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The current article focuses on the morphological and molecular characterization of the often inconspicuous genus Amicula. This recently erected genus from brackish and marine sediments was monotypic but here we describe two new tropical species: Amicula micronesica sp. nov. and Amicula vermiculata sp. nov. Once considered an incertae sedis genus regarding its higher rank taxonomy, its position among the family Diploneidaceae is proposed here by molecular phylogenetics. The complete plastid and mitochondrial genomes of Amicula micronesica sp. nov. are also presented here. It appears that the 177614-bp long mitogenome is the biggest yet recorded among stramenopiles, due to its invasion by 57 introns. Moreover, it utilizes the genetic code 4 for translation instead of the code 1 usually found among diatoms.

Ardissonea was resurrected from Synedra in 1986 and was included as a genus by Round, Crawford and Mann (“The Diatoms”) in its own Family and Order. They commented that there might be several genera involved since the type species of the genus possesses a double-walled structure and other taxa placed in Ardissonea have only a single-walled structure. Two other genera of “big sticks,” Toxarium and Climacosphenia, were placed in their own Families and Orders but share many characters with Ardissoneaceae, especially growth from a bifacial annulus. Eighteen taxa (11 new species) from Micronesia were compared with the literature and remnant material from Grunow’s Honduras Sargassum sample to address the concepts of Ardissonea and Ardissoneaceae. Phylogenetic and morphological analyses showed three clades within Ardissonea sensu lato: Ardissonea emend. for the double-walled taxa, Synedrosphenia emend. and Ardissoneopsis gen. nov. for single-walled taxa. New species include Ardissonea densistriata sp. nov.; Synedrosphenia bikarensis sp. nov., S. licmophoropsis sp. nov., S. parva sp. nov., and S. recta sp. nov.; Ardissoneopsis fulgicans sp. nov., A. appressata sp. nov., and A. gracilis sp. nov. Transfers include Synedrosphenia crystallina comb. nov. and S. fulgens comb. nov. Synedra undosa, seen for the first time in SEM in Grunow’s material, is transferred to Ardissoneopsis undosa comb. nov. Three more genera have similar structure: Toxarium, Climacosphenia and Grunowago gen. nov., erected for Synedra bacillaris and a lanceolate species, G. pacifica sp. nov. Morphological characters of Toxarium in our region support separation of Toxarium hennedyanum and T. undulatum and suggest additional species here and elsewhere. Climacosphenia moniligera was not found but we clarify its characters based on the literature and distinguish C. soulonalis sp. nov. from it. Climacosphenia elongata and a very long, slender C. elegantissima sp. nov., previously identified as C. elongata, were present along with C. scimiter. Morphological and molecular phylogenetics strongly suggested that all these genera belong in one family and we propose to include them in the Ardissoneacae and to reinstate the Order Ardissoneales Round.

Divergita biformis, Lobban, sp. nov. Figs. 26–28. Diagnosis:— Valves straight, lanceolate with weakly capitate apices. Striae biseriate and decussate only on the mantle, striae on valve face mostly uniseriate with quadrangular areolae; sternum linear, very narrow. Description:— Live cells not observed. Valves seen in LM (Figs 24, 25) were from different samples from the SEM holotypes and could not be identified to D. divergita vs. D. decipiens (see below). Valves straight, 76 µm long, 4 µm wide, lanceolate with weakly capitate apices (Fig. 26). Striae 26–28 in 10 µm, biseriate on the margin with triangular areolae alternating and thus forming a decussate pattern, becoming largely uniseriate on the valve face with up to four quadrate areolae (Figs 27, 28). Sternum linear and very narrow. A hyaline area at each apex with a rimoportula in each. Apical pore field apparently with three rows of pores and not sunken. Holotype hic designatus:— Figs 26–28 from stub 1116 (GUAM diatom herbarium, catalog # 701116), according to Article 40.5 of the International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) (Turland et al. 2018). Registration: http://phycobank.org/102756. Type locality: — F.S. M. Yap: reef flat near channel to Colonia, 