Revision of the Diaphanosoma modigliani – Diaphanosoma dubium species group (Crustacea: Ctenopoda: Sididae), with description of a new species from Tropical Asia

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Hydrobiologia 361: 113–123, 1998. c 1998 Kluwer Academic Publishers. Printed in Belgium.

Revision of the Diaphanosoma modigliani – Diaphanosoma dubium species group (Crustacea: Ctenopoda: Sididae), with description of a new species from Tropical Asia N.M. Korovchinsky A.N. Severtsov Institute of Ecology and Evolution of Russian Academy of Sciences, Leninsky prospect 33, 117071 Moscow, Russia Received 16 January 1997; in revised form 16 September 1997; accepted 18 November 1997

Key words: Diaphanosoma modigliani, D. dubium, D. tropicum sp.nov., taxonomic revision, tropical Asia

Abstract We provide a taxonomic differentiation of species related to Diaphanosoma modigliani Richard s.str., recorded outside its type locality (Lake Toba, Sumatra, Indonesia) for the first time. Diaphanosoma tropicum sp.nov. is described on material from Sri Lanka, Malaysia, Thailand, Philippines and China with analysis of interpopulation morphological variability supplemented by notes on geographical distribution and biology of the species. Introduction Diaphanosoma modigliani Richard, 1894, originally described from Lake Toba (Sumatra, Indonesia), was long considered widely distributed in tropical Asia. Recent reinvestigation of the topotypical material of the species showed that all subsequent records are either unsubstantiated of erroneous (Korovchinsky, 1991). The specification of Diaphanosoma modigliani s.str. also allowed to suggest the occurrence of related, yet unknown Diaphanosoma species in tropical Asia, first of all in Malaysia and Sri Lanka from where representatives were described in more detail (Idris & Fernando, 1981; Rajapaksa & Fernando, 1982). The investigation of additional abundant material from the collection of Professor C.H. Fernando (University of Waterloo, Canada) (CHF-collection) and some other sources confirmed this suggestion and has led to the taxonomic revision of a group of species in tropical Asia.

Material and methods Abbreviations: ad – adult parthenogenetic females, juv – juvenile parthenogenetic females.

Most of the material examined was in the tubes with formalin. Diaphanosoma modigliani Richard: Indonesia, Sumatra, Lake Toba (type locality): 1) Prapat, 3.07.1977 (CHF 3–37), 1 ad; 2) Prapat, littoral, 4.07.1977 (CHF 3–38), 3 ad; 3) st.5, 4.07.1977 (CHF 3–302), 13 ad; 4) southern part, Sitamiang, 6.09.1984 (CHF 3–300.1), 5 ad; 5) southern part, Balige, 6.09.1984 (CHF 3–301.1), 35 ad, 6 juv; 6) southern part, Nainggolan, 6.09.1984, 18 ad. Indonesia, Sulavesi, Lake Tempe (4 060 S; 119 0 57 E), 25.07.1977 (CHF 3–34), 6 ad. Diaphanosoma tropicum sp.nov.: Sri Lanka, Chandrika wewa: 1) 23.12.1970 (CHF 4–42), 1 ad, 1 juv; 2) 11.01.1980, 105 ad; 3) total mount, 11.01.1980 (CHF 4–42) with 8 ad labelled ‘Sri Lanka, Diaphanosoma sp.’ and then ‘Diaphanosoma modigliani”. Malaysia, Batu Barendam, Old Pottery Pond: 1) 10.01.1973, littoral (CHF 1–104.2), 2 ad, 1 juv; 2) 10.01.1973, pelagial (CHF 1–104.3), 79 ad; Perak State, Ipoh, fish pond, 11.10.1974 (CHF II–208.2), 72 ad, 2 juv; Pahang State, Bubit Tiaggi, pond, 29.8.1975 (CHF 1–134), 68 ad, 7 juv.

