Anthalona sanoamuangae, Sinev, Artem Y. & Kotov, Alexey A., 2012
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Anthalona sanoamuangae sp. nov.
Ethymology. The species is named in honor of our friend and colleague, Prof. La-orsri Sanoamuang.
Type locality. A tributary of the Mekong River, Dong Luang District, Mukdahan Province, Thailand, 31.01. 1998, coll. L. Sanoamuang.
Holotype. Parthenogenetic female from the type location, MMU Ml- 110.
Paratypes. Parthenogenetic female from the type location, MMU Ml- 111; parthenogenetic female from a roadside ditch in Dong Nai National Park, Dong Nai Province, Vietnam, 22.10. 2009, coll. A. B. Vasilieva, MGU Ml- 112. A single parthenogenetic female from the type location and a single male from a roadside ditch in Dong Nai National Park, Dong Nai Province, Vietnam, 22.10. 2009, coll. A. B. Vasilieva were dissected and discarded afterward, not deposited.
Diagnosis. Parthenogenetic female. In lateral view body oval, maximum height at the middle of body, length/ height ratio 0.6–0.63. Dorsal margin curved, postero-dorsal and postero-ventral angles broadly rounded. Posterior margin weakly convex. Postero-ventral corner of valves with about 60 small setules of variable length. Ventral margin with about 45 short setae. Head typical for genus. Eye larger than ocellus. Shape of head shield typical for genus, posterior margin of head shield broadly rounded. Two main head pores, PP about 1 IP. Lateral head pores with trilobed cosmaria, located about 1 IP distance from midline, at level of anterior major head pore. Labrum without denticles on anterior margin of keel. Postabdomen moderately short and broad, with broadly rounded distal portion, length about 2.3–2.4 height; ventral margin straight; distal angle broadly rounded; dorsal margin concave in postanal part and convex in anal part, with distal part about 1.3 times longer than preanal one, with postanal portion slightly longer than anal one; preanal angle as long blunt protrusion; postanal angle weakly defined; 5–6 very short marginal postanal denticles; about ten well-developed lateral fascicles of setules; posteriormost setae of postanal fascicles three times longer than marginal denticles; Postabdominal claw weakly curved, slender, little shorter than preanal margin of postabdomen; basal spine moderately short, thin, about 1 / 4 length of claw itself. Antennule typical for the genus. Antenna with antennal formula setae 0- 0-3 / 1 - 1-3, spines 1 - 0-1 /0- 0-1. Antennal setae thin. Spine on basal segment of exopodite 1.5 times longer than middle segment. Apical spines 1.5 times longer than apical segments. Clusters of very long setules at the base of basal segment and at the end of middle segment of endopodite. Limb I with IDL setae long and thin, armed with thin setules. Setae on limb I endites long, of different length. Exopodite of limb II without seta, scraping spines not differentiated. Exopodite of limb III with seta 4 and 5 of similar length. Endopodite IV with three flaming-torch setae, distalmost seta much larger than two others.
Male. Body oval, slightly lower than in female. Ocellus and eye larger than in female, eye two times larger than ocellus. Postabdomen narrow, weakly narrowing distally, not curved; ventral margin straight, with clear step in region of gonopores; gonopores located at 1 / 5 length of ventral margin from the end of postabdomen; distal angle broadly rounded, postanal and anal margin straight; postanal angle not defined, preanal angle as prominent as in female; clusters of short setules in place of marginal denticles, lateral fascicles of setules similar to those of female, but with thinner distal setules; postabdominal claw two times shorter than that of female, strongly curved, with long thin basal spine about 1 / 3 length of claw itself. Thoracic limb I with short U-shaped copulatory hook; IDL setae 2 and 3 setae subequal in length, much thinner than in female; male seta thick, almost straight, slightly shorter than seta 3.
Differential diagnosis. A. sanoamuangae sp. nov. can be easily differentiated from most species of Anthalona by the morphology of IDL setae, which are thin, not hook-like, and bear short thin setules. The only other species with such IDL morphology is the Congolese Anthalona simplex Van Damme, Sinev & Dumont 2011, which differs from Alona sanoamuangae sp. nov. in: (1) the simple round cosmaria of lateral pores; (2) more short and robust scrapers 6–8 of limb II; (3) weakly developed first flaming-torch seta of limb IV; and (4) less prominent preanal angle of postabdomen.
Description. Parthenogenetic female. General shape. In lateral view body oval, lower than in most other species of the genus, ( Fig. 3 View FIGURE 3 A, B, 4 A, 6 A) maximum height at the middle of body, length/height ratio 0.6–0.63. Dorsal margin curved, postero-dorsal and postero-ventral angles broadly rounded. Posterior margin weakly convex.
