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. 2012 Mar 19;7(3):e32198. doi: 10.1371/journal.pone.0032198

Meloneis Gen. Nov., a New Epipsammic Genus of Rhaphoneidaceae (Bacillariophyceae)

Ioanna Louvrou, Daniel B Danielidis, Athena Economou-Amilli 1,*
Editor: Jonathan H Badger2
PMCID: PMC3307707  PMID: 22442663

Abstract

The diatom family Rhaphoneidaceae is characterized by high generic diversity and low species diversity with most genera known to have long stratigraphic ranges. The genera within this family are neritic marine, and mostly epipsammic. A new modern and epipsammic genus, Meloneis gen. nov., is described herein and is compared to all genera within Rhaphoneidaceae and especially to Rhaphoneis Ehrenberg s.l. Within Meloneis three new species and one variety are distinguished and described herein: M. mimallis sp. nov., M. mimallis var. zephyria var. nov., M. akytos sp. nov., and M. gorgis sp. nov.

Introduction

The marine order Rhaphoneidales Round consists of two families, Psammodiscaceae Round & Mann in Round et al. 1990 [1] and Rhaphoneidaceae Forti 1912 [2]. The former includes only one living taxon: Psammodiscus nitidus (Gregory) Round & Mann. The latter includes the following thirteen genera: Adoneis G.W.Andrews & P.Rivera 1987 [3] with one living species and also one fossil species [4]; Delphineis G.W.Andrews 1977 [5] emend. G.W.Andrews 1981 [6] with many both living and fossil taxa; Detonia Frenguelli 1949 [7] with one living and one fossil species, recently transferred to Neodetonia S.Blanco 2011 [8] (see however [9]); Dickensoniaforma R.P.Scherer 1997 [10] with two fossil species; Diplomenora K.L.Blazé 1984 [11] with one species both fossil and living; Drewsandria P.A.Sims & R.Ross 1996 [12] with one fossil species; Incisoria Hajós, in Hajós & Stradner 1975 [13]) with three fossil species; Lancineis G.W.Andrews 1990 [14] with seven fossil species; Neodelphineis Takano 1982 [15] with two living species; Perissonoë G.W.Andrews & Stoelzel 1984 [16] with few, mainly living species; Rhaphoneis Ehrenberg 1844 [17] (see also [18], [19]) with many fossil and living species; Sceptroneis Ehrenberg 1844 [17] with more than 10 mainly fossil species requiring reinvestigation (see [1], [20]). Another genus (Polygoneis) of Rhaphoneidaceae was unofficially proposed as new in 2008 [21].

In this paper, a new genus of Rhaphoneidaceae, named Meloneis, is established, with four infraspecific taxa. Genus Meloneis is taxonomically distinct from the related genera Rhaphoneis, Neodelphineis and Perissonoë, or the superficially similar genera Adoneis and Dickensoniaforma. The new taxa of Meloneis were found as epipsammic around submarine hydrothermal vents of Milos Island (Greece). Another genus of Rhaphoneidaceae, i.e. Detonia Frenguelli, was taxonomically rearranged from epipsammic material of the same area ([22]). A catalogue of epilithic diatoms found distant of the vents is also available [23], together with euendolithic chlorophytes and cyanobacteria (see also [24]).

Materials and Methods

Milos is an island in the middle of the Hellenic Volcanic Arc with some 35 km2 of geothermally active seabed [25], and Palaeochori Bay (24°31.00′E; 36°40.11′N) on the southeastern Milos is one of the most active geothermal submarine areas of the Aegean Sea [26]. The hydrothermal fluids of the submarine vents in Palaeochori are warm (max. 115°C), acidic (min. pH 3.54), highly saline, generally enriched over seawater in chloride, calcium, strontium, barium, sodium, potassium, lithium, silicon, iron, manganese, zinc, cobalt, lead, nickel, yttrium, vanadium but depleted in magnesium and sulphate [27]. The gases in these fluids contain mainly carbon dioxide up to 91.9%; methane, hydrogen, and hydrogen sulphide are also released at concentrations of up to 9.7%, 3.0%, and 8.1% respectively [25].

Sediment samples were collected from submarine hydrothermal vents in Palaeochori Bay during two multidisciplinary field trips of some European institutions in June 1996 and June 1997 in the framework of EU-funded programmes. The study area is open to the public and is not under any protection act, therefore, no specific permits were required for visiting the area, working in the field and collecting samples. Furthermore, the collection did not involve in any way endangered or protected species of any kind. Each vent is surrounded by three characteristic concentric zones of distinctive color precipitates [25]–[26], [28]–[29]: yellow (Y), white (W), and brown (B). The yellow color of the innermost zone results from sulfur condensing on sand grains; the nature of the white precipitates of the intermediate zone is a mixture of amorphous silica, Si nodules and hollow tubes containing elemental sulfur on the outer surfaces; the outermost brownish zone of the vent system consists of Mn-oxides which predominately precipitate at increasing distances from the vent outlet. Material was studied from all the three color precipitates in both collections (in 1996 at a depth of 7 m; and in 1997 at a depth of 4 m and 7 m), and additionally from a control site (C) outside of the vents (in 1997, at a depth of 4 m and 7 m). The collected samples were preserved in formaldehyde solution. Material was oxidized and slides were prepared for diatom analyses according to standard procedures [30]. Observations were made using Zeiss Axiolab microscope equipped with a Sony DSC-S85 digital camera and Jeol JSM-35 Scanning Electron Microscope equipped with Adda 3 Olympus Soft Imaging Solutions and Scandium Universal SEM Imaging Platform.

