Disparalona, Fryer, 1968

Neretina, Anna N., Garibian, Petr G., Sinev, Artem Y. & Kotov, Alexey A., 2018, Diversity of the subgenus Disparalona (Mixopleuroxus) Hudec, 2010 (Crustacea: Cladocera) in the New and Old World, Journal of Natural History 52 (3 - 4), pp. 155-205 : 161-173

1. Disparalona (M.) hamata ( Birge, 1879)

( Figures 1 – 5 )

Synonymy

Pleuroxus hamatus Birge, 1879, pp. 22 – 23 , pl. 2: figures 13, 14; Herrick 1884, pp. 110 – 111, pl. h: figure 1

(Continued) Pleuroxus hamulatus Birge 1910, p. 1052 ; Birge 1918, p. 728, figures 1142, 1143; Kiser

1950, pp. 245 – 247, pl. 2: figures 1 – 4 Alonella hamulata (Birge) in Frey 1961, p. 138 Disparalona hamata (Birge) in Elías-Gutiérrrez et al. 2008, p. 90, figure 30(3 – 6)? Pleuroxus chappuisi Brehm in Brehm 1937, pp. 507 – 509, figure 4? Alonella hamulata (Birge) in Rey and Vásquez 1986, p. 150, pl. 5: figures 13 – 20; Zoppi

de Roa and Vásquez 1991, p. 56, figure 10

Type material

Most probably lost. Samples and slides of E.A. Birge were incorporated into the collection of David G. Frey at Indiana University and gifted to the Smithsonian Institution ’ s National Museum of Natural History (accession number 403,774) upon Frey ’ s death ( Berner 1997; Kotov and Ferrari 2010). Several dried semi-permanent slides (e.g. numbers A-2 – 1, A-2 – 2, A-2 – 5, A-2 – 10, A-2 – 11, A-2 – 12, A-2 – 20) labelled as Pleuroxus hamatus or P. hamulatus are present in E.A. Birge ’ s metal file cabinet with slides, but all these slides are dated as 1903 or 1917 years; therefore they could not belong to type series of the taxon published in 1879. Liquid samples of E.A. Birge are also incorporated into D.F. Frey collection, but there is no detailed inventory of them, e.g. with the animal identifications by Birge. There is a chance that any individuals of D. hamata could be found in the samples of 1879, but whether they can be regarded as belonging to the type series will be problematic: they were not separated by the author from the total samples, and most probably were not seen by him.

Type locality

‘ Southampton, Mass. ’, USA ( Birge, 1879).

Material examined.

USA. Five females from Swan Pond (N 40.9060°, W 72.7960°), Long Island , New York, coll . 6.2004 by D.J. Taylor and A.A. Kotov, AAK 2005 – 215; 12 females from Round Pond (N 40.9860°, W 72.2910°), Long Island , New York, coll . 12 June 2004 by D.J. Taylor and A.A. Kotov, AAK 2005 – 223; 7 females from Storrs Pond (N 43.7250°, W 72.2640°), Hanover , New Hampshire, coll . June 2004 by W. Piel and A.A. Kotov, AAK 2005 – 263; Many females from Sunset Lake , North Carolina, coll . 18 October 1977 by D.G. Frey, DGF 4403. Canada. Many females and males from Jordan Harbor (N 43.1800°, W 79.3700°), Ontario, coll . 25 September 2002 by S.J. Connelly, AAK M-1170 and AAK M-1192.

