Archangeliphausia, Dzik & Ivantsov & Deulin, 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 : 86

ARCHANGELIPHAUSIA GEN. NOV.

Type species: A. spinosa sp. nov.

Diagnosis: A generalized anthracophausiid with abdominal pleura bearing a single small spine on their ventral margin.

Etymology: Derived from the latinized name of Arkhangelsk and phausis (Greek = shine).

Affinities: Brooks (1962) indicated a recessed ‘eye socket’ of the proximal segment of peduncle of antennules as the diagnostic character of his Anthracophausiidae . This feature is not represented in the new genus, which is quite generalized in this respect and may have been anatomically close to the Devonian eocaridids, as indicated also by the long abdominal pleura. However, the more general aspects of Anthracophausia listed by Brooks (1962) - weak sclerotization of generally smooth carapace, margins reinforced with an unusually narrow band, a short rostrum, and lateral flattening of the body due to compression - fit well the Russian material.

The Carboniferous species of Anthracophausia reveal dramatically different outlines of abdominal pleura from those in the Russian species. In A. strongi Brooks, 1962 , from the Late Carboniferous Mazon Creek fauna of Illinois, the pleural lobes of the abdominal tergites are broadly rounded. In A. dunsiana from the Early Carboniferous Glencartholm Volcanic Beds of Scotland they narrow to form a sharp apex ( Schram, 1979). In the new species, rounded lobes are armed with short spines, which seems to be enough to substantiate its taxonomic distinction. Another possible difference between the Russian form and the Carboniferous species of Anthracophausia is the increasingly posterior orientation of the abdominal pleural lobes towards the telson (although not easily discernible because of strong flattening of the specimens). In fact, the faint parabolic lines visible on the paratype of A. strongi (Brooks, 1962; pl. 48: 3) may also indicate a similar shape of the posterior pleural lobes in that species. Some gradient in the shape of pleural lobes is also observable in A. dunsiana .

All these distinguishing characters are probably primitive (plesiomorphic) and the new genus is probably transitional between the benthic Eocarididae and typical Carboniferous Anthracophausiidae . It may represent the beginning of the lineage of Anthracophausia . Because of the significant time and morphological distance it seems practical, however, to separate them at the generic level.

The Anthracophausiidae probably gave rise to the Recent euphausiaceans, closest to the ancestry of Eumalacostraca among the extant orders ( Jarman et al., 2000). The identified distinction of the anthracophausiids in respect to the euphausiaceans is invariably connected with their basal position in the evolutionary tree: the wide telson, lack of hinge-like connection between the first pleotergite and the carapace, and ventrally extended lobes of the carapace.

The Late Carboniferous anthracophausiids are considered near-shore marine filter feeders ( Schram, 1981). Offshore eumalacostracan communities are inadequately known, with the available evidence restricted to the British late Early Carboniferous, the low diversity community being represented there by schooling species preserved in great numbers of individuals probably as an effect of mass killing ( Schram, 1981).

ARCHANGELIPHAUSIA SPINOSA SP. NOV.

( FIGS 2 –4, 5B)

Figures

Figure 2. Archangeliphausia spinosa sp. nov. A, holotype (PIN 4983/1a: right) and associated specimen (PIN 4983/1b). B, largest specimen found (PIN 4983/35), with relatively thick cuticle. C, juvenile specimen (PIN 4983/37). E, specimen with dorsoventrally compressed telson and uropods (PIN 4983/28; see also Fig. 4C). D, posterior part of abdomen with well preserved 6th pleosomite and telson (PIN 4983/8).