Daphnia sakhalinensis, Garibian & Kotov, 2020

Garibian, Petr G. & Kotov, Alexey A., 2020, A new species of the Daphnia sinevi group (Crustacea: Cladocera: Daphniidae) from Sakhalin Island, Russian Far East, Zootaxa 4820 (3), pp. 485-505 : 490-501

Daphnia sakhalinensis sp.nov.

( Figs. 4–12 )

Daphnia sinevi group clade F in Kotov & Taylor 2019: figs. 1–2.

Etymology. This species is named after Sakhalin, a huge island in the Russian Far East, where the taxon was found.

Type locality. Japanese sewage pond 3 (47.31561ºN, 142.7009ºE) near Sosnovka , southern portion of Sakhalin Island, Russia. The type series was collected on 15.09.2008 by A.A. Kotov & N.M. Korovchinsky .

Type material. Holotype. An adult male in 90% alcohol, MGU Ml194.

Allotype. A large parthenogenetic female, MGU Ml195.

Paratypes. 20 females, MGU Ml196.

Other material studied here. Sakhalin Area: Many males, ephippial & parthenogenetic females from: a puddle in the River Susuya valley , Yuzhno-Sakhalinsk , coll. on 11.09.2008 by A.A. Kotov & N.M. Korovchinsky (46.95055ºN, 142.7023ºE) , AAK M-0851; Japanese sewage pond 3 near Sosnovka, coll. on 15.09.2008 by A.A. Kotov & N.M. Korovchinsky (47.31561ºN, 142.7009ºE) , AAK M-0870-0872; a small forest pool near Japanese sewage ponds near Sosnovka, coll. on 15.09.2008 by A.A. Kotov & N.M. Korovchinsky (47.31642ºN, 142.7005ºE) AAK M-0873; remains of dried pond near Japanese sewage ponds near Sosnovka, coll. on 15.09.2008 by A.A. Kotov & N.M. Korovchinsky (47.31728ºN, 142.6994ºE) AAK M-0874; puddle 2 near Japanese sewage ponds near Sosnovka, coll. on 15.09.2008 by A.A. Kotov & N.M. Korovchinsky (47.31995ºN, 142.7049ºE) , AAK M-0868; puddles near Pokrovka, coll. on 15.092008 by A.A. Kotov & N.M. Korovchinsky (47.3223ºN, 142.7053ºE), AAK M-0867; a dirty puddle on the road to Naiba River, coll. on 10.09.2008. by A. A. Kotov & N. M. Korovchinsky (47.41925ºN, 142.7783ºE), AAK M-0839; a puddle in the City Park , Tymovskoe, coll. on 13.09.2008 by A.A. Kotov & N.M. Korovchinsky (50.85539ºN, 142.655ºE) , AAK M-0856; a puddle near River Tim’ , near Voskresenovka, coll. on 26.08.1997 by D. Zavarzin (50.91ºN, 142.67ºE), NMK 2432 .

Diagnosis. Parthenogenetic female. Body subovoid, caudal spine relatively short. Rostrum of moderate length, its tip not bent, and subdivided into two lobes by a “line” of pre-rostral fold. Posterior margin of head with a strong prominence proximally to antenna I and a strong depression between this prominence and labrum. Antero-dorsal head portion sometimes provided with a median crest. Dorsal margin of valve covered by spinules only in 1/6-1/4 of its length; ventral margin with spinules only in 1/3 of its length. On inner surface of posterior margin, setae with setules between them. First abdominal process long, slightly bent anteriorly; second process relatively long; third process large; all processes covered with fine setules. Postabdominal claw long; second (medial) pecten varies from 5-7 strong teeth to a series of more numerous and thinner teeth (but never similar to the longispina type, when the second pecten consists of setules of the same size as third pecten!). Body of antenna I small, but present; aesthetascs protruding postero-ventrally, their tips almost reaching tip of rostrum. Largest seta of ODL of limb I bilaterally feathered; seta 1 on IDL also bilaterally feathered; seta 4 shorter than seta 3. Seta 1 on inner-distal portion of limb II about 3/4 of soft seta; seta 4 on gnathobase II does not reach tip of seta e. Exopodite IV with two setae bearing small denticles; seta 1 on exopodite IV with short setules; seta 2 on exopodite V as long as seta 1 to 2/3 of size of seta 1.

Ephippial female. As in other species of the D. curvirostris complex. Postero-dorsal portion of valves incorporated into ephippium.