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114 Thailand, Nong-kai Prov., Tha-bo distr., vegetated back-water of Hui mong stream, 25.7.1996, 7 ad (leg. Renu Sirimongkonthaworn). Philippines, Luzon Island, Talisay Batangas, 22.7.1994, 2 juv (leg. V. Comacho). China, Hubei Prov., Czinpiertan, 5.10.1958, numerous deformed ad and juv (collection of Zoological Museum of Moscow State University). Diaphonasoma dubium Manuilova: Malaysia, Perak State, Kuala Kangsar, fish pond, 11.10.1974 (CHF II–213.2), numerous ad. Sri Lanka, total mount, 4.01.1980 (CHF 4–412) with 2 ad labelled ‘Ridiyagana Tank, Diaphonasoma sp.’ Besides, we investigated two total mounts with Diaphonasomas (3 ad) from Philippine Islands (Calovach, Maravi and Lake Lanao) obtained by A. Mamaril from the collection of Professor D. Frey (Indiana University, USA) and identified as ‘Diaphanosoma modigliani’. In fact they contained another species, not identified correctly due to deformation of specimens and invisibility of some important diagnostic details. Figures were made by means of an RA – 4 drawing apparatus, and measurements of body parts were performed according to Korovchinsky (1978).

Descriptions and remarks Diaphanosoma modigliani Richard, 1894 All diagnostic features of specimens from the type locality (Lake Toba) were in agreement with those given before (Korovchinsky, 1991). Only maximum body length of new specimens was slightly larger, reaching 1.22 mm. The finding of the species outside its type locality, in Lake Tempe (Sulavesi Island), despite of low number of specimens, provided an opportunity for a preliminary interpopulation comparison. The main diagnostic features (head and valve form, armament of swimming antennae, valve margin and postabdominal claws) were quite characteristic (Figures 1–8). Interpopulation differences were rather small, and concerned the form of dorso-posterior shell’s corner (Figures 1, 6). Besides, the eye of Sulavesi specimens was somewhat larger (av. 7.6% of body length vs. 6.6% in type locality).

Diaphanosoma tropicum sp.nov. Idris & Fernando, 1981: 235–236, Figures 2–4 (D. modigliani); Rajapaksa & Fernando, 1982: Figures 12–16 (D. modigliani); Idris, 1983: 11–13, Figure 3, A–C (D. modigliani). Parthenogenetic female. Measurements of body parts of specimens from different populations are shown in Table 1. Head (Figures 9, 10, 15) large, its dorsum greatly protruding; general form of anterior body part coneshaped. Ventrally, anterior part of head with rounded bulge under the eye. The form of head may be somewhat different (Figure 10). Eye of average size or rather large, noticeable closer to ventral side of head. Swimming antennae long, their distal ends reaching posterior margin of valves. At apical end of basipodite (Figure 11) one small dorsal outgrowth corresponded to another one on the base of upper antennal branch, and in the middle of outer side, a comparatively long seta, tapering distally, noticeably longer seta on the basipodital inner apical part. End of proximal segment of 2-segmented upper branch with small spine (Figure 12). End of distal segment (Figures 13, 16–19) with comparatively large and noticeably curved spine often having hook-like appearance, and pointed or rounded lateral outgrowth (sometimes it seems absent). Antennal setal formula 4-8/0-1-4. The pattern of setal setulation as described in D. modigliani (Korovchinsky, 1991). Valves oblong-oval, upper posterior margin protruding, then curving down and forward, gradually passing into ventral margin (Figures 9, 15). The latter with rather large ventral inflexion (Figure 27), not shifted proximally, and bearing 7–11 long feathered setae. The proximal of them shorter and passing on the internal side of inflexion, and distalmost may sit on the lower part of postero-ventral margin (Figure 23). The latter and part of posterior margin with long row of 15– 58 (usually 25–43) denticles (Figures 20–26), the lowermost of which noticeably larger than uppermost, and their number usually differing on both valves: 39/43, 34/38, 23/30, 36/34, 40/48, etc.). Number of denticles increasing with body size. The row of denticles usually subdivided into unsharply delineated groups by 2–7 denticles with 7–12 thin setules between them, but infrequently there may be the single larger denticles in the row (Figures 20, 22). There is a row of minute supramarginal spinules along the inner side of posteroventral margins (Figures 25, 26). No dorsal spine at posterior margin of valves.