Diagnosis

Parthenogenetic female. Species of typical size for the genus (length of adult parthenogenetic female up to 0.6 mm). In lateral view, body regularly ovoid, dorsal keel is not developed. Head with relatively long rostrum (distance between centre of eye and ocellus is two times shorter than distance between centre of ocellus and tip of rostrum). Posteroventral angle of valve without denticles. Posterior margin of valve bears a row of numerous fine setules located quite close to the edge of its margin. Sculpture of valves and head strongly developed. Outer surface of posterior and anterior portion of valves is covered by long parallel sometimes anastomosing lines, between them short sometimes wavy lines are located. Central portion of valves and head are covered only by short lines. Structure of head pores are typical for the subfamily Chydorinae : two major bordered head pores and two lateral pores (sensu Kotov 2013) between them. Surface between pores is also covered by short lines. Labral keel short, its anterior margin is straight or slightly convex, distal angle is acute. Postabdomen relatively long (postanal margin two times longer than anal margin). Postanal and ventral margin are rather convergent, although the ventral margin is clearly convex whereas the dorsal margin is straight. Distal angle of postabdomen is almost right. Postanal margin is armed distally by composite denticles, decreasing in size proximally, proximal half of margin with groups of denticles of decreasing length proximally in each group, anal margin is covered by bunches of fine setules. Also, bunches of fine short setules cover lateral surfaces of these margins. Postabdominal claw is long, subequal in length to anal margin, with two basal spines. The longest basal spine is slightly longer than the base of claw and two times longer than the smallest spine. Antenna I typical for chydorids, antennular sensory seta arising subdistally, almost subequal to antennular body. Antenna II with a very small spine on proximal exopod segment, it shorter than 1/4 length of the middle exopod segment. Five thoracic limbs. The number of setae on each thoracic limb as for genus. Inner distal lobe of thoracic limb I with two thin setae are unequal in size, and one long thick hook-like seta. Exopodite of limb IV with two thin setae covered by short setules are unequal in length, lateralmost seta is almost two times shorter than nearest seta. Ephippial female is similar with parthenogenetic female. Ephippium dark brownish with single egg. Male. Body ovoid, elongated, up to 0.48 mm in length. Armature of valves and ornamentation similar to parthenogenetic female. Dorsal side of postabdomen straight or slightly concave. Two spines are unequal in length on postabdominal claw. Gonopores open laterally at short distance from claw bases. Antenna I with male seta located at the middle of antennular body near sensory seta. Limb I with massive copulatory hook.

Redescription

Parthenogenetic female ( Figures 1–4 ). In lateral view body oval ( Figures 1 (a), 2(a)), relatively elongated (body height/length ratio about 0.58 both for adults and juveniles), maximum height almost at the middle of body. Body moderately compressed laterally ( Figure 1 (b, c)), dorsal keel and lateral processes on valves absent ( Figure 1 (c)). Dorsal margin uniformly curved, depression between head and rest of body absent ( Figures 1

(a), 2(a)). Posterodorsal and posteroventral angles rounded ( Figures 1 (a), 2(a)). Posterior margin slightly convex ( Figures 1 (a), 2(a)). Sculpture of valves and head strongly developed ( Figures 1 (a – h), 2(a, c, e, i – k)).

Head small, not keeled, triangular ( Figures 1 (d), 2(b)), its dorsal margin broadly rounded. Rostrum long, protruding downward. Compound eye larger than ocellus, distance between centre of eye and ocellus two times shorter than distance between centre of ocellus and tip of rostrum. Head shield elongated, with a maximum width immediately behind mandibular articulation, its posteriormost extremity triangular ( Figure 2 (c)). Structure of head pores are typical for the subfamily Chydorinae (Kotov 2013) : two major head pores at body midline, PP = 0.6 – 0.8IP ( Figures 1 (e, f)) 2(c)). Minute pores located slightly asymmetrically to midline, closer to anterior major pore than to posterior one. Surface of head between pores with ornamentation represented by short lines ( Figure 2 (c)), same with rostrum ( Figure 2 (l)).

Labrum large ( Figure 2 (d)). Distal labral plate densely setulated. Labral keel short, triangular, its anterior margin is straight or slightly convex, distal angle is acute.

Valve subovoid ( Figure 2 (e)). A row of numerous fine setules located quite close to posterior margin, these setules gradually increasing in size to posteroventral angle ( Figure 2 (e, f)), anterior setae located exactly at the valve margin and clearly not articulated, posterior setae internally articulated. Ventral margin convex, covered by densely pubescent setae of different size ( Figure 2 (f – h)). Anteroventral angle broadly rounded ( Figure 2 (k)). Outer surface of posterior and anterior portion of valves covered by long parallel sometimes anastomosing lines, with short sometimes wavy lines between them ( Figure 2 (e), 2(i)). Ornamentation of central portion of valves represented by short lines only ( Figure 2 (j)).

Thorax long ( Figure 2 (a)), abdomen relatively short ( Figure 2 (a)).

