Page 366 - Introduction to Paleobiology and The Fossil Record

SPIRALIANS 2: MOLLUSKS 353

ally arranged needles of calcite with, at its forms) that extends anteriorly (Fig. 13.22).
anterior end, a conical depression or alveolus This assemblage, situated on the dorsal side
that houses the apical portion of the conical of the animal, is analogous to the chambered
phragmocone, consisting of concave septa shells of nautiloids and ammonoids. Soft parts
and a ventral siphuncle, and the spatulate of belemnites, including the contents of ink
pro-ostracum (corresponding to the dorsal sacs and tentacle hooks, are also occasionally
wall of the body chamber of ectocochliate preserved.

ventral head anterior (dorsal) dorsal
(anterior) (posterior)
visceral hump
mantle cavity
opening of posterior (ventral)
mantle cavity
(a)
internal digestive
beak radula remnant diverticulum cecum
of shell
gonad
arms

mouth brain heart
tentacle funnel mantle anus kidney
cavity
(b)

pro-ostracum phragmocone guard
(c)

Hibolites
Middle Jurassic – Late Cretaceous

Duvalia
Hastites Middle Jurassic – Late Cretaceous
Late – Middle Jurassic

Actinocamax Belemnitella
Upper Cretaceous Upper Cretaceous
(d)
Figure 13.22 Coleoid morphology: (a) reconstruction of a living belemnite, (b) soft-part morphology of
the belemnites, (c) internal skeleton of the belemnites, and (d) some belemnite genera. (From Peel et al.
1985.)