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Sargassum siliquosum J. Agardh (1848: 316) (Fig. 6A–F) Thallus up to 60 cm high, attached by discoidal holdfast, 1 cm in diameter. Main axes terete, smooth, 0.15 cm wide, producing 3–5 primary branches. Primary branches cylindrical, smooth, terete 2–3 cm at base. Lateral branches numerous, alternate at an interval of 3–4 cm. Basal leaves thick, large, oval, 2.5–5.0 cm long, 0.3–1.0 cm wide; upper leaves 1.5– 3 cm long and up to 0.6 cm wide, with shallowly dentate margin. Midrip conspicuous but fading towards the apex. Cryptostomata irregularly scattered. Vesicles oval or lanceolate, about 0.3–0.5 cm long and up to 0.2 cm wide, with very short flat petioles, mucronate. Plant monoecious. Receptacles cylindrical, smooth, simple to once furcate, about 2 cm long or more. Maturation in spring in the southwestern Vietnam. Habitat:— Sargassum siliquosum grows on rock and dead coral in the lower intertidal zone. Specimens examined:— Duong Dong, Phu Quoc, lower intertidal, 01 Mar. 2018 V. T . Nguyen, S.M. Boo (NVT2043, NVT2044, NVT2045), Duong Dong, lower intertidal, 16 Feb. 2019, V. T . Nguyen (NVT2510, NVT2511). Taxonomic remarks: — Sargassum siliquosum is distinguished from other species by having numerous small vesicles, secondary axis somewhat compressed and smooth at lower part. The syntype localities of this species are Jakarta in Indonesia and Singapore (Silva et al. 1996). The cylindrical and warty axes described by Nguyen (2007) were not observed in specimens from the Phu Quoc Island. Primary branches are terete, 2–3 cm at base, basal leaves are longer and bigger than those positioned at the lateral branches. Leaves of Vietnamese specimens are shorter than those from China (Tseng & Lu 1992). Vesicles are oval to lanceolate, sharply pointed or rounded, 0.2 cm in length, as Chinese plants (Tseng & Lu 1992). Identification of species from southwestern Vietnam: In the present study, eleven species of Sargassum including five species described above were collected and examined (Table S1). Six species commonly occur along the east coast of Vietnam, and their morphologies and descriptions have been introduced by my thesis and other reports (Pham 1969, Nguyen 2007, Nguyen 2014, Nguyen 2020, Nguyen & Boo 2020). Based on morphological descriptions and illustrations, a key for identification of species from southwestern Vietnam is given below., Published as part of Tu, Nguyen Van, 2023, Morpho-anatomical study of Sargassum (Fucales, Phaeophyceae) diversity reveals noteworthy collections and range extensions from southwestern Vietnam, pp. 281-290 in Phytotaxa 600 (5) on pages 286-287, DOI: 10.11646/phytotaxa.600.5.3, http://zenodo.org/record/8129374, {"references":["Agardh, J. G. (1848) Species genera et ordines algarum. Seu descriptiones succinctae specierum, generum et ordinum, quibus algarum regnum cnstituitur. Volumen Primum. Algas fucoideas complectense. C. W. K. Gleerup, Lund, 363 pp.","Silva, P. C., Basson, P. W. & Moe, R. L. (1996) Catalogue of the benthic marine algae of the Indian Ocean. University of California Publications in Botany 79: 1 - 1259.","Nguyen, H. D. (2007) Flora of Vietnam. Science and Technology Publishing House, Hanoi, 117 pp.","Tseng, C. K. & Lu Baoren (1992). Studies on the malacocarpic Sargassum of China II. Racemosae J. Agardh. In: Abbott, I. A. (Ed.) Taxonomy of economic seaweeds with reference to some Pacific species. Vol. 3. California Sea Grant College Program, La Jolla, CA. pp. 11 - 34.","Pham, H. H. (1969) Marine algae of south Vietnam. Sai Gon study Center. Ministry of Education and Youth, 558 pp.","Nguyen, V. T. (2014) Seaweed diversity in Vietnam, with an emphasis of the brown algal genus Sargassum. Ph. D. thesis. Ghent University, Ghent, 191 pp.","Nguyen, V. T. & Boo, S. M. (2020) Distribution patterns and biogeography of Sargassum (Fucales, Phaeophyceae) along the coast of Vietnam. Botanica Marina 63: 463 - 468. https: // doi. org / 10.1515 / bot- 2019 - 0082"]}