Adult male. Body low, dorsal margin straight, not elevated above head level. Head with a short rostrum. Supra-ocular depression absent. Antenna I long and relatively straight, with very small antennular seta (its length approximately third of antenna I diameter), located far from the distal end of antenna I body. Male seta on top of distal process, long and bisegmented, its distal segment with a hooked tip. First and second abdominal processes presented by small mounds. Morphological structure of postabdomen as in female, but preanal margin shorter and postanal angle expressed. Postabdominal claw with second pecten of five to nine teeth clearly increasing in size distally. Inner distal lobe of limb I with a curved copulatory hook and two setae of different size, endite 3 with four setae. Limb II with a modified hook-like seta setulated distally.

Size. Parthenogenetic and ephippial female up to 2.0 mm; male up to 1.5 mm.

Description. Parthenogenetic female. General. In lateral view body subovoid, maximum height in the middle of valves ( Figs. 4A , 5A , 6A ); in anterior view laterally compressed, with a low dorsal crest ( Fig. 4B ). Dorsal margin of valves slightly raised above head level; slightly and regularly convex; a depression between head and the rest of body slight; postero-dorsal angle with a relatively short caudal spine.

Head relatively large, with a moderate rostrum with not curved tip, subdivided in two lobes by a ‘line’ of pre rostral fold; anterior lobe always bigger than posterior one ( Figs 4C , 5 B–D, 6B–C). Posterior head margin with a strongly to moderately developed prominence dorsally to antenna I. Compound eye large situated ventrally to middle body axis; ocellus relatively small.

Labrum large ( Fig. 5 C–D).

Valve subovoid, its postero-ventral portion with internally located setae and rows of setules between them ( Figs 4F , 6J , 7 A–F). Caudal spine covered by small denticles, which also occupy less than half of dorsal and ventral valve margin from posterior end ( Figs 5A , 7G ).

Abdomen consist of four segments. The first abdominal process more or less straight, directed anteriorly, the second one somewhat shorter, the third one shortened and massive, each of them covered by rare setules; the last (fourth) process reduced ( Figs 5 E–F, 6D).

Postabdomen ( Figs 5 E–F, 6D) elongated and conical in distal part, with a straight ventral margin covered by minute setules. Preanal angle clear, postanal angle not pronounced. Postanal and anal portions bear eleven to twelve pairs of spines, their size continuously increasing distally.

Postabdominal seta longer than preanal margin, its distal segment shorter than basal one ( Fig. 6D ).

Postabdominal claw evenly curved, its tip pointed ( Figs 4 D–E, 5G, 6G–H). On outer side of claw, three successive pectens along the dorsal margin. The first (proximal) pecten consisting of stout, thin teeth; the second (medial) one composed of 4–6 large teeth or 10–13 finer and thinner teeth decreasing in length proximally ( Figs. 4 D–E, 5E–J, 6D–J); the third one composed of numerous, fine setules that do not reach claw tip. Ventral claw margin convex and bearing fine denticles at distal end of medial pecten, in middle of third pecten and in distal portion.

Antenna I as a stump bearing nine aesthetascs of different length and antennular sensory seta that rises from the surface of head; aesthetascs projecting post-ventrally and their tips do not reach tip of rostrum ( Fig. 7H ).

Antenna II ( Fig. 7I ) with a narrow coxal part; basal segment elongated having well-developed distal sensory seta on posterior margin ( Fig. 7J ). Antennal branches elongated; endopod with three segments slightly longer than exopod with four segments. Each of them having series of minute denticles ( Fig. 7 K–L). Antennal setae formula: 00-1-3/1-1-3. Apical segments bearing rudimentary spines; spine on second segment of exopod small and thick ( Fig. 7K ). Swimming seta with basal and distal segments bilaterally setulated, chitinous insertion within distal segments near connection with basal segment ( Fig. 7 M–O).

Limb I ( Figs 8A , 9A ) without an accessory seta; outer distal lobe (ODL) carry a long seta bilaterally armed distally with short setules, and a short thin seta bilaterally setulated distally (length about 2 diameters of ODL) ( Figs 7B ; 9B ). IDL (endite 4) with a single, long anterior seta covered by short setules distally. Endite 3 with a long anterior seta 2 armed with minute setules and two posterior setae ( Fig. 9D ). Endite 2 with a short and thin anterior seta 3 ( Fig. 9D ) and two posterior setae. Endite 1 with a small anterior seta 4 ( Fig. 9E ) and four posterior setae. Two ejector hooks of different length.

Limb II ( Fig. 8C ) with ovoid epipodite; distal portion as a large lobe carrying two soft and setulated seta. Four endites altogether armed by five setae, one them is anterior (stiff and unilaterally setulated) seta ( Fig. 9 F–G). Gnathobase with two rows of setae, four anterior seta and 11–12 posterior setae on gnathobasic ‘filter plate’ ( Fig. 9H ).