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Figures 1–8. Diaphanosoma modigliani Richard, 1894, parthenogenetic female, Lake Tempe (Sulavesi Island, Indonesia). 1. general lateral view; 2. distal part of antennal basipodite, outer side; 3. distal end of first segment of upper 2-segmented antennal branch; 4. distal end of second segment of upper 2-segmented antennal branch; 5. distal part of lower 3-segmented antennal branch; 6. posterior and postero-ventral valve margin; 7. denticles of postero-ventral valve margin; 8. postabdomen, lateral view.

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Figures 9–14. Diaphanosoma tropicum sp.nov., parthenogenetic females, Chandrika wewa (Sri Lanka). 9. general lateral view; 10. variability of head form, lateral view; 11. distal part of antennal basipodite, outer side; 12. distal part of first segment of upper 2-segmented antennal branch; 13. distal part of second segment of upper 2-segmented antennal branch; 14. distal part of lower 3-segmented antennal branch.

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1. Chandrika weva, Sri Lanka, 11.01.1980 (n = 15) 0 .70–1.05 40.3–48.0 23.5–28.0 7.1–9.2 66.0–74.3 0.91 (0.89) 44.1 25.4 8.1 69.8 0.096 2.08 1.39 0.62 2.48 10.5 4.72 5.48 7.70 3.47 2. Old Pottery Pond, Batu Barendam, Malaysia, 10.1.1973 (n = 15) 0.84–1.18 40.6–45.6 23.2–25.3 5.8–8.3 64.1–73.3 1.01 (0.93) 43.1 24.3 7.4 67.4 0.11 1.30 0.76 0.71 2.93 10.6 3.02 3.12 9.57 4.35 3. Fish pond, Ipoh, Perak State, Malaysia, 11.10.1974 (n = 15) 0.87–1.08 42.9–47.6 23.1–25.4 7.0–8.1 63.1–75.3 0.92 (0.88) 44.5 24.2 7.7 68.7 0.054 1.49 0.74 0.29 3.66 5.87 3.35 3.04 3.77 5.32 4. Pond, Bubit Tiaggi, Pahang State, Malaysia, 29.08.1975 (n = 15) 0.74–1.09 43.8–50.0 23.2–28.2 7.0–8.5 69.0–79.2 0.92 (0.83) 46.8 26.2 7.8 72.5 0.098 3.27 1.26 0.48 2.73 10.6 6.99 4.81 6.15 3.76

Body length Head length: Head height: Diameter of eye: Length of (mm) Body length Body length Body length swimming (%) (%) (%) antennal: Body length (%)

43.5–49.4 46.3 2.06 4.45 42.4–51.4 45.4 2.36 5.19

65.7–76.5 70.2 3.27 4.66

44.0–54.7 48.3 3.30 6.84

69.1–84.1 75.5 4.01 5.32 65.9–75.8 71.7 2.88 4.02

44.3–56.0 52.2 3.08 5.90

Length of lower 3-segmented antennal branch: Length of basipodite (%)

69.0–90.7 79.5 5.76 7.26

Length of upper 2-segmented antennal branch: Length of basipodite (%)

61.1–68.5 64.7 2.39 3.69

59.6–70.5 64.6 2.73 4.23

60.6–70.8 64.0 2.72 4.25

59.6–73.4 65.7 3.96 6.02

64.3–79.2 70.0 3.92 5.61

64.7–71.0 68.0 1.96 2.88

67.2–79.4 72.5 3.32 4.58

72.6–83.3 77.5 3.52 4.54

Length of lower Length of antennal branch setae natatoriae: Length of upper Body length antennal branch (%) (%)