Key for Sargassum from southwestern Vietnam 1a. Axes with spines.................................................................................................................................................................................2 1b. Axes smooth.......................................................................................................................................................................................3 2a. Holdfasts lobed.................................................................................................................................................................. S. confusum 2b. Holdfasts conical, giving rise to stolon-like branches.................................................................................................... S. polycystum 3a. Axes compressed................................................................................................................................................................................4 3b. Axes cylindrical..................................................................................................................................................................................6 4a. Leaves with entire margin................................................................................................................................................... S. swartzii 4b Leaves with serrate margin.................................................................................................................................................................5 5a. Vesicles with terminal spines; petioles compressed or leaf-shaped; leaves thin........................................................... S. oligocystum 5b. Vesicles on leaves; petioles compressed; leaves thick curved inside branches..................................................................... S. feldmannii 6a. Leaves with entire or sparse spines, undulate....................................................................................................................................7 6b. Leaves with sharply serrated margin..................................................................................................................................................8 7a. Basal leaves blunt at the apex; vesicles ovate................................................................................................................... S. cinereum 7b. Basal leaves thick, larger and oval; vesicles oval or lanceolate...................................................................................... S. siliquosum 8a. Vesicles spherical to obovate..............................................................................................................................................................9 8b. Vesicles leaf-shaped..........................................................................................................................................................................10 9a. Vesicles numerous; leaves lanceolate........................................................................................................................... S. microcystum 9b. Vesicles few; leaves obovate to spathulate................................................................................................................................... S. ilicifolium 10a. Leaves serrated; midribs conspicuous up to ¾ of leaves................................................................................................. S. aquifolium 10b. Leaves spathulate to obovate; midribs inconspicuous..................................................................................................................... S. mcclurei, Published as part of Tu, Nguyen Van, 2023, Morpho-anatomical study of Sargassum (Fucales, Phaeophyceae) diversity reveals noteworthy collections and range extensions from southwestern Vietnam, pp. 281-290 in Phytotaxa 600 (5) on pages 287-288, DOI: 10.11646/phytotaxa.600.5.3, http://zenodo.org/record/8129374

