Leydigia Kurz, 1875

Kotov, Alexey A., 2009, A revision of Leydigia Kurz, 1875 (Anomopoda, Cladocera, Branchiopoda), and subgeneric differentiation within the genus, Zootaxa 2082 (1), pp. 1-84 : 7-9

Genus Leydigia Kurz, 1875

Kurz 1875, p. 57; Hellich 1877, p. 88; Lilljeborg 1901, p. 492–493; Keilhack 1909, p. 90; Sars 1916, p. 328; Behning 1941, p. 287; Šrámek-Hušek et al. 1962, p. 354; Herbst 1962, p. 90; Olivier 1962, p. 242; Smirnov 1971, p. 449; Flössner 1972, p. 324; Margaritora 1983, p. 128–129; Margaritora 1985, p. 267, 269; Røen 1995, p. 248; Alonso 1996, p. 359, 361; Flössner 2000, p. 352.

Type species. Leydigia quadrangularis (Leydig) in Kurz (1875). This is a junior synonym of Alona leydigi Schoedler, 1863 , which is currently understood as L. leydigi (Schoedler, 1863) .

When Kurz (1875, p. 51) described his new genus, he referred to two earlier described species: "Alle Forscher dem Lynceus quadrangularis (Leydig) und acanthocercoides (Fischer) eine Sonderstellung unter den Alonen eingeräumt, da sie in wichtigen morphologischen und anatomischen Merkmalen von dem Genus Alona abweichen". There are no problems in the translocation of Fischer's species to the new genus, but the combination ' L. quadrangularis (Leydig) ' is strange in the light of recent Zoological Nomenclature. There are two ways to explain the logic of Kurz, when he used the name ' L. quadrangularis (Leydig) ': (1) he decided that Leydig (1860) really established a new taxon (although the latter did not claim this, and both epithets of this binomen were old), or (2) Kurz really established a new species, but transferred authorship to Leydig (1860). In any case, Kurz (1875) clearly said that his ' L. quadrangularis (Leydig) ' is the same as Alona leydigi Schoedler (1863) , so there is no doubt that this taxon was described. The author said nothing about the type species of the genus, as was common at that time. So, according to paragraph 69.1 of ICZN (2000), the right to select a type species belonged to following authors.

Unfortunately, systematics of the Cladocera in the first two-thirds of the 20th century paid little attention to the Rules of Zoological Nomenclature. No author selected a type species for any genus not typified by its author. The first authors to designate a type species of the genus Leydigia were Šrámek-Hušek et al. (1962), who selected L. leydigi (Schoedler, 1863) . This was valid according to case of 69.2.2. of ICZN (2000). Although Šrámek-Hušek et al. (1962) used a nominal taxon, that was not among two (nominal!) species originally included in the genus by its author (see above), they clearly recorded Kurz's ' Lynceus quadrangularis ' in the list of synonyms of L. leydigi . Later, L. leydigi or ' L. quadrangularis Leydig' was reported as the type species also by Manuilova (1964), Smirnov (1971), Flössner (1972), Negrea (1983), and Margaritora (1985). Recently Alonso (1996) and Flössner (2000) designated L. acanthocercoides as the type species, but this is not acceptable, as a type species cannot be changed.

Amended diagnosis of the genus. Parthenogenetic female. In lateral view, body subovoid to triangularovoid, high, postero-dorsal angle (well-defined or ill-defined) located near level of highest point of dorsal margin; postero-ventral angle completely smoothed, ventral margin convex. In anterior view, body compressed laterally. Head triangle-round, with short, downwardly directed, pointed rostrum. Compound eye small, ocellus usually larger than the eye. Head shield wide, three major head pores with a relatively wide connection between them, lateral head pores at varying distances from midline, without special depressions. Labral keel large, wide, its anterior margin with setulation, lateral groups of setules on its sides. Valves with numerous setae of different sizes in different regions of ventral margin; at posterior margin, a submarginal row of setules, plus a marginal membrane. Postabdomen broad for family, strongly compressed laterally, anus near base. On postanal margin, a row of short marginal denticles, and fascicles of stout lateral setae, evenly passing into fascicles of lateral setules on basal half of postanal and anal margin. Postabdominal claw with or without a basal spine. Antenna I relatively long for family, not reaching tip of rostrum, with transverse rows of setules on anterior face and antennular sensory seta in distal half; nine aesthetascs of different size projecting behind tip of rostrum. Antenna II stout, coxal part with two sensory setae, basal segment with transverse series of setules and rudimentary distal spine. Antennal branches elongated. A series of relatively long and stout spinelike setules (which are not homologues to true spines) on first, and second endopod segment. Antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1.

