Bythotrephes longimanus Leydig 1860

• Main Author: Korovchinsky, Nikolai M.
• Format: Text
• Language: unknown
• Published: Zenodo 2015
• Subjects: Biodiversity; Taxonomy; Animalia; Arthropoda; Branchiopoda; Diplostraca; Cercopagidae; Bythotrephes; Bythotrephes longimanus; Bergen; Beck; Seta; Gam; Boden; Christiania; Juv; English Lake; Lampert; Tbilisi; Røen; Arktis*; Subarctic
• Online Access: https://dx.doi.org/10.5281/zenodo.5611000; https://zenodo.org/record/5611000

Bythotrephes longimanus Leydig, 1860 (Figs. 2–9) Bythotrephes longimanus : Leydig 1860, pp. 244‒246, Taf. 10, Fig. 73‒75; Weismann 1876, pp. 12‒14, Fig. 1; Ischreyt 1934 a, pp. 261, 277, Abb. 16 c.; 1935, p. 199; 1936, p. 361; 1937, p. 55; 1939, p. 110, 118, 119, 128, Abb. 1, 3, 4, 5; Margaritora 1985, pp. 338‒341, Fig. 134, 135; Litvinchuk 2002, p. 128, Fig. 38; 2007, p. 192. B. longimanus longimanus : Flössner 1972, pp. 405–406, Abb. 190 a; 2000, p. 375, Abb. 136 d. B. longimanus brigantinus Ischreyt, 1930, pp. 266, 302, 320 ‒ 321, Fig. 6 b, 9 c, 12, 13a–c, 14‒16. Bythotrephes lariano ( B. longimanus lariano ) Agnesotti, 1935, pp. 157‒172, Fig. 1, 2. B. longimanus v. carnica Ischreyt, 1939, p. 110, 119, 125 ‒ 126, 128, Abb. 6. B. Cederströmii Schödler: Beck 1883, pp. 780–782, pl. 12, figs 1–8. Non Bythotrephes longimanus Leydig: Lilljeborg 1861, p. 268, Taf. 8, Fig. 23‒29; Sars 1861 [1993], p. 156, Plates 106‒109; Sars 1890, p. 51; Lilljeborg 1901, pp. 604‒617, Tab. 80, fig. 10‒19; Tab. 81, fig. 1‒2; Tab. 82, fig. 1‒10; Ekman, 1904, pp. 28–29; Rylov 1935 a, pp. 152–155, figs 230–233; Behning 1941, pp. 352‒356, Fig. 146; Manuilova 1964, pp. 291‒293, Fig. 160; Flössner 1972, pp. 403‒408, Abb. 189, 190 b (partim); 2000, pp. 371‒376, Abb. 136, a‒c, e‒g; Mordukhai- Boltovskoi & Rivier 1987, pp. 149‒152, Fig. 44, 93; Vekhov 1987, pp. 28‒29, Fig. 1, 2; Røen 1995, pp. 322‒324, Fig. 146; Rivier 1998, pp. 169‒173, Fig. 215, 216. Material examined. Germany : Boden See ( type locality ), leg. H.-B. Stich, having three main areas: 1 ) Zeller See, 0 4.05.2009, 4 ad.; 2 ) Fischbach-Uttwil, 0 7.09. 2009, numerous ad. and juv.; 3 ) Bregenzer Bucht, 0 7.09.2009, 10 ad., 1 juv.; 4 ) “ Bythotrephes longimanus Leydig, Bodensee, 1892, Lampert G.”, 2 females of first generation, 5 ad., 1 juv., 1 male, (MNB, № 9596). Switzerland: 1 ) Lake Geneva (Lac Leman, Genfer See): a) “ Bythotrephes longimanus, Lac Leman, Forel, 1879 ”, 11 ad., 2 juv. (deformed), ZIN (№ 1638), b) 2 ad., 3 juv., “ B. longimanus s.str., Swit., Lac Leman, 0 7.1887, coll. P.T. Cleve”, MEUU (№ 2671), c) “ B. longimanus , Genfer See, 24.10. 1899, H. Blanc S.”, 23 ad., MNB (N º 18910), d) “ B. longimanus, Genfer See, 28.7. 1900, Blanc G.”, numerous ad., MNB (N º 18910), e) “ B. longimanus, Genfer See, 9.10. 1900, Blanc S.G.”, 12 ad., 1 juv., MNB (N º 18910); 2 ) Vierwaldstättersee, “ B. longimanus , 7.11 ”, 8 ad., 3 juv. (deformed), coll. Verestchagin, ZIN (N º 6855); 3 ) Lake Neuchâtel: a) “Neuchateler See, Februar, Fuhrmann”, 22 ad., 4 juv., MNB (N º 18910), b) “Neuchateler See, July, Fuhrmann”, 5 ad., MNB (N º 18910), c) “ Bythotrephes longimanus Leydig, Schweiz, Neuchateler See, October, Blanc I Fuhrmann G.”, 13 ad., MNB (N º 18910). Italy: 1 ) Lago di Como (Lago Lario, Comer See), “ Bythotrephes longimanus Leydig, 1860, Comer See, bis 72 m tief, leg. Besana, 23.9. 1900, ded.Weltner”, some dried ad., MNB (N º 18909); 2 ) Lago di Garda (Gardasee), “ Bythotrephes longimanus Leydig, 1860, Gardasee, 0‒70 m, leg. Bullemer, 8.1910, ded. Weltner, 1.1918 ”, numerous ad., MNB (N º 18845). Austria: 1 ) Mondsee, 0 7.1993, 5 ad.., leg. H. Löffler and S. Gaviria-Melo; 2 ) Millstättersee, 0 8.11.2011, 2 ad., 3 juv., 1 male, leg. G. Santner; 3 ) Grundlsee, 18.07.2007, 20 ad., 31.08.2007, 15 ad., leg. M. Luger and R. Schabetsberger. Great Britain: 1 ) bottle (MNB (N º 18929)) with a label: “ Bythotrephes longimanus Leydig, England, Scourfield G.” and four tubes: a) “Windermere, English