Carapace. Postero-ventral corner of valves with about 60 small setules of variable length ( Fig. 3 View FIGURE 3 C), in posterior part organized into groups. A row of about 90 setules of variable length along posterior margin at some distance from one on inner side of carapace. Ventral margin almost straight, with about 45 short setae. Valves with several weak longitudal lines in posteroventral portion.
Head triangle-round in lateral view. Eye larger than ocellus. Shape of head shield as usual for the genus, with maximum width behind the mandibular articulation. Rostrum short, broadly rounded ( Fig. 4 View FIGURE 4 B, C, 6 B). Posterior margin of head shield broadly rounded. Two main head pores with narrow connection between them ( Fig. 3 View FIGURE 3 D), posterior major head pore larger than anterior, PP about 1 IP. Lateral head pores with trilobed cosmaria, located about 1 IP distance from midline, at level of anterior major head pore.
Labrum morphology usual for the genus. Labral keel with a blunt apex ( Fig. 3 View FIGURE 3 E). Anterior margin of keel convex, without denticles, posterior margin without any clusters of setules. Indentations on the lateral sides of labrum similar to those found in species of Karualona (see Dumont & Silva-Briano, 2000).
Thorax and a bdomen subequal in length.
Postabdomen ( Fig. 3 View FIGURE 3 F, 4 D,E, 6 D) moderately short and broad, with broadly rounded distal portion, length about 2.3–2.4 height. Ventral margin straight. Distal margin almost straight, rounded angle between distal and dorsal margins. Dorsal margin convex in postanal part and concave in anal part, with distal part about 1.3 times longer than preanal one, with postanal portion slightly longer than anal one. Preanal angle as long blunt protrusion, postanal angle weakly defined. Preanal margin weakly concave. Postabdomen provided with 5–6 very short marginal postanal denticles, and with 3–4 groups of marginal setules on anal margin. About ten well-developed lateral fascicles of setules ( Fig. 6 E View FIGURE 6. A – E ), posteriormost setae of postanal fascicles very thick and long, three times longer than marginal denticles. Postabdominal claw ( Fig. 4 View FIGURE 4 G) weakly curved, slender, little shorter than preanal margin of postabdomen. Basal spine moderately short, thin, about 1 / 4 length of claw itself. One-two small spines located near the base of claw before the basal spine.
Antennule ( Fig. 3 View FIGURE 3 G, 4 H, 6 C) with four clusters of setules on inner face. Antennular sensory seta slender, two times shorter than antennule, arising at 2 / 3 distance from the base. Nine aesthetascs, longest of them subequal in length to antennule, others little shorter. All aesthetascs projecting beyond anterior margin of the head shield.
Antenna ( Fig. 3 View FIGURE 3 H, 4 I) with antennal formula setae 0- 0-3 / 1 - 1-3, spines 1 - 0-1 /0- 0-1. Basal segment massive, branches of moderate length, basalmost segments of both branches 1.5 times longer than others. Seta arising from basal segment of endopodite thin, not reaching tip of distal segment. Seta arising from middle segment of endopodite of similar size with apical setae. Apical setae of similar size and thickness. Spine on basal segment of exopodite 1.5 times longer than middle segment. Apical spines 1.5 times longer than apical segments. Clusters of very long setules at the base of basal segment, and at the end of middle segment of endopodite.
Mandibles as for genus.
Maxillae ( Fig. 3 View FIGURE 3 I) with two setae setulated in distal part.
Thoracic limbs: five pairs.
Llimb I ( Fig. 4 View FIGURE 4 J, 5 A, B) of moderate size. Epipodite oval, with short finger-like projection. Accessory seta not found. ODL seta with short setules in distal part. IDL setae long, longer as ODL seta, without any denticles, with strong setules in distal part. Endite 3 with four setae subequal in length. On endite 2 there are three setae of different length, middle of them (e) longer than ODL seta. Endite 1 with two 2 -segmented setae (g –h), and a flat, geniculated, plumose seta in distal part (i) shifted to the limb base. No naked setae on anterior face of limb were found. Six rows of long setules on ventral face of limb. Two ejector hooks, one of them 1.5 times longer than other.
Limb II triangle-rounded ( Fig. 5 View FIGURE 5 C, D). Exopodite elongated, of irregular shape, no exopodite seta was found. Inner portion of limb with eight scraping spines increasing progressively in length distally, with exception of scraper 6, which is shorter than scraper 7. Scrapers 3 and 6 with denticles slightly larger than that of surrounding scrapers. Distal armature of gnathobase with four elements. Filter plate II with seven setae, two posteriormost member considerably shorter than others.