Limb III with a subglobular epipodite and flat exopodite carrying four distal ( Fig. 8D : 1–4) and two lateral (5–6) setae; seta 2 the longest, setulated distally and base setules of distal part somewhat thickened ( Fig. 8E ). Endite 4 bearing a single, long anterior seta and a posterior seta ( Fig. 8F ). Endite 3 bearing single anterior seta 2 and a single posterior seta. Endite 2 with a rudimentary anterior seta 3 and two posterior setae. Endite 1 with one long anterior seta 4 and four posterior setae. The rest part of limb is gnathobase, bearing numerous filtering setae and a single anterior seta.

Limb IV with a large and setulated pre-epipodite, ovoid epipodite and a wide, flat exopodite ( Figs 8G , 9I ). Like previous limb, it is bearing four distal setae; seta 2 short and setulated distally ( Figs 8 H–I, 9J), and two lateral setae. Inner-distal portion consists of completely fused endites, inner margin with gnathobasic filter plate consisting of numerous filtering setae.

Limb V ( Fig. 8J ) with a small, setulated pre-epipodite and subovoid epipodite. Exopodite triangular, with two short distal setae 1–2 approximately equal in length and large lateral seta 3 ( Fig. 9K ). Inner limb portion as an ovoid flat lobe, with setulated inner margin bearing a single seta.

Juvenile female. Body subrectangular, with a straight posterior margin, long caudal spine and posterior half of ventral valve margin covered by spinules ( Fig. 6K ). Head with a straight ventral margin, short rostrum, convex dorsal margin. Head bears a single neck tooth; dorsal organ posteriorly to it. Second pecten of postabdominal claw consists of more numerous and smaller teeth as compared to adult ( Fig. 6M ).

Ephippial female. Body as in parthenogenetic female, but dorsal margin almost straight. Ephippium darkly pigmented with two resting eggs which axes perpendicular to dorsal margin; egg chambers separated from each other; most part of ephippium body covered with reticulation. Caudal spine and whole postero-dorsal part of valves incorporated into ephippium ( Figs. 10 A–C).

Adult male. General. Body low; dorsal margin straight, not elevated above head level; depression between head and valves absent; postero-dorsal angle distinct, with a relatively short caudal spine ( Fig. 10D ).

Head with a short rostrum; region of antenna I joint with special depression ( Figs 10 E–K, 11A). Supra-ocular depression absent; eye large, ocellus small.

Valve with antero-ventral angle distinctly prominent ventrally; ventral margin with a row of numerous long setae; postero-ventral portion of valve with shorter setae and setules between them, located on inner side of valve ( Fig. 11 C–H).

Abdomen with reduced processes; first and second segments presented by small mounds ( Fig. 12 ).

Postabdomen with structure in general as in female, but preanal margin shorter and postanal angle expressed. Anal margin covered by 8–10 paired teeth increasing in size distally. Gonopore opens subdistally, without general papilla.

Postabdominal claws with a basal pecten of fine setules; second pecten with five to nine teeth clearly increasing in size distally; third pecten consisting of fine setules ( Fig. 12 E–G).

Antenna I long and relatively straight, with very small antennular seta (its length approximately third of antenna I diameter), located far from the distal end of antenna I body ( Fig. 11B ). Aesthetascs of different length, three largest 1.5 times longer than antenna I maximum diameter. Male seta on top of distal process, long and bisegmented, its distal segment with a hooked tip ( Fig. 11 A–B).

Limb I ( Fig. 11 I–J) with a large, cylindrical outer distal lobe, bearing a rudimentary seta and a very large seta supplied with minute setules distally. Inner distal lobe with a curved copulatory hook and two setae of different size; endite 3 with four setae ( Fig. 11J ). Limb II with a modified hook-like seta setulated distally ( Fig. 11 L–M).

Size. Parthenogenetic female 0.69–2.0 mm (height 0.41–1.10 mm); male 0.8–1.5 mm (height 0.34–0.54 mm).

Distribution. To date, D. sakhalinensis sp.nov. is found only in Sakhalin Island.

Differential diagnosis. D. sakhalinensis sp.nov. is a member of the D. sinevi species group which is a part of the D. curvirostris complex ( Kotov et al. 2020). D. sinevi group differs from other taxa of the curvirostris -complex in having (although reduced) stump-like body of antenna I, while all other species have no body of antenna I at all. D. sakhalinensis sp.nov. is maximally similar to D. sinevi , but differs from the latter in ( Fig. 13 ): (1) a variable morphology of the second pecten on postabdominal claw (in both females and males) which could be represented by either 4–6 large teeth, or more numerous thinner teeth; (2) denticles on proximal portion of the distal segment of seta 2 on exopodite III are located more densely as compared to following denticles ( Fig. 13 : G–J); (3) exopod setae 1 and 2 on limb V of subequal size; (4) remarkably large male size; (5) shorter male rostrum ( Fig. 13 : A–F; (6) second pecten of male postabdominal claw bearing teeth strongly increasing in size distally.