Lake District, Scourfield G.”, 4 ad., b) “Grasmere, English Lake District, Scourfield G.”, 1 ad., c) “Llyn Quellyn, North Wales, Scourfield G.”, 1 ad., 1 male, d) “Llyn Padarn, North Wales, Scourfield G.”, 1 ad., 1 male; 2 ) bottle (MNB (N º 18913) with a label: “ Bythotrephes longimanus Leydig, 1860, Schottland, ded. Thomas Scott and Scourfield / Weltner” and two tubes: a) “Loch Ness, Scotland, Scourfield G.”, 3 ad., b) “Loch Lochy in Inversness, Scotland ”, 14 gam., 3 males. Data on body and body parts measurements of two populations are presented in Table 1. The main part of the description is based on a population from Bodensee. Data from other populations have been taken into consideration for comparison. Description. Female. General body appearance and segmentation. Body elongated and divided into four parts: head, thorax, abdomen, and postabdomen with long caudal process (Fig. 2 A). Its longitudinal axis is conspicuously incurved when head is located at almost right angle to the thorax. Also highly movable abdomen can be either at straight line with the thorax or stays at different angles to it. Head large with rounded anterior part filled by the enormously developed compound eye and bearing small antennules ventrally. Posterior part of head bears long swimming antennae and mouth parts consisting of mandibles, maxillules (mx I), and upper lip (labrum). Thorax with strongly developed muscular ventral side bearing four pairs of thoracic limbs of different size directed antero-ventrally. Dorsally, thorax bears sack-like carapace transformed into brood pouch sometimes reaching large size. Abdomen (metasome) is elongated, cylindrical, inconspicuously three-segmented and flexible, connected with small postabdomen, bearing ventrally a pair of straight claws and posteriorly very long straight caudal process with a pair of similar claws proximally. General body length of females (without caudal process) may reach 3.0 mm or slightly more (in the examined specimens it ranges from 1.62 to 2.66 mm) while the length of caudal process may surpass the body length considerably. Head. Comparatively very large (36.8‒44.6 % of body length) and subdivided into two parts: rounded anterior part mostly filled by large compound eye (18.4‒22.8 % of body length) and posterior part bearing dorsally a large saddle-shaped neck organ, swimming antennae and mouth parts. Eye contains numerous ommatidia (~ 300 or> 200 ommatidia according to Miltz (1899) and Martin & Cash-Clark (1995), respectively) and have large pigment spot which occupies about one-third or at most a half of the eye’s volume (see also Ekman 1904). Ocellus (naupliar eye) is absent (Elofsson 1966). Antennules. Small and situated on the ventral side of the anterior head part beneath the eye. They are bulbous (Fig. 2 C) and sit on the joined basis slightly split anteriorly. Terminally they bear five regular aesthetascs in two groups, in three and two in each one, and one shorter and thinner aesthetasc-like structure, situated in a group with two regular aesthetascs, and having slightly widened apical end with dark granular structure inside (“accessory simple seta” according to Scourfield (1896)). Swimming antennae. Comparatively long (56.6‒77.3 % of body length), with elongated cylindrical basipodite (43.7 % of body length) (Fig. 2 A) which has dorsal thin naked seta on its folded proximal part (Fig. 2 D) and tiny distal sharp outer denticle located closer to base of lower branch (Fig. 2 E, arrowed) (this denticle is not always well visible, possibly sometimes it may be absent). Of two antennal branches, the lower three-segmented one (endopodite), sitting on the apical basipodital prominence, is slightly longer than upper branch (33.3 % vs. 29.8 % of body length). The upper branch is four-segmented (length of segments from proximal to distal: 8.7 % (first rudimentary one + second segment), 9.1 %, and 12.3 % of body