Climaconeis minaegensis, Lobban, 2021

Lobban, Christopher S., 2021, New species of benthic marine diatoms (Bacillariophyta) from the Western Pacific islands of Guam and Yap, Phytotaxa 508 (3), pp. 235-265 : 249-250

Climaconeis minaegensis, Lobban , sp. nov. Figs 50–60 .

Diagnosis:— Slightly bent and curved species without craticular bars or stauros, differing from C. petersonii Lobban, Ashworth & Theriot 2010: 300 in the shorter length, (internal) silica ribs bordering the raphe, and the quadrate to transapically elongate areolae.

Description:— Valve neither straight nor arcuate, but slightly curved toward the apices (more pronounced in the longer specimens) and the raphe branches near the center at 4–6º to one another; lacking a stauros ( Figs 50–53 ). Dimensions in the Yap population length 228–247 µm, width 5.0 µm inflated to 8.3 µm at center and 7.6 µm at apex; Bikar Atoll specimens 124–145 µm long, width 3.9 /5.8 / 5.1 µm ( Figs 52–54 ). Striae consistently 19 in 10 µm, mostly parallel but radiating at center, convergent at apices. Areolae circular/quadrate to transapically rectangular, becoming transapically elongate in several striae near the central area ( Figs 54–59 ); one row of areolae larger along each side of the raphe. Central area scarcely broader than sternum ( Fig. 55 ). Raphe straight, not deflected at center ( Figs 51, 52, 55 ). Raphe externally overlapped by irregular silica flap ( Figs 55, 56 ), internally bordered by ribs that are continuous except at the central area ( Figs 54, 57–60 ). No evidence for craticular bars.

Holotype hic designatus:— Specimen at 14.6 mm E, 1.3 mm S of the mark on slide 2824, deposited at ANSP, accession # ANSP-GC20096 . Figs 50, 51 . Registration: http://phycobank.org/102761.

Type locality:— F.S. M. Yap: Ruul Municipality, Yinuuf, Minaeg , 9.489 N, 138.099 E; floating algal mat in mangal channel, sample Y18 E. C.S. Lobban and M. Schefter, 21 September 1988 .

Etymology:— Named for the type locality.

Additional Records:— MARSHALL ISLANDS. Bikar Atoll: BA-5!, BA-6!.

Comments:— Climaconeis petersonii , described from Guam, is 350–380 µm long, lacks craticular bars, and has square to apically rectangular areolae ( Fig. 61 ). The presence of ribs along each side of the raphe in C. minaegensis is a novel feature in this genus. It is very likely that C. minaegensis lacks craticular bars because although I did not find valvocopulae attached to acid-cleaned valves, a thorough search of the SEM stub and one slide, on which there were many valves, revealed no valvocopulae with bars, nor broken parts. If this conclusion is wrong, the new species cannot be assigned to either of the two species that have craticular bars, i.e., Climaconeis lorenzii and C. coxiae Reid & Williams 2002: 311 . Climaconeis lorenzii was described as 160–180 µm long ( Cox 1982) but Prasad et al. (2000) found unusually long (178–425 µm) specimens, however it differs from the new species in having the raphe deflected at the central area. New SEM images (see below) show the areolae to be larger along only one side of the raphe. The valve of C. coxiae differs from C. minaegensis in having a simple external raphe slit, without silica flaps ( Reid & Williams 2002).

Climaconeis lorenzii Grunow. Figs 62–69 .

