Prochydorus ROTUNDUS SMIRNOV 1992
Creators: name: Kotov, Alexey A.
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Branchiopoda
Diplostraca
Prochydoridae
Prochydorus

description: PROCHYDORUS ROTUNDUS SMIRNOV, 1992
(FIGS 1A,B, 2A–H, 3A–C)
Smirnov, 1992a: 112, figs 4E, 8C–E, 9E, F, 10, 12E, 13; Dumont & Negrea, 2002: 226–227.
Type locality: Khotont. The northern part of Mount Ukra, 6 km west of Khotont Somon in the valley of the Orkhon, north-eastern Hangay, Arhangay Aimag, Mongolia. More than 1500 impressions of different insects were collected from this locality (Rasnitsyn & Quicke, 2002).
Age: The absolute age of this locality was not estimated, but its palaeofauna consists of both Jurassic and Cretaceous taxa, and the age is estimated as near the Jurassic–Cretaceous boundary (Rasnitsyn & Quicke, 2002).
Holotype: PIN, 4307/2024 and 2040 (impression and counter-impression).
Paratypes: PIN 4307 /2019, 2020, 2025, 2038, 2039 (counter-impression of 19).
The current condition of Smirnov’s (1992a) paratype 4307/2020 prevents accurate determination. Impression 4307/2017, also listed by the author as a paratype of P. rotundus, may belong to Archeoxus mirabilis.
Other material studied: PIN 4307/2002, 2007, 2013, 2016, 2032 (counter-impression of 13), 2041.
Diagnosis: As for the genus.
Description: Body very high (height/length = 0.83– 0.92), rounded in lateral view, dorsum regularly convex, postero-dorsal angle well defined, posteroventral portion broadly rounded. Head about 0.4¥ body length, massive, head capsule of the ‘daphniid-type’, with head shield supplied with a distinct fornix, rostrum pointed. Valve ventral margin without denticles or setae. Postabdomen with claw supplied with minute denticles. Antenna II short. Exopod length 0.21–0.25¥ body length, its proximal segment large, longer than 2 + 3 segments. Endopod somewhat shorter than exopod, its proximal segment only somewhat longer than second segment. Antennal formula (5)–(1)–(3)/(1)–(1)–(3). A short spine on apical segment of exopod. Mandible small, mandibular joint (Figs 2G, 3B: maj) located on valve margin (Figs 2G, 3B: vam), at a distance from point where margins of head and valve come together (Figs 2G, 3B: phv), instead of being attached to head shield (Figs 2G, 3B: hsm). Length 2.0– 2.5 mm.
Comments: The animal may have been subglobular in shape, as are the extant chydorids Chydorus Rak and Indialona (Smirnov & Timms, 1983; Smirnov, 1996; Kotov, 2000).
SPECIMEN 4307/2031 (Figs 1C, 3D–F)
A specimen (PIN 4307/2031) from Khotont possessed unusual features. Unfortunately, its postero-dorsal half is not preserved. The animal, about 2.1 mm in length, has a high body and head of Prochydorus - type, with type of mandibular joint unknown. Each left and right antenna II has formula (?)–(1)–(1)–(1)–(1)–(1)– (?)–(?)/(1)–(1)–(3). Most probably, it is an atypical specimen of Prochydorus, with the large proximal segment of antennal exopod subdivided into six small ‘segments’, each with a single seta. The structure of antenna II may be an atypical recapitulation to an ancestral ‘conchostracan-like’ state. If the specimen is not atypical, it belongs to a new, undescribed order of the branchiopods instead of Prochydorus.
description: Published as part of Kotov, Alexey A., 2009, A revision of the extinct Mesozoic family Prochydoridae Smirnov, 1992 (Crustacea: Cladocera) with a discussion of its phylogenetic position, pp. 253-265 in Zoological Journal of the Linnean Society 155 (2) on pages 254-257, DOI: 10.1111/j.1096-3642.2008.00412.x, http://zenodo.org/record/4687730