length, respectively) and lower branch is threesegmented (10.3 %, 7.9 % and 15.1 % of body length, respectively). Proximal most segment of the upper branch is rudimentary and clearly visible only externally, all other segments of both branches are much more developed. Internally, two proximal segments seem fused rather firmly while distally their junction probably is more flexible. Integument of antennal basipodite and branches are covered by tiny spinules, which are situated in rows (Fig 3 A). Small denticle with a saw-like row of surrounded minute prominences on the end of second segment of upper antennal branch (Fig. 3 A), similar prominences on the end of third segment of the same branch (Fig. 2 F), and small apical denticle on the distal segment of the same branch (Fig. 2 G). The distal segment of the lower branch is also armed by a small apical spine (Fig. 2 H). Small proximal-most segment of upper branch lacks setae, while other segments possess a row of two-segmented swimming setae of more or less similar size except distal of them which are shorter (the comparative lengths of setae of three segments of upper branch from proximal to distal ones are as follows: (32.1), (32.9, 35.3), (32.5, 32.5, 28.6, 23.4, 17.5) % of body length; the same for the four segments of lower branch: (31.3), (35.3), (34.5, 33.7, 32.1, 31.0, 22.6) % of body length. The length of basal setae segments are about 50‒63 % of their total length. All setae are bilaterally armed with rows of uniform thin setules. General formula of antennal setae: 0‒1 ‒ 2‒5 / 1 ‒ 1‒5. Mouth parts. They are represented by upper lip (labrum), mandibles, and maxillules (maxilla I). The upper lip (Fig. 3 E) is composed of two parts; the posterior thick and flattened slightly triangular lobe and anterior large proboscis-like outgrowth. The latter is separated from the former one by a deep indention of the cuticle. The triangular lobe bears numerous papillae (Fig. 3 F) along its posterior-internal (oral) margin while the outgrowth is armed with tiny spinules. Mandibles are bilobed and adapted for biting (Fig. 3 B), with a toothed, blade-like posterior lobe and small anterior lobe (mandibular process) armoured with a cluster of 12‒15 long prominences, bearing some tiny spinules distally (Fig. 3 C). Posterior lobe is strongly sclerotized and divided in two tooth-shaped parts, the larger (posterior) of which has a small additional tooth about midway along its border (Fig. 3 B). The inner surface of the mandible bears a small field of about 10 tiny spines (Fig. 3 D). Maxillules (mx I) look like two cylindrical structures situated posterior to mandibles (Fig. 2 I). Distally, they bear short central seta and some papillae near it. Maxillae (mx II) are absent; the openings of maxillar glands are situated near the bases of tl I laterally (see Olesen et al. 2003). Carapace. It looks like a bag-like structure, strongly modified into closed brood pouch (Fig. 2 A). It is attached to the dorsal side of thorax and reaching sometimes rather big size, surpassing body length. The females of first generation possess the biggest brood pouch, containing up to 22 embryos which distend its walls greatly (Zozulja 1977). The postero-ventral region of the brood pouch near its junction with dorsal side of thorax always appears to be indented. Thoracic limbs. Four pairs of strongly chitinized, stenopodous limbs are densely situated along the muscular ventral side of thorax and directed antero-ventrally (Fig. 2 A). All of them have complex and variously setaceous armament along their inner side. Limbs of three anterior pairs are five-segmented and those of the last fourth pair are three-segmented. Protopodites of all of them, covered by comparatively softer cuticle, are inconspicuously delimited into two parts (segments), coxa and basis, (Fig. 4 B, 4 C) while the endopodites of limbs of three anterior pairs are composed of three well developed segments and