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21Pinnularia arkadii sp. nov., a new diatom (Naviculales, Bacillariophyceae) from Shemya Island, Alaska, USA
A. A. Neplyukhina, D. A. Chudaev, M. A. Gololobova
Faculty of Biology, M. V. Lomonosov Moscow State University, Moscow, Russia Corresponding author: A. A. Neplyukhina, [email protected]
Abstract. Based on a unique combination of morphological characters, a new species of the raphid pennate diatom genus Pinnularia was described from the sediments in MacDonald Point peat-bog, Shemya Island, Alaska, USA. P. arkadii sp. nov. has linear valves with parallel margins, widely rounded ends and central area forming wide fascia; striae are relatively coarse, 5.6-6.6 in 10 ^m, not crossed by longitudal bands. This taxon was compared to other morphologically similar species of Pinnularia: P. aestuarii, P. brebissonii, P. eifelana, P. franconica, P. idsbensis, P. inconstans, P. laperousei, P. li-nearidivergens, P. rabenhorstii var. subantarctica and P. tolottiana. The main morphological characters of P. arkadii and similar taxa are discussed.
Keywords: Pinnularia, taxonomy, new species, peat-bogs, Alaska, Shemya Island, USA.
Pinnularia arkadii (Naviculales, Bacillariophyceae) — новый вид диатомовых водорослей с острова Шемья (Аляска, США)
А. А. Неплюхина, Д. А. Чудаев, М. А. Гололобова
Биологический факультет Московского государственного университета им. М. В. Ломоносова, Москва, Россия Автор для переписки: А. А. Неплюхина, [email protected]
Резюме. Основываясь на уникальном сочетании морфологических признаков, новый вид шовной пеннатной диатомовой водоросли рода Pinnularia был описан из торфяного отложения MacDonald Point (остров Шемья, Аляска, США). P. arkadii sp. nov. имеет линейные створки с параллельными краями, широко закругленными концами и центральное поле в виде широкой фасции; штрихи относительно грубые, 5.6-6.6 в 10 мкм, не пересекаются продольными полосами. Проведено сравнение P. arkadii sp. nov. с другими морфологически сходными видами рода: P. aestuarii, P. brebissonii, P. eifelana, P. franconica, P. idsbensis, P. inconstans, P. laperousei, P. linearidivergens, P. rabenhorstii var. subantarctica и P. tolottiana. В работе приведено обсуждение основных морфологических признаков P. arkadii и сходных таксонов.
Ключевые слова: Pinnularia, новый вид, таксономия, торфяники, Аляска, остров Шемья, США.
Despite of a large number of publications on the diatoms of the American North-West (Bahls, 2005, 2010, 2011, 2012), this taxonomic group has been poorly studied in Alaska and Aleutian Islands. Few studies on the species diversity in some parts of Alaska have been previously performed (Foged, 1971, 1981; Hein, 1990), but both modern and fossil diatoms from Shemya Island have been never studied before. Climate and vegetation changes during the Holocene in the western Aleutians have been also studied inadequately.
To improve our knowledge, a diatom analysis of a core taken from MacDonald Point peatbog was carried out for paleoecological purposes (Neplukhina et al., in prep.). In the course of this analysis, a new species of Pinnularia Ehrenb. was found.
Material and methods
Shemya (52°43'27"N, 174°07'08"E) is a small island in the Near Islands group of the Semichi Islands in the Aleutian Archipelago, southwestern Alaska, USA. Shemya is a flat-topped seamount of approximately 2.7 km wide and 7.1 km long along a west-east axis; it has an area of 1.425 ha. A shoreline stretches for 22 km (Corbett et al., 2010).
A 372-cm core was taken from MacDonald Point peat deposit (52°42'30.37"N, 174°09'03.76"E), located closely to the shoreline. Deposits consisted of about 4 m of interlay-ered peat and windblown sand resting on bedrock. A radiocarbon dating indicates that the soil deposition began 9500 years ago (9550 ± 130 BP, IEMAE-1261) (Savinetsky at al, 2014).
Samples of peat-bog sediments were collected in 1999 by A. B. Savinetsky, N. K. Kiseleva and B. F. Khasanov. The samples were divided into layers of 3-5 cm thick. Diatom frustules were cleaned according to Kelly et al. (2001) by boiling in hot hydrogen peroxide and hydrochloric acid. Permanent slides were made using aniline-formaldehyde mount medium (n=1.67-1.68). Light microscopy (LM) observations were performed with 100 x oil immersion planapochromatic objective with numerical aperture 1.40 at Leica DM2500 microscope equipped with differential interference contrast (DIC) optics and DFC 495 camera. Scanning electron microscopy (SEM) observations were performed using a Jeol JSM-6380 microscope. For SEM investigation drops of cleaned material were air-dried on pieces of aluminium foil mounted on brass stubs with double sided carbon tape and coated with Au-Pd in a Giko IB-3 ion coater. All slides and samples used in this work are stored in diatom collection of Department of Mycology and Algology, Moscow State University, Moscow, Russia.
Pinnularia arkadii Neplyukhina, Chudaev et Gololobova, sp. nov. (Plates I, II)
Valves linear with parallel margins and widely rounded ends. Valve 45.8-66.0 ^m long (average 54.3 ^m), 11.2-13.2 ^m wide (average 12.1 ^m) (n=14 valves). Axial area narrow, 1/7-1/5 of valve breadth, slightly widening towards the central area. Central area forming wide fascia, sometimes slightly asymmetric, rhomboid near raphe. Raphe narrowly lateral. External proximal central pores small, but distinct, drop-like, bent towards the primary valve side. External terminal raphe fissures curved towards secondary side of valves, sickle-like. Internal proximal raphe ends unilaterally curved, with intermissio. Internal distal raphe endings very weakly developed helictoglossae. Striae density 5.6-6.6 in 10 ^m (average 6.0 ^m, n=14 valves). Transapical striae radiate in the middle, parallel to slightly convergent near poles. Central nodule present but weakly developed internally and not covering proximal raphe ends. Striae not crossed by longitudal bands. Copulae bear a single row of perforations.
