Smirnouidaphnia smirnoui, Kotov, 2007

Kotov, Alexey A., 2007, Jurassic Cladocera (Crustacea, Branchiopoda) with a description of an extinct Mesozoic order, Journal of Natural History 41 (1 - 4), pp. 13-37 : 24-30

Smirnouidaphnia smirnoui sp. nov.

( Figures 4 , 5 A–C)

Type locality

Ust’-Baley.

Etymology

This species is also dedicated to Professor N. N. Smirnov.

Material studied

Holotype: indistinct body with AII (0)-(> 11)-(.10)/(0)-(1)-(4), PIN 1873 /100 ( Figure 4A, B ) . Paratypes: indistinct body with postabdominal claws and AII (0)-(.8)- (?)/(0)-(1)-(4), PIN 1873 /29; indistinct body with AII (0)-(.8)-(12)/(0)-(0)-(?), PIN 1873 /33; AII (0)-(10)-(12)/(0)-(?)-(4), PIN 1873 /56; AII (0)-(9)-(?)/(0)-(?)-(4), PIN 1873 / 59; AII?/(0)-(1)-(4), PIN 1873 /63; AII (0)-(> 12)-(.10)/(0)-(1)-(4), PIN 1873 /68; AII (0)-(.9)-(?)/(0)-(?)-(4), PIN 1873 /72; AII (0)-(8)-(?)/(0)-(?)-(?), PIN 1873 /75; AII (0)- (.6)-(?)/(0)-(?)-(?), PIN 1873 /77; body with distinct head, valves, mandibles, and thoracic limbs, PIN 1873 /92; body with less distinct limbs, PIN 1873 /93; AII (0)-(.10)-(.13)/(0)- (1)-(4), PIN 1873 /103; AII (0)-(?)-(?)/(0)-(1)-(4), PIN 1873 /104; a body with AII (0)- (.7)-(?)/(0)-(?)-(4), AII (0)-(12)-(13)/(0)-(0)-(?), PIN 1873 /105; AII?/(0)-(1)-(4), PIN 1873 /111; AII (0)-(.6)-(.6)/(0)-(?)-(> 3), PIN 1873 /112; AII?/(0)-(1)-(4), PIN 1873 / 114; AII (0)-(11)-(.9)/ (0)-(?)-(?)/, PIN 1873 /118; AII?/(0)-(1)-(4), PIN 1873 /119; AII (0)-(12)-(> 11)/(0)-(1)-(4), PIN 1873 /122.

Description

Body oval, elongated. Head small, about 25% of body length, without head shield. Valves thin-walled, delicate, suboval, lacking marginal setae. Postabdominal claws short, massive, lacking denticles ( Figure 4E ).

AII with basal segment thick, massive ( Figure 4C ). Exopod significantly longer than endopod, three-segmented, first segment of moderate size, second segment large, thin, with numerous (up to 12) setae, third (apical) segment longer than second segment, thin, with numerous (more than 13) setae ( Figures 4A, B , 5B, C). Endopod approximately as long as basal segment, three-segmented, its first (proximal) segment small, without setae, second segment long, with a single seta near its distal end, third (apical) segment small, with three apical setae and a single lateral seta, all endopod setae uniform, unspecialized. Antennal formula (0)-(8–12)-(9–.13)/(0)-(1)-(4). No spines were found on any of the antenna segments. Mandibles small, strongly chitinized ( Figure 4D ). Maxilla I as a small body with numerous (at least 10) setae ( Figures 4G , 5A, arrow). Six limbs of similar structure, each limb with well-developed gnathobase supplied with numerous (more than 10) setae, large basal endite and three unfused distal endites ( Figure 4H , arrows), exopods were not preserved. No eggs were found.

Size 0.92–1.30 mm (from anteriormost extremity to tip of postabdominal claw, because posterior margin of valves was indistinct in majority of specimens).

Differential diagnosis

It differs from S. testacea in its small size and in having thinner segments of antennal branches, especially of the second segment of the exopod.

Comments

There were several exceptionally well-preserved specimens of S. smirnoυi with thoracic limbs ( Figures 4 E–H, 5A) (note that S. smirnoυi sp. nov. in any state of preservation can be easily differentiated from L. zherikhini sp. nov. from the same locality in structure of AII and absence of head shield). Obviously, S. smirnoυi sp. nov. has six serially similar filtratory limbs, so it belongs to the Ctenopoda . In addition, the specimens from Ust’-Baley have AII with endopod strongly shorter than exopod, with armature of both branches similar to Recent sidid ctenopods. These specimens are therefore attributed to the family Sididae , namely to the tribe Sidini of the subfamily Sidinae .

Smirnouidaphnia testacea ( Smirnov, 1971)

( Figures 5 D–J, 6)

Archedaphnia testacea Smirnov 1971, p 120 –121, Figures 1 , 2 ; Zherikhin 1985, p 100, Plate 7, Figures 10–12.

Type locality

Novospasskoe.

Material studied

Holotype: PIN 3000 /40.

Other material studied. Fifty specimens, PIN 3000/1–22, 24–39, 41, 42, 45, 46, 59–66.

Redescription

Body moderately elongated ( Figure 6A, G ). Head large, about third of body length, without a head shield. Valves suboval, lacking marginal setae. Postabdominal claws relatively short, massive, lacking denticles ( Figure 6E ).