Results

Meloneis Louvrou, Danielidis & Econ.-Amilli gen. nov.

Latin Diagnosis. Genus novum Rhaphoneidacearum. Valvae planes facie, substrictis limbis, late lanceolatae usque lateribus laeviter convexis et apicibus leniter productis. Area axialis hyalina, distincta, angusta, recta adusque mediocriter lanceolata. Areolae circulares adusque ovatae velis rotoidibus dispositae in striis radialibus curvatis axialis areae. Striae transversae non frontales trans aream axialem. Una continua series areolarum super limbum observata; areolae limbi continuae transversis striis. Magna rimoportula unica locata inter areolas ultimae transversae striae ad ambo apices valvae. Ambo apices valvae pseudocellum duobus adusque nonnullis porellis minutis forma magis rotunda. Margo valvae facies decorata irregulari serie demissarum silicearum papillarum sinilium cupolae forma.

Description. New genus in Rhaphoneidaceae described herein. Valves with flat surface, shallow mantles, broadly lanceolate outline, smoothly convex sides and slightly produced apices. Axial area hyaline, distinct, narrow, linear to slightly lanceolate. Valve surface covered with round to ovate rota-type areolae, radiating in curved transverse striae from the axial area. Transverse striae not aligned across the axial area. A single continuous row of areolae runs along the mantle; mantle areolae aligned with the transverse striae. A single large rimoportula placed in-between the areolae of the last transversal stria at each valve end. A pseudocellus consisting of 2 to several fine pores in a rather circular pattern at each valve end. Edge of the valve face ornamented by an irregular row of low siliceous dome-like papillae.

GENUS TYPE: Meloneis mimallis Louvrou, Danielidis & Econ.-Amilli, sp. nov.

DERIVATION OF NAME: Me.lo.ne'.is. femin., N.G. fem. Melos = the name of the greek island Mήλος (also written Milos) and the greek suff. neis, from N.G. ναũς (gen. νηός) = boat.

Meloneis mimallis Louvrou, Danielidis & Econ.-Amilli spec. nov. var. mimallis

Figures 1A–E, 2A–E, 3A–B

Figure 1. Species of Meloneis gen. nov. under LM.

Figure 1

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Figure 1A . Meloneis mimallis sp. nov., type of the genus. Figures 1B–E . Morphological variation of M. mimallis in the type locality. Figure 1F . M. mimallis var. zephyria var. nov.; the type. Figure 1G . The type of M. akytos, with two pseudocelli consisting of 3 & 4 pores respectively; note the robust areolae, and the distant striae. Magnified valve apices in Figs. 1Ga and 1Gb. Figure 1H . A valve of M. akytos with 2 pores per each pseudocellus, otherwise morphologically similar to the type. Magnified valve apices in Figs. 1Ha and 1Hb. Figures 1I–K . Morphological variation of M. gorgis sp. nov.; figure 1I represents the type. [Scale bars = 10 µm; the grey bar only for Figs. 1Ga, 1Gb, 1Ha, 1Hb).]

Figure 2. External valve views of Meloneis mimallis sp. nov. under SEM.

Figure 2

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Figure 2A . M. mimallis with two pseudocelli consisting of 5 pores (lower valve apex) & 6 pores (upper valve apex); note the two sizes of edge papillae, the larger ones usually in groups of 3–4 between the areolae rows. Figure 2B . Detail of the valve apex showing the circular pattern of pseudocellus consisting of 6 pores (black arrow); grey arrow indicates the external opening of the rimoportula; black arrow with white outline points to the extra incomplete row of small papillae (see also the complete rows in Fig. 2C). Figure 2C . Note the presence of an extra short continuous row of fine papillae at each pole (arrows) (cf. Fig. 2B). Figure 2D . A specimen with two pseudocelli, consisting of 3 pores (black arrow) & 4 pores (white arrow). Figure 2E . Detail of the valve end showing the round to ovate rota-type areolae with central pits. [Scale bars: Figures 2A, C, D = 10 µm, Figure 2B = 1 µm, Figure 2E = 2 µm].

Figure 3. Internal valve views of Meloneis mimallis sp. nov. and Meloneis akytos sp. nov. under SEM.