24–33 28.0

23–44 33.1

34–58 42.9

22–43 33.6

The number of denticles on ventro-posterior valve margins

Table 1. The measurements of body parts of specimens of Diaphanosoma tropicum sp. nov. from four populations (In each column from top to bottom: limits, mean, SD, CV)

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Figures 15–26. Diaphanosoma tropicum sp.nov., parthenogenetic females (15–17, 19, 23 – Batu Barendam, Malaysia; 18 – Bubit Tiaggi, Malaysia; 20, 21, 25 – Chandrika wewa, Sri Lanka; 22, 24, 26 – Ipoh, Malaysia). 15. general lateral view; 16–19. distal part of second segment of upper 2-segmented antennal branch with hooked apical denticle; 20–24. posterior and postero-ventral valve margins; 25. denticles of postero-ventral valve margin, outer side; 26. the same, inner side.

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Figures 27–35. Diaphanosoma tropicum sp.nov., parthenogenetic female (27, 29 – Ipoh, Malaysia; 28 – Chandrika wewa, Sri Lanka). 27. ventral valve inflexion; 28. postabdomen, lateral view; 29. basal spines of postabdominal claw, inner side. Diaphanosoma dubium Manuilova, 1964, parthenogenetic female, Kuala Kangsar, Malaysia. 30. general lateral view; 31. distal part of antennal basipodite, outer side; 32. distal part of first segment of upper 2-segmented antennal branch; 33. distal part of second segment of upper 2-segmented antennal branch; 34. posterior and postero-ventral valve margin; 35. postabdomen, lateral view.

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120 Postabdomen somewhat prominent dorsally, laterally and distally with groups of spinules. Claws relatively large with three basal spines of average size (Figure 29). Distal to the latter along the dorsal edge a row of spinules, some spinules also located ventrally. Setae natatoriae long. Body length 0:69 1:19 mm. Juveniles similar to adults, but with relatively longer swimming antennae and fewer denticles on valve margin (15–23). Males unknown. Interpopulation morphological variability Four studied populations differed in mean body length. In general this length was smaller than in 15 specimens selected for detailed analysis (indicated in parenthesis in first column of Table 1). The largest size was in specimens from Batu Barendam, the smallest in specimens from Bubit Tiaggi. The latter were characterized by especially large heads and long swimming antennae with comparative long basipodite and short antennal branches. Their setae natatoriae were comparatively short, which was also characteristic of specimens of Ipoh. The specimens from Sri Lanka had a noticeable shorter basipodite and longer branches of swimming antennae as well as especially long setae notatoriae and a large eye. The number of denticles along the postero-ventral valve margin correlated with body size. They were more numerous in larger specimens from Batu Barendam and fewest in from Bubit Tiaggi. On the other hand, comparatively large representatives from Thailand with body length 0.87–1.19 mm possessed unusually few denticles (15–27). In Sri Lankian specimens, the spine on the end of upper antennal branch was noticeably less curved. Bubit Tiaggi’s specimens lacked small internal outgrowth near the apical antennal spine (Figure 18), and the neighbouring lateral outgrowth was unusually pointed. Remarks This species was recorded almost simultaneously under the name ‘D. modigliani Richard’ by Idris & Fernando (1981), Rajapaksa (1981), Kanduru (1981) and Rajapaksa & Fernando (1982) from Malaysia, Sri Lanka and South India. The descriptions make it possible to recognize species correctly from diagnostic features such as a cone-like head, curved apical spine

