A check-list of the Mastogloia
Thwaites ex W. Sm. species
from the Mediterranean area.
Maurice
LOIR
Abstract – One hundred
and two Mastogloia species were found
in samples collected on the coasts of Corfu, Crete, Dalmatia, Greece, Menorca
and Sardegna. Eighty two are determined species while fifteen are undetermined.
The objective of this study was to provide new information on the biogeography
of the genus Mastogloia. In addition,
the morphology of eleven undetermined taxa was described using LM.
Résumé – Liste des espèces du genre Mastogloia Thwaites ex W. Sm.
présentes dans le bassin méditerranéen. Cent deux espèces appartenant au genre Mastogloia ont été répertoriées dans des prélèvements effectués sur
les côtes de Corfou, de Crète, de Dalmatie, de Grèce, de Minorque et de
Sardaigne. Quatre-vingt-deux espèces sont identifiées. Quinze sont
indéterminées. Cette étude apporte de nouvelles informations sur la
distribution géographique des espèces appartenant au genre Mastogloia. En outre, onze espèces non identifiées sont décrites en
microscopie photonique.
INTRODUCTION
Mastogloia Thwaites ex W. Smith is predominantly a marine genus (Round et al. 1990) and it is one of the largest
diatom genera (more than 400 published taxa, Novarino 1989). This genus has
naviculoid valves which are usually isopolar. Species of Mastogloia are easily distinguished from those of other genera by
the presence of the partectal ring which represent a modification of the
valvocopula (Paddock & Kemp 1990). The partectal ring bears a number of
hollow chambers, the partecta, which may be regular or variable in shape and
size. The arrangement of this feature can be clearly observed in the LM and
provides, with the striation of the valves, a practical way of describing the
differences between most species.
The Mastogloia genus should be
a modern one, still undergoing rapid evolution and, likely, the full extent of
this genus has not yet been mapped (Paddock & Kemp 1990). It has a tropical
and subtropical worldwide distribution (Hustedt, 1931-1959, Voigt 1942, 1952,
Ricard 1987, Witkowski et al. 2000, Pennesi
et al. 2011, Lobban et al. 2012, Lobban & Pennesi 2014, Loir &
Novarino, 2013). During previous decades, many
studies have proposed lists of either marine diatom taxa or only Mastogloia taxa, from various littoral
areas of the Mediterranean Sea and related seas: eastern coast of Spain
(Tomas,1982), Sardegna (Zanon, 1948), western coast of Italy (Rampi 1942; Zanon
1947), Venise lagoon (Marchesoni, 1954), coast of Croatia (Vilicic et al., 2002), eastern coast of Greece,
(Politis, 1960; Belegratis et Economou-Amilli, 2002), Greek islands in the
front of Turkey (Foged, 1985a, 1985b), Aegean coast of Turkey (Sabanci, 2013).
In this paper we present a checklist of the benthic Mastogloia species found in sand samples
collected in 6 areas of the Mediterranean Sea and related seas, to provide a
contribution to the knowledge of the biogeography of this genus. In addition, we describe twelve
undetermined Mastogloia taxa.
MATERIALS AND METHODS
Samples were collected from 2010 to
2018, in september-october, along the coasts of the six following islands and
continental areas:
Menorca (Balearic islands): samples
collected on 7 beaches of the southern and eastern coasts and 2 beaches of the
northern coast. Sardegna: 4 samples collected on the north-eastern littoral of
the island (Tyrrhenian sea). Dalmatia (Croatia, Adriatic sea): 6 samples
collected on beaches south-east of Dubrovnik. 2 samples at Lopud island
(42°41’14N, 17°56’15E), and 2 samples on beaches south-east of Split. Corfu (Ionian sea): 6 samples collected on
beaches on the north-eastern littoral of the island. Crete: 3 samples collected
at the north-east of the island, northward of Agios Nikolaos. Greece, Attica
(Aegean sea): 2 samples collected on beaches southward of Marathon (38°06’15N,
23°58’51E) and 1 sample at Egine island (37°44’52N, 23°25’28E).
Samples of sandy sediments were
collected by snorkelling, between 2.5 and 5 m. depth. Excepted at Menorca,
where the diatom flora was insufficiently dense, the areas susceptible to support
diatom assemblages are easily located as they display a more or less intense
yellow-brown tint. Each sample was obtained by scraping away the top
3-5 mm of sandy sediment with a 50-ml Falcon tube at two or three adjacent
places. After diluting 50: 50 with seawater, the sample was vigorously shaken,
then allowed to rest briefly to allow settlement of mineral and large
particles. The supernatant was collected and allowed to rest for 24 hours. The
obtained pellet was suspended in 3 ml seawater with 4% neutral formaldehyde.
