Pechoracaris, 2004

Dzik, Jerzy, Ivantsov, Andrey Yu. & Deulin, Yuriy V., 2004, Oldest shrimp and associated phyllocarid from the Lower Devonian of northern Russia, Zoological Journal of the Linnean Society 142 (1), pp. 83-90 : 85

PECHORACARIS ACULICAUDA SP. NOV.

( FIGS 1 , 5 A )

Holotype: PIN 4983/21b ( Fig. 1D )

Type horizon and locality: Dark-grey claystone from between 4255.0 and 4262.7 m, Early Devonian (Lochkovian?). Borehole Medynskoye 1 in the Timan-Pechora region of polar Russia.

Material: Thirty relatively complete specimens and many more fragments.

Diagnosis: As for the genus.

Etymology: Derived from Latin acus (needle) and cauda (tail), referring to the form of the telson.

Material: Sixty relatively well preserved specimens, mostly with abdomen.

Description: The carapace lacks any hinge or separate dorsal plates, as visible in slightly obliquely compressed specimens. The lower margin frequently shows a narrow strengthening belt, probably a little thicker than the rest of the cuticle, perhaps representing a doublure. In specimens PIN 4983/20 and 4983/7, minute sparsely distributed denticles are recognizable near the posterior end of the carapace at its margin. Two somewhat more prominent spines arm the ventro-posterior lobe of the carapace in PIN 4983/1d. The anterior end of the carapace narrows parabolically and is a little pointed, as shown by PIN 4983/8a. The carapace length in the studied material ranges from 2.5 mm to 4.7 mm ( Fig. 1B ). In most specimens dark crushed mandibles are visible across the compressed carapace near its anterior end ( Fig. 1F ). Appendages of the abdomen are transformed into paired sharp spines ( Fig. 1D ), somewhat longer than their segments. The caudal spine is definitely much longer than the carapace ( Fig. 1E ) but its exact length is difficult to trace in the fossils, the spine being either exfoliated or hidden in the sediment.

Figures

Figure 1. Pechoracaris aculicauda sp. nov. from the Medynskoye 1 borehole, Timan-Pechora region, polar Russia, depth 4255.0–4262.7 m, Lower Devonian (Lochkovian?); flattened specimens in laminated claystone. A, carapace with abdomen and partially preserved spine (PIN 4983/21a). B, slightly obliquely compressed specimen (PIN 4983/31a). C, specimen with well preserved dorsal margin of the carapace (PIN 4983/10). D, holotype showing spinose appearance of abdominal appendages (PIN 4983/21b). E, partially preserved specimen with complete abdominal spine (PIN 4983/7). F, specimen with clearly visible crushed mandibles (PIN 4983/31b).

Figure 5. Restoration of (A) Pechoracaris aculicauda sp. nov. and (B) Archangeliphausia spinosa sp. nov.