Postabdomen subrectangular, postabdomen length/height ratio about 2.5 ( Figure 3 (a)). Ventral margin straight to slightly convex. Preanal and anal margins almost equal in length, postanal margin is about two times longer than preanal and anal margins. Preanal and postanal angles well expressed. Postanal margin almost parallel to ventral margin and straight. Distal angle of postabdomen almost straight, somewhat rounded ( Figure 3 (b)). Each side of postanal portion provided with a row of thin and rather long postanal composite teeth, increasing in size distally. Row of postanal denticles evenly turned into a row of bunches of fine setules on anal margin. Bunches of fine short setules cover lateral surfaces of postanal and anal margins. Postabdominal claw massive and long (subequal in length to anal margin), slightly curved ( Figure 3 (b)). Dorsal edge of claw armed with a pecten of fine setules decreasing in size distally. Two basal spines on each claws. Distal basal spine long (slightly longer than the base of claw). Proximal basal spine relatively short (two times shorter than distal spine). Postabdominal seta relatively long, about times longer than preanal margin. Its distal segment supplied with delicate setules.

Antenna I not reaching tip of rostrum, slightly narrowing distally. Antennular sensory seta slender, almost subequal to antennular body, arising subdistally ( Figure 3 (c)). Nine short aesthetascs, subequal in size.

Antenna II relatively short ( Figure 3 (d, e)). Antennal formula: setae 0 – 0-3/1 – 1-3, spines 1 – 0-1/0 – 0-1. Coxal part folded, with two sensory setae. Basal segment robust, with a rudimentary distal spine between exopod and endopod. Antennal branches relatively elongated, subequal in length, all their segments cylindrical, proximal exopod segment slightly longer than proximal endopod segment. Apical setae long, unequal in length, with chitinous insertions in their distal segments. Seta arising from proximal endopod segment thin and relatively long (subequal in size to endopod branch with apical spine). Seta of the middle endopod segment long, reaches tips of longest apical setae. Spine of proximal exopod segment very short (shorter than 1/4 of the middle exopod segment length). Spines on both apical segments long. Endopod apical spine slightly longer than exopod spine.

Thoracic limbs: five pairs.

Limb I large. Accessory seta short (not represented in Figure 3 (f), because located on other side of limb corm), ODL conical, relatively small, bears a long seta with setulated distal segment and a short seta with bilaterally setulated distal segment ( Figure 3 (g)). IDL thicker than ODL, the former supplied by series of setules; first IDL seta short, setulated in distal portion, second IDL seta long, armed distally with short, fine setules and long third seta represented by thick, strongly curved hook, its concave side supplied by a series of minute spinules in its third quarter ( Figure 3 (h)). Limb corm almost rectangular in lateral view. Endite 4 ( Figure 3 (f: e4)) with three soft posterior setae ( Figure 3 (f: a – c)) and a stiff anterior seta 1. All these setae subequal in size. Endite 3 with a short posterior seta d, very long setae e and shorter seta f, and a stiff anterior seta 2. Endite 2 with three posterior long setae (g – i) and short seta j, and anterior stiff seta 3. Three robust long setules located between seta 2 and 3. Endite 1 with a short seta, a remnant of maxillar process ( Figure 3 (f: e1)). Fascicles of thin setules on inner face of limb, plus bunches of longer thicker setules at ventral margin of limb. Two slender long ejector hooks unequal in length ( Figure 3 (f: ejh)).

Limb II triangular-rounded. Exopodite ( Figure 4 (a: ext)) ovoid, with a long seta (with length of 3 – 4 exopodite body lengths). Inner portion of limb with eight scrapers ( Figure 4 (a: 1 – 8). Among them scrapers 1 – 3 especially long, scrapers 4 – 5 shorter, subequal in size, 6 – 8 even shorter, also subequal in size. A series of small projections posteriorly to distal setae, and a large sensillum between scraper 3 and 4. A shallow incision between endite 2 and endite 1. Distal side of gnathobase (=endite 1 sensu Kotov, 2013; Figure 4 (a: e1)) with rows of fine, short and especially long setules. Distal armature of gnathobase with four elements, one of them represented by minute sensillum. Filter plate with eight setae, increasing in size proximally.