Frustules/valves were cleaned using hydrogen peroxide and/or sodium
hypochlorite, then mounted in Melmount™ (ND = 1.704; Cargill Labs., Cedar
Grove, N.J., USA). They were observed and photographed using an Olympus CH40
microscope.
Species identification was performed
with the aid of standard and new monographs such as: Peragallo & Peragallo
(1897-1908), Voigt (1942), Voigt (1952), Hustedt (1931-1959), Witkowski et al. (2000), Pennesi et al. (2011), Lobban et al. (2012), Loir & Novarino (2013),
Sabanci (2013). The data obtained for each of the samples collected in a
geographical area were pooled to establish a check-list for each of the six
areas. Frustule/valve measurements and striae counts were carried out on
numerical micrographs at magnifications equal or higher to x3500. Valve
outlines are described according to Hendey (1964) and the terminology for the
morphological features is that proposed by Paddock & Kemp (1990).
RESULTS
In the 6 areas, the genus Mastogloia was predominant in the collected diatom flora (between
277 and 344 diatom taxa; only 190 taxa for Greece. For the pictures of these
taxa, see Loir, 2010-2018 ). It represents 16 to 20 percent (27 percent for
Greece) of the the diatom populations. We have recorded 58 Mastogloia taxa at Corfu, 53 at Crete, 51 at Dalmatia, 51 at
Greece, 51 at Menorca and 46 at Sardegna.
The Mastogloia species
A total of 102 Mastogloia taxa was
found in the 6 areas (Table 1). Eighty
two taxa were identified as their morphological features and biometric
data conform to those indicated in the original and in the new diagnoses. On
that subject, we have noted that several species have measurements near or
sometimes below the inferior limit given by the diagnoses. Sixteen of these identified
taxa were present in the 6 investigated areas and fifteen were present
in 5 areas. Twenty one were
found in only one area.
As observed
previously (Loir & Novarino, 2013) valves/frustules which conform to most
of the diagnotic characters of Mastogloia
erythraea (Hustedt, 1931-1959) display high variations of their shape and
size and three forms f1, f2 and f3 were characterized which represent likely a
complex of related offsprings. Only the f1 valves possess the longitudinal
ridges bordering the raphe, characteristic of Mastogloia erythraea Grunow (Stephens & Gibson, 1980; Novarino
& Muftah, 1991). The form f1 was more or less abundant in the 6 areas, the
form f2 was present in 4 areas, while the form f3 was rather scarce.
Valves/frustules
of five taxa either conform only partly with the diagnosis of a species or
their characters are near those of two species. These taxa were rather rare: we
have found only one to four specimens of each of them. Mastogloia sp. cf. exilis
previously named Mastogloia sp. 6 was
described by Loir & Novarino (2013). Mastogloia
sp. cf. smithii previously named Mastogloia sp. W was described by Loir
(2016). The three other taxa are described below.
Fifteen taxa, also rarely found, are undetermined. Seven of them have a length equal
to or below 20 µm. Mastogloia sp. 3, Mastogloia sp. 8, Mastogloia sp. 15 and Mastogloia
sp. 17 are identical to the four undetermined taxa which have been described by
Loir & Novarino (2013). Mastogloia
sp. F and Mastogloia sp. P were
previously found in Brittany and were described by Loir (2016).
Description of
undetermined Mastogloia species
Mastogloia sp. cf. acutiuscula
var. elliptica Hustedt (Fig. 1). Two
specimens 17.2 and 21 µm long, 8 and 8.9 µm broad were found. Most of their
characters are similar to those of Mastogloia
acutiuscula var. elliptica.
However they differ by a greater number of partecta in 10 µm: 9 vs. 5-8, and by
the apparent absence of longitudinal lines.
Mastogloia sp. cf. kariana Grunow in Cleve & Grunow
(Fig. 2). The sole found specimen, 34 µm
long, 8.8 µm broad differs from Mastogloia
kariana by the number of striae in 10 µm: 29 vs. 20-22 (Witkowski et al.,
2000) and by a slightly higher number of partecta in 10 µm: 2.6 vs. 1.5-2.
Mastogloia sp. cf. ovum paschale (A. Schmit) Mann (Fig. 3).
Several characters of the valve of the sole found specimen are similar to those
of Mastogloia ovum paschale. However,
the size is smaller (32 µm long, 20 µm broad vs. 45-60 and 25-40 µm), but such
smaller specimens were found in the French Lesser Antilles (Loir &
Novarino, 2013). The number of transapical striae in 10 µm is higher: 18 vs.