of upper antennal branch and number of denticles along ventro-posterior valve margins. At the same time Idris & Fernando (1981) and then Idris (1983) omitted setules between ventro-posterior denticles and incorrectly mentioned the presence of a spine on the posterior valve margin as well as the small length of swimming antennae not reaching posterior shell margin. Differential diagnosis The differences between D. tropicum sp.nov. and D. modigliani are summarized in Table 2. The average numbers from particular populations and their average sum indicate stable differences in body proportions between both species. The representatives of D. tropicum have comparatively larger head, eye, longer swimming antennae and setae natatoriae as well as fewer denticles on the ventro-posterior valve margin. Besides, it has been found that the ranges of D. tropicum sp.nov. and D. dubium Manuilova (= D. dubia, name emended by Korovchinsky & Mirabdullaev (1994)), originally described from the Amur River basin in Russian Far East, partly overlap. The specimens of the latter species from Malaysia also had large head with greatly developed dorsal part and eye shifted ventrally (Figure 30), long swimming antennae with thin seta on the outer distal side of basipodite, curved apical spine on the upper branch (Figures 31, 33), and distal part of shell lacking posterior spine and having a row of small uniform marginal denticles with setules between them (Figure 34). Besides, the postabdomen of both species has a prominent dorsal side (Figures 28, 35). On the other hand, D. dubium differs from the new species by even more massive head and longer swimming antennae having larger spine on the end of proximal segment of upper antennal branch (Figure 32), and by different form of posterior part of shell with prominent dorso-posterior angle and less numerous, smaller and more sparsely distributed marginal denticles. The specimens of D. tropicum from Thailand reminded of D. dubium in number of marginal valve denticles but differed in all other above mentiones respects. D. chankensis Ueno (Lake Chanka, Far East) is also close to D. tropicum sp.nov., but differs in having a noticeably smaller head, shorter swimming antennae, another structure of posterior and postero-ventral valve margins, and by the absence of setules between marginal valve denticles together with a curved spine at the end of the upper antennal branch.

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121 Table 2. The morphological differences between Diaphanosoma tropicum sp. nov. and D. modigliani Richard Traits 1. 2.

Spine on the end of upper antennal branch Ventral valve inflexion

3.

Denticles of ventroposterior valve margin

4.

Postabdomen and terminal claws

5. 6. 7. 8.

Head length: Body length (%) Head height: Body length (%) Diametr of eye: Body length (%) Length of swimming antennae: Body length (%) Length of setae natatoriae: Body length (%)

9.

D. tropicum sp. nov.

D. modigliani

Strongly curved Comparatively long and not shifted proximal Comparatively large and not very numerous (22–58) Dorsal part prominent, basal spines comparatively long 44.6 25.0 7.8 69.6

Slightly curved or strength Comparatively short and shifted proximal

Dorsal part not prominent, basal spines comparatively short 39.8 21.7 6.6 63.7

72.0

66.0

Small and very numerous (55–86)

 The average figures from four populations.  The average figures from type population.

Figure 36. The localities of Diaphanosoma modigliani (white circle) and D. tropicum (black circles).

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122 Type material Holotype: a parthenogenetic female 0.97 mm long from Chandrika wewa (Sri Lanka) in a tube with formalin deposited in the collection of Zoological Institute of Russian Academy of Sciences (St-Peterburg), N 55015. Paratypes: 3 parthenogenetic females from the same population in formalin were also deposited in Zoological Institute (St-Peterburg), and 3 other parthenogenetic females in British Natural History Museum (London), N 1996. 1410–1412. All other specimens are in the author’s collection. Etymology The species was named Diaphanosoma tropicum after its range in the tropical zone.

Discussion The recent revision of D. modigliani s.str. (Korovchinsky, 1991) and the present work reveal a group of close related species which co-occur in tropical and subtropical Asia. It includes D. modigliani, D. dubium and D. tropicum sp.nov. All them are characterized by a strongly protruding head, valves with more or less numerous uniform denticles and long setules along the ventro-posterior and posterior margins, absence of a spine near the latter one, and presence of a thin seta instead of a spine on the outer distal end of antennal basipodite along with usually curved apical spine on upper branch. It is interesting that tropical representatives of D. dubium from Malaysia showed more similarity with two other species of the group than those from the north that lacked the thin seta on the basipodital outer end and the curved apical spine of the upper antennal branch (Korovchinsky, 1992). The stability of these differences across the wide latitudinal distribution of the species needs further attention. These three species were confused for a long time with D. modigliani. Idris & Fernando (1981) and Rajapaksa & Fernando (1982) did not record D. dubium though this species was present in their material from Malaysia and Sri Lanka together with D. tropicum, while Kanduru (1981) differentiated both species in India. A study of specimens from the Philippines confirmed the opinion that Mamaril & Fernando (1978) did not have material of this species group (Korovchinsky,