Figure 3

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Figure 3A . M. mimallis with diagonally positioned rimoportulae in relation to the apical axis. Figure 3B . Detail of the apex showing the elongated slit-like internal opening of the rimoportula (black arrow), and the pseudocellus consisting of 4 fine pores (black arrow with white outline). Figure 3C . A specimen of M. akytos with distant striae and diagonally positioned rimoportulae in relation to the apical axis. Figure 3D . M. akytos showing the elongated slit-like internal opening of the rimoportula (white arrow), and the pseudocellus with 2 fine pores (black arrow). Figure 3E . Tilted specimen of M. akytos; note the two (white arrow) or three (black arrowhead) struts of the rotae in the areolae. [Scale bars: Figures 3A, C = 10 µm, Figure 3B = 1 µm, Figures 3D, E = 2 µm].

Latin Diagnosis. Valvae planes facie, substrictis limbis, late lanceolatae, usque lateribus laeviter convexis et apicibus minime productis et rotundatis; 21.5–29 µm longitudine, 14.5–18.5 µm latitudine. Area axialis hyalina, distincta, angusta, recta adusque mediocriter lanceolata. Areolae magnae circulares adusque ovatae velis rotoidibus dispositae in striis radialibus curvatis axialis areae. Areolae in striis radialibus, in medio (7.5) 8–8.5 (9)/10 µm, in margine 6–7 (7.5)/10 µm, non frontales trans aream axialem. Areolae etiam dispositae in lineis minime curvatis in longitudinem, 6–7.5–(8)/10 µm in medio. Paucae breves striae marginales raro praesentes inter perfectas strias. Una continua series areolarum trancurrit limbum valvae; areolae limbi continuae transversis striis. Rimoportulae, una in singulam apicem, locatae in diagonio vel in utram partem axis apicalis. Rimoportulae rotundo externali porello, et parte interna longa unica caesa. Valvae pseudocello extenuato ambobus apicibus. Pseudocelli se constant tribus adusque septem porellis minutis per valvam. Margo valvae facies decorata irregulari serie demissarum silicearum papillarum sinilium cupolae forma; una series praeterea subtilarum papillarum solum in polis.

Description. Valves with flat surface, shallow mantles, broadly lanceolate outline, smoothly convex sides, and rounded slightly produced ends; length 21.5 to 29 µm, width 14.5 to 18.5 µm. Axial area hyaline, distinct, narrow, linear to slightly lanceolate. Valve surface covered with large circular to ovate rota-type areolae radiating in curved transverse striae from the axial area. Transverse striae radial, in the middle (7.5) 8–8.5 (9)/10 µm, at the margin 6–7 (7.5)/10 µm, not aligned across the axial area. Areolae arranged also in slightly curved longitudinal rows, 6–7.5–(8)/10 µm at the middle. Few short marginal striae rarely present between complete striae. A single continuous row of areolae runs along the valve mantle; mantle areolae aligned with the transverse striae. Rimoportulae one at each pole, positioned diagonally or on the same side of the apical axis. Rimoportulae with a round external pore, and an elongate slit-like internal opening. A reduced pseudocellus consisting of 3–7 fine pores at each valve end. Edge of the valve face ornamented by an irregular row of low siliceous dome-like papillae; presence of an extra row of finer papillae at the poles.

DERIVATION OF NAME: mi.ma.lli′s. femin., N.G. fem. Mιμαλλίς = a nymph, also another ancient name of Milos Island cited by Callimachus (310/305-240 BC).

HOLOTYPE: Botanical Museum of the Athens University, Greece; ADH slide 1317, England Finder Ref. L21/3; Figure 1A in this paper.

TYPE LOCALITY: Palaeochori Bay, Milos Island, Greece; marine, neritic, epipsammic.

SAMPLES EXAMINED: depth-zone-year = 4m-Υ-1997, 4m-W-1997, 7m-W-1996, 7m-W-1997, 7m-B-1997, 7m-C-1997.

Meloneis mimallis var. zephyria Louvrou & Econ.-Amilli var. nov. Figure 1F

Latin Diagnosis. Valvae forma simillimae speciei M. mimallis, sed apicibus magis productis latitudine et rariora ordine linearum longarum areolarum, in medio 4–4.5/10 µm.

Description. Valves morphologicaly identical to the species M. mimallis but with broader produced apices and with loosely spaced longitudinal rows of areolae, 4–4.5/10 µm at the middle.

DERIVATION OF NAME: ze.phy.ri'.a. femin., N.G. femin. Ζεϕυρία, previous name of Milos island (according to Aristotle) possibly from the prevailing there western winds, Zephyros.

HOLOTYPE: Botanical Museum of the Athens University, Greece; ADH slide 1314, England Finder Ref. N47/0; Figure 1F in this paper.

TYPE LOCALITY: Palaeochori Bay, Milos Island, Greece

SAMPLES EXAMINED: depth-zone-year = 7m-W-1996.