Climaconeis lorenzii was reported by Lobban et al. (2010) from Yap on the basis of LMs of valve and craticulate valvocopula, and from Palau on the basis of a live cell, but the putative record from Guam, on the basis of a valvocopula, has not been confirmed ( C. coxiae has been positively identified from Guam and C. lorenzii was removed from the flora: Lobban et al. 2012). There were 19 pairs of plastids in the live cell. I have since been able to observe the Yap sample in SEM and found several specimens that show valves and copulae ( Figs 62–69 ). Valves ( Figs 62, 63 ), 140–146 µm long and 6.25 µm wide increasing to 7.8 µm at the middle, had weakly radiating striae 15 in 10 µm, comprising quadrate to oval areolae, the latter oriented either apically and transapically. A row of larger areolae along the side of the raphe sternum opposite the side towards which the central raphe endings are deflected ( Fig. 62 arrow); these areolae not necessarily aligned with the striae. In girdle view ( Figs 64–66 ), a valvocopula distinguished adjacent to the valve, with very large pores in the pars exterior except at the apices, apparently a closed band, yet there is a small gap at one end ( Fig. 69 , and see Round et al. 1990, p. 521, fig. k, Prasad et al. 2000, fig. 42). The craticular structure of the valvocopula comprises the outer frame with a hollow, boxlike structure ( Figs 67, 68 ) and matching ingrowths, probably also hollow, connected by interlocking campyloid surfaces ( Figs 68, 69 ). The desktop SEM used here was not powerful enough to determine whether there were papillae at these junctions as shown by Reid & Williams (2002) for C. coxiae . There were similar pores on at least two surfaces of the pars interior ( Fig. 68 ): those on the abvalvar surface (these are also readily seen in LM—a valvocopula from this sample was shown by Lobban et al. 2010, fig. 34), and those on the proximal surface, which has a crenulated margin, presumably fitting between the virgae ( Fig. 68 larger arrow). The density of these pores is 18 in 10 µm, slightly higher than the valvar stria density. The other four bands (pleurae) ( Figs 64–66 ) each have one row of smaller pores and are clearly open. The bands in most non-craticulate species of Climaconeis , as far as known, are not differentiated into copulae and pleurae; C. leandrei Lobban 2018: 353 is an exception. SEM may show that the long Florida specimens Prasad et al. (2000) identified as C. lorenzii belong to a new species.

Table 1 shows comparative dimensions of the new and similar species of Climaconeis . An appendix gives a revised key to all species of Climaconeis . In revising the key I noticed that C. mabikii is closer to C. fasciculata (Grunow ex Cleve 1894: 152) E.J. Cox 1982: 166 than to C. undulata , but the areolae of C. fasciculata are not known from SEM.

Parlibellus E.J. Cox (1988: 19)

Since Cox’s (1988) thorough investigation of certain Navicula species in Sect. Microstigmaticae, following her earlier paper on some tube-dwelling species ( Cox 1978), and the erection of the genus Parlibellus , there has been a large number of naviculoids with circular areolae transferred into the genus or described as new, mostly by Witkowski et al. 2000, where there are detailed descriptions illustrated by LM. Many of the taxa treated by Cox (1988), including the dubious P. densepunctatus (Van Landingham 1975: 2738) E.J. Cox 1988: 23 , have not been supported by SEM, and the genus is in need of another revision. There are a few freshwater species, but some of these have been moved into Prestauroneis K. Bruder & Medlin 2008: 325 (e.g., Genkal & Yarushina 2017). Meanwhile, two species in our flora can be distinguished from the known species. One of these is certainly tube-dwelling.

Figures

FIGURES 50–61. Climaconeis minaegensis (Figs 50–60) and C. petersonii (Fig. 61). Figs 50–52 LM DIC, Figs 53–61 SEM. Figs. 50, 51. C. minaegensis holotype, entire valve and higher power view of one half, Y18E, Yap. Fig. 52. Specimen from BA-5, Bakir Atoll, Marshall Islands, broken valve showing length and bend in valve. Figs 53, 54. Whole valve and detail of central portion, internal view, BA-6, Bakir. Figs 55, 56. External central and apical portions, Y18E. Figs 57, 58. Internal central and apical portions, Y18E. Fig. 59. Internal view with broken raphe sternum showing ribs on both sides of the raphe (arrow). Figs, 60, 61. Internal apical comparison of C. minaegensis (Fig. 60) and C. petersonii (Fig. 61) sternum structure and areola shape. Scale bars: Figs 50–53 = 10 µm, Figs 54–61 = 5 µm.

FIGURES 62–69. Climaconeis lorenzii SEM, Y26C, Yap. Figs 62, 63. Central and apical portions of frustule in valve view showing deflected central raphe endings and row of larger pores along one side of sternum (Fig. 62 arrow). Fig. 64 Frustule showing craticular bars. Figs 65, 66. Central and apical portions of frustule in girdle view, showing large pores on pars exterior of the valvocopula (VC). Figs 67–69. Valve with valvocopula. Fig. 67. Entire (incomplete) specimen. Fig. 68. Detail of valvocopula showing the abvalvar surface on the left, hollow box structure shown at small arrow; on the right side below the break the frame is rotated inward to also show the pars exterior (arrowhead). and above the break rotated outward to show the proximal side of the box with crenulated margin (large arrow). Fig. 69. Detail of apex of valvocopula showing apparent break in the frame at the apex, the lack of pores near the apex, and the interlocking surfaces of the craticular bars. Scale bars: Figs 62–66, 69 = 5 µm, Fig. 67 = 10 µm, Figs 68 = 2 µm.