13.464 N, 144.656 E, dense farmer fish turf scraped from Acropora coral, ca. 1 m deep, sample Y45-5. C.S. Lobban and M. Schefter, 31 May 2014 . Etymology:— named for the two patterns of areolae in the striae. Additional Records:— F.S.M. Yap: Nimpal MPA, Y36-2!, Y36-4!; GUAM: GU52Q-1a!, GU44AP-8! Comments:— Similar specimens occurred in several samples from each of Guam and Yap but were always rare. There was considerable variation among these specimens and some clear differences, so I have chosen to define two species on the basis of ultrastructural details. For this species, defined on the specimen from Y45-5, I found no internal aspect but for D. decipiens the internal view shows the characteristics of Divergita, which do not vary between species., Published as part of Lobban, Christopher S., 2021, New species of benthic marine diatoms (Bacillariophyta) from the Western Pacific islands of Guam and Yap, pp. 235-265 in Phytotaxa 508 (3) on page 242, DOI: 10.11646/phytotaxa.508.3.1, http://zenodo.org/record/5425968, {"references":["Turland, N. J., Wiersema, J. H., Barrie, F. R., Greuter, W., Hawksworth, D. L., Herendeen, P. S., Knapp, S., Kusber, W. - H., Li, D. - Z., Marhold, K., May, T. W., McNeill, J., Monro, A. M., Prado, J., Price, M. J. & Smith, G. F. (Eds.) (2018) International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) adopted by the Nineteenth International Botanical Congress Shenzhen, China, July 2017. Regnum Vegetabile 159. Glashutten: Koeltz Botanical Books. https: // doi. org / 10.12705 / Code. 2018"]}

Divergita decipiens Lobban, sp. nov. Figs 29–32. Diagnosis:— Differing from D. biformis in striae on valve face comprising irregular, transapically oval areolae with wide virgae, and in having a prominent, lanceolate sternum. Description:— Valves straight, 94 µm long, 4 µm wide, lanceolate with weakly capitate apices (Figs 29, 30, 32). Striae 28 in 10 µm, decussate on margin becoming uniseriate on valve face with generally three narrow, irregular, transapically elongated areolae, separated by wide virgae compared to D. biformis (Figs 30, 31). Sternum broad and lanceolate. A hyaline area at each apex with a rimoportula in each. Internally, the rimoportulae asymmetrical and a line of foramina along each boundary between valve face and mantle (Fig. 32). Holotype hic designatus:— Figs 29–31 from stub 566 (GUAM diatom herbarium, catalog # 700566), according to Article 40.5 of the International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) (Turland et al. 2018). Registration: http://phycobank.org/102757. Type locality:— GUAM: Apra Harbor, Outhouse Beach, 13.464 N, 144.656 E, in algal turf from farmer fish (Stegastes nigricans) territory, ca. 3 m deep, sample GU52R-2. C.S. Lobban and M. Schefter, 24 July 2013 . Etymology:— Named for its deceptive similarity to D. biformis. Comments:— This species was initially confounded with D. biformis, because length and stria densities are very similar. However, given the use of sternum characters to distinguish species in the related genus Hyalosynedra (Sabir et al. 2018), the broader, lanceolate sternum here, combined with the different appearance of areolae on the valve face, marked D. decipiens as a separate species, and required that both be typified by SEM images. This species seems slightly narrower than D. biformis (compare Figs. 26, 29) but several other specimens from Guam with some further variation in characters have been left unidentified for the present. It is likely that there is more diversity in Divergita to be discovered through SEM surveys of coral reef samples. It is possible that the rarity of these specimens is because they are being deposited into the samples from elsewhere (planktonic?), rather than growing in the farmer fish territories., Published as part of Lobban, Christopher S., 2021, New species of benthic marine diatoms (Bacillariophyta) from the Western Pacific islands of Guam and Yap, pp. 235-265 in Phytotaxa 508 (3) on page 242, DOI: 10.11646/phytotaxa.508.3.1, http://zenodo.org/record/5425968, {"references":["Turland, N. J., Wiersema, J. H., Barrie, F. R., Greuter, W., Hawksworth, D. L., Herendeen, P. S., Knapp, S., Kusber, W. - H., Li, D. - Z., Marhold, K., May, T. W., McNeill, J., Monro, A. M., Prado, J., Price, M. J. & Smith, G. F. (Eds.) (2018) International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) adopted by the Nineteenth International Botanical Congress Shenzhen, China, July 2017. Regnum Vegetabile 159. Glashutten: Koeltz Botanical Books. https: // doi. org / 10.12705 / Code. 2018","Sabir, J. S. M., Theriot, E. C., Lobban, C. S., Alhebshi, A. M., Al-Malki, A. L., Hajrah, N. H.,. Khiyami, M. A, Obaid, A. Y., Jansen, R. K. & Ashworth, M. P. (2018) Systematics of araphid diatoms with asymmetric rimoportulae or densely packed virgae, with particular attention to Hyalosynedra (Ulnariaceae, Bacillariophyta). Phytotaxa 347: 1 - 49. https: // doi. org / 10.11646 / phytotaxa. 347.1.1"]}