We have specially compared the morphology of Daphnia sakhaliensis sp.nov. and D. sinevi male. Fig. 14 illustrates differences between continental and Sakhalin populations based on comparison of 20 males from each locality. Note that in both cases there are no unequivocal hiatuses between two clouds of values, but two taxa could be differentiated based on these measurements.

Figures

FIGURE 4. Daphnia sakhaliensis sp.nov., parthenogenetic female from a puddle near River Tim’, near Voskresenovka, Sakhalin Area, Russia, NMK 2432. A, adult, lateral view. B, its antero-dorsal view. C, head, lateral view. D–E, postabdominal claws with different morphology. F, armature of inner face of posterior valve margin. G, exopodite III. Scale bars denote 0.1 mm for A–E, I, and 0.01 mm for F–H.

FIGURE 5. Daphnia sakhaliensis sp.nov. from the Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M- 0871.A, adult parthenogenetic female. B–D, its head. E–F, postabdomen. G–J, postabdominal claw. Scale bars denote 1 mm for A, and 0.1 mm for B–J.

FIGURE 6. Daphnia sakhaliensis sp.nov. from a puddle near River Tim’, near Voskresenovka, Sakhalin Area, Russia, NMK 2432. A, adult parthenogenetic female. B–C, its head. D, postabdomen. E–I, postabdominal claw. J, armature of inner side of posterior margin. K, juvenile female, instar I. L, juvenile male, instar I, head. M, postabdominal claw of male I. Scale bars denote 1 mm for A, D, and 0.1 mm for B–C, E–O.

FIGURE 7. Daphnia sakhaliensis sp.nov. from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia,AAK M-0871. A–F, armature of postero-ventral and posterior margin of valve. G, caudal spine. H, antenna I. I–J, antenna II and proximal portion of its basal segment. K–L, second segment of its exopod and its distal segment. M–O, apical setae of different individuals. Scale bars denote 0.1 mm.

FIGURE 8. Daphnia sakhaliensis sp.nov. from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia,AAK M-0871. A, limb I. B, ODL of limb I. C, limb II. D, limb III. E, seta 2 of exopod III. F, inner portion of limb III. G, limb IV. H–I, seta 1 of exopod IV. J, limb V. Scale bars denote 0.1 mm.

FIGURE 9. Daphnia sakhaliensis sp.nov. from a puddle near River Tim’, near Voskresenovka, Sakhalin Area, Russia, NMK 2432.A, limb I. B, ODL of limb I. C, seta of inner distal lobe = seta 1. D–E, setae 3 and 4. F–G, inner-distal portion of limb II. H, fragment of gnathobase II. I, seta 2 of exopod III. J, seta 1 of exopod IV. K, setae 1–2 of exopod V. Scale bars denote 0.1 mm.

FIGURE 10. Daphnia sakhaliensis sp.nov. from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M- 0871.A, ephippial female, lateral view. B, reticulation on central portion of ephippium. C, dorsal portion of ephippium. D, adult male, lateral view. E–K, head, lateral view. Scale bars denote 0.1 mm.

FIGURE 11. Daphnia sakhaliensis sp.nov., adult male from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M-0871. A–B, male antenna I. C, anterior and ventral margin of valves. D, setae at posterior portion of ventral margin. E–G, armature of postero-ventral and posterior margin of valve in male. H, caudal spine. I–J, limb I. K, copulatory hook of IDL. L–M, stiff setae of inner-distal portion of limb II. Scale bars 0.1 mm.

FIGURE 12. Daphnia sakhaliensis sp.nov. from Japanese sewage pond 3 near Sosnovka, Sakhalin Island, Russia, AAK M- 0871. A–D, male postabdomen. E–G, postabdomenal claw. Scale bars denote 0.1 mm.

FIGURE 13. Daphnia sakhaliensis sp.nov. (A–C, G–H) and Daphnia sinevi (D–F, I–J). A–F, head. G–J, seta 2 of exopod III. Scale bars denote 0.1 mm.

FIGURE 14. Morphometric comparison of Daphnia sakhaliensis sp.nov. (red quadrates) and Daphnia sinevi (blue triangles) males. A, x—rostrum length; y—rostrum length/head height ratio. B, x—rostrum length/head height ratio; y—1st postabdominal teeth/ 5th teeth length ratio.