Sargassum cinereum J. Agardh (1848: 305) (Fig. 2A–F) Thallus 30–50 cm high, attached by a conical holdfast that is slightly discoidal lacking lobes, and 1 cm wide. Main axes cylindrical, up to 1 cm long and 0.2 cm wide. Primary branches cylindrical, smooth, 0.1 cm wide; lateral branches sparsely alternate at intervals of 3–5 cm, 10–20 cm long. Basal leaves 2–4 cm long and 0.5–1 cm wide, blunt at the apex; tapering toward apex; leaves on axes and branches about 4 cm long and 0.3 cm wide, with undulate margin and some spines. Midribs percurrent, occurring on the surface of leaf. Cryptostomata arranged in two rows. Vesicles ovate, 0.2–0.3 cm wide, with petioles ½ shorter than vesicle length. Plant dioecious. Receptacles arise in clusters between leaf axils or vesicles. Male receptacles cylindrical, 2–3 times furcate. About 2 cm long and 0.12 cm wide. Female receptacles triquetrous at the base to compressed, simple to one furcate, about 1 cm long and 0.15 cm wide. Maturation in spring to early summer in the southwestern Vietnam. Habitat:— Sargassum cinereum grows on rocks in the lower intertidal to subtidal zone at two locations on the Phu Quoc Island. Specimens examined:— Duong Dong, Phu Quoc, lower intertidal, 16 Feb. 2019, V. T . Nguyen (NVT2497, NVT2498, NVT2499); An Thoi, Phu Quoc, subtidal, 17 Feb. 2019, V. T . Nguyen (NVT2504, NVT2505, NVT2506, NVT2511). Taxonomic remarks:— Sargassum cinereum is distinguished by ashy-grey(cinerascent) color, dioecious reproduction, leaves having midrib that vanishes from the middle part. The type locality of this species is Hong Kong (Silva et al. 1996). This species was first described in Phu Quoc by Pham (1985). Although it was reported in northern and central Vietnam (Nguyen et al. 1997, Nguyen 2007), its occurrence was doubtful because later sampling trips didn’t collect the species and voucher specimens were absent in any institute and personal herbaria (Nguyen 2014). Specimens from Duong Dong and An Thoi are similar in most of characteristics, but the subtidal specimens from An Thoi is larger than lower intertidal specimens from Duong Dong. Specimens from the Phu Quoc Island are very similar in the shape of leaves with cuneate bases and dentate margins and shapes of receptacles to specimens from Malaysia and Thailand (Ajisaka et al. 1999, Noiraksar & Ajisaka 2008). Two sequences of internal transcribed spacer 2 of nuclear gene from Thailand specimens are released on GenBank, but yet to wait for publication. This study is the first report S. cinereum in Vietnam., Published as part of Tu, Nguyen Van, 2023, Morpho-anatomical study of Sargassum (Fucales, Phaeophyceae) diversity reveals noteworthy collections and range extensions from southwestern Vietnam, pp. 281-290 in Phytotaxa 600 (5) on page 283, DOI: 10.11646/phytotaxa.600.5.3, http://zenodo.org/record/8129374, {"references":["Agardh, J. G. (1848) Species genera et ordines algarum. Seu descriptiones succinctae specierum, generum et ordinum, quibus algarum regnum cnstituitur. Volumen Primum. Algas fucoideas complectense. C. W. K. Gleerup, Lund, 363 pp.","Silva, P. C., Basson, P. W. & Moe, R. L. (1996) Catalogue of the benthic marine algae of the Indian Ocean. University of California Publications in Botany 79: 1 - 1259.","Pham, H. H. (1985) The plants of Phu Quoc Islands. Ho Chi Minh Publishing House, Hochiminh, 183 pp.","Nguyen, H. D. (1997) Sargassaceae in Vietnam resources and utility. Agriculture Publishing House, Hanoi, 199 pp.","Nguyen, H. D. (2007) Flora of Vietnam. Science and Technology Publishing House, Hanoi, 117 pp.","Nguyen, V. T. (2014) Seaweed diversity in Vietnam, with an emphasis of the brown algal genus Sargassum. Ph. D. thesis. Ghent University, Ghent, 191 pp.","Ajisaka, T., Phang, S. M. & Yoshida, T. (1999) Preliminary report of Sargassum species collected from Malaysian coasts. In: I. A. Abbott (Ed.) Taxonomy of economic seaweeds with reference to some Pacific species. Vol. 7. California Sea Grant College Program, La Jolla, CA. pp. 23 - 41.","Noiraksar, T. & Ajisaka, T. (2008) Taxonomy and distribution of Sargassum (Phaeophyceae) in the Gulf of Thailand. Journal of Applied Phycology 20: 963 - 977. https: // doi. org / 10.1007 / s 10811 - 008 - 9327 - 3"]}

