Archangeliphausia SPINOSA 2004
- Dataset
- Oldest shrimp and associated phyllocarid from the Lower Devonian of northern Russia
- Rank
- GENUS
- Published in
- 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): 83-90, DOI: 10.1111/j.1096-3642.2004.00121.x, URL: https://academic.oup.com/zoolinnean/article-lookup/doi/10.1111/j.1096-3642.2004.00121.x
Classification
- kingdom
- Animalia
- phylum
- Arthropoda
- class
- Malacostraca
- order
- Eocaridacea
- genus
- Archangeliphausia
description
(FIGS 2 – 4, 5 B)
description
Description: The largest specimen, PIN 4983 / 35, probably belongs to this species (Fig. 2 B). It measures 12.5 mm in length from the carapace rostrum to the end of the telson. The smallest reasonably complete specimen is PIN 4983 / 37 (Fig. 2 C) with an estimated length of c. 6.5 mm. The size of most specimens is close to the mean between these values. As the specimens are mostly complete skeletons, not exuvia, the dominance of larger individuals may reflect the structure of the original population at its repeated catastrophic extinctions. Three basal segments of the 1 st antenna are preserved in specimens PIN 4983 / 18 and 25. The proximal segment is approximately three times longer than the third one, while the second segment is intermediate in length (Fig. 5 B). Of the 2 nd antenna only the scaphocerite is preserved in a few specimens, the most complete being those of PIN 4983 / 2, 18, and 24 (Fig. 3 A). The scaphocerite is oval, represented only by an organic film on the rock surface and its margins are not easy to trace. The carapace has a sharp, relatively short rostrum, the ocular sinus being clearly visible in specimens PIN 4983 / 24 A and B. The lower margin of the carapace, well preserved in holotype specimen PIN 4983 / 1 a, has a very narrow band (Figs 2 A, 4 A). Being thicker, this band would have strengthened the cuticle. It is calcified and shows openings of pore canals; the posterior margin is hardly discernible except in the isolated dorsoventrally compressed carapace of specimen PIN 4983 / 43. Laterally compressed sternites of thoracic segments are preserved in many specimens. The boundaries between the segments are discernible some distance dorsally of the sternites. All segments except for the first are recognizable in the specimen associated with the holotype (Figs 2 A, 4 B). They disappear at approximately half the height of the body, which probably corresponds to the limit of connection of the body with the carapace. No remnants of the apparently weakly calcified thoracopods are preserved. Some faint marks may correspond to pleopods, but they are completely undefined morphologically. The pleosomites increase gradually in length posteriorly, the 6 th pleomere being very much longer than the preceding ones. Their pleura are somewhat expanded posteriorly to form oval lobes. The lobe of the 5 th pleuron appears to extend almost to the midlength of the 6 th pleosomite. All pleura bear sharp spines at their ventral tips, best preserved in specimens PIN 4983 / 31 and 24 b (Fig. 3 G). The 6 th pleosomite has almost parallel sides when, as in PIN 4983 / 36, compressed dorsoventrally (Fig. 3 F). There is a kind of hinge connection with the basal segment of the uropods. The telson is best preserved in PIN 4983 / 28 (Figs 2 E, 4 C), although its parts are recognizable in several other specimens. Its sides are gently convex but almost parallel to each other. The posterior margin bears about eight indistinct indentations probably corresponding to bristle bases. The surface, as preserved in some stronger sclerotized fragmentary specimens (e. g. PIN 4983 / 32; Fig. 3 B), is externally smooth. The rami of the uropods were strongly sclerotized only along their external margins. This prevents delineation of their shapes, but they were probably rather wide.
diagnosis
Diagnosis: As for the genus.
materials_examined
Holotype: Specimen PIN 4983 / 1 a (Figs 2 A, 4 B). Type horizon and locality: Dark-grey claystone from a depth of 4255.0 – 4262.7 m, Lower Devonian (Lochkovian?). Borehole Medynskoye 1, Timan-Pechora region of polar Russia. Material: Sixty more or less complete compressions.