Tabularia kobayasii Hidek. Suzuki & Mitsuishi, 2015

Suzuki, Hidekazu, Mitsuishi, Kyoko, Nagumo, Tamotsu & Tanaka, Jiro, 2015, Tabularia kobayasii: a new araphid diatom (Bacillariophyta, Fragilariaceae) from Japan, Phytotaxa 219 (1), pp. 87-95 : 89-95

Tabularia kobayasii Hidek. Suzuki & Mitsuishi sp. nov. ( Figs 2–32 )

Cells needle-like, grow either solitary or in tufted or band-like colonies attached to substrate by mucilage pads ( Figs 2, 4, 5 ); valves only rarely joined face-to-face ( Fig. 3 ). Each cell with several plate-like chloroplasts along valve inner wall ( Fig. 3 , arrowheads). Valves lanceolate with parallel to sub–parallel margins, tapering towards rounded poles ( Figs 6–14, 17, 18 ); length 11.5–87.5 μm, width 5.0–7.5 μm. Cells elongated, rectangular in girdle view ( Figs 15, 16 ), larger cells gently arcuate, possibly initial cells ( Figs 6, 7 ). Valve face flat ( Fig. 19 ), with transition to valve mantle gently steeped ( Figs 19, 22 ). Transapical plane of valve rectangular to trapezoidal. Striae density at valve center 10–12 in 10 μm. Striae parallel on valve face, becoming slightly radiate at pole ( Figs 7–14, 17 ). Each stria (width: 0.2 μm, ‘a’ in Fig. 33 ) consisting of a cribrate areola with several vimines ( Figs 21 , arrowheads, 22), continuing up to edge of valve ( Figs 19, 22 ). Its outside edge bends through a right angle at junction between valve face and mantle ( Figs 19, 22 ). Viewed internally, most of areolae sunk deeply between short ribs (virgae) ( Figs 20, 21 ). Sternum wide lanceolate and occupying at least half of valve surface ( Figs 7–14, 17 ). Single rimoportula at one end of sternum ( Figs 17, 18 , arrows), off-center and aligned with stria, opening to exterior as small rectangular slit pore ( Fig. 23 , arrow), internally as a shallow process ( Fig. 24 , arrow). Distinct ocellulimbus at both poles (0.47–0.80 μm, asterisks in Figs 23–26 and ‘b’ in Fig. 36 ), swelling at center ( Fig. 25 , double arrowhead). Ocellulimbus composed of 6–8 rows of 8–9 poroids, enclosed by a small rim. Rim on its advalvar side is plain, without spines or flaps. Externally, areolae do not reach poles but terminate in a single row of unoccluded small pores ( Figs 23, 25 , arrowheads). Mature cingulum consisting of 4–6 girdle bands ( Figs 27–29 ), open at one pole, divided into two types: Valvocopula (VC) has a crenulated edge (pars interior) fitting on top of valve ribs ( Figs 29, 30 , arrowheads), without areolae ( Fig. 30 ); copulae (3) narrower and thinner than valvocopula, with uniseriate row of areolae ( Fig. 29 ), without fimbriae.

Type: — JAPAN. Keihin Canal (35˚ 63’ N, 138˚ 75’ E), the estuary of Meguro River, Konan , Minato-ku , Tokyo, collected from surface of Caloglossa ogasawaraensis, K. Mitsuishi , 3 August 2008 (holotype BM! 101792, illustrated in Fig 6 ; isotype MTUF! AL 43062 ) .

Etymology:—The specific epithet “kobayasii ” is dedicated to the late Dr. Hiromu Kobayasi in recognition of his significant contribution to taxonomic research in diatoms.

Ecology:—With the sampling program undertaken, salinity ranges of 10.7–15.4, 8.1–25.6, 7.6–19.9 and 4.7–13.7, and temperature ranges of 8.3–27.2 ºC, 15.0–32.3 ºC, 11.5–28.0 ºC and 18.8–27.5 ºC were recorded in estuary of Naka River, Meguro River, Tsurumi River and Matsukoshi River respectively ( Table 2), where Tabularia kobayasii was found growing abundantly (46.7–96.6% relative abundance) as an epiphyte on Caloglossa ogasawaraensis for a full year (predominantly summer and autumn months). Tabularia kobayasii can be described as a brackish-water, epiphytic diatom with high rate of productivity during summer months.