Meloneis akytos Louvrou & Econ.-Amilli spec. nov.  Figures 1G–H, 3C–E

Latin Diagnosis. Valvae planes facie, substrictis limbis, late lanceolatae, usque lateribus laeviter convexis et apicibus acriter productis; 21.5–32 µm longitudine, 14–19.5 µm latitudine. Area axialis hyalina, distincta, angusta, recta adusque mediocriter lanceolata. Areolae magnae circulares adusque ovatae velis rotoidibus dispositae in striis radialibus curvatis axialis areae. Areolae in striis radialibus, in medio 4.5–6 in 10 µm (in primis 5/10 µm), in margine 5–6.5/10 µm (in primis 6/10 µm), non frontales trans aream axialem. Areolae etiam dispositae in lineis minime curvatis in longitudinem, 5–6/10 µm in medio. Breves striae marginales praesentes inter perfectas strias. Una continua series areolarum trancurrit limbum valvae; areolae limbi continuae transversis striis. Rimoportulae, una in singulam apicem, locatae in diagonio vel in utram partem axis apicalis. Rimoportulae rotundo externali porello, et parte interna longa unica caesa. Valvae pseudocello extenuato ambobus apicibus. Pseudocelli se constant tribus et tribus an tribus et quattor (rariter duobus et duobus) porellis minutis per valvam. Margo valvae facies decorata irregulari serie demissarum silicearum papillarum sinilium cupolae forma.

Description. Valves with flat surface, shallow mantles, broadly lanceolate outline smoothly convex sides and acutely produced apices; length 21.5 to 32 µm, width 14 to 19.5 µm. Axial area hyaline, distinct, narrow, linear to slightly lanceolate. Transverse striae composed of very large circular to ovate areolae with rota-type vela, not aligned across the axial area. Transverse striae radial, in the middle 4.5–6/10 µm (mainly 5/10 µm), at the margin 5–6.5/10 µm (mainly 6/10 µm). Areolae arranged also in slightly curved longitudinal rows, 5–6/10 µm at the middle. Short marginal striae present between complete striae. A single continuous row of areolae runs along the mantle of the valve; mantle areolae aligned with the transverse striae. Rimoportulae one at each pole, positioned diagonally or on the same side of the apical axis. Rimoportulae with a round external pore, and an elongate slit-like internal opening. A reduced pseudocellus at each valve end consisting either of 3 and 3 or 3 and 4 (rarely 2 and 2) fine pores. Edge of the valve face ornamented by an irregular row of low siliceous dome-like papillae.

DERIVATION OF NAME: A'.ky.tos. femin., N.G. fem. Άκυτος = unlivable, unsuitable for residence; also, old name of Milos island.

HOLOTYPE: Botanical Museum of the Athens University, Greece; ADH slide 1318, England Finder Ref. T31/1; Figure 1G in this paper.

TYPE LOCALITY: Palaeochori Bay, Milos Island, Greece; marine, neritic, epipsammic.

SAMPLES EXAMINED: depth-zone-year = 4m-Υ-1997, 7m-W-1996, 7m-W-1997, 7m-B-1997.

Meloneis gorgis Louvrou & Econ.-Amilli sp. nov.  Figures 1I–K

Latin Diagnosis. Valvae planes facie, substrictis limbis, late lanceolatae, usque lateribus laeviter convexis et apicibus acriter productis; 17–25 µm longitudine, 11–14 µm latitudine. Area axialis hyalina, distincta, recta et angusta ad polos valvae, et clariter latior in medio. Areolae circulares adusque ovatae velis rotoidibus dispositae in striis radialibus curvatis axialis areae. Areolae in striis radialibus, in medio 10–12/10 µm, in margine (8) 8.5–10/10 µm, non frontales trans aream axialem. Areolae etiam dispositae in lineis minime curvatis in longitudinem, (8.5) 9–10.5 (11)/10 µm in medio. Absentia brevium striarum marginalium inter perfectas strias. Una continua series areolarum trancurrit limbum valvae; areolae limbi continuae transversis striis. Rimoportulae, una in singulam apicem, locatae in diagonio vel in utram partem axis apicalis. Rimoportulae rotundo externali porello, et parte interna longa unica caesa. Valvae pseudocello extenuato ambobus apicibus. Pseudocelli se constant nonnullis porellis minutis per valvam. Margo valvae facies decorata irregulari serie demissarum silicearum papillarum sinilium cupolae forma.

Description. Valves with flat surface, shallow mantles, broadly lanceolate outline, smoothly convex sides and acutely produced apices; length 17 to 25 µm, width 11 to 14 µm. Axial area hyaline, distinct, linear and narrow at the valve ends and slightly widened at the middle. Transverse striae composed of circular to ovate areolae with rota-type vela, not aligned across the axial area. Transverse striae radial, in the middle 10–12/10 µm, at the margin (8) 8.5–10/10 µm. Areolae arranged also in slightly curved longitudinal rows, (8.5) 9–10.5 (11)/10 µm at the middle. Absence of short marginal striae between complete striae. A single continuous row of areolae runs along the mantle of the valve; mantle areolae aligned with the transverse striae. Rimoportulae one at each pole, positioned diagonally or on the same side of the apical axis. Rimoportulae with a round external pore, and an elongate slit-like internal opening. A reduced pseudocellus consisting of several fine pores at each valve end. Edge of the valve face ornamented by an irregular row of low siliceous dome-like papillae.