Sargassum confusum C. Agardh (1824: 301) (Fig. 3A–F) Thallus 60–80 cm high, attached by a lobed holdfast, up to 2 cm in diameter. Main axes somewhat compressed, up to 2 cm long, producing 3–5 primary branches. Primary branches cylindrical to slightly compressed, about 0.2 cm, 0.4 cm wide; lateral branches bearing spines, about 15 cm long, alternately branched at an interval of 3–5 cm. Basal leaves up to 7 cm long and 0.5–0.8 cm wide, hard, linear, with entire or sparsely serrated margin. Midrips narrow at the base of leaves and diluted in the middle part of leaves. Cryptostomata sparse. Vesicles numerous, small, spherical or somewhat obovate. Plant dioecious. Male receptacles cylindrical, slightly curved, sometimes with small protuberances, simple to once furcate, about 0.8 cm long and 0.08–0.1 cm wide. Female receptacles triquetrous, simple to once furcate, about 0.3 cm long and 0.1 cm wide. Maturation likely in late spring to early summer in the southwestern Vietnam. Habitat:— Sargassum confusum grows on rocks in the lower intertidal to subtidal zone. Specimens examined:— Duong Dong, Phu Quoc, lower intertidal to subtidal, 01 Mar. 2018, V.T . Nguyen, S.M. Boo (NVT2039, NVT2040, NVT2070, NVT2071, NVT2072), Duong Dong, Phu Quoc, lower intertidal, 05 Mar. 2020, V.T . Nguyen (NVT2500, NVT2532). Taxonomic remarks:— Sargassum confusum is distinguished by having its main branches usually armed with spines, coriaceous leaves in texture, small vesicles of less than 5 mm in diameter. The type locality of this species is Japan (Yoshida 1983). Because S. confusum is similar to S. gracilimum in its dark colour when dried, more rounded vesicles, and cylindrical and longer receptacles, identification of S. confusum needs careful examination of specimens. Yoshida et al. (2002) argued against the occurrence of S. confusum in Vietnam because of the lack of voucher specimens. Cho et al. (2012) analyzed ITS2, cox 3, psa A, and rbc L from S. confusum from Korea and revealed its close relationship with S. fulvellum (Turner) C.Agardh (Agardh 1820: 34), S. miyabei Yendo (Yendo 1907: 112), and S. muticum (Yendo) Fensholt (Fensholt 1955: 306) that are considered natives to northeastern Pacific (Yoshida 1983, Cho et al. 2012). This is the first report on the occurrence of S. confusum in Vietnam., Published as part of Tu, Nguyen Van, 2023, Morpho-anatomical study of Sargassum (Fucales, Phaeophyceae) diversity reveals noteworthy collections and range extensions from southwestern Vietnam, pp. 281-290 in Phytotaxa 600 (5) on page 284, DOI: 10.11646/phytotaxa.600.5.3, http://zenodo.org/record/8129374, {"references":["Agardh, C. A. (1824) Systema algarum. Literis Berlingianis, Lundae, 312 pp.","Yoshida, T. (1983) Japanese species of Sargassum subgenus Bactrophycus (Phaeophyta, Fucales). Journal of the Faculty of Science, Hokkaido University 13: 99 - 246","Yoshida, T., Dai, N. H., Ajisaka, T. & Noro, T. (2002) Verification of Sargassum species identified with subgenera Bactrophycus, Phyllotrichia, and Schizophycus in Vietnam. In: I. A. Abbott & K. McDermid (Eds.) Taxonomy of economic seaweeds with reference to some Pacific species. Vol. 8. California Sea Grant College Program, La Jolla, CA. pp. 95 - 102.","Cho, S. M., Lee, S. M., Ko, Y. D., Mattio, L. & Boo, S. M. (2012) Molecular systematic reassessment of Sargassum (Fucales, Phaeophyceae) in Korea using four gene regions. Botanica Marina 55: 473 - 484. https: // doi. org / 10.1515 / bot- 2012 - 0109","Agardh, C. A. (1820) Species Algarum, Vol. 1, Part 1, Fucoideae, 168 pp.","Yendo, K. (1907) The Fucaceae of Japan. Journal of College of Science, Imperial University of Tokyo 21: 1 - 174.","Fensholt, D. E. (1955) An emendation of the genus Cystophyllum (Fucales). American Journal of Botany 42: 305 - 322."]}