Trunk limb I without accessory seta, ODL large, with a long seta, armed unilaterally. IDL large, with 3–4 medial and 3 marginal clusters of setules, and three bisegmented setae. Each of endites 1–3 with three soft setae, and a stiff seta, the latter large on endite 3 and small on endites 1–2. Maxillar process a lobe with a row of setules. Trunk limb II with small, ovoid exopodite, without setae, but with a bunch of setules. Inner portion of limb with eight scrapers, the distalmost long, on distal lobe with bundle of setules. Portion of gnathobase bordering inner-distal portion of limb (so-called 'endopodite') somewhat inflated, and densely setose, distal armature of gnathobase with four elements, including a small sensillum; filter plate with seven setae of subequal size. Limb III with exopodite bearing 3–7 setae, distal endite with 3 stiff setae, a small sensillum near each seta 2 and 3, basal endite with four setae, on posterior limb face, four soft setae, distal armature of gnathobase with 4 setae, among them a thick, bottle-shaped sensillum; filter plate with six setae. Limb IV with large exopodite, subovoid, supplied with six setae; inner portion of limb with four marginal setae; on posterior limb face, three soft setae and a straight, tripartite sensillum (a member of row of soft setae); distal armature of gnathobase with 4 setae, among them a thick, bottle-shaped sensillum, filter plate with five setae, distalmost with inflated basal segment, all setae with inflated tips. Limb V with exopodite large, supplied with four densely setose setae; inner portion as elongate, flat lobe, with setose inner margin, two setose setae distal to gnathobase; distal armature of gnathobase a lobe; two setae in 'filter plate'.

Ephippial female. In lateral view, shape similar to parthenogenetic female, dorsal wall of carapace with thickened chitin, forming a thin dorsal plate. In anterior view, body with a thick dorsal keel. A chamber for resting egg expands laterally. Ephippium with a single resting egg. No distinct border of ephippium: this appears in the course of its casting off.

Adult male. Head larger and rostrum longer than in female. Marginal denticles of postabdomen reduced in size as compared with female. Penis present or absent, gonopores paired. Antenna I more robust than in female, with 12 aesthetascs and additional male seta (in primitive state not differing in habitus from aesthetasc). Trunk limb I with slender, U-shaped copulatory hook, IDL with male seta, beside this, 2–3 setae. Copulatory brush setae present.

Size. Large alonines, up to 1200 µm.

Terminological comments. Spine-like setules on antenna II. Fryer (1968) described these structures as ‘spines’. But they are not homologous with true spines (Kotov 2003; Kotov 2006; Kotov et al. 2003a; Kotov et al. 2003b), and not included in the antennal formula.

Filter plates of limbs. Observations of living animals led to the conclusion, that these structures do not participate filtration ( Fryer 1968). But I use here the traditional term ‘filter plates’, keeping in mind their homology in different anomopods, that utiliuze filter- and non-filter feeding ( Smirnov 1971; Smirnov 1992).

Setae on limbs. Fryer (1968) called some of them ‘spines’. I prefer to speak about setae on limbs (in two rows), following Smirnov (1971).

Comment. Leydigia fimbriata Fordyce, 1901 and Leydigia glabra Smirnov, Ponce et Silva-Briano, 2000 do not conform to the generic diagnosis, having no lateral setae on the postabdomen: their generic status is not clear at this stage of alonine study.