Archeoxus, MIRABILIS SMIRNOV, 1992

Kotov, Alexey A., 2009, A revision of the extinct Mesozoic family Prochydoridae Smirnov, 1992 (Crustacea: Cladocera) with a discussion of its phylogenetic position, Zoological Journal of the Linnean Society 155 (2), pp. 253-265 : 257

ARCHEOXUS MIRABILIS SMIRNOV, 1992 ( FIGS 1D–E , 4A–H)

Smirnov, 1992a: 112, figs 1A–C, 2A, B, 4A, F, 9C, 12A, F

Type locality: Khotont, Jurassic–Cretaceous boundary (see above).

Holotype: PIN 4307 /2028 and 2036 (impression and counter-impression).

Paratypes: PIN 4307 /2001, 2007, 2011, 2012, 2015, 2023 and PIN 4307 /2033.

The recent state of Smirnov’s (1992a) paratypes PIN 4307 /2006, 2010, 2034 and 2037 is too poor for their accurate determination .

Other material studied: PIN 4307 /2007-2 (an impression on the same rock fragment with paratype 2007), 2018, 2041, 2047 .

Diagnosis: As for the genus.

Description: Body moderately high (height/length = 0.72–0.79), subovoid in lateral view, dorsum regularly convex, postero-dorsal angle ill defined or absent. Head about 0.4¥ body length, head capsule of the ‘chydorid-type’, covered with a ‘flat’ head shield, with thin, pointed rostrum. Valve ventral margin without denticles or setae. Postabdominal claw supplied with denticles. Antenna II relatively long. Exopod length 0.32–0.35 body length, its proximal segment large, with length approximately as length of 2+3 segments. Endopod somewhat shorter than exopod, its proximal segment somewhat longer than second segment. Antennal formula (4–5)–(1)–(3)/(1)–(1)–(3). Mandible small, mandibular joint located exactly at the point where margins of head and the well-chitinized valves come together. In specimens where the head and valve were separated, the mandibular joint remained associated with valve ( Fig. 4B ). Gut thin, not convoluted ( Fig. 4A ). Length 2.0– 2.9 mm.

Figures

Figure 1. Drawings of Upper Mesozoic Prochydoridae based on SEM photographs. A, Prochydorus rotundus from Khotont, reconstruction based on a series of specimens. B, antenna II of holotype, PIN 4307/2040. C, specimen PIN 4307/2031 from Khotont, antenna II. D, Archeoxus mirabilis from Khotont, reconstruction based on a series of specimens. E, antenna II of specimen PIN 4307/2018. F, ‘Archeoxus’ vetrosus from Khotont, antenna II of holotype PIN 4307/2027. G, Palaeorak scherbakovi gen. nov., sp. nov. from Khasurty, holotype 5026/178. H, reconstruction of general view based on series of specimens. I, postabdominal claw, 5026/177. J, antenna II, 5026/179. Scale bars: 1 mm.

Figure 4. SEM micrographs of Archeoxus mirabilis from Khotont, Mongolia. A–C, holotype PIN 4307/2028, general view, head and ventral margin of valve. D, E, PIN 4307/2018, general view and antenna II. F, G, paratype PIN 4397/2007, antenna II and postabdominal claws. H, paratype PIN 4307/2012, general view. Scale bars: A, D, H, 1 mm; B, C, E–G, 0.1 mm.