The Anomalocaris Homepage
last revised 27 October 2008 by S.M. Gon III
· History 1
· Bauplan
Gallery 1 ·

History 2

Species 1

Gallery 2

Species 2

Gallery 3

Species 3

Species 4

Species Accounts II - Parapeytoia yunnanensis & Opabinia regalis
This page features images of the fossils and reconstructions of two unusual species that some consider anomalocaridids, including Opabinia regalis, considered by some a close relative of anomalocaridids, and by others as a full member of the anomalocarid clade.

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.
parapeytoia haikoucaris
yohoia forticorceps
all line drawing above by S.M. Gon III ©2005

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. 

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).

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.

As an endnote, I present below the best preserved dorsal specimens of Opabinia regalis (camera lucida drawings shown below). They show that the distal grasping organs of the anterior proboscis were split medially, rather than oriented dorso-ventrally. This suggests that the popular reconstructions of Opabinia are in need of adjustment. My reconstruction of Opabinia in dorsal view is at far left. Specimen identification notes: USNM = US National Museum (Smithsonian), YPM = Yale Peabody Museum, GSC = Geological Survey of Canada. YPM 5809 best shows the arrangement of the five eyes (the anterior pair and median eye clustered in a triangle on short eyestalks, with the posterior pair on longer stalks), but the USNM specimens best show the proportion of the two outer eyes (Ro) as larger than the interior and median eyes.  They also appear to be borne on longer eyestalks.
Opabinia regalis
Reconstruction by S. Gon ©2002

Opabinia regalis
USNM 205258

Opabinia regalis
USNM 57684

Opabinia regalis
YPM 5809

Opabinia regalis
GSC 40251