those ones of the fourth pair are unisegmented (Figs. 2 J, 4 D, 4 G, 6 A, 6 B). Limbs of first pair (tl I) are especially long and strong, their length often surpasses body length (83.1–112.8 % of body length) (Fig. 2 A, 2 J). Terminally, the inner side of their protopodite bears a small triangular lobe, “gnathobasic” process (the nature and homology of this structure will be discussed below), armed laterally and distally with two denticles and numerous spinules (Figs. 2 K, 4 B). The external part of protopodite is longer than internal one and bears apically a small conical outgrowth, having at its tip a tiny spine (Fig. 4 B, arrowed, 4 C). The first segment of endopodite is long (30.7–35.4 % of tl I length) and bears 4–7 (mostly 5–6) anterior lateral setae (their number on limbs of one individual can vary) (Fig. 2 K) of type “j” with rough spine-like setules (Fig. 4 J, 5 A). Distally, this segment bears short thorn-like anterior seta of type “j” and long posterior finely setulated seta of type “k” (Figs. 2 M, 2 N, 4 K). The second segment of endopodite is conspicuously shorter and bears only two apical setae: very short anterior seta of type “j” (sometimes it may be reduced up to small prominence, see Fig. 2 P) and longer posterior one (Figs. 2 O– 2 R); both of them often seem naked. The terminal third segment of endopodite is also long (27.2–35.3 % of tl I length), almost equal or even surpassing the length of first segment (79.1–114.3 % of the latter), and bears apically four long roughly spinulated setae, two of them terminally and two subterminally (Fig. 2 J, 2 L); the anterior subterminal of them is shorter than others. Basally, these setae are armed by a row of smaller spines (Fig. 4 F, 5 F), while distally—by larger lanceolate spines directed terminally (Fig. 5 B). The limbs of second pair (tl II) are considerably shorter, their protopodite, again externally, is conspicuously longer and bears a conical outgrowth (Fig. 4 A, 4 C). The first, basal segment of their endopodite, bears a row of 4– 7 (mostly 5–6) rather long anterior lateral setae of type “l” (their number also can vary in one individual) (Table 2) (Fig. 4 D, 4 E, 4 L). Sometimes there is one posterior lateral seta of the same type on this segment (Table 2). The terminal setae of the segment are of the same type “l” but may be longer, especially posterior one. Internally, this segment bears stout cylindrical “gnathobasic” process, possessing some prominences of different size, one small, thin seta, and a pore apically (Figs. 4 D, 5 D). The second segment is short with only two setae, the anterior of which is of “j”- type, but comparatively thicker with more rough setules than it was in respective setae of tl I (Fig. 4 D, 4 J). The distal, third segment of endopodite of the limb bears four setae, two terminal and two subterminal ones (Fig. 4 D). Of the latter, the anterior seta is of type “m”; it is comparatively short, thick and armed with a number of thin lateral denticles, while its distal part is naked and slightly hooked apically (Fig. 4 D, 4 M). Its neighboring posterior subterminal seta is considerably longer and similar with subterminal and terminal setae of tl I, having sharp straight apex (Fig. 4 D). The anterior terminal seta is of type “n”; thick and comparatively short with longitudinal ribs, few thin lateral denticles, and slightly hooked apically as well (Figs. 4 D, 4 N). The posterior terminal seta similar to the respective subterminal one but shorter, has fewer denticles and slightly hooked apical end (Fig. 4 D). The limbs of the third pair (tl III) are generally similar to those of the previous ones, differing in some details. The external outgrowth of their protopodite is conspicuously larger (Fig. 4 C) and lateral anterior setae of first segment of endopodite are fewer (3–4) while posterior ones were not observed at all (Table 2) (Fig. 4 G, 4 H). These setae bear fewer proximal spinules. The “gnathobasic” process is similar to that one of tl II (Fig. 5 E). Of setae of second segment, the anterior one is thinner, longer, and more finely setulated than the respective seta of tl II. Terminal and subterminal setae of third segment are similar to those of tl II but shorter and bear fewer denticles (Figs. 4 G, 4 I, 5 C). The limbs of the fourth pair (tl IV) are considerably reduced; their protopodite bears externally and posteriorly distally spinulated seta sited on a short cylindrical base (Figs. 5 G, 6 A, 6 B, 6 E). The only segment of endopodite has two rows of comparatively short spine-like setae. The external row always consists of two setae, and the internal row of 5–7 (usually 5–6) setae, which differ in their appearance. Most of them (both external setae and four internal setae, located closer to protopodital seta, are stronger and armed with few proximal spinules (Figs. 6 A, 6 B, 6 D), while two anteriormost setae are slightly thinner and more feathered (Fig. 6 C). Almost the whole internal part of the endopodital segment is occupied by the reduced “gnathobasic” process armed by some denticles and thin seta (Figs. 5 G, 5 H, 6 B). The apex of the process probably has a pore covered by membrane (Fig. 5 H). The bulbous structure is situated just after the tl IV (Fig. 2 A). Abdomen (metasome) (Fig. 2 A, 2 S) is often deformed, compressed and for this reason it may be hardly measured (approximately its length is about 15–20 % of body length). It is inconspicuously delimited in two parts (segments?), short proximal and longer distal with prominent fold in the middle dorsal side. Due to softness of the abdomen’s integument, some additional smaller folds disguise its “segmentation”. Postabdomen is comparatively small (6.3–9.1 % of body length), the anal opening is situated between postabdominal claws. The latter are large and more or less straight, directed downwards or slightly curved posteriorly (6.6–10.9 % of body length) (Figs. 2 A, 2 S, 6 F, 6 G). Sometimes the line divided postabdomen in two longitudinal parts, proximal and distal ones, may be observed, to the latter of whose the claws are attached (Figs. 2 S, 6 G, arrowed). Caudal process is directly connected with postabdomen either invisibly (Fig. 6 F) or being separated from it by a conspicuous border (Fig. 6 G) and then proceeds as a very long and straight spine-like structure variable in its length (186.0–301.0 % of body length), thus surpassing the body length in 1.8 –3.0 times (Fig. 2 A, 2 B). Basally it bears a pair of claws similar to those of postabdomen (6.0– 13.2 % of body length) (Fig. 6 F, 6 G), and apically two minute setae arose from common base (Fig. 2 T). Two pairs of claws sit closely (distance between them 7.5–14.9 % of body length). Between them, the thickness of the structure is considerable, reaching 40.0–123.0 % of the interclaw distance (Table 1). The caudal process is strongly chitinized and its surface is covered by numerous minute spinules (Fig. 5 I). Female of first generation hatched from resting eggs. Three such specimens were found, one (deformed) in the sample from Bodensee taken in the beginning of May 2009 and other two in old sample from the same lake stored in MNB (Nº 9596). One of the latter had body : Published as part of Korovchinsky, Nikolai M., 2015, Redescription of Bythotrephes longimanus Leydig, 1860 and B. cederströmii Schödler, 1877 (Crustacea: Cladocera: Onychopoda), with notes on the morphology and systematics of the genus Bythotrephes Leydig, 1860, pp. 1-44 in Zootaxa 3955 (1) on pages 6-21, DOI: 10.11646/zootaxa.3955.1.1, http://zenodo.org/record/288438 : {"references": ["Leydig, F. (1860) Naturgeschichte der Daphniden. Laupp & Siebeck, Tubingen, 252 pp.", "Weismann, A. (1876) Das Thierleben im Bodensee. Schriften des Vereinsfur Geschichte des Bodensee und seiner Umgebung, 7, 132 - 161.", "Ischreyt, G. 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