11-15, as is the number of partecta in 10 µm: 7 vs. 5-6.
Mastogloia sp. B (Fig. 4). Valves elliptic-lanceolate with broadly rounded apices, 48-53 µm long, 14-15 µm broad. Raphe wavy, external central endings distant, axial and central areas narrow, both enclosed by two marginal ribs. Transapical striae parallel to slightly radiate towards the apices, 18-19 in 10 µm, crossed by delicate longitudinal lines 15-16 in 10 µm. Partecta inseparable, equal, rectangular, apically elongated, 8 in 10 µm, 0,7 µm wide, extending shortly below the apices. Inner margins flat.
Mastogloia sp. C (Fig. 5). Valves
elliptic-lanceolate with capitate apices, 21-24 µm long, 6 µm broad. Raphe
straight, axial area narrow enclosed by two longitudinal ribs, central area very
small. Transapical striae slightly radiate, 27-28 in 10 µm. Partectal ring 0,6
µm broad, partecta equal, separable and not adjacent to each other, with inner
margin convex, 3-3,5 in 10 µm.
Mastogloia sp. D (Fig. 6).
Valves (five were found) lanceolate with rostrate apices, 17-20.6 µm long,
6.8-7.1 µm broad. Raphe straight, axial area narrow enclosed by two
longitudinal ribs, central area very small. Transapical striae not straight,
convergent near the axial area and slightly radiate near the valve margin, 22-24
in 10 µm. Partecta equal, inseparable, apically elongated, 0.6-0.7 µm broad, 6.3-7
in 10 µm.
Mastogloia sp. J (Fig. 7).
Valve 11.3 µm long, 3.3 µm broad, lanceolate, linear elliptic with broadly
rounded apices. Raphe straight, central area small circular. Transapical striae
in the middle parallel towards apices becoming slightly radiate, 28 in 10 µm.
Partectal ring 0.5 µm wide, partecta separable, equal, apically elongated, 6.5
in 10 µm.
Mastogloia sp. K (Fig. 8).
Valve elliptic with subrostrate apices, slightly heteropolar, 18 µm long 7.3 µm
broad. Raphe straight, axial area narrow, central area small, circular,
enclosed by two longitudinal ribs. Transapical striae parallel in the middle
then slightly radiate towards the apices 27-28 in 10 µm. One median large
partecta 1.4 µm wide and groups of 3 smaller partecta 1 µm wide. At each side
of the valve, identical number of partecta.
Mastogloia sp. M (Fig 9). Valve
broadly elliptic with subrostrate round apices, 11.2 µm long 5.8 µm broad.
Raphe straight, axial area narrow, central area small, circular. Transapical
striae slightly radiate, 26-27 in 10 µm. Partecta separable, equal, apically
elongated, 4.3 in 10 µm, 0.6 µm wide.
Mastogloia sp. N (Fig. 10).
Valve broadly elliptic with rostrate apices, 17.5 µm long, 9.5 µm broad. Raphe
slightly undulating, axial area narrow, central area small slightly apically
elongated. Transapical striae slightly radiate, 23 in 10 µm. Partecta
inseparable, equal, apically elongated, 4.5-5 in 10 µm, 1 µm wide.
Mastogloia sp. U (Fig. 11).
Valve broadly elliptic with subrostrate rounded apices, 13 µm long, 6.9 µm
broad. Raphe slightly ondulating, axial area narrow, central area small slightly
apically elongated. Transapical striae parallel, 21 in 10 µm crossed by
longitudinal lines, 15 in 10 µm. Partecta inseparable, equal, apically
elongated, 4.4 in 10 µm, 0.6 wide.
Mastogloia sp. Z (Fig. 12).
Valve elliptic with subrostrate apices, 20 µm long, 9.3 µm broad. Raphe
straight, axial and central areas narrow, both enclosed by two longitudinal
ribs. Transapical striae, punctate, radiate, 18 in 10 µm, puncta 18 in 10 µm.
Partecta inseparable, equal, apically elongated, 7 in 10 µm, 1 µm wide.
DISCUSSION
Since the
beginning of the twentieth century, researches were conducted on the microalgal
populations, including the genus Mastogloia,
from the Mediterranean area (see introduction), especially on the coasts of the
Adriatic Sea, of the Aegean Sea and of the Tyrrhenian Sea and here and there on
the coasts of Spain and of France. None investigation was carried out at
Menorca, at Corfu and at Crete.