DERIVATION OF NAME: Gor.gi's. femin., N.G. fem. Γοργίς = old name of Milos island.

HOLOTYPE: Botanical Museum of the Athens University, Greece; ADH slide 1315, England Finder Ref. Q27/3; Figure 1I in this paper.

TYPE LOCALITY: Palaeochori Bay, Milos Island, Greece; marine, neritic, epipsammic.

SAMPLES EXAMINED: depth-zone-year = 4m-Y-1997, 7m-W-1996, 7m-W-1997, 7m-B-1997, 7m-C-1997.

Discussion

Taxa of the order Rhaphoneidales are generally characterized by bipolar, multipolar or circular valves, areolae occluded by rotae, and rimoportulae usually present at the apices. The established genera of the family Rhaphoneidaceae, already mentioned in the introduction chapter, are distinguished by the type of valvar outline, type of areolae, number and position of rimoportulae, position and form of pseudocellus (apical pore field), alignment/nonalignment of the transverse rows of areolae across the axial area, presence/lack of spines or papillae, and presence/lack of surface furrows along the transapical striae [3], [5]–[7], [10]–[18], [20].

The detailed morphology of the new genus Meloneis is characterized by (i) valves broadly lanceolate with smoothly convex sides and slightly produced ends, forming an outline similar to that of Adoneis, some Rhaphoneis, and the fossil Dickensoniaforma, (ii) areolae circular or ovate, containing solid, simple rotae connected to the valve by two or scarcely three struts aligned parallel to the margin of the valve closest to the areola, a feature reminiscent of Adoneis, Delphineis, Neodelphineis, Diplomenora; areolae externally showing central pits like those of Adoneis and Perissonoë, (iii) transverse rows of areolae fully nonaligned across the axial area, as found in Neodelphineis, Adoneis, Dickensoniaforma, Diplomenora, Detonia, and some Rhaphoneis, (iv) a single row of areolae at the mantle below the marginal ridge in alignment with the transverse rows of areolae, a common feature of many genera such as Delphineis, Neodelphineis, Perissonoë, Adoneis, Diplomenora, and Rhaphoneis (at least sensu Round et al. 1990 [1]), (v) rimoportulae one at each pole, diagonally or laterally positioned in relation to the longitudinal axis and lying at the last transverse row of areolae, as observed in Neodelphineis, Perissonoë (with 1–4 rimoportulae per valve), Rhaphoneis (?), and Lancineis (?), (vi) pseudocelli one at each pole, consisting of two to seven very fine pores in a rather circular pattern between the last transverse row of areolae and the marginal ring of papillae, a feature unique for Meloneis and vaguely similar to those of Neodelphineis (with one pore), Perissonoë (with pores in a rather radiating pattern), and Rhaphoneis and Lancineis (with many pores in a rather disorganised pattern), (vii) lack of surface furrows along the transapical striae, similarly to the genera Adoneis, Detonia, Dickensoniaforma, Diplomenora, Lancineis, Perissonoë, Sceptroneis and most possibly Rhaphoneis, in contrast to the genera Drewsandria, Neodelphineis and most Delphineis having grooved external valve face (the valves of the Delphineis surirella group are usually smooth or very slightly grooved [6], [31]); (viii) presence of a ring of papillae at the valve margin, a feature also found in Perissonoë, some Delphineis, and partly in Adoneis (Neodelphineis bears short spines).

The above descriptive comparison shows a closer similarity of Meloneis to the genera Rhaphoneis, Neodelphineis, and Perissonoë especially concerning the fine structure of the apex (Table 1).

Table 1. Valve morphology - according to the available literature and photodocumentation cited in this paper - differentiating Meloneis from the related genera of the family Rhaphoneidaceae (for the genus Rhaphoneis s.s. characters of the type species Rhaphoneis amphiceros were considered).

Related Genera of Rhaphoneidaceae Meloneis Neodelphineis Perissonoë Rhaphoneis s.s.
Specimen Status1 Re Re Re, Fo Re, Fo
Valve Outline2 La Li, Elo-Ell Mu Rh
Rota of the areolae3 So So Pe Co
Mantle areolae4 SRa SRa SRa SRna
Number of Rimoportulae 2 2 1–4 2
Types of Apical Pore Field5 Ps RP1 Ps Ps
Number of pores in Apical Pore Field6 F 1 M M
Pattern of pores in Apical Pore Field7 Ci Rd Di
Position of Apical Rimoportula and Apical Pore Field8 vE→ Ps→ (R-Lr) vE→ RP1→ (R-Lr) vE→ Ps→ (R-Lr) vE→ Ps→ ? R→ ? Lr
External furrows along the transapical striae9 A P P, A A
Protrusions10 Pa Sp Pa A
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1

Fo = fossil, R = recent.