Limb III with ovoid densely setulated preepipodite ( Figure 4 (b: pep)) and ovoid epipodite ( Figure 4 (b: epp)). Exopodite ( Figure 4 (b: ext)) subrectangular, its width about half of its length, with three bilaterally setulated lateral setae and four distal setae differing in size and armature. Among them two setae covered by long setules and two setae covered by short stiff setules. Distal endite (in terms of Kotov 2013) with three anterior setae (1, 2, 3 in Figure 4 (b, c)): setae 1 and 2 subequal in size and significantly longer than seta 3. Proximal endite with four small anterior setae and a very small sensillum. Six soft setae on posterior face of limb ( Figure 4 (c: a – f)). Distal armature of gnathobase with four elements (thick bottle-shaped sensillum and three small setae) and a bunch of long setules. Filter plates with eight setae subequal in length.

Limb IV with ovoid densely setulated preepipodite ( Figure 4 (d: pep)) and ovoid epipodite ( Figure 4 (d: epp)) with a small finger-like projection. Exopodite ( Figure 4 (d: ext)) rounded, bears seven setae of different length. Among them five setae covered by long setules and two setae covered by short setules, the latter unequal in length, lateralmost seta almost two times shorter than next seta. Inner distal portion of limb IV with four setae ( Figure 4 (e: 1 – 4)): distalmost seta 1 stout, with short setules; three other setae (2 – 4) with inflated bases and long setules on distal segments. Four soft setae (a – d) on posterior face of limb IV. Distal armature of gnathobase with four elements: three sensillae and a long bisegmented seta. Filter plate with six setae subequal in length.

Limb V with ovoid densely setulated preepipodite ( Figure 4 (f: pep)) and ovoid epipodite ( Figure 4 (f: epp)) supplied by a small finger-like projection. Exopodite large ( Figure 4 (f: ext)), oval, with a single, short distal seta and three long lateral setae. Inner limb portion as elongated, flat lobe, with setulated margin, supplied with setae 1 and 2 (distal segments of both setae covered by especially robust setules). Distal armature of gnathobase as a small elongated projection. Filter plate with four long setae (longest as long as seta 2).

Ephippial female. Shape as in parthenogenetic female, no demarcation line of ephippium and rest of valve, ephippium region dark brownish ( Figure 5 (a)). Ephippium carries a single large egg.

Adult male. Body elongated, rectangular-oval in the lateral view, height/length ratio about 0.55. Maximum height at first third of body ( Figure 5 (b)). Dorsal margin slightly convex, posterodorsal angle expressed, posteroventral angle broadly rounded. Ventral margin almost straight.

Head relatively large, narrow ( Figure 5 (b)). Rostrum shorter as compared with female, its tip pointed posteriorly. Compound eye slightly larger than ocellus. Distance from tip of rostrum to centre of ocellus somewhat larger than distance between centres of ocellus and eye.

Labrum with a short, triangular labral keel, its apex rounded ( Figure 5 (c)).

Postabdomen long and narrow, not curved, narrowing distally ( Figure 5 (d)), postabdomen length/height ratio about 4. Ventral margin in general straight, but somewhat undulated in postanal portion. Preanal margin straight, anal and postanal margins slightly concave. Postanal margin 1.5 times longer than preanal margin and 2 times longer than anal margin. Postanal and preanal angles smooth. Distal angle expressed, but rounded. Postanal margin armed by bunches of setules of similar size through all the margin length, following by clusters of short setules on anal margin. Bunches of fine setules on lateral surfaces of postanal and anal margins. Postabdominal claw almost straight, subequal in length to anal margin, with a thin basal spine subequal in length to claw diameter at base, and a minute second basal spine. Gonopores open laterally at a distance from claw bases.

Antenna I cylindrical, with nine terminal aesthetascs ( Figure 5 (e)). Male seta thick, long, located at middle of antennular body near sensory seta. Antenna II relatively short, basal segment robust, with a rudimentary spine ( Figure 5 (f)). Antennal branches relatively elongated, exopod and endopod subequal in length, all segments cylindrical, antennal formula, setae 0 – 0-3/1 – 1-3, spines 1 – 0-1/0 – 0-1. Apical spine on endopod longer than apical spine of exopod.