Plate II. 11, 12 — Pinnularia arkadii sp. nov.: 11 - external valve view; 12 - internal valve view. SEM. Scale bars: 10 ^m.
Type . Shemya Island, Alaska, USA, MacDonald Point peat deposit, 52°42'30.37"N, 174°09'03.76"E, peat sediments, A. Savinetsky, N. Kiseleva and B. Khasanov (holotype: slide No. 640s1 (Pl. I, 3), Diatom collection of the Department of Mycology and Algology, M. V. Lomonosov Moscow State University, Moscow, Russia).
Distribution. To date, P. arkadii is known with certainty only from the type locality. It was found in samples No. 630-641 (Diatom collection of the Department of Mycology and Algology), at 215-270 cm depth from ground level. The species was most abundant in the sample No. 640 (260-265 cm, 4060 ± 80 BP, IEMAE-1262). P. arkadii was observed together with other Pinnularia species: P. inconstans A. Mayer, P. intermedia (Lagerstedt) Cleve, P. cf. islandica 0strup (dominant species), P. cf. renata Krammer.
Etymology. The species named after our colleague and friend Dr. Arkady Sav-inetsky.
Differentiation. For confirmation of the novelty Pinnularia arkadii should be compared to a number of morphologically similar taxa of Pinnularia. P. franconica (Krammer) Kulikovskiy, Lange-Bert. et Metzeltin, nom. illeg., P. rabenhorstii (Grunow) Krammer var. subantarctica Van de Vijver et Le Cohu and P. idsbensis Pavlov et Levkov differ from P. arkadii mainly by the absence of fascia and coarser striae. P. linearidiver-gens Kulikovskiy, Lange-Bert. et Metzeltin differs from P. arkadii in bayonet-shaped terminal raphe fissures, presence of thickenings at the margins of fascia and significantly higher density of striae. P. brebissonii (Kutz.) Rabenh. possesses more distinctly radiate and convergent striae near the valve centre and apices, respectively. It also has a higher density of striae and less broadly rounded valve ends. Both P. eifelana Krammer and P. inconstans have wider axial area, abruptly narrowing towards valve ends, narrower fascia and less coarser striae. P. aestuarii Cleve differs from P. arkadii in semicomplex raphe, narrower fascia, almost parallel striae and greater valve size. P. tolottiana LangeBert. et Metzeltin, generally, has softly triundulate margins and subparallel striae of higher density. P. laperousei Van de Vijver et Beyens differs from P. arkadii in slightly protracted valve ends and greater number of striae in 10 ^m. The characters of P. arkadii and those of the mentioned above similar taxa are summarized in Table. The unique combination of morphological characters (linear valves with wide fascia and relatively coarse striae) differentiates P. arkadii as a separate species.
Acknowledgments
The work was carried out within the framework of the state program of the Moscow State University, part 2, item 01 10. The authors also thank their colleagues from the Laboratory of Historical Ecology of A. N. Severtsov Institute of Ecology and Evolution: Arkady B. Savinetsky, Olga A. Krylovich and Bulat F. Khasanov for provided materials, information and friendly support. The analysis of taxonomic references by M. A. Gololobova
Table
Comparison of Pinnularia arkadii sp. nov. with morphologically similar species
Valve outline Valve Valve Number
Taxon Apices length width of striae Fascia References
(Pm) (pm) in 10 pm
P. arkadii linear rounded 45.8-66.0 (54.3) ± 1.78* 11.1-13.2 (12.1) ± 0.13* 5.6-6.0 (6.0) ± 0.07 present original data
P. franconica linear broadly subrostrate 45-67 12-13.5 4-5 absent Krammer, 2000**
P. rabenhorstii linear rounded 40-58 12-14 5-6 absent Van de
var. subantarctica Vijver et al, 2002
P. linearidiver- linear broadly 50-80 12-16 10-11 present Krammer,
gens rounded 2000***
P. brebissonii linear-elliptical broadly rounded 15-87 5.6-12 9-13 present Krammer, 2000
P. eifelana linear cuneate rounded 38-75 8-11 7-10 present Krammer, 2000
P. inconstans linear cuneiform rounded 40-80 10.2-14.5 7-9 present Krammer, 2000
P. laperousei linear, slightly convex margins slightly protracted, obtusely rounded 44-55 8-10 1 0-1 1 present Van de Vijver et al, 2002
P. aestuarii linear broadly cuneiform rounded 66-120 14-16 6-8 present Krammer, 2000
P. tolottiana softly triun-dulate broadly rounded 33-52 7.5-10 1 0-1 1 present Lange-Bertalot et al., 2003
P. idsbensis linear broadly rounded 33.0-71.5 11.0-14.0 4-6 absent Pavlov, Levkov, 2013
Note. Median values are given in brackets (n=14 valves); * — standard error, ** — as P. rabenhorstii var. franconica Krammer, *** — as P. divergens W. Sm. var. linearis 0strup
was supported by the Russian Foundation for Basic Research (grant 15-04-08552-a). The morphological analysis of new species by D. A. Chudaev was supported by the Russian Science Foundation (project N14-50-00029). The work is performed at the User Facilities Center of Moscow State University under financial support of the Ministry of Education and Science of Russian Federation.
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