A new species of the genus Ovalona Van Damme & Dumont, 2008 (Cladocera: Anomopoda: Chydoridae) from South-East Asia, related to Australian Ovalona archeri (Sars, 1888) Author Sinev, Artem Y. Department of Invertebrate Zoology, Biological Faculty, M. V. Lomonosov Moscow State University, Leninskie Gory 1 - 12, Moscow 119991, Russia Author Dadykin, Ivan A. A. N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences, Leninsky Prospect 33, Moscow 119071, Russia Author Đ ịnh, Nguyên Southern Branch of Joint Vietnam-Russian Tropical Science and Technology Research Center, No. 3, 3 / 2 Street, District 10, Ho Chi Minh City, Vietnam text Zootaxa 2024 2024-05-10 5448 2 273 282 http://dx.doi.org/10.11646/zootaxa.5360.3.8 journal article 10.11646/zootaxa.5448.2.7 1175-5326 11231641 6D86D560-150B-4353-858B-D6E93E809FD4 Ovalona garibiani sp. nov. ( Figs. 1–3 ) Idris, 1983: 110–113 , fig. 42 ( Alona cf. karelica ); Maiphae, Pholpunthin & Dumont, 2008: 38 , fig 4–5 ( Alona archeri ). Etymology . The species is named after its collector, our friend and colleague, Russian cladocerologist Dr. Petr Grigorievich Garibian. Type locality. Water hyacinth bed at channel in Tràm Chin National Park , Dong Thap province , Vietnam ( 10.690834 N , 105.550008 E ), 9 April 2023 . Material collected by P.G. Garibian and A. A. Kotov. Type material. Holotype . Parthenogenetic female from the type locality, deposited at Zoological Museum of M. V . Lomonosov Moscow State University , Ml –272. Paratypes . 6 parthenogenetic females from the type locality, deposited at Zoological Museum of M. V . Lomonosov Moscow State University , Ml –273 . Other material studied. Several parthenogenetic females from the type locality were dissected and subsequently not preserved. Few parthenogenetic females from channels at Tràm Chin National Park , Dong Thap province , Vietnam (at localities 10.681685 N 105.555709 E and 10.685221 N , 105.553588 E ) 9 April 2023 ; material collected by P.G. Garibian and A. A. Kotov. Description. Parthenogenetic female. General. In lateral view body regularly-ovoid, of moderate height ( Fig. 1A–B , 2A–B ), maximum height at middle of body, in adults height/length ratio 0.65–0.70. Carapace evenly colored in light yellow to almost transparent. Dorsal margin uniformly curved; postero-dorsal and postero-ventral angles broadly rounded; posterior margin uniformly curved; ventral margin almost straight; antero-ventral angle rounded. Body strongly compressed laterally. Valves with tubercular sculpture in all studied specimens; specimens from Malaysia , reported by Idris (1983) , have oblique valves. Ventral margin ( Fig. 1C ) with about 35 setae, about 10 anterior setae long, increasing in length distally; next 10 setae short, posterior setae of moderate length. Postero-ventral angle ( Fig. 1D ) with about 100 short setules not organized in groups. A row of very small setules along the posterior margin on inner side of valve. Head of moderate size, triangular-round in lateral view, rostrum short, pointing downward. Eye two times larger than ocellus. Distance from tip of rostrum to ocellus in adults slightly greater than that between ocellus and eye. Head shield with a tubercular sculpture, its shape typical of the genus; rostrum short, broadly rounded; posterior margin of head shield broadly rounded, slightly wavy in some specimens. Three major head pores ( Fig. 1E–F ) with very narrow connection between them, middle pore smaller than other two pores; PP about 0.3–0.4 IP. Lateral head pores minute, located at about 0.7–0.8 IP distance from midline, at the level between anterior and median main head pore. Labrum ( Fig. 1G–H ) of moderate size, labral keel wide (height about 1.2–1.3 widths), with blunt apex; anterior margin of keel almost straight in its middle part, posterior margin without any setulae. Postabdomen ( Fig. 1I–J, L ) narrow, with parallel margins and strongly prominent dorso-distal angle with a rounded tip, length about 2.5–2.8 height. Ventral margin weakly convex. Distal margin clearly convex. Dorsal margin with distal part 1.5 times longer than preanal one; postanal and anal portions of similar length. Postanal portion of distal margin straight, anal portion concave. Preanal angle well-defined, postanal angle weakly defined. Postabdomen with 3–4 large marginal denticles in distal part, followed by five-six much smaller denticles; length of largest denticles about 1.5 widths of postabdominal claw base. Nine to ten narrow groups of lateral setulae, distalmost setula of each fascicle longer and thicker than others, length of longest distalmost setulae close to 1.5 widths of claw base; distance between groups in postanal portion greater or equal to the width of groups. Postabdominal claw slightly longer than preanal portion of postabdomen. Basal spine straight, thin, about 0.2 length of claw. Antennule ( Fig. 1K ) of moderate size, length about 2.5 widths, with four clusters of short setulae at anterior