BIO 385 — Invertebrate Zoology
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Invertebrate Diversity
Phylum Mollusca
Class Cephalopoda

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Cephalopod Characteristics

  • Shell chambered (if present), reduced, or absent
  • Prehensile tentacles surround mouth
  • Mouth with radula and beak
  • Muscular siphon provides jet propulsion
  • Well developed brain, eyes
  • Closed circulatory system
  • Marine
More Cephalopod Fossils

Subclass Nautiloidea — Nautiluses


Characteristics

  • Shell chambered (coiled in extant forms, but straight in many fossil forms)
  • 80-90 tentacles surround mouth
  • Shell chambers connected by central siphuncle
  • 6 extant species
  • Marine environments, primarily deep water
  • With fossil groups, may not be monophyletic
Chambered Nautilus
Chambered Nautilus, Nautilus pompilius
Chambered Nautilus Shell
Median slice of a Chambered Nautilus, Nautilus pompilius, shell
Nautiloid fossil
Cut fossil of Cymatoceras sp. nautiloid (Madagascar; Cretaceous); note the siphuncle
Geisomoceras fossil
Fossil Geisonoceras sp., polished (Morocco; Devonian)
Nautiloid fossil
Internal mold of Nautiloid (Kentucky; Ordovician); note gaps (septa) are straight
Nautiloid Models
Models of possible life appearance of some Paleozoic nautiloids

Subclass Ammonoidea: Ammonites


Characteristics:

  • Extinct
  • Chambered shell; sutures that divide chambers have complex shapes
  • Shell usually coiled (but there are exceptions)
  • External shell often marked with knobs and ridges

More Ammonite Fossils


Pleuroceras Ammonite
Ammonite fossil, Pleuroceras sp., with pyrite replacement of original shell (Germany; Early Jurassic Period)
Binatisphinctes Ammonite
Ammonite fossil, Binatisphinctes rjasanensis, showing external shell and shape of septum (Russia; Late Jurassic Period)
Perisphinctes Ammonite
Ammonite fossil, Perisphinctes sp., showing external structure (Late Cretaceous Period, SD)
Ammonite Models
Models of possible life appearance of various ammonites showing diversity. The top row are typical monomorph ammonites while the rest are heteromorph ammonites. Not to scale.
Ammonite 3d sutures
Model of a half shell of the Ammonite Phylloceras, showing the complex shapes of the septa
Cleoniceras Ammonite
Ammonite fossil, Cleoniceras sp., showing sutures (Madagascar; late Cretaceous Period)
Ammonite
Ammonite fossil Craspedites nodiger, showing sutures (Russia; Jurassic Period)
Cut Ammonite
Cleoniceras sp. ammonite fossil cut to show chambers (Madagascar, early Cretaceous)
Dactylioceras Ammonite
Dactylioceras sp. ammonite fossil (Germany, early Jurassic)
Baculites Ammonite
Part of an unusual straight-shelled ammonite, Baculites compressus, but note complex suture shapes that distinguish it from straight nautiloids (Late Cretaceous Period, SD)
Nostoceras Amonite model
Fossil and model of possible life appearance of Nostoceras sp., a heteromorph ammonite
Crioceratites Amonite
Crioceratites duvali, a heteromorph ammonite that is loosely coiled (Early Cretaceous Period, France)
Hamites Ammonite
A heteromorph ammonite, Hamites maximus (Early Cretaceous Period, France)

Subclass Coleoidea: Squid, Octopuses, & Relatives


Characteristics:

  • Shell absent or reduced and internal
  • 8-10 tentacles/arms with suckers
  • Force water from siphon for jet propulsion
  • Release ink to confuse/deter potential predators
  • All are predators
  • All are marine
Large Squid Dissection
Dissections of large, fresh squid, probably Ommastrephes bartramii
See also labeled photo.
Small Squid Dissection
Dissections of small, fresh squid, probably Doryteuthis sp.
See also labeled photo.
Squid Beak
Beak of the Humboldt Squid, Dosidicus gigas; anterior is to the right (Order Teuthoida)

Clade Decapodiformes: Squid & Cuttlefish


Order Sepiida: Cuttlefishes

  • 8 arms and 2 tentacles
  • Internal shell ("cuttlebone") is calcified with tiny chambers to regulate buoyancy
  • Body generally broader and with longer fins than in squid
  • Near benthic in shallow waters
Cuttlebone
Cuttlebone, the internal shell of cuttlefish, most likely Sepia officinalis or S. pharaonis
Cuttlefish
Broadclub Cuttlefish, Sepia latimanus
Flamboyant Cuttlefish
Flamboyant Cuttlefish, Metasepia pfefferi
Dwarf Cuttlefish
Stumpy-spined (or Dwarf) Cuttlefish, Sepia bandensis

Squid ("Teuthida")

  • 8 arms and 2 tentacles
  • Internal shell forms a cartilage-like (non-calcified) support
  • Generally more elongated and streamlined with posterior fins than in cuttlefish
  • Generally pelagic
  • Divided into at least 2 orders: Myopsida (coastal squid) and Oegopsida (neritic squid)
Market Squid
Common Market Squid, Doryteuthis opalescens (Order Myopsida)
Giant Squid
Giant Squid, Architeuthis sp., preserved specimen
Georgia Aquarium, Atlanta (Order Oegopsida)
Firefly Squid
Firefly Squid, Watasenia scintillans; preserved specimen (Order Oegopsida)

Other Decapodiformes:

  • Order Spirulida contains a single extant species, the Ramshorn Squid
  • Belemnites are extinct squid-like animals with internal shell

More Coleoid Fossils
Ramshorn squid shell
The coiled internal shell of the Ramshorn Squid, Spirula spirula
Belemnite fossils & models
Two fossil rear guards of belemnites and their approximate position in belemnite models
Dorateuthis fossil
Fossil of an extinct squid, Dorateuthis syrica, showing rare soft-tissue preservation, including arms

Clade Octopodiformes


Order Octopoda: Octopuses:

  • 8 arms only
  • Lacks any shell
  • Body rather bulbous; not streamlined
  • Primarily benthic
  • Vampyromorphida (the "vampire squid") are in a separate order in the Octopodiformes
Octopus
Pacific Giant Octopus, Enteroctopus dofleini
Octopus
Two-spot Octopus, Octopus bimaculoides
Juvenile Octopus
Juvenile Two-spot Octopus, Octopus bimaculoides; La Jolla, CA

Octopus
Brown Argonaut egg case, Argonauta hians
This page last updated 3 January 2025 by Udo M. Savalli ()
Images and text © Udo M. Savalli. All rights reserved.