2

Mu = multipolar, La = lanceolate, Rh = rhomboid, Ell = elliptic, Li = linear, Elo = elongate.

3

So = solid, Pe = perforate, Co = concentric.

4

SRa = presence of a single row of areolae even around the apices, SRna = presence of a single row of areolae but not around the apices.

5

Ps = pseudocellus, RP1 = apical pore field reduced to 1 pore.

6

x = number, M = many, F = few.

7

Ci = rather circular, Di = rather disorganised, Rd = rather radiating.

8

Rimoportula (R) and Apical Pore Field (Ps, RP1) in relation to vE = valve edge, and in relation to Lr = last transverse row of areolae. For instance: (R-Lr) = rimoportula positioned between the areolae of the last transverse row, vE→ Ps = pseudocellus positioned next to the valve edge. The question marks indicate unclear position of the rimoportula in relation to pseudocellus and to the last transverse row.

9

P = presence, A = absence.

10

Sp = spines, Pa = papillae, A = absence of protrusions.

  • -

    Concerning genus Rhaphoneis sensu lato (see [32]) there is a lack of knowledge about the fine structure of some taxonomic features in several species. Therefore, comparison can be made to Rhaphoneis amphiceros (Ehrenberg) Ehrenberg [18], [19], the type species of the genus in which certain rhombic or broadly lanceolate forms were attributed as synonyms (i.e. R. rhombus (Ehrenberg) Ehrenberg, R. amphiceros var. rhombica Grunow in Van Heurck, R. amphiceros f. minor Grunow in Van Heurck) or remained as valid taxa [i.e. R. amphiceros var. amazonica (Grunow in Pantocsek) M.Peragallo, R. amphiceros var. gemmifera (Ehrenberg) Peragallo & Peragallo]. Besides, some drawings of R. amphiceros var. rhombica depicted later by several authors (e.g. [33] p. 29, fig. 10/17–19; [34] p. 329, fig. 83/22–23; and [35] p. 100, fig. 5/7 as R. rhombica Andrews), as well as the variety R. amphiceros var. intermedia (Pantocsek) M.Peragallo and the species R. debyi Pantocsek and R. subtilissima Pantocsek, are reminiscent in general appearance of Meloneis. Generally, in R. amphiceros the areolae are occluded by perforated rotae, the pseudocellus is composed by many pores in a rather non-oriented pattern and there is absence of papillae or spines [1]; additionally, it seems that the single row of marginal areolae on the mantle of the valve is not continuous around the apices. However, within R. amphiceros there were also classified some discrepant individuals clearly having some valve structure characteristics of Meloneis (e.g. [36] p. 51, fig. 9/2; [37] p. 101, fig. 8/5; [38] figs 16 & 47).

  • -

    Although Neodelphineis and Perissonoë have a different outline (elongate to elliptical valves, and quadrate or triangular respectively) from that of Meloneis, the three genera show similarities in the position of both pseudocelli and rimoportulae. However, in Perissonoë there are many pores in an almost radiating pattern, in Neodelphineis there is a reduction of the number of fine pores to one, whereas Meloneis with a rather circular pattern of 2 to several pores keeps an intermediate position between them concerning this particular feature.

  • -

    Similarities of Meloneis to other genera such as Adoneis and Dickensoniaforma are considered as rather superficial since they are restricted mainly to the general valve appearance and outline. Specifically, genus Adoneis bears an apical rimoportula at each pole positioned among the pores of pseudocellus, and additional rimoportulae at each lateral valve margin; genus Dickensoniaforma lacks pseudocelli and the apical pore fields, ocelli, appear to be consiting of vestigial (?) areolae i.e. fine areolae.

Therefore, the unique combination of features cited above and especially the morphology of pseudocellus and papillae suggest a new taxon deserving a distinct taxonomic status, i.e. Meloneis gen. nov. Within genus Meloneis, three species and one variety (i.e. M. mimallis, M. mimallis var. zephyria, M. akytos, M. gorgis) are discernible (see Table 2) mainly differing in size and polar outline of the valves, size of areolae, pore number in pseudocelli, and densities of transapical striae and areolae.

Table 2. Characters of valve morphology differentiating the four taxa of Meloneis.

Taxon valve length (µm) valve width (µm) valve apices transverse striae striae density (in 10 µm) areolae areolae density (in 10 µm) pores of pseudocellus
Meloneis mimallis var. mimallis 21.5–29 14.5–18.5 rounded, slightly produced radial (7.5) 8–8.5 (9) large 6–7.5 (8) 3–7
Meloneis mimallis var. zephyria 26.5–27 17.5–18 rounded, broadly produced noticeably radial 7.5 large, loosely spaced 4–4.5 not seen
Meloneis akytos 21.5–32 14–19.5 acutely produced noticeably radial 4.5–6 very large, loosely spaced 5–6 2–4
Meloneis gorgis 17–25 11–14 acutely produced radial 10–12 small (8.5) 9–10.5 (11) not seen
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Acknowledgments

Sofia Papaioannou, Professor of Latin literature in the Athens University, kindly helped in the Latin diagnoses.