Limb III ( Fig. 5 View FIGURE 5 E –F). Epipodite oval, without any projection. Exopodite elongated, with six setae. Seta 3 longest, 3 times longer than setae 4 and 5, seta 4 little shorter than seta 5, all other setae very short. Setae 1–4 plumose, seta 5 with thick setules in distal part, seta 6 naked. Distal endite with 3 setae, two distalmost members (1–2) slen- der, with denticles in distal part and small sensillum located between their bases; basalmost seta (3) small, flattened, bilaterally provided with setules. Basal endite with 4 setae. Four slender sharp soft setae; a small-sensillumlike element near the basalmost of them. Gnathobase with sensillum and geniculated seta. Filter plate III with seven setae.
Limb IV ( Fig. 5 View FIGURE 5 H, I). Pre-epipodite setulated, epipodite oval, with short finger-like projection. Exopodite subrectangular. Setae 1–4 long, plumose, seta 3 being longest, setae 5–6 short, naked, 3 times shorter than seta 3. Inner portion of limb IV with four setae, a scraper (1) and three flaming torch setae (2–4), and a sensillum. Distalmost flaming-torch (2) seta 3 times larger than others. Three soft setae increasing in size basally. Gnathobase with a long 2 -segmented seta and a small projection distally. Filter plate with five setae.
Limb V ( Fig. 5 View FIGURE 5 J). Pre-epipodite setulated. Epipodite oval, with short finger-like projection. Exopodite oval, not subdivided into two lobe, with four plumose setae. Setae 1–3 long, evenly decreasing in size basally, seta 4 short, 5 times shorter than seta 1. Inner lobe broad oval, with setulated inner margin. At inner face, two setae, one equal in length to seta 2 of exopodite, other 2.5 times shorter. No filter plate.
Ephippial female. Unknown.
Male. A single somewhat deformed specimen was studied and afterwards dissected. Body oval ( Fig. 3 View FIGURE 3 J), appear to be slightly lower than that of female. Ocellus and eye larger than in female, eye two times larger than ocellus.
Postabdomen ( Fig. 3 View FIGURE 3 K) more narrow than in female, weakly narrowing distally, not curved. Ventral margin straight, with clear step in region of gonopores. Gonopores located at 1 / 5 length of ventral margin from the end of postabdomen. Distal angle broadly rounded, postanal and anal margin straight. Distal part of postabdomen 2 times longer than preanal part. Postanal angle not defined, preanal angle as prominent as in female. Clusters of short setules in place of marginal denticles, lateral fascicles of setules similar to these of female, but with thinner distal setules. Postabdominal claw two times shorter than that of female, strongly curved, with long thin basal spine about 1 / 3 length of claw itself.
Thoracic limb I more stout than that of female ( Fig. 5 View FIGURE 5 K –L), with short U-shaped copulatory hook 2 times shorter than limb itself. Copulatory brush present, copulatory brush seta short. Ventral face of limb below them with ten long setules, followed by ten shorter setules. IDL setae 2 and 3 subequal in length, much thinner than in female, male seta thick, almost straight, slightly shorter than seta 3.
Size: length of three adult female was 0.34–0.37 mm, in single deformed adult male length was about 0.32 mm.
Distribution. Recorded from North-East Thailand and South Vietnam. Possibly distributed all over Indochina.
Taxonomic notes. Anthalona sanoamuangae sp. nov. shares numerous common features with A. simplex Van Damme, Sinev & Dumont, 2011, the presumed basalmost species of Anthalona (Van Damme et al. 2011). Three of them are unique for the genus: (1) no typical scraping modifications on the first and second limbs (IDL and P 2 scrapers); (2) an expanded gnathobase on the second limb, and (3) a cluster of long setules on basal segment of antennal exopodite. The two first features are adaptations for feeding on fine organic particles (Van Damme et al.
2011), while the significance of the third is unclear. Like in A. simplex , the fourth and fifth limbs in A. sanoamuangae sp. nov. have longer plumose setae than in other Anthalona species, required for obtaining oxygen in benthic environments. So, like A. simplex (see Van Damme et al. 2011), A. sanoamuangae sp. nov. is a presumable muddweller, specialized on feeding on a fine organic matter. It is well-known that the clusters of strong setules on the antenna exopodite are characteristic of bethic anomopods ( Kotov 2006). A. simplex and A. sanoamuangae sp. nov. form a separate group within the genus, which is characterized by its own apomorphies, this clade is a sister group to the main branch of the Anthalona, which evolved as scrapping animals. Limited distribution and rarity suggest the relict nature of the simplex -branch sensu Korovchinsky (2006).
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