Tu, Nguyen Van (2023): Morpho-anatomical study of Sargassum (Fucales, Phaeophyceae) diversity reveals noteworthy collections and range extensions from southwestern Vietnam. Phytotaxa 600 (5): 281-290, DOI: 10.11646/phytotaxa.600.5.3, URL: http://dx.doi.org/10.11646/phytotaxa.600.5.3

Sargassum microcystum J. Agardh (1848: 323) (Fig. 5A–F) Thallus 30–80 cm high or more, attached by a discoidal to conical shaped holdfast, warty, up to 1 cm in diameter. Main axes cylindrical, up to 0.4 cm long, producing 3–5 primary branches. Primary branches cylindrical or somewhat compressed at lower part, smooth, 0.15–0.2 cm in diameter. Lateral branches coarse. Leaves thick, crisp, lanceolate, with short petioles, obtuse to round at the apex, with irregularly denticulate margin. Midrib inconspicuous, vanishing to the apex, 2–4 cm long and up to 0.4–1 cm wide. Cryptostomata conspicuous, scattered over leaf surface. Vesicles numerous, 0.15–0.2 cm long, spherical to obovate, bearing a fine spine or dentate wing. Plant dioecious. Receptacles in racemose branchlets. Male receptacles cylindrical, about 0.5 cm long and 0.1 mm wide. Females receptacles triquetrous, about 0.35 cm long and 0.15 cm wide. Maturation in spring in the southwestern Vietnam. Habitat:— Sargassum microcystum grows on rock and dead coral in the lower intertidal to subtidal zone. Specimens examined:— Ganh Dau, Phu Quoc, subtidal, 15 Feb. 2019, V. T . Nguyen (NVT2468, NVT2469, NVT2471, NVT2492, NVT2493), Duong Dong, lower intertidal, 16 Feb. 2019, V. T . Nguyen (NVT2517). Taxonomic remarks:— Sargassum microcystum is distinguished from other species by having numerous small vesicles without rhizoids and secondary axes that are smooth and somewhat compressed on the lower parts. The syntype localities are “marfi Indico”, Moluccas in Indonesia, Manila in the Philippines, and Singapore (Silva et al. 1996: 685). Yendo (1907) described leaves of S. microcystum as being narrow; however, specimens from Phu Quoc have typical lanceolate leaves, and basal leaves are ovate and longer than upper ones, as described by Pham (1967). Cryptostomata are conspicuous, a feature not described by Pham (1967)., Published as part of Tu, Nguyen Van, 2023, Morpho-anatomical study of Sargassum (Fucales, Phaeophyceae) diversity reveals noteworthy collections and range extensions from southwestern Vietnam, pp. 281-290 in Phytotaxa 600 (5) on page 286, DOI: 10.11646/phytotaxa.600.5.3, http://zenodo.org/record/8129374, {"references":["Agardh, J. G. (1848) Species genera et ordines algarum. Seu descriptiones succinctae specierum, generum et ordinum, quibus algarum regnum cnstituitur. Volumen Primum. Algas fucoideas complectense. C. W. K. Gleerup, Lund, 363 pp.","Silva, P. C., Basson, P. W. & Moe, R. L. (1996) Catalogue of the benthic marine algae of the Indian Ocean. University of California Publications in Botany 79: 1 - 1259.","Yendo, K. (1907) The Fucaceae of Japan. Journal of College of Science, Imperial University of Tokyo 21: 1 - 174.","Pham, H. H. (1967) Contribution a lʹetude des algues littorales du Vietnam: le genre Sargassum. Annales de la Faculte des Sciences de Saigon 1967: 259 - 332."]}