Footnotes

Competing Interests: The authors have declared that no competing interests exist.

Funding: Research was conducted as part of MAST-III projects financed by the Commission of the European Community (Contract no: MAS3-CT95-0021). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

References

  • 1.Round FE, Crawford RM, Mann DG. The diatoms. Biology & Morphology of the Genera. Camdidge Univ Press; 1990. [Google Scholar]
  • 2.Forti A. Contribuzioni diatomologiche. Metodo di classificazione delle Bacillariee Immobili fondato sull'affinità morfologica dei frustoli ed ei relazione con l'evoluzione dell'auxospora. Atti Reale Inst Veneto Sci Lett Art. 1912;71:677–731. [Google Scholar]
  • 3.Andrews GW, Rivera P. Morphology and evolutionary significance of Adoneis pacifica gen. et. sp. nov. Diatom Res. 1987;2:1–14. [Google Scholar]
  • 4.Kociolek JP, Fourtanier E, Rubinstein J, Encinas A. Adoneis miocenica, a new species from Chile, with comments on the morphological separation of centric and pennate diatoms. Diatom Res. 2007;22:309–316. [Google Scholar]
  • 5.Andrews GW. Morphology and stratigraphic significance of Delphineis, a new marine diatom genus. Nova Hedwigia Beih. 1977;54:243–260. [Google Scholar]
  • 6.Andrews GW. Revision of the diatom genus Delphineis and morphology of Delphineis surirella (Ehrenberg) G.W. Andrews, n. comb. In: Ross R, editor. Proc 6th Int Symp Rec Foss Diatoms. Koeltz Koenigstein; 1981. pp. 81–92. [Google Scholar]
  • 7.Frenguelli J. Diatomeas fòsiles de los yacimentos chilenos de Tiltil y Mejillones. Darwinia. 1949;9:97–157. [Google Scholar]
  • 8.Blanco S. Neodetonia nom. nov., a replacement name for Detonia Frenguelli (Bacillariophyceae). Phycologia. 2011;50:327–327. [Google Scholar]
  • 9.Louvrou I, Danielidis DB, Parmakelis A, Economou-Amilli A. (2031) Proposal to conserve the name Detonia Freng. (Bacillariophyceae) against Detonia Sacc. (Ascomycetes). Taxon. 2011;60:1768–1769. [Google Scholar]
  • 10.Scherer RP. Dickensoniaforma: a new diatom genus in the family Rhaphoneidaceae, with two new fossil species from the Norwegian Greenland Sea. Diatom Res. 1997;12:83–94. [Google Scholar]
  • 11.Blazé K. Morphology and taxonomy of Diplomenora gen. nov. (Bacillariophyta). Brit phycol J. 1984;19:217–225. [Google Scholar]
  • 12.Sims PA, Ross R. Drewsandria, a new genus of araphid diatoms. Nova Hedwigia Beih. 1996;112:301–306. [Google Scholar]
  • 13.Hajós M, Stradner H. Late Cretaceous Archaemonadaceae, Diatomaceae, and Silicoflagellatae from the South Pacific Ocean. Initial Rep Deep Sea. 1975;29:913–1009. [Google Scholar]
  • 14.Andrews GW. Morphology and stratigraphic significance of the marine araphid diatom Lancineis, gen. nov. In: Simola H, et al., editors. Proc 10th Int Symp Rec Foss Diatoms. Koeltz Koenigstein; 1990. pp. 127–137. [Google Scholar]
  • 15.Takano H. New and rare diatoms from Japanese marine waters-VIII. Neodelphineis pelagica gen. et sp. nov. Bull Tokai Reg Fish Res Lab. 1982;106:45–53. [Google Scholar]
  • 16.Andrews GW, Stoelzel VA. Morphology and evolutionary significance of Perissonoë, a new marine diatom genus. In: Mann DG, editor. Proc 7th Int Symp Rec Foss Diatoms. Koeltz Koenigstein; 1984. pp. 225–240. [Google Scholar]
  • 17.Ehrenberg CG. Mittheilung über zwei neue Lager von Gebirgsmassen aus Infusorien als Meeres-Absatz in Nord-Amerika und eine Vergleichung derselben mit den organischen Kreide-Gebilden in Europe und Afrika. 1844. pp. 57–97. Bericht über die zur Bekanntmachung geeigneten Verhandlungen der königlichen Akademie der Wissenschaften zu Berlin. Kong Akad Wiss Berlin.
  • 18.Jahn R, Kusber W-H. Algae of the Ehrenberg Collection: 1. Typification of 32 names of diatom taxa described by C. G. Ehrenberg Willdenowia. 2004;34:577–595. [Google Scholar]