Parlibellus paschalis Lobban, sp. nov. Figs 70–78. Diagnosis:— Differing from P. delognei (Van Heurck 1880: pl. 11) E.J. Cox 1988: 19 in lacking the cuniculus and pores in the central area and smaller size, and from P. berkeleyi (Kützing 1849: 106) E.J. Cox 1988: 21 in width and stria density. Description:— Tube-dwelling cells with plastids reminiscent of a hot cross bun in valve view, a butterfly in girdle view (Figs 70–72). Frustules, often remaining together after acid cleaning (Fig. 73), with numerous copulae (Fig. 74). Valves elliptico-lanceolate, 28–35 µm long, 10.5–12.5 µm wide (Figs 75–78). Striae 25–26 in 10 µm except slightly more distant (21 in 10 µm) in those adjacent to central area, weakly radiate in the central area, otherwise parallel, continuing around the apices (Figs 75–78). Striae punctate, the external areolae openings circular to transapically elongate, internally circular. Areolae closest to the raphe sternum somewhat more prominent (Fig. 77, arrow). Central area lacking isolated pores. External central raphe endings 4–6 striae apart, straight, extending into the narrowly oval central area, which as defined by the line of areolae is 11–12 striae long. External terminal raphe endings subapical (ca. 5 striae short of apex) with a small hook into a small hyaline area 1–2 striae wide. Internal raphe endings straight, a small helictoglossa at each terminus; no cuniculi at the central endings. Holotype hic designatus:— specimen at 16.1 mm E and 9.7 mm S of the mark on slide 192, deposited at ANSP, accession # ANSP-GC20094. Fig. 75. Registration: http://phycobank.org/102762. Type locality:— GUAM: Apra Harbor, GabGab reef, 13.443 N, 144.643 E, farmer fish (Plectroglyphidodon lacrimatus) territory 7–8 m depth, sample GU44L-C. C.S. Lobban and M. Schefter, 2 March 2008. Etymology:— paschalis, L. adjective referring to Easter, with reference to the resemblance of the live cells in valve view to the Eastertime bakery item, hot cross buns. Additional Records:— GUAM: GabGab reef, Apra Harbor, GU44I-2!, GU44K-6!. Comments:— This species is most like P. delognei f. elliptica (Lobban 1983: 287) Cox 1988: 21 but differs in lacking the cuniculus that is characteristic of both forms of delognei, along with associated pores in the central area. [A cuniculus (Ross et al. 1979, Cox 1978) “comprises a simple pore in the external central area connecting with an elongate perforate raised structure terminating the internal raphe fissures in the central area.”] It is also shorter and narrower than that form, though wider than P. berkeleyi. The colony structure is similar to the narrow threads of the nominate variety of P. delognei but much different from the large, cold-water colonies of var. elliptica (Cox 1988, Lobban 1983). The stria density is higher than other similar species (Table 2), including P. berkeleyi (16–18 in 10 µm)., Published as part of Lobban, Christopher S., 2021, New species of benthic marine diatoms (Bacillariophyta) from the Western Pacific islands of Guam and Yap, pp. 235-265 in Phytotaxa 508 (3) on pages 251-252, DOI: 10.11646/phytotaxa.508.3.1, http://zenodo.org/record/5425968, {"references":["Van Heurck, H. (1880) Synopsis des Diatomees de Belgique Atlas. Anvers: Ducaju et Cie. pls I - XXX [pls 1 - 30].","Cox, E. J. (1988) Taxonomic studies on the diatom genus Navicula. V. The establishment of Parlibellus gen. nov. for some members of Navicula sect. Microstigmaticae. Diatom Research 3: 9 - 38. https: // doi. org / 10.1080 / 0269249 X. 1988.9705014","Kutzing, F. T. (1849) Species algarum. pp. [i] - vi, [1] - 922. Lipsiae [Leipzig]: F. A. Brockhaus.","Lobban, C. S. (1983) Colony and frustule morphology of three tube-dwelling diatoms from eastern Canada. Journal of Phycology 19: 281 - 289. https: // doi. org / 10.1111 / j. 0022 - 3646.1983.00281. x","Ross, R., Cox, E. J., Karayeva, N. I., Mann, D. G., Paddock, T. B. B., Simonsen, R. & Sims, P. A. (1979) An amended terminology for the siliceous components of the diatom cell. Nova Hedwigia Beihefte 64: 513 - 533.","Cox, E. J. (1978) Taxonomic studies on the diatom genus Navicula Bory. Navicula grevillii (C. A. Ag.) Heiberg and N. comoides (Dillwyn) H. & M. Peragallo. Botanical Journal of the Linnaean Society 76: 127 - 143. https: // doi. org / 10.1111 / j. 1095 - 8339.1978. tb 01502. x"]}