face. Antennular sensory seta slender, about 2/3 length of antennula, arising at 2/3 distance from the base. Nine terminal aesthetascs, the longest two about 2/3 length of antennule, others of about 1/3 length of antennule. Antenna relatively short ( Fig. 3A–B ). Antennal formula, setae 0-0-3/1-1-3, spines 1-0-1/0-0-1. Basipodite robust, branches of moderate length and width, basal segments of both branches 1.5 times longer than others. Basal segment of exopodite massive, almost two times wider than middle segment. Middle segments of both branches almost square in lateral view. Middle segment of endopodite with cluster of long setulae. Seta arising from basal segment of endopodite slightly longer than endopodite. Seta arising from middle segment of endopodite of similar size of shortest apical setae. On both branches, one apical seta much shorter than two others. Spine on basal segment of exopodite as long as the middle segment. Apical spines of similar length as the respective apical segments. FIGURE 1. Ovalona garibiani sp. nov. from a channel at Tràm Chin National Park, Dong Thap province, Vietnam (type locality). A–K, adult parthenogenetic female. A–B, lateral view. C, ventral margin of valve. D, posteroventral angle of valve. E–F, head pores. G–H, keel of labrum. I–J, postabdomen. K, antennule. L, postabdomen of juvenile female of instar II. M, Ovalona archeri ( Sars, 1888 ) , postabdomen of adult parthenogenetic female (after Sinev 2002 ). FIGURE 2 . Ovalona garibiani sp. nov. from channel at Tràm Chin National Park, Dong Thap province, Vietnam (type locality), parthenogenetic female. A–B, lateral view. Thoracic limbs : five pairs. Limb I ( Fig. 3C–E ) of moderate size. Epipodite ovoid. ODL with a long seta, armed with minute setules in distal part. IDL with three setae; seta 3 longer than ODL seta, seta 2 slightly shorter than ODL seta, both armed with thin setules in distal part, seta 1 of about 1/3 length of seta 3. Endite 3 with four setae, inner seta (1) shorter and thinner than outer setae (a,b,d). Endite 2 with three setae (c,e,f), seta e as long as ODL seta, seta f slightly shorter than seta e. Endite 1 with two 2-segmented setae, both setulated in distal part. No inner setae on endites 1–2. Six-seven rows of thin long setules on ventral face of limb. Two ejector hooks of similar size. Limb II ( Fig. 3F–G ). Exopodite elongated, with seta three-four times shorter than exopodite. Eight scraping setae (1–8), armed with spinules of similar shape, increasing in length distally, scrapers 1–5 long, of similar length, scrapers 6–8 much shorter. Distal armature of gnathobase with four elements. Filter plate with seven setae, the posteriormost seta two times shorter than others. Limb III ( Fig.3H–I ). Epipodite oval; exopodite subtriangular, with seven setae. Seta 3 being longest, seta 6 about 1/2 length of seta 3, setae 1 and 4 of about 1/3 length of seta 3, other setae short. Seta 6 armed with thick long setules in distal part, seta 7 naked, all other setae plumose. Distal endite with three setae, two distalmost members slender, sharp, of similar length; basalmost seta (3) shorter, bilaterally armed with setules. Inner portion of limb of typical for the genus morphology. Limb IV ( Fig. 3J–K ). Preepipodite setulated, epipodite with very short process. Exopodite rounded, with six plumose setae. Seta 3 longest, setae 1–2 slightly shorter than seta 3, setae 4, 5 and 6 of 1/3, 2/3 and 1/3 length of seta 3, respectively. Inner-distal portion of limb IV with four setae and small cylindrical sensillum: seta 1 slender, sharp; three flaming-torch setae (2–4) decreasing in size basally, armed with 6–7 short setulae each. Small sensillum near the base of seta 2. Three long inner setae (a–c) long, slightly increasing in size basally. Gnathobase with a bisegmented seta, small sensillum, and a small hillock distally. Filter plate with five setae. Limb V ( Fig. 3L ). Preepipodite setulated. Epipodite oval, without process. Exopodite oval, with four plumose setae, evenly decreasing in size basally; seta 4 three times shorter than seta 1. Inner limb portion as oval lobe with setulated inner margin, only slightly smaller than exopodite. At inner face, two setae, outer one equal in length to seta 2 of exopodite, inner one shorter. No filter plate. Ephippial female and male . Unknown. Size. Length of adult female in studied material was 0.36–0.43 mm , height 0.24–0.3 mm . Length of single studied juvenile female of instar II was 0.28 mm , height 0.17 mm . Differential diagnosis. Ovalona garibiani sp. nov. belongs to the cambouei -group of Ovalona . It differs from species of the nuragica -group by much smaller size and fully connected head pores, and from species of the setulosa -group by narrow, elongated (length over 2.5 heights) postabdomen (see Sinev 2015b ). O. garibiani sp. nov. differs from most species of the cambouei -group by postabdomen with narrow, sparsely spaced lateral group of