Limb I of moderate size, copulatory hook U-shaped ( Figure 5 (g)). Copulatory brush seta short, slender. IDL with four setae: setae 1 – 2 slender, of unequal length, seta 3 as a massive hook; male seta slender, curved in distal portion, about 2/3 length of seta 1.

Juvenile male of instar II. Body shape subovoid ( Figure 5 (h)) as in juvenile female of same instar. Postabdomen broad, with a rounded distal angle and composite teeth substituted by clusters of setules ( Figure 5 (i)). Antennas I and II as in female ( Figure 5 (j, k)). On limb I copulatory hook short, slightly curved, IDL with three setae, while male seta not yet developed ( Figure 5 (l)).

Size. Maximum length of adult parthenogenetic females up to 0.63 mm, maximum height 0.40 mm (therefore females could be larger than previously reported by Birge (1879) – 0.45 mm and Smirnov (1971) – 0.6 mm). Maximum length of ephippial females up to 0.56 mm, height 0.30 mm. Maximum length of adult males up to 0.48 mm, height 0.29 mm.

Variability. No significant variability between investigated individuals was found.

Distribution and ecology. D. hamata is widely distributed in the New World (from North America to Central America). It occurs in stagnant and rheophilic habitats (lakes, ponds, rivers and oxbows). In an arid zone of Mexico specimens morphologically similar to D. hamata (and wrongly identified as Picripleuroxus cf. quasidenticulatus ) were found in bromeliads ( Romero et al. 2011). In this case bromeliads seem an important refugium for aquatic organisms during the dry season ( Jocque et al. 2013).

Figures

Figure 1. Disparalona (M.) hamata (Birge, 1879), parthenogenetic female from Sunset Lake, NC, USA. (a) Adult parthenogenetic female, lateral view; (b) adult parthenogenetic female, lateroventral view; (c) adult parthenogenetic female, dorsal view; (d) head; (e–f) head pores and ornamentation of head near them; (g–h) posteroventral portion of valve, outer view. Scale bars 0.1 mm for a–d, 0.01 mm for e–h.

Figure 2. Disparalona (M.) hamata (Birge, 1879), parthenogenetic female from Swan Pond, Long Island, New York, USA. (a) Adult parthenogenetic female, lateral view; (b) head; (c) head pores and ornamentation of head near them; (d) labrum; (e) valve; (f) armature of posteroventral portion of valve, inner view; (g) armature of ventral portion of valve, inner view; (h) armature of anterior portion of valve, inner view; (i) ornamentation of posteroventral portion of valve, outer view; (j) ornamentation of central portion of valve, outer view; (k) ornamentation of anterior portion of valve, outer view; (l) ornamentation of rostrum. Scale bars 0.1 mm.

Figure 3. Disparalona (M.) hamata (Birge, 1879), parthenogenetic female from Swan Pond, Long Island, New York, USA. (a) Postabdomen; (b) distal portion of postabdomen and postabdominal claw from outer view; (c) antenna I; (d) antenna II, general view; (e) exopod and endopod of antenna II; (f) corm of limb I; (g) outer distal lobe of limb I; (h) inner distal lobe of limb I. Scale bars 0.1 mm.

Figure 4. Disparalona (M.) hamata (Birge, 1879), thoracic limbs of parthenogenetic female from Long Island, New York, USA. (a) Limb II. (b) Limb III. (c) Fragments of gnathobase and filter plate of limb III. (d) Limb IV. (e) Fragments of gnathobase and filter plate of limb IV. (f) Limb V. (g) Fragments of gnathobase and filter plate of limb V. Scale bars 0.1 mm.

Figure 5. Disparalona (M.) hamata (Birge, 1879), ephippial female and adult male from Jordan Harbor, Ontario, Canada. (a) Ephippial female, lateral view; (b) adult male, lateral view; (c) labrum of adult male; (d) postabdomen of adult male; (e) antenna I of adult male; (f) antenna II of male; (g) limb I of adult male; (h) juvenile male of II-nd instar male, lateral view; (i) postabdomen of juvenile male II; (j) antenna I of juvenile male II; (k) antenna II of juvenile male II; (l) limb I of juvenile male II. Scale bars 0.1 mm.