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
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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
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Chambered Nautilus, Nautilus pompilius
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Median slice of a Chambered Nautilus, Nautilus pompilius, shell
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Cut fossil of Cymatoceras sp. nautiloid (Madagascar; Cretaceous); note the siphuncle
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Fossil Geisonoceras sp., polished (Morocco; Devonian)
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Internal mold of Nautiloid (Kentucky; Ordovician); note gaps (septa) are straight
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Models of possible life appearance of some Paleozoic nautiloids
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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
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Ammonite fossil, Pleuroceras sp., with pyrite replacement of original shell (Germany; Early Jurassic Period)
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Ammonite fossil, Binatisphinctes rjasanensis, showing external shell and shape of septum (Russia; Late Jurassic Period)
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Ammonite fossil, Perisphinctes sp., showing external structure (Late Cretaceous Period, SD)
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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.
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Model of a half shell of the Ammonite Phylloceras, showing the complex shapes of the septa
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Ammonite fossil, Cleoniceras sp., showing sutures (Madagascar; late Cretaceous Period)
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Ammonite fossil Craspedites nodiger, showing sutures (Russia; Jurassic Period)
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Cleoniceras sp. ammonite fossil cut to show chambers (Madagascar, early Cretaceous)
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Dactylioceras sp. ammonite fossil (Germany, early Jurassic)
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Part of an unusual straight-shelled ammonite, Baculites compressus, but note complex suture shapes that distinguish it from straight nautiloids (Late Cretaceous Period, SD)
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Fossil and model of possible life appearance of Nostoceras sp., a heteromorph ammonite
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Crioceratites duvali, a heteromorph ammonite that is loosely coiled (Early Cretaceous Period, France)
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A heteromorph ammonite, Hamites maximus (Early Cretaceous Period, France)
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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
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Dissections of large, fresh squid, probably Ommastrephes bartramii
See also labeled photo.
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Dissections of small, fresh squid, probably Doryteuthis sp.
See also labeled photo.
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Beak of the Humboldt Squid, Dosidicus gigas; anterior is to the right (Order Teuthoida)
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Order Sepioida: Cuttlefishes
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Characteristics:
- 8 arms and 2 tentacles
- Internal shell ("cuttlebone") is calcified with tiny chambers to regulate buoyancy
- Broad body, with long lateral fins
- Near benthic in shallow waters
Cuttlebone, the internal shell of cuttlefish, most likely Sepia officinalis or S. pharaonis
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Broadclub Cuttlefish, Sepia latimanus
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Flamboyant Cuttlefish, Metasepia pfefferi
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Stumpy-spined (or Dwarf) Cuttlefish, Sepia bandensis
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Order Teuthoida: True Squids
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Characteristics:
- 8 arms and 2 long tentacles
- Internal shell forms a cartilage-like (non-calcified) support
- Fairly elongated and streamlined with posterior fins
- Pelagic
- This order is likely paraphyletic and sometimes split into 2 or more separate orders
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Common Market Squid, Doryteuthis opalescens
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Giant Squid, Architeuthis sp., preserved specimen
Georgia Aquarium, Atlanta
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Firefly Squid, Watasenia scintillans; preserved specimen
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Order Octopoda: Octopuses
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Characteristics:
- 8 arms only
- Lacks any shell
- Body rather bulbous; not streamlined
- Primarily benthic
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Pacific Giant Octopus, Enteroctopus dofleini
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Two-spot Octopus, Octopus bimaculoides
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Juvenile Two-spot Octopus, Octopus bimaculoides; La Jolla, CA
Brown Argonaut egg case, Argonauta hians
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Other Coleoids
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- Order Spirulida contains a single species, the Ramshorn Squid, which is more closely related to the extinct belemnites
- Belemnites are extinct squid-like animals with internal shell
- Order Vampyromorphida are the "vampire squids" (but more closely related to octopuses)
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The coiled internal shell of the Ramshorn Squid, Spirula spirula
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Two fossil rear guards of belemnites and their approximate position in belemnite models
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Fossil of an extinct "Vampire Squid," Trachyteuthis sp.; (Order Vampyromorphida, an order that is probably more closely related to the Octopoda and contains a single living species)
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