PALEO LABORATORY # 5, PAGE 1
PALEO LAB # V - WORMS, ICHNOLOGY AND ARTHROPODS
A. Phylum Annelida
In early classifications, all worm-like organisms were placed within a single phylum, the
However, subsequent research has shown that many distinct forms may be encased in a
Consequently, modern classifications may divide worm-like organisms into as
many as fourteen phyla, which is about half of all animal phyla!
However, only one phylum
(Annelida) has a substantial fossil record.
Annelids are characterized by a high degree of segmentation (although some specialized
sessile annelids may lose most traces of segmentation).
As annelids are usually soft-bodied, they
are rare in the fossil record except as trace fossils or where they secrete hard living tubes.
major classes of annelids are generally recognized; the earthworms (Oligochaeta), bristleworms
(Polychaeta) and leeches (Hirudinea).
Of these, the polychaetes are the most important fossils.
Annelids are primarily differentiated on the basis of "soft" anatomy.
assisted peristaltic burrowing.
Successive waves of muscle contraction that passes posteriorly
along the body, coupled with elongation and shortening of the body, enables annelids to burrow
within the substrate.
Polychaetes show advancement over this primitive locomotory type in the
addition of parapodia, unjointed fleshy appendages that develop along the lateral body walls.
Another paleontologically-significant development within polychaetes is the evolution of hard,
jaw-like features termed scolecodonts.
These elements range from Ordovician to Holocene and
are relatively common in shallow marine facies.
However, they have not been used extensively
for biostratigraphic zonation, probably due to the taxonomic chaos that makes scolecodonts a
rather ill-defined group.
Trace fossils of probable annelid origin are common within Phanerozoic (and Proterozoic?)
However, these primarily consist of burrows and trails whose "creators" are virtually
impossible to identify.
However, some polychaetes secrete sturdy, calcareous living tubes.
of these polychaetes,
, are quite abundant as fossils.
EXERCISE # 1 - Sketch a specimen of
(TSU IP 129)
a calcareous tube secreted by a
Lower Permian polychaete.
This form typically consists of small, coiled calcareous shells often
found attached to shells of other fossils.
ranges from the Ordovician to Holocene.
EXERCISE # 2 - Sketch a specimen of
(TSU IP 130 - IP 131), colonial polychaete tubes
from the Texas Cretaceous.
These polychaetes currently form "serpulid reefs" along tropical and
subtropical coasts; their biostratigraphic range is from the Silurian to Holocene.
EXERCISE # 3