setulae; distance between postanal groups is slightly greater than group width. This character is shared only by its sibling-species, O. archeri . Within the cambouei -group, O. garibiani sp. nov. clearly differs from O. karelica (Stenroos, 1897) and O. bromelicola (Smirnov, 1988) in a well-developed basal spine of postabdominal claw, from O. aguascalientensis (Sinev & Silva-Briano, 2012) , O. capensis (Rühe, 1921) and O. cambouei (Guerne & Richard, 1983) in completely connected main head pores, and from O. cambouei , O. pulchella King, 1853 and O. glabra (Sars, 1901) in a broadly rounded distal angle of postabdomen, protruding forward above the level of the base of the claw. FIGURE 3. Ovalona garibiani . sp. nov. from channel at Tràm Chin National Park, Dong Thap province, Vietnam (type locality). A–L, appendages of adult parthenogenetic females. A, antenna. B, exopodite of antenna. C–L, thoracic limbs. C, limb I. D, setae a, b, d of limb I. E, ODL and IDL of limb I. F–G, inner and outer portion of limb II. H, exopodite of limb III. I, distal endite of limb III. J, limb IV. K, inner portion of limb IV. L, limb V. M, Ovalona archeri ( Sars, 1888 ) , antenna of adult parthenogenetic female (after Sinev 2002 ). O. garibiani sp. nov. differs from O. archeri in the proportions of antennal segments (see Fig. 3M ), O. garibiani sp. nov. have much shorter exopodite and endopodite. Length of basal segment of exopodite is only slightly greater than segment width in O. garibiani sp. nov . and it is about two segments width in O. archeri . Spine of basal segment of antenna exopodite is as long as middle segment in O. garibiani sp. nov. and is much shorter that middle segment in O. archeri . Distal angle of postabdomen protrudes forward over the level of the claw base in O. garibiani sp. nov . , but does not protrude over the level of the claw base in O. archeri (see Fig. 1M ). Also, these two species differ in proportions of setae of limbs II and III. The differences between the species are summarized in Table I. TABLE 1 . Morphological differences between of Ovalona garibiani sp. nov. and O. archeri ( Sars, 1888 ) .

Character	Ovalona garibiani sp. nov.	Ovalona archeri ( Sars, 1888 )
Valves and head shield	With tubercular sculpture or oblique	Oblique
Distal angle of postabdomen	Projecting forward above the level of the base of the claw, broadly rounded	It does not protrude forward above the level of the claw base, with a blunt and weakly rounded apex
Antenna	Length of both exopodite and endopodite about 1.5 basipodite lengths	Length of both exopodite and endopodite about 2 basipodite lengths
Basal segment of antenna exopodite	Very massive, with a length slightly greater than its width	Narrow, with a length about two widths
Spine on the basal segment of the antennal exopodite	As long as the middle segment or slightly shorter	Almost twice as short than middle segment
Middle segments of exopodite and endopodite of antenna	The length is slightly greater than the width	Length approximately two widths
Scraping setae of limb II	Scrapers 7 and 8 short, about 1/3 and 1/4 length of scraper 1, respectively	Scrapers 7 and 8 longer, about 1/2 and 1/3 length of scraper 1, respectively
Exopodite of limb III	Length of seta 6 and 4 about 1/2 and 1/3 length of seta 3, respectively	Length of seta 6 and 4 about 4/5 and 2/3 length of seta 3, respectively

Distribution and ecology . Ovalona garibiani sp. nov. is known from several localities at Tràm Chin National Park, Mekong Delta, southern Vietnam (our data), Thalenoi marsh, Pattalung Province, southern Thailand ( Maiphae et al . 2008 ), and Klang Gate Reservoir, Selangor State , Malaysia ( Idris 1983 ). It is the first record of the species in Vietnam . In the studied samples, most specimens were collected from roots of water hyacinth. In the studied localities, Ovalona garibiani sp. nov . co-occurred with a diverse chydorid fauna, including Anthalona harti harti Van Damme, Sinev & Dumont, 2011 , Biapertura affinis (Leydig, 1860 ) , Euryalona orientalis (Daday, 1898) , Leberis diaphanus (King, 1853) , Notoalona globulosa (Daday, 1898) , Oxyurella singalensis (Daday, 1898) , Alonella excisa (Fisher, 1854) , Chydorus eurynotus Sars, 1901 , Ephemeroporus barroisi (Richard, 1894) and E. malaysiaensis Sinev & Yusoff 2016 . Other cladoceran species present in the localities were Pseudosida szalayi Daday, 1898 , Bosminopsis africanus (Daday, 1908) , Ceriodaphnia cornuta Sars, 1901 , Simocephalus cf. latirostris Stingelin, 1906 , S. congener (Koch, 1841) . Macrothrix spinosa King, 1853 , M. triserialis (Brady, 1896) , Grimaldina brazzai Richard, 1892 , Guernella raphaelis Richard, 1892 , and Ilyocryptus spinifer Herrick, 1882 . Most of these species are quite common in Vietnam and in South-East Asia in general ( Sinev & Korovchinsky 2013 ), but E. malaysiaensis is a rare species known from several overgrown lakes and reservoirs in continental Malaysia ( Sinev & Yusoff 2016 ).