Daphnia (Daphnia) cavicervix Ekman, 1900

Kotov, Alexey A. & Gololobova, Maria A., 2005, Types of cladoceran species described by Sven Ekman in the Swedish Museum of Natural History, with redescription of Daphnia cavicervix Ekman, 1900 (Daphniidae, Anomopoda, Cladocera), Journal of Natural History 39 (33), pp. 3059-3074 : 3063-3064

Daphnia (Daphnia) cavicervix Ekman, 1900

( Figures 1–5 )

Daphnia cavicervix Ekman 1900, p 62 –65, Plate 3: Figures 1 –7.

Not Daphnia cf. cavicervix in Brandlova et al. 1972, p 1393 –1395, Figures 75–83.

Lectotype (selected here): an adult parthenogenetic female, 1.76 mm, in 90% alcohol, tube SMNH 5870 . Label of the lectotype: ‘‘ Daphnia cavicervix Ekman, 1900 , 1 ad. ♀ from Morro Chico, S. Patagonia, Chile, LECTOTYPE’ ’. Paralectotypes (selected here): 64 parthenogenetic females, nine ephippial females, two juvenile males and one adult male, in 90% alcohol, tube SMNH 5871 ; parts of a parthenogenetic female on nine slides, SMNH 5872 ; parts of an adult male on seven slides, SMNH 5873 .

Type locality

Unknown water body near Morro Chico, km 146 of the highway 9 (Punta Arenas–Puerto Natales), Chile (approximately 52 ° 059200S, 71 ° 229270W). Ekman (1900) said of two localities where D. cavicervix was found: ‘‘Die Art ist bei Morro Chico in fliessendem, schmutzigem Wasser und bei Rio Ruben in kleinen Tümpeln gefunden’’. Any specimens from the second locality are absent from SMNH, while the sample Cladocera 34 (4068) is apparently from the first locality, which now becomes the type locality as a result of the lectotype designation.

Emended diagnosis

Parthenogenetic female. Body widely rhomboid, dorsal margin of valves elevated above head, a depression between head and rest of body, postero-dorsal angle as a rounded projection. Rostrum with slightly bent tip, no crest on head. Fornix narrow, no secondary fornix. Valves with submarginally located setae of different size on different portions of the ventral margin. The first abdominal projection long, protruding basally and with bent tip, the second projection short, bent distally; the third one very short, rounded, the fourth segment completely lacking projections. Postabdomen subtriangular, postanal portion with about 10–11 paired teeth, some of them with bifid tips. Postabdominal claw with basal pecten consisting of seven to nine strong spines, the second pecten consisting of 9–10 longer spines, the third and fourth pectens with numerous fine setules. Antenna I short, partly fused with the posterior margin of head, with antennular sensory seta at base. ODL of limb I with a long seta armed distally with short setules, and a short seta; IDL with a single, long anterior seta. Endite 1 with a short anterior seta and four posterior setae. Exopodite V with a small distal and a large lateral setae, inner limb portion with a single, large seta.

Ephippial female. Dorsal margin of valves straight to slightly convex, postero-dorsal angle acute. Ephippium with two resting eggs, axes of which perpendicular to its dorsal margin, egg chambers well separated from each other.

Adult male. Body subovoid, dorsal margin of valves not elevated above head, depression between head and valves absent, postero-dorsal angle distinct, with a short caudal needle. Region of antenna I joint with a special depression, anteriormost head extremity as a low dome with a shallow supra-occular depression posteriorly to it. Valve with prominent antero-dorsal angle, a ‘‘step’’ in anterior third of ventral margin; long, numerous setae submarginally on inner face of valve at anterior and ventral margin. Abdomen with only two short projections. Postabdomen with gonopore opening subdistally near dorsal margin of postabdomen, without a genital papilla. Antenna I free, long, with series of fine setules; antennular sensory seta small, protruding for a distance of about 1.5–2 times its length from distal end of antenna I. Male seta on top of a low, distal projection. This seta long, bisegmented, its distal segment regularly curved, with setulated distal portion and with tip as a sharp hook. ODL of limb I with two minute setae, and a very large seta setulated distally; IDL with a short, bent copulatory hook. Inner-distal portion of limb II with distalmost endite bearing a modified hook-like anterior seta. Anterior seta on distalmost endite of limb III stiff, with specially short setules.

Size. Up to 1.80 mm.

Figures

Figure 1. Daphnia cavicervix from unknown water body near Morro Chico, Chile. (A) Adult parthenogenetic female, lectotype; (B) its head; (C) juvenile female; (D) its head; (E) its postabdomen; (F) ephippial female; (G) sculpture of ephippium; (H) juvenile male, pre-reproductive instar; (I) its head; (J) adult male; (K) its head. Scale bars were not taken.

Figure 2. Daphnia cavicervix, parthenogenetic female from unknown water body near Morro Chico, Chile. (A) Adult parthenogenetic female, lectotype; arrows show portions of ventral margin enlarged in (H–M); (B) posterodorsal region; (C) reticulation on valves; (D, E) head and rostrum; (F) head shield, dorsal view; (G) labrum; (H– M) armature of ventral margin of valve; (N) postabdomen; (O, P) postabdominal claw in outer and inner view; (Q) juvenile female, second instar; (R, S) its postabdominal claw and abdominal projections. Scale bars: 0.1 mm.

Figure 3. Daphnia cavicervix, female from unknown water body near Morro Chico, Chile. (A) Antenna II; (B, C) apical segments of exopod and endopod; (D) limb I; (E) limb II; (F, G) limb III and its inner-distal portion; (H, I) limb IV and its inner-distal portion; (J) limb V. Scale bars: 0.1 mm.

Figure 4. Daphnia cavicervix from unknown water body near Morro Chico, Chile. (A) Ephippial female; (B) sculpture of ephippium, marginal portion; (C) sculpture of ephippium, portion close to egg chamber; (D) sculpture on egg chamber; (E) juvenile male (pre-reproductive instar); (F) its antenna I; (G) distal portion of its limb I. Scale bars: 0.1 mm.

Figure 5. Daphnia cavicervix, adult male from unknown water body near Morro Chico, Chile. (A) Lateral view; (B) head; (C) dissected valve; (D, E) postero-ventral portion of valve; (F, G) postabdomen and its distal portion; (H, I) antenna I; (J) limb I; (K) ODL; (L) armature of seta of ODL; (M) IDL; (N) tip of copulatory hook; (O) inner-distal portion of limb II; (P) inner-distal portion of limb III. Scale bars: 0.1 mm.