Sargassum feldmannii Pham-Hoàng (1967: 297) (Fig. 4A–F) Thallus 30–40 cm high, attached by a discoidal holdfast that is up to 1 cm in diameter. Main axes cylindrical, short, up to 0.3 cm wide, producing 2–3 primary branches. Primary branches compressed, smooth, 0.3–0.4 cm in diameter; lateral branchs short, raising at an interval of 1–3 cm. Leaves thick, elliptic to linear, 2–3 cm long and up to 1 cm wide, obtuse or rounded at the apex, sometimes double serrated or forming a cup–shape, with short cylindrical petioles, bearing some spines at top. Midribs vanishing near the apex. Cryptostomata numerous, irregularly scattered over leaf surfaces. Vesicles on leaves, spherical to elliptic, normally arranged at the central or distal part of the vesicle–leaves, with sharply dentate margins, 0.6–0.8 cm wide. Plant monoecious. Receptacles forming dense cymes, branched, cylindrical and warty, up to 0.7 cm long. Maturation likely in late spring in the southwestern Vietnam. Habitat:— Sargassum feldmannii grows on rocks and dead corals in the subtidal zone in the Phu Quoc and Tho Chu islands. Specimens examined:— Ganh Dau, Phu Quoc, subtidal, 15 Feb. 2019, V. T . Nguyen (NVT2461, NVT2462), Bai Dong, Tho Chu, subtidal, 21–23 Mar. 2019, V. T . Nguyen (NVT2563, NVT2564, NVT2634, NVT2667, NVT2669, NVT2670). Taxonomic remarks:— Sargassum feldmannii is distinguished from other species by having compressed branches, vesicles with terminal leaves that are thick, inwardly curved branches, and serrated margins of leaves. The type locality of this species is Nha Trang, Vietnam (Pham 1967). It differs from S. aquifolium (Turner) C.Agardh (Agardh 1820: 12) by its large leaf size, and the shape of its vesicles (Nguyen 2014). Sargassum feldmannii has short lateral branches, usually curved, thick leaves to stem compared to S. carpophyllum J.Agardh (Agardh 1848: 304). Based on morpho-anatomical examination of specimens from Phu Quoc Island, S. feldmannii is distinct from S. crassifolium J.Agardh (Agardh 1848: 326), a species currently treated as a synonym of S. aquifolium (type locality, Sunda Strait, Indonesia, Silva et al. 1996)., Published as part of Tu, Nguyen Van, 2023, Morpho-anatomical study of Sargassum (Fucales, Phaeophyceae) diversity reveals noteworthy collections and range extensions from southwestern Vietnam, pp. 281-290 in Phytotaxa 600 (5) on page 285, DOI: 10.11646/phytotaxa.600.5.3, http://zenodo.org/record/8129374, {"references":["Pham, H. H. (1967) Contribution a lʹetude des algues littorales du Vietnam: le genre Sargassum. Annales de la Faculte des Sciences de Saigon 1967: 259 - 332.","Agardh, C. A. (1820) Species Algarum, Vol. 1, Part 1, Fucoideae, 168 pp.","Nguyen, V. T. (2014) Seaweed diversity in Vietnam, with an emphasis of the brown algal genus Sargassum. Ph. D. thesis. Ghent University, Ghent, 191 pp.","Agardh, J. G. (1848) Species genera et ordines algarum. Seu descriptiones succinctae specierum, generum et ordinum, quibus algarum regnum cnstituitur. Volumen Primum. Algas fucoideas complectense. C. W. K. Gleerup, Lund, 363 pp.","Silva, P. C., Basson, P. W. & Moe, R. L. (1996) Catalogue of the benthic marine algae of the Indian Ocean. University of California Publications in Botany 79: 1 - 1259."]}

In this study, we presented a report on effect of growth parameters (seeding promoter, growth temperature, Ar gas flow rate) on the formation of MoS2 monolayer. The morphology and structure of as-grown MoS2 were investigated in detail by optical microscopy, atomic force microscopy, Raman and photoluminesence spectroscopy techniques. The results showed that a highly reproducible growth of dense MoS2 triangular flakes with the size of ~35 µm over large area (~1.5x1 cm2) can be obtained by using a optimized parameters. The MoS2 field effect transistors based on the as-grown MoS2 exhibited carrier mobility of 0.5–2 cm2V−1s−1 and On/Off ratio of ~104. Our results can provide a useful information to realize large area, high quality of MoS2 for real electronic applications.

In a timestamp-base packet scheduler, which is an important part of Quality of Service (QoS) enabled network systems, Tag Sorting is the most critical step. This paper presents a high throughput pipelined architecture for Tag Sorting targeting FPGA technology. Our implementation results on Xilinx Virtex II pro 50 chip have shown that our design can run at a maximum clock frequency of 216 MHz and process one tag every 2 clock cycles, thus provides 108 million tags per second throughput and can support 100 Gbps line speeds.

