Parapeytoia yunnanensis
#1
an
anomalocaridid with legs?
This photo of the holotype
specimen of the Chengjiang fossil Parapeytoia
yunnanensis, is not complete, but shows a pair
of strongly developed anterior appendages, lateral lobes (but with
segmented legs!) and a series of sternites (ventral body plates). These
features
seem to point clearly to arthropod affinities, and may suggest that
this
is a megacheiran, rather than an anomalocaridid (or point to affinities
between those two "great appendages" groups). |
Parapeytoia yunnanensis
The camera
lucida drawing of the
specimen at left shows considerable disarticulation, with lateral lobes
in multiple orientations. A series of axial sternites (s) runs downward
from the head reagion, where an arguably Peytoia-like
mouth (m)
lies between two massive anterior appendages (1). The best-preserved
lateral
lobe (7) shows not only the segmented leg, but gnathobasic teeth on
both
the leg and the base of the lobe. |
Illustration by Javier Herbozo
This
reconstruction of Parapeytoia in Hou et al 1995
shows several items that are consistent with the holotype specimen, but
several others that are speculative. For example, the legs on lateral
lobes are consistent, but a fantail (last three lobes) bearing
rudimentary legs is conjectural. The ventral sternites are consistent,
but the backward-facing mouth and ventral orientation of the anterior
appendages is not consistent with any other anomalocarid species
(though the backward-facing mouth woud be
consistent with that of Opabinia).
|
 
My
reconstruction of the dorsal and ventral view of Parapeytoia
yunnanensis as an anomalocaridid depicts the anterior
appendages in a forward orientation, the mouth in typical ventral
orientation, and no legs on the (conjectural) fantail. Because
of the well-developed sternites, I depicted dorsal tergites. I also
graced
the creature with eyes on stalks lateral to the mouth, as in the
majority of anomalocarids. However, if Parapeytoia is
a more typical megacheiran, its eyes would be antero-ventral. |
Below (top
left), Parapeytoia yunnanensis is reconstructed as
a megacheiran "great-appendage" arthropod, and compared with
reconstructions of others in that group, including Haikoucaris
ercaiensis, Yohoia tenuis, Fortiforceps
foliosa, and Jiangfengia multisegmentalis.
When depicted in this way, the similarities of the anterior appendages
becomes quite clear, casting doubt on the anomalocaridid status of Parapeytoia.
Alternately, the great anterior appendages of anomalocaridids and
megacheirans may be homologous.
 
all line drawing
above by S.M. Gon III ©2005
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Opabinia
regalis #1
This specimen of Opabinia
regalis displays some of the clear similarities with
anomalocarids: elongate, metameric body, bearing lateral swimming
lobes, anterior stalked eyes (albeit 5 of them!), ventral mouth,
anterior grasping organs (paired and spine-bearing at the distal end),
even a dorsal fantail behind the swimming lobes. Opabinia is
a small animal (about 4 cm in length) vs the 25-50 cm length of the
larger Anomalocaris specimens. However, some of
the Chengjiang anomalocarid specimens are also smaller than those of
the Burgess Shale, leading some researchers to claim that they
represent juvenile specimens.
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Opabinia
regalis #2
This dorsal preservation of
Opabinia regalis (Yale Peabody Museum 5809)
better shows how similar its bauplan is to that of anomalocarids. If
the frontal grasping organs were not so elongate and fused, there would
be little argument on its affinities to anomalocarids. Multiplicity of
eyes in Opabinia notwithstanding, the finer
structure of the eyes is otherwise very similar to that of Anomalocaris.
See the camera lucida drawing of this specimen at page bottom (YPM
5809).
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Probably
the best-known reconstruction of Opabinia regalis.
Note the pattern of imbrication
of the dorsal fantail, identical with that of Anomalocaris
species.
The gill-like structures associated with the lateral lobes are also
seen
(albeit not as clearly) in specimens of Laggania.
The number of lateral
lobes is very similar to that of Anomalocaris and Laggania. |
.
My
reconstruction of Opabinia
regalis is very similar, but depicts the fantail arrangement
as more
compact, and shows the paired appendages at the end of the grasping
organ
as split medially, rather than dorsoventrally. Specimens are
somewhat
ambiguous in this regard, but most of the specimens preserved in a
dorsal
aspect with proboscis present show bilateral symmetry of the grasping
end. Medial splitting is more consistent with the lateral pairing of
appendages
in anomalocarids. |