Observations:— Tabularia kobayasii can be compared to: Tabularia barbatula (Kützing) D. M. Williams & Round (1986: 322) (basionym: Synedra barbatula Kützing 1844: 68 ), T. fasciculata (C. Agardh) D. M. Williams & Round (1986: 326) (basionym: Diatoma fasciculata C. Agardh 1812: 35 ), T. investiens (W. Smith) D. M. Williams & Round (1986: 324) (basionym: Synedra investiens W. Smith 1856: 98 ), T. parva (Kützing) D. M. Williams & Round (1986: 324) (basionym: Synedra parva Kützing 1849: 46 ), T. variostriata M. A. Harper in Harper et al. (2009: 293) and T. waernii Snoeijs in Snoeijs & Kuylenstierna (1991: 352). The fine structures of the valves of Tabularia , such as areolae, ocellulimbus and cingulum, have been described in detail for these species ( Tabularia barbatula in Williams & Round 1986; T. fasciculata in Williams & Round 1986, Snoeijis 1992 and Kuriyama et al. 2008, T. investiens in Williams & Round 1986 and Kuriyama et al. 2010, T. variostriata in Harper et al. 2009 and T. waernii in Snoeijs & Kuylenstierna 1991). Their characteristics can be summarized as following: they have araphid valves; the valves are elongate, linear or lancolate; the striae are transverse, separated internally by distinct ribs; the areolae are occluded externally by cribra with distinct cross bars; they have an ocellulimbus, which is small, with few poroids per plate; there is one rimoportula situated close to ocellulimbus; and the cingulum consists of a few open, ligulate bands.

Our SEM observations on Tabularia kobayasii confirm it is a member of Tabularia . It is most similar to T. investiens and T. variostriata as these species have cribra with heavily silicified cross-members in structure of areolae. All three species, Tabularia kobayasii , T. investiens and T. variostriata , belong to “Group 2” of Williams & Round (1986). The cingulum of the three species is typical in having a non-areolate open valvocopula and several open copulae with a single row of poroids.

The following features distinguish T. kobayasii from T. investiens and T. variostriata , are thus diagnostic for T. kobayasii (listed in Table 3): a) lanceolate valves; b) narrow striae; c) small ocellulimbus; and d) denser vimines.

... continued on the next page immature areolae.

showing the ocellulimbus (asterisks) and a rimoportula (arrow).

Tabularia kobayasii can be readily distinguished from T. investiens as the latter has a linear-elliptical valve outline, a convex valve plane ( Fig. 35 ), a narrow lanceolate sternum, wider striae (0.6 μm, Figs 33, 34 ), a larger ocellulimbus (1.00–1.87 μm, Fig. 36 ) and less dense vimines (5 in 1 μm, Fig. 33 ); it can be also differentiated from T. variostriata by the latter having a different valve outline and shape of its sternum, and the rim structure of the ocellulimbus: T. variostriata has nearly isopolar to distinctly heteropolar valves, striae of various lengths forming an undulated edge to wide lanceolate sternum, and two to four advalvar spines on the rim of the ocellulimbus-type pore-fields ( Harper et al. 2009).

Figures

FIGURES 2–5. Tabularia kobayasii. Epiphytic on Caloglossa ogasawaraensis from Keihin Canal, Meguro River Estuary collected in 18 June 2008, LM (2, 3) and SEM (4, 5). 2. Living tufted and band–like colonies. 3. Living cells attached by small mucilage pads. Arrowheads indicate four plastids after cytokinesis. 4, 5. Tufted colonies.

FIGURES 6–18. Tabularia kobayasii. LM (6–16) and SEM (17, 18), holotype and other specimens. 6, 16. Girdle views of two frustules. 7– 14. Valve views. 6, 7. Initial valves. 8. Specimen from holotype slide. 15. Girdle view of a frustule.17. External view of a whole valve.Arrow indicates the opening of rimoportula. 18. Internal view of a whole valve.Arrow indicates the rimoportula. Scale bars = 5 μm (17, 18).

FIGURES 19–22. Tabularia kobayasii. SEM. 19. External view of valve mantle showing the areolae with cross-bars (= vimines). 20. Internal view of the areolae. 21. Detail of the cross section of areolae. Arrowheads indicate cross-bars (= vimines). 22. External view of

FIGURES 23–26. Tabularia kobayasii. SEM.23, 25. External polar views showing the ocellulimbus (asterisks),the opening of rimoportula (arrow) and the tiny simple pores (arrowheads). 25. Double arrowhead indicates a small bulge of ocellulimbus. 24, 26. Internal polar views

FIGURES 27–30. Tabularia kobayasii. SEM. 27, 28. Terminal views of the same cingulum composed of a valvocopula (VC) and three bands (B2–B4). 29. Internal view of a valvocopula (VC) and four bands (B2–B5). Arrowheads indicate the crenulated pars interior of valvocopula. 30. Valvocopula. Arrowheads indicate the crenulated pars interior.

FIGURES 31–36. Tabularia kobayasii (31, 32) and T. investiens (33–36). SEM. 31, 33. Detail of external views of cribrate areolae. Arrowheads indicate the cross-bars (= vimines). 32, 34. Detail of internal views of areolae. 35. External view of valve face showing the areolae. 36. External polar view showing the ocellulimbus (asterisk) and the opening of rimoportula (arrow). Scale bars = 0.5 μm (31–34). ‘a’: length of the minor axis of areola, ‘b’: length of the major axis of ocellulimbus. See Material and Methods for details.