Climaconeis tarangensis Lobban, sp. nov. Figs 45–49. Diagnosis:— Curved species without craticular bars or stauros, differing from Climaconeis riddleae A.K.S.K. Prasad 2003: 14 in its lower stria density (20 vs 24–27 in 10 µm) and regular apically rectangular areolae. Description:— Living cells not observed. Valves arcuate, 121–124 µm long, 4.5 µm wide at center, gradually tapering to 3.0 µm just before the weakly capitate apices, 3.5 µm wide (Fig. 45). Striae 20–21 in 10 µm, parallel except convergent near apices and radiating around the apex; areolae apically rectangular (Figs 46–49). Raphe biarcuate (Fig. 45), the raphe slit partially covered by an irregular flap along the ventral side (Figs 46, 47). External central raphe endings turned slightly ventral, terminal endings nearly straight. Internal raphe with a rib along one side, helictoglossa at the apex (Figs. 48, 49). Copulae with two rows of apically-oriented pores similar to those on the valve (Figs 46, 47). Holotype hic designatus:— Specimen at 9.0 mm E, 6.4 mm S of the mark on slide 512, deposited at ANSP, accession # ANSP-GC20095. Fig. 45. Registration: http://phycobank.org/102760. Type locality:— F.S.M. Yap State: Tarang (“ O’Keefe’s Island ”), 9.525 N, 138.132 E; subtidal sediments from 15 m depth, sample Y26 C. C.S. Lobban and M. Schefter, 25 September 1988 . Etymology:— Named for the type locality. Comments:— This species is very similar to C. riddleae, which has been recorded from Guam (Lobban et al. 2011) and Chuuk (Park et al. in prep.), but Prasad (2003) described the areolae of that species thus: “squarish or subrectangular poroids… [sometimes] slightly apically elongated, especially at the apices.” In C. tarangensis the areolae are distinctly apically elongate even in the central part of the cell. Prasad’s images show a row of somewhat larger, square areolae along the ventral side of the raphe sternum (the same side that bears the silica flaps). While the differences in stria density and areola shape are small, it has become clear in this genus that such details must be taken into account in discriminating species [e.g., in distinguishing C. mabikii J.Park, Khim & J.H.Lee 2016: 592 from C. undulata (Meister 1932: 41) Lobban, Ashworth & E.C.Theriot 2010: 295 – Park et al. 2016]. For C. tarangensis, with C. riddleae known from the region, it is especially clear that the differences cannot be dismissed as geographic variation between Atlantic and Pacific Ocean basins., Published as part of Lobban, Christopher S., 2021, New species of benthic marine diatoms (Bacillariophyta) from the Western Pacific islands of Guam and Yap, pp. 235-265 in Phytotaxa 508 (3) on page 246, DOI: 10.11646/phytotaxa.508.3.1, http://zenodo.org/record/5425968, {"references":["Prasad, A. K. S. K. (2003) Fine structure and taxonomy of two species of the marine diatom genus Climaconeis (Berkeleyaceae, Bacillariophyta): C. silvae sp. nov. and C. riddleae sp. nov. from the Caribbean Sea and Florida Bay, U. S. A. Hidrobiologica 13: 9 - 22. [http: // www. scielo. org. mx / scielo. php? script = sci _ arttext & pid = S 0188 - 88972003000100002]","Lobban, C. S., Schefter, M. & Ruck, E. C. (2011) Licmophora flucticulata sp. nov. (Licmophoraceae, Bacillariophyceae), an unusual flabellate species from Guam and Palau. Phycologia 50: 11 - 22. https: // doi. org / 10.2216 / 09 - 85.1","Meister, F. (1932) Kieselalgen aus Asien. Berlin: Gebruder Bornetraeger.","Park, J., Lee, J. H. & Khim, J. S. (2016) The identity of ' Berkeleya scopulorum ' from northeast Asia: report on Climaconeis mabikii sp. nov. from temperate marine waters with notes on biogeography of the genus. Ocean Science Journal 51: 591 - 598. https: // doi. org / 10.1007 / s 12601 - 016 - 0059 - z"]}