist film on lichens, mosses, and other small plants
  • Capable of cryptobiosis: suspended animation to withstand drying
  • Video of a marine heterotardigrade
Water Bear
Water Bear, probably Hypsibius sp. (Class Eutardigrada)
Water Bear
Water Bear, probably Hypsibius sp.
Marine Tardigrade
Marine tardigrade (Class Heterotardigrada)

Phylum/Class Dinocaridida — Dinocarids

Characteristics

  • Extinct; Primarily from Cambrian Period but one species survived into Devonian Period
  • Segmented with broad lateral lobes
  • Well-developed eyes (either 2 or 5)
  • Ventral mouth
  • Segmented feeding appendage(s)
  • Anomalocarids included the largest predators of their time
  • Sometimes considered a Class within Phylum Arthropoda
Anomalocarids
Radiodontids exhibit a diversity of feeding styles and persisted into the Devonian Period. Large image identifies genera, along with diet and geological period.
Opabinia
Two unusual basal Dinocaridids from the Cambrian Period: Opabinia (top) and Kerygmachela (bottom)
Opabinia Fossil
Fossil replica of Opabinia, from Burgess Shale, Cambrian Period


Phylum Arthropoda — Class Trilobita

Characteristics

  • Extinct, but diverse fossil forms from 540-252 Ma
  • Body divided into median and 2 lateral lobes by 2 longitudinal furrows
  • Anterior cephalon (and in most, posterior pydigium) covered by platelike shields
  • Segmentation visible in middle section (thorax)
  • Appendages biramous (branched)
  • Photos at right are organized by geological time period and Orders
See additional trilobite fossils here

Cambrian Period:
Trilobite Model
Life model of the Cambrian trilobite Olenoides sp. (Order Corynexochida)
See also labeled photo.
Naraoia Stem-Trilobite
Naraoia spinosa head shield (Order Nektaspida; a stem-trilobite); Cambrian Period, China
Trilobite
Trilobite fossil, Elrathia kingi (Order Ptychopariida); Cambrian Period, UT
Diacalymene Trilobite
Trilobite fossil, Cambropallas telesto (Order Redlichiida); Cambrian Period, Morocco
Oryctocephalus Trilobite
Cephalon (head shield) of Oryctocephalus indicus (Order Corynexochida); Cambrian Period, Nevada
Trilobite
Agnostid Trilobite fossil, Ptychagnostus sp. (Order Agnostida); Cambrian Period, UT

Ordovician Period:
Trilobite
Trilobite fossil, Declivolithus titan (Order Asaphida); Ordovician Period, Morocco
Flexicalymene Trilobite
Trilobite fossil, Flexicalymene retrorsa (Order Phacopida); Ordovician Period, Ohio
Ampyx Trilobites
At least four Ampyx priscus trilobites in a migratory chain (Order Trinucleida); Ordovician Period, Morocco

Devonian Period:
Chotecops Trilobite
Trilobite fossil, Chotecops ferdinandi (Order Phacopida); Devonian Period, Germany
Akantharges Trilobite
Trilobite fossil, Akantharges mbareki (Order Lichida); Devonian Period, Morocco
Trilobite
Trilobite fossil, Cyphaspis sp. (Order Proetida); Devonian Period, Morocco
Harpes Trilobite
Trilobite fossil, Harpes perradiatus (Order Harpetida); Devonian Period, Morocco
Dicranurus Trilobite
Trilobite fossil, Dicranurus monstrosus (Order Odontopleurida); Devonian Period, Morocco
Paralejurus Trilobite
Trilobite fossil, Paralejurus sp.? (Order Corynexochida); Devonian Period

Carboniferous Period:
Kaskia Trilobite
Enrolled trilobite fossil, Kaskia sp., in right lateral view (Order Proetida); Carboniferous Period, AL
This page last updated 13 May 2023 by Udo M. Savalli ()
Images and text © Udo M. Savalli. All rights reserved.