Fróðskaparrit - 01.07.2004, Page 49

FØROYSKAR VATNKLUKKUR
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redefinition of Stictotarsus to include the
griseostríatus-complex. This is not the fi-
nal position as mitochondrial DNA studies
(Ribera et al., 2002) have revealed the arti-
ficial nature of Stictotarsus and the need to
reassign the griseostriatus complex once
more, an extraordinarily unstable situation
reflecting the difficulty in understanding
the affinities of this group.
HELOPHORIDAE
Helophorus aequalis Thomson. Angus
(1992) differentiated three species of large
Helophorus in the northern Palaearctic
area, H. aquaticus (L.), H. aequalis Thom-
son and H. grandis Illiger. Angus (1970)
noted that Linne’s material formerly as-
sumed to be the larger species named as
aquaticus was in fact a smaller species,
leaving the name grandis to be applied to
the largest species. This arrangement, with
reference to the larger grandis and the
smaller aquaticus pertained until Angus
(1982) discovered that the smaller species
in fact comprised two species with distinc-
tive karyotypes, the more western aequalis
Thomson and the eastern and montane
aquaticus (L.). Thus it is difficult to be sure
which species is intended in distribution
papers published over this period, includ-
ing that of Bengtson (1981), who referred
only to H. aquaticus.
H. aquaticus and aequalis are smaller
than H. grandis and have finer teeth on the
last visible (seventh) abdominal sternite,
those of grandis giving the rear edge a
strongly castellated appearance. H. ae-
qualis is the more western of the two small-
er species, H. aquaticus being recorded in
the north-west only from Denmark and Fin-
land, and known from neither Norway nor
Sweden (Hansen, 1987). H. grandis is rare
in northern Scotland, not being known
from Shetland or the Outer Hebrides,
whereas H. aequalis is more common in
Scotland, occurring in the Uists and on
Unst, the nearest Shetland island to the
Faroes. On this basis, the expectation is that
only one species, aequalis, is to be expect-
ed in the Faroes. We found this species
abundant in grass-edged pools and ditches
in the meanders of the river in Kollfjarðar-
dalur on Streymoy