1991). They possibly had D. orghidani transamurensis Korovchinsky, recently recorded in Lake Lanao (Mindanao Island, Philippines) (Korovchinsky, op.cit.), and in Luzon Island together with D. dubium (unpublished data). Now the presence of D. tropicum in Philippines has been confirmed as well. The present investigation reveals the first occurrence of D. modigliani outside type locality in Lake Tempe in Sulavesi Island. D. tropicum is more widely distributed in Asia, from the equatorial zone to about 30 N: in Southern India (Coimbatore) (Kanduru, 1981), Sri Lanka (Rajapaksa, 1981; Rajapaksa & Fernando, 1982; present study), Malaysian peninsula (Idris & Fernando, 1981; Idris, 1983; present study), Thailand, Philippines and Central-East China (present study) (Figure 36). Due to confusion with D. dubium the number localities in Sri Lanka and Malaysia remains unclear. The specification of all other records of ‘D. modigliani’ is difficult because were not supplemented by descriptions and illustrations. However, D. tropicum sp.nov. as well as D. modigliani and D. dubium are undoubtedly rare, found only in few of more than 1500 zooplankton samples taken in the above mentioned areas. In the long-term investigated reservoir Parakrama Samudra (Sri Lanka), representatives of the group (‘D. modigliani’) were recorded only once (Fernando & Rajapaksa, 1983). D. tropicum sp.nov. lives in large and small reservoirs, mostly in limnetic but also in littoral zone, in ponds, fish ponds, mining pools and stream backwaters. D. modigliani inhabits as well the shallow, brackish, vegetated Lake Tempe as the large, deep freshwater Lake Toba. D. modigliani and D. tropicum sp.nov. usually cooccur with other Diaphanosoma species. Thus, the former was accompanied by D. sarsi Richard in Lake Toba and by much more abundant D. excisum Sars in Lake Tempe. D. tropicum sp.nov. mostly co-occurs with D. excisum, and in the littoral of Old Pottery Pond (Batu Barendam, Malaysia) it was found together with D. sarsi, D. excisum and D. volzi Stingelin. In Czinpiertan (China) it was found together with D. macrophthalma Korovchinsky & Mirabdullaev and D. orghidani transmurensis. Parthenogenetic females of D. tropicum sp.nov. from Batu Barendam and Bubit Tiaggi (Malaysia) carried up to 5 (mostly 1–3) eggs in their brood pouches, with smallest egg-bearing females 0.69 mm long. No evidence of gamogenesis in the species or in

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123 D. modigliani was recorded, confirming Rajapaksa’s (1986) study. D. modigliani and D. tropicum sp.nov. are comparatively large-bodied species, reaching up to 1.22 and 1.19 mm respectively, which surpasses other cooccurring Diaphanosoma species (Rajapaksa & Fernando, 1982). This may negatively affect the distribution of such taxa in tropical waters, with their high predation pressure (Kerfoot & Lynch, 1987; Gliwicz, 1994). At the same time, morphological structures like long swimming antennae and massive muscles testify to a good swimming ability, which probably helps to co-exist with predators.

Acknowledgements I thank Professor C. H. Fernando (University of Waterloo, Canada) who invited me to work in his laboratory and donated the material for present study. I also thank Dr M. V. Geptner (Zoological Museum of Moscow State University) for the loan of material from the Museum’s collection. This paper was written during my work in the laboratory of Professor H. J. Dumont (University of Ghent, Belgium). I wish to thank him for his attention to my studies and many useful corrections, and the staff of this laboratory Mrs S. Maas and Mr S. DeClerk for their varied help. Dr J. Paggi (Limnological Institute, Santa Fe, Argentina) also made useful comments which improved the manuscript. The present work was partly supported by Russian Research Science Foundation (RFFI, grant N 96-0448063).

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