  • 19.Sato S, Watanabe T, Nagumo T, Tanaka J. Research Note: Valve morphogenesis in an araphid diatom Rhaphoneis amphiceros (Rhaphoneidaceae, Bacillariophyta). Phycol Res. 2011;59:236–243. [Google Scholar]
  • 20.Sims PA, Mann DG, Medlin LK. Evolution of the diatoms: Insights from fossil, biological and molecular data. Phycologia. 2006;45:361–402. [Google Scholar]
  • 21.Watanabe T, Sato S, Toyoda K, Kumada M, Nagumo T, et al. Phylogeny of the order Rhaphoneidales. 2008. 236 Jasprica N, Car A, Čalić M, editors. Abstract Book 20th Int Symp Rec Foss Diatoms. Dubrovnik.
  • 22.Louvrou I, Danielidis DB, Economou-Amilli A. Ognjanova-Rumenova N, Manoylov K, editors. Taxonomic status of Detonia Frenguelli and the establishment of Detonia dobrinae sp. nov. (Bacillariophyceae). Festschrift in Honour of Prof. Dobrina Temniskova-Topalova. Adv Phycol Studies. 2006. pp. 123–131.
  • 23.Pantazidou A, Belegratis MR, Louvrou I, Economou-Amilli A. Euendolithic algae and patterns of diatom colonization on biotic carbonate substrates. In: Economou-Amilli A, editor. Proc 16th Int Symp Rec Foss Diatoms. University of Athens; 2001. pp. 381–392. [Google Scholar]
  • 24.Pantazidou A, Louvrou I, Economou-Amilli A. Euendolithic shell-boring cyanobacteria and chlorophytes from the saline lagoon Ahivadolimni on Milos Island, Greece. Eur J Phycol. 2006;41:189–200. [Google Scholar]
  • 25.Dando PR, Hughes JA, Leahy Y, Niven SJ, Taylor LJ, et al. Gas venting rates from submarine hydrothermal areas around the island of Milos, Hellenic Volcanic Arc. Cont Shelf Res. 1995b;15:913–929. [Google Scholar]
  • 26.Wenzhöfer F, Holby O, Glud RN, Nielsen HK, Gundersen JK. In situ microsensor studies of a hot vent at Milos (Greece). Mar Chem. 2000;69:43–54. [Google Scholar]
  • 27.Valsami-Jones E, Baltatzis E, Bailey EH, Boyce AJ, Alexander JL, et al. The geochemistry of fluids from an active shallow submarine hydrothermal system: Milos island, Hellenic Volcanic Arc. J Volcanol Geoth Res. 2005;148:130–151. [Google Scholar]
  • 28.Dando PR, Hughes JA, Thiermann F. Preliminary observations on biological communities at shallow hydrothermal vents in the Aegean Sea. Geol Soc Spec Publ. 1995a;87:303–317. [Google Scholar]
  • 29.Fitzsimons MF, Dando PR, Hughes JA, Thiermann F, Akoumianaki I, et al. Submarine hydrothermal brine seeps off Milos, Greece: Observations and geochemistry. Mar Chem. 1997;57:325–340. [Google Scholar]
  • 30.Simonsen R. Vegetation und Vegetationsbedingungen in der westlichen Ostsee (Kieler Bucht). Kieler Meeresforschungen. 1962;20:157–168. [Google Scholar]
  • 31.Andrews GW. Round FE, editor. Evolutionary trends in the marine diatom genus Delphineis G.W.Andrews. Proc 9th Int Diat Symp Biopress Ltd & Koeltz Sci Books, Koenigstein. 1988. pp. 197–206.
  • 32.Andrews GW. Taxonomy and stratigraphic occurrence of the marine diatom genus Rhaphoneis. Nova Hedwigia Beih. 1975;53:193–227. [Google Scholar]
  • 33.Frenguelli J. Resultados de la Primera Expedición a Tierra del Fuego (1921) - Diatomeas de Tierra del Fuego. 1924;98:5–63, pl. 1–13. [Google Scholar]
  • 34.Peragallo MMH, Peragallo M. Diatomées marines de France et des districts maritimes voisins. 1897–1908. 491 137 pls. Micrographs-Éditeur, à Grez-sur-Loing.
  • 35.Foged N. Diatoms from Viti Levu, Fiji Islands. Bibl Diatom. 1987;14:1–194. [Google Scholar]
  • 36.Foged N. Some littoral diatoms from the coast of Tanzania. Bibl Diatom. 1975;16:1–127. [Google Scholar]
  • 37.Foged N. Diatoms in New Zealand, the North Island. Bibl Phycol. 1979;47:1–225. [Google Scholar]
  • 38.The Stuart R. Stidolph Diatom Atlas, Marine Diatoms from the Azores. Available: http://www.awi.de/fileadmin/user_upload/Research/Research_Divisions/Biosciences/Biological_Oceanography/Diatom_Herbarium). Accessed 2011 Aug 30.

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