An intriguing Eunotia species (Bacillariophyta) from Gough Island (Tristan da Cunha Archipelago)

Abstract

Gough Island (40°21’ S, 9°53’ W), is a small remote uninhabited island of a volcanic origin, positioned in southern Atlantic Ocean and some 350 km south of the rest islands from Tristan da Cunha archipelago. Despite its very interesting geographical position, its oceanic origin, an isolation and the number of interesting habitats, the non-marine diatom flora of Gough Island is only poorly known. Carter described in 1966 numerous of new diatom species from Tristan da Cunha Island group, reporting the presence of a very diverse diatom flora with a large number of new taxa that so far have been only rarely observed elsewhere. Recently, a new survey of moss-inhabiting diatom flora on Gough Island has started and so far, several taxa were discovered belonging to the genera Eunotia, Frustulia and Pinnularia, that could not be identified using the currently available literature. One species belonging to the genera Eunotia is of our particular interest. This species, which Carter (1966) newly described as Pseudoeunotia linearis, has some morphological features that clearly differs it from the other species of the same genera known so far. Based on a detailed LM and SEM observation, we can now present a complex description of this highly interesting species that differs morphologically (i.e., the overall valve shape, the presence of spines on sides, areolae and striae density and their structure based on the position, as well as the absence of a terminal nodules). All differentiating characteristics are highlighted on the poster. The comparison and the unification with the same species found in original material of Carter (1966) is added and also the correction of the species name is suggested. Notes on the ecology are also added. KEYWORDS: GOUGH ISLAND, DIATOMS, EUNOTIA REFERENCES: Carter, J. (1966): “Some freshwater diatoms of Tristan da Cunha and Gough Island”. Nova Hedwigia 9: 443-492.

Full text

The position and map of Gough Island with stars indicating places where
the species was found. It is apparently a moss-inhabiting species, present on
exposed areas, most abundant on localities close to the sea, from where it was
originally described by Carter.
An intriguing Eunotia species (Bacillariophyta) from
Gough Island (Tristan da Cunha Archipelago)
Petra Vinšová1, Kateřina Kopalová1 and Bart Van de Vijver2,3
1Charles University in Prague, Faculty of Science, Department of Ecology, Viničná 7, CZ-12844 Prague 2, Czech Republic
2Botanic Garden Meise, Department ofBryophyta & Thallophyta, Nieuwelaan 38, B-1860 Meise, Belgium (bart.vandevijver@jardinbotaniquemeise.be)
3University of Antwerp, Department ofBiology, ECOBE, Universiteitsplein 1, B-2610 Wilrijk, Belgium
INTRODUCTION
Gough Island (40 ° 21'S, 9 ° 53 'W), is a small remote and uninhabited island of volcanic origin, positioned in
the cool-temperate zone in the southern Altantic Ocean. Despite its very interesting geographical position,
oceanic origin, extreme isolation and the number of interesting habitats, our knowledge of the non-
marine diatom flora of Gough Island is very poor. Carter (1966) described many new species in the Tristan
da Cunha Island Group, and reported the presence of a very diverse diatom flora including a large number
of new taxa, now rarely seen elsewhere. Recently, a new analysis of the moss-inhabiting flora of Gough
Island has started. The dominant genera include Eunotia, Frustulia and Pinnularia. Several taxa of these
genera can not be identified using the currently available taxonomic literature.
One species, originally described by Carter (1966) in the genus Pseudoeunotia as P. linearis, but most likely
belonging to the genus Eunotia, is of our particular interest.
Pseudo-eunotia
Grunow in Van Heurck
(Koizumi & Yanagisawa 1990)
‘Differs from Eunotia by the absence of terminal
nodules and from Synedra and Ceratoneis by the
absolute lack of a median line’
Differences from Eunotia
Raphe structure
Presence of raised costae/ridges on valve face
Biseriate striae
ACKNOWLEDGEMENTS: The authors wish to thank Dr. Niek Gremmen who performed the sampling on Gough Island.
REFERENCES: Carter, J. (1966): ‚Some freshwater diatoms of Tristan da Cunha and Gough Island‘. Nowa Hedwigia 9: 443-492. Koizumi, I., &
Yanagisawa, Y. (1990): ‚Evolutionary change in diatom morphology—an example from Nitzschia fossilis to Pseudoeunotia doliolus‘. Transactions
and Proceedings of the Palaeontological Society of Japan 157:347-359.
TAXONOMICAL CONCLUSION
Clearly, based on its morphology, the position of this taxon in the genus Pseudo-
eunotia is doubtful. A transfer in the genus Eunotia is likely but still remains to be
analyzed due to several unique features such as the spines, the structure of the
areolae and the absence of rimportulae.
Described by Carter (1966): Valves linear with rounded ends about 10–35 µm long and 4 µm
wide. Striae irregular about 11 in 10 µm minutely punctated.‘
OUR EXAMINATION • Valves length 10 to 39 µm, width 2,2 to 3,7 µm, striae from 8 to 15 in
10 µm (middle) and up to 17 when close to apex. • Frustule length 11,5–33 µm, width 4,1–10 µm,
and striae 7–20 in 10 µm (mostly one side is denser). Aerolae mostly 4 in 1 µm.
Pseudoeunotia linearis
Carter (1966)
Unusual morphology for the genus Eunotia
Presence of spines on the junction between valve face
and mantle
Colony formation
Presence of granules on the mantle
Girdle composed of several copulae
•
Visually, number of striae in 10 µm rather low
Striae composed of large round areolae bordered by a
small raised edge
Raphe quite short, sometimes bordered by ridges
Rimportulae and apical pore fields absent
Helictoglossae poorly developed
•