Clarias gracilentus sp. nov. (Fig. 1) Clarias Nieuhofi (non Bleeker)��� Pellegrin & Chevey, 1937: 315. Clarias nieuhofi (non Bleeker)��� Rainboth, 1996: 163. Type material. Holotype: UMMZ 248862, 189.6 mm SL; Vietnam: Phu Quoc Island, swamp draining into Rach Vem, 10 �� 22 'N 103 �� 56 'E (coordinates approximate); V. T. Nguyen and T. H. Le, 26 February 2010. Paratypes: BMNH 1937.9.17: 39���40 (2), 173.2���207.5 mm SL; Cambodia: Kampot province, Bokor; J. Delacour & W. Lowe, 1928. NLHC 2010.RV 1 (1) 251.5 mm SL; NLHC 2010.RV 2 (1) 254.5 mm SL; NLHC 2010.RV 3 (1) 299.5 mm SL; NLHC 2010.RV 4 (1) 317.5 mm SL; NLHC 2010.RV 5 (1) 265.5 mm SL; UMMZ 248863 (4), 151.0��� 224.1 mm SL; ZRC 52046 (1), 221.4 mm SL; data as for holotype. NLHC 2010.RT 1 (1), 281.5 mm SL; NLHC 2010.RT 2 (1), 260.5 mm SL; NLHC 2010.RT 3 (1), 294.5 mm SL; NLHC 2010.RT 4 (1) 305.5 mm SL; Vietnam: Phu Quoc Island, swamp draining into Rach Tram, 10 �� 24 'N 103 �� 58 'E (coordinates approximate); V. T. Nguyen and T. H. Le, 13 January 2010. Diagnosis. Clarias gracilentus can be distinguished from all Southeast Asian congeners, except for C. nieuhofii, C. nigricans and C. pseudonieuhofii in having a greatly elongate body with correspondingly long dorsal- and anal-fin ray bases. This elongation is manifested in the higher number of total vertebrae (74���84 vs. 54���71), dorsal- (81���101 vs. 62���80) and anal-fin (68���89 vs. 47���70) rays seen in all four species of the C. nieuhofii species complex compared to all other Southeast Asian Clarias. Clarias gracilentus differs from C. nieuhofii in having a narrower head (11.9���12.9 % SL vs. 13.2���15.8), more slender body (8.2���11.7 % SL vs. 10.8���14.4) and shorter pelvic fin (4.3���5.5 % SL vs. 5.0��� 6.3), from C. nigricans in having a larger eye (5.4���7.2 % SL vs. 4.5���5.6), larger interorbital distance (42.7 ���48.0% HL vs. 40.3 ���44.0), shorter distance between the occipital process and the base of the first dorsal-fin ray (5.3���8.4 % SL vs. 8.1���9.8) and longer pectoral fin (8.5���10.1 % SL vs. 5.2���8.5), and from C. pseudonieuhofii in having a longer occipital process (7.8���14.7 % HL vs. 4.6���6.8), shorter pelvic fin (4.3���5.5 % SL vs. 6.4���7.5) and longer anal-fin base (60.0��� 63.9 % SL vs. 56.0��� 58.9). Description. Biometric data in Table 1. Head depressed; dorsal profile slightly convex and ventral profile almost straight. Bony elements of dorsal surface of head covered with thick skin; bones not readily visible, but sutures sometimes evident. Anterior pair of nostrils tubular and medial to maxillary barbel base. Posterior pair of nostrils bordered by nasal barbels anteriorly and fleshy membrane posteriorly; posteromedial to maxillary barbel base. Eye ovoid, horizontal axis longest, subcutaneous; located dorsolaterally on head. Anterior fontanel short and squat (���shoe-shaped��� of Teugels, 1986); anterior tip reaching to line through middle of orbits. Occipital process rounded. Gill openings narrow, extending from dorsal-most point of pectoral-fin base to isthmus. Gill membranes free from isthmus but united to each other with 8 (n= 8) branchiostegal rays. First branchial arch with 3 + 13 * (n= 2), 3 + 14 (n= 2) or 4 + 13 (n= 2) gill rakers. Mouth subterminal, with fleshy, plicate lips. Oral teeth small and in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rectangular, with median notch on posterior edge. Dentary tooth band much narrower than premaxillary tooth band at symphysis, tapering laterally. Vomerine tooth band unpaired, continuous across midline, crescentic and smoothly arched along anterior and posterior margins. Premaxillary and dentary teeth viliform; vomerine teeth subgranular. Barbels in four pairs; long and slender with thick fleshy bases. Maxillary barbel extending to base of third or fourth dorsal-fin ray. Nasal barbel, extending to middle of pectoral fin. Inner mandibular-barbel origin close to midline; barbel thicker and longer than nasal barbel and extending just beyond base of last pectoral-fin ray. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to midway between base of last pectoral-fin ray and base of first pelvic-fin ray. Holotype Range Mean ��SD % SL Body anguilliform and cylindrical, becoming compressed towards caudal peduncle. Dorsal profile rising very gently from tip of snout to origin of dorsal fin and thereafter almost horizontal to end of caudal peduncle. Ventral profile slightly convex to middle of head and thereafter almost horizontal to end of caudal peduncle. Skin smooth. Lateral line complete and midlateral in position. Vertebrae 22 + 58 = 80 (n= 1), 23 + 58 = 81 * (n= 1), 22 + 60 = 82 (n= 1), 23 + 59 = 82 (n= 2), 23 + 60 = 83 (n= 1), 24 + 59 = 83 (n= 1) or 22 + 62 = 84 (n= 1). Dorsal fin with long base, spanning posterior three-quarters of body; with 96 (n= 1), 97 (n= 2), 99 (n= 1), 100 * (n= 3) or 101 (n= 1) rays covered by thick layer of skin and without spine. Dorsal-fin margin straight, parallel to dorsal edge of body. Pectoral fin with small spine, sharply pointed at tip, and 8,i (n= 8) rays. Almost entire length of anterior spine margin with a series of small serrations; posterior spine margin smooth or with uneven asperities. Pectoral-fin margin straight anteriorly, convex posteriorly. Pelvic-fin origin at anterior third of body, with i, 5 (n= 8) rays and convex margin; tip of adpressed fin reaching base of first two or three anal-fin rays. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Anal fin with long base, extending for posterior three-fifths of body, and 84 (n= 1), 85 * (n= 2), 86 (n= 1), 87 (n= 1) or 89 (n= 3) rays covered by thick layer of skin; margin straight and parallel to ventral edge of body. Caudal peduncle very short. Caudal fin rounded, with i,6,6,i (n= 8) principal rays. Coloration. In 70 % alcohol: dorsal and lateral surfaces of head and body dark gray, fading to pale gray on ventral surfaces. Fifteen to twenty-one vertical rows of two to five white spots present, subtended ventrally by two irregular rows of white spots running below lateral line. Dorsal and caudal fins dark gray with very thin hyaline distal margin. Anal fin light gray, with thin hyaline distal margin. Pectoral-fin rays dark gray, with hyaline interradial membranes. Pelvic fins hyaline. Barbels and pectoral spines dark gray dorsally and light gray ventrally. Distribution. Clarias gracilentus is known from the Rach Tram and Rach Vem drainages on the northern part of Phu Quoc Island, Vietnam, and from the Kampot River drainage in southern Cambodia (Fig. 2). This species is expected to occur elsewhere on Phu Quoc Island and southern Cambodia, but further surveys are needed to verify this. Habitat and ecology. On Phu Quoc Island, C. gracilentus inhabits forested swamps and slow-flowing streams. During the dry season, the fish hides in small holes under dead-tree roots. At the type locality, the water was clear, cool (24���27 ��C), tinted brown, acidic (pH 4.5���5.5) and well oxygenated (DO 4 mgl - 1). Other fishes collected at the type locality were Monopterus albus (Synbranchidae), Channa sp. (Channidae), and Betta cf. prima (Osphronemidae). Gut contents of dissected specimens consisted of smaller fishes (frequently Channa and Betta, and occasionally smaller individuals of C. gracilentus), freshwater crabs, molluscs, and terrestrial arthropods (insects and spiders). Etymology. The specific epithet is the Latin adjective gracilentus, meaning slender, in reference to the slender body of this species when compared to C. nieuhofii., Published as part of Ng, Heok Hee, Hong, Dang Khanh & Tu, Nguyen Van, 2011, Clarias gracilentus, a new walking catfish (Teleostei: Clariidae) from Vietnam and Cambodia, pp. 61-68 in Zootaxa 2823 on pages 62-65, DOI: 10.5281/zenodo.201228, {"references":["Pellegrin, J. & Chevey, P. (1937) Poissons d'Indochine recueillis par MM. J. Delacour et Lowe. Description d'une espece nouvelle. Bulletin de la Societe Zoologique de France, 62, 313 - 318.","Rainboth, W. J. (1996) Fishes of the Cambodian Mekong. FAO Species Identification Field Guide for Fishery Purposes. FAO, Rome, 265 pp.","Teugels, G. G. (1986) A systematic revision of the African species of the genus Clarias (Pisces; Clariidae). Annales du Musee Royal de l'Afrique Centrale (Zoologie), 247, 1 - 199."]}