Mandibles small, strongly chitinized, left and right asymmetrical ( Figures 5E, 6C, D ). AII relatively small, basal segment massive. Exopod significantly longer than exopod, threesegmented, first segment small, second segment large, thick, with numerous setae (poor preservation of specimens does not allow their number to be counted) ( Figure 6B, F , arrows), third (apical) segment approximately as long as second segment, but thinner, also with numerous setae (their maximum number unknown). Endopod approximately as long as basal segment, three-segmented, its first (proximal) segment small, second segment long, seeming to lack setae, third (apical) segment approximately half of third segment, with three apical setae, a sub-lateral seta, and a small spine. There is a possibility that some setae on AII (specially a latero-distal seta on second endopod segment, as in the majority of ctenopods) were lost. No spines were found on any segments except the distal segment of the endopod, but these may have been lost. Reconstruction of AII based on a series of specimens is represented in Figure 5J. Within brood pouch there are numerous (up to 26) resting eggs, brownish, surrounded with a strong membrane ( Figure 6G, H ).

Size 2.27–4.32 mm, but edges of impressions are not distinct enough; in addition, specimens were strongly compressed and deformed.

Comments

Smirnov (1970) described his genus Archedaphnia with four species based on material from mudstones of the Maichat and Ak-Kolka Formations, at the Karaungir River in Saur Range, East Kazakhstan, Upper Changhsigian age, the uppermost Permian. Archedaphnia kazakhstanica Smirnov, 1970 was selected as the type species. My re-examination of Smirnov’s Permian specimens led to the conclusion that they are not cladocerans, and, most probably, not arthropods: not one segmented appendage was found. So, the generic name Archedaphnia is not applicable to ‘‘ Archedaphnia ’’ testacea Smirnov, 1971 , which is an apparent cladoceran.

Smirnov (1971) placed A. testacea in the family Daphniidae (Anomopoda) . But this determination was erroneous, based on the details of the holotype. Smirnov himself ( Smirnov 1971, p 120) noted strong membranes of the eggs in fossil specimens. I have no doubts that these eggs ( Figure 6G, H ) were resting eggs. But any traces of an ephippium, a most characteristic trait of the anomopods, are absent in specimens from Novospasskoye. So, the taxon does not belong to the Anomopoda . Both the ‘‘helmet’’ on the head and the ‘‘caudal needle’’ on the posterior portion in Smirnov’s (1971) reconstruction (reproduced here as Figure 5D), appeared due to deformation of the specimen marked as the holotype ( Figure 6A ). My reconstruction of the holotype’s appearance is represented in Figure 5E, regions of the ‘‘helmet’’ and the ‘‘caudal needle’’ marked by arrows. Other studied specimens have no projection on the anteriormost and posteriormost extremities of the body.

AII is poorly preserved in the holotype, but is relatively more clear in some other specimens. Reconstruction of AII ( Figure 5J), based on a series of better preserved specimens ( Figure 5 F–I), led me to the conclusion that ‘‘ Archedaphnia ’’ testacea is a ctenopod from the tribe Sidini of the subfamily Sidinae , like the animal from Ust’-Basley. The generic status of ‘‘ Archedaphnia ’’ testacea is not fully resolved due to relatively poor preservation of all available specimens. Most probably, it belongs to the genus Smirnoυidaphnia gen. nov., like S. smirnoυi from Ust’-Baley. The seta on the second endopod segment, the absence of which ‘‘distinguishes’’ S. testacea from S. smirnoυi, was most probably lost in all studied specimens of the former, which are significantly more poorly preserved as compared with the latter.

Differential diagnosis

See section on S. smirnoυi.

Figures

Figure 1. SEM (A–E, G, H) and optical (F) micrographs of Leptodorosida zherikhini gen. nov., sp. nov., Ust’- Baley, Asian Russia. (A) Holotype, PIN 1873/106; (B) paratype, general view, PIN 1873/102; (C) antenna II, PIN 1873/101; (D, E) antenna II, PIN 1873/115; (F) antenna II, PIN 1873/123; (G) head and thoracic limbs, PIN 1873/107; (H) thoracic limbs, PIN 1873/116. Scale bars: 1 mm (A, B); 0.1 mm (C–H).

Figure 2. Mesozoic Cryptopoda ord. nov. (A) Leptodorosida zherikhini gen. nov., sp. nov. from Ust’-Baley, reconstruction based on several impressions; (B, C) antenna II, PIN 1873/115 and 1873/121; (D) Leposida ponomarenkoi gen. nov., sp. nov. from Chalunikha, general view of holotype, PIN 4042/60, see also Figure 3A; (E) reconstruction based on several impressions; (F) postabdomen, PIN 4042/65; (G–I) antenna II, PIN 4042/60 (holotype), 4042/61, and 4042/62; (J, K) Leposida ponomarenkoi gen. nov., sp. nov. from Unda, antenna II, PIN 3015/2415 and 3015/2421. Scale bars: 1 mm.

Figure 4. SEM micrographs of Smirnoυidaphnia smirnoυi gen. nov., sp. nov., Ust’-Baley, Asian Russia. (A, B) Holotype, antenna II, PIN 1873/100; (C, D) paratype, PIN 1873/105, two antennae II and mandibles; (E–H) paratype, PIN 1873/92, general view, and details of morphology. Scale bars: 0.1 mm.

Figure 6. Optical (A, B) and SEM (C–H) micrographs of Smirnoυidaphnia testacea, Novospasskoe, Asian Russia. (A) Holotype, PIN 3000/40; (B) antenna II, PIN 3000/46; (C) PIN 3000/1, general view; (D) its mandibles and antenna II; (E) its postabdominal claws; (G, H) PIN 3000/015, general view and resting eggs. Scale bars: 1 mm (A, C, G); 0.1 mm (B, D–F, H).