Most of the investigations
have studied phytoplanktonic populations (Rampi, 1942; Marchesoni, 1954; Vilicic
et al., 1982). Two studies (Sabanci,
2013; Tomas, 1982) have considered the benthic (epiphytic, epilithic and
epipelic) diatom flora. One study was focused on the epiphytic diatom flora
(Belegratis & Econommou-Amilli, 2002). Our study has considered exclusively
epi/endopelic and epispammic diatom assemblages.
On the coasts
of Spain (Tomas, 1982), of Greece (Belegratis & Economou-Amilli, 2002) and
of Turkey (Sabanci, 2013) 22, 36 and 8 Mastogloia
species were respectively found in the
benthic diatom flora, while 27 species were found in the phytoplankton of the Northern
Adriatic Sea (Vilicic et., 1982). In the six geographical areas that we have
investigated, we have found 46 to 58 epi/endopelic/epipsammic Mastogloia taxa. In none of the
above-mentioned studies were collected, as we have done, samples of sublittoral
sand the yellow-brown color of which reveals dense diatom assemblages. This points
out that the diatom assemblages that live either freely on and in the sediments
or attached to sand grains display a higher specific diversity of the Mastogloia genus than every where and
especially in the plankton, most of the Mastogloia
species being tychoplanktonic (Ricard, 1987; Round et al., 1990). We have collected our Greek samples at a short
distance of the station where Belegratis & Economou-Amilli (2002) have
collected their samples: we found 51 Mastogloia
taxa while only 36 were found on macroalgae. In the 6 collected diatom flora,
the genus Mastogloia was dominant as
was already observed (Loir & Novarino, 2014; Pennesi et al., 2011). After Belegratis & Economou-Amilli (2002), this
genus was also dominant in the epiphytic flora collected in the Evoikos Gulf.
Most of the
82 identified species were already recorded in the Mediterranean area (Table 1).
The 16 species which are present in the six areas likely are common and several
of them have been previously frequently recorded. At the opposite, 21 species
present in only one area would be rather uncommon. Seven of them were not
previously recorded. It would be also the case for 5 species, present in 2
areas and never recorded.
Although they
were recorded previously once to three times, some Mastogloia species were not found in our samples: Mastogloia affirmata (Leudiger-Fortmorel)
Cleve (Witkowski et al., 2000), M. aquilegiae Grunow (Tomas, 1982;
Sabanci, 2013), M. baldjikiana Grunow
(Belegratis & Economou-Amilli, 2002), M.
baltica Grunow (Tomas, 1982), M.
obliqua Hagelstein (Witkowski et al.,
2000), M. quinquecostata Grunow
(Belegratis & Economou-Amilli, 2002; Vilicic et al., 2002; Sabanci, 2013), M.
schmidti Heiden (Hustedt, 1931-1959; Vilicic et al., 2002) and M. smithii var. lacustris Grunow (Tomas, 1982). This suggests that the knowledge of
the Mastogloia species present in the
Mediterranean area still need further investigations.
Seven among
the 20 undetermined Mastogloia
species have been already recorded in the Lesser French Antilles (Loir &
Novarino, 2014) and on the Atlantic oast (Loir, 2016). Seven taxa that we
describe in this paper belong to the nanophytobenthos. It may not be excluded
that some of these 20 taxa have been already described.
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Legends for figures
Fig. 1. Mastogloia sp. cf. acutiuscula var. elliptica, two valves. Scale bar = 10 µm.
Fig. 2. Mastogloia sp. cf. kariana, one valve in two different LM
focal views. Scale bar = 10 µm.
Fig. 3. Mastogloia sp. cf. ovum paschale, one valve, each half
valve in two different LM focal views. Scale bar = 10 µm.
Fig. 4. Mastogloia sp. B, two
valves. Scale bar = 10 µm.
Fig. 5. Mastogloia sp. C, two
valves. Scale bar = 10 µm.
Fig. 6. Mastogloia sp. D, one
valve in two different LM focal views. Scale bar = 10 µm.
Fig. 7. Mastogloia sp. J, one
valve in two different LM focal views. Scale bar = 10 µm.
Fig. 8. Mastogloia sp. K, one
valve in two different LM focal views. Scale bar = 10 µm.
Fig. 9. Mastogloia sp. M, one
valve in two different LM focal views. Scale bar = 10 µm.
Fig. 10. Mastogloia sp. N, one
valve in two different LM focal views. Scale bar = 10 µm.
Fig. 11. Mastogloia sp. U, one
valve in two different LM focal views. Scale bar = 10 µm.
Fig. 12. Mastogloia sp. Z, one
valve in two different LM focal views. Scale bar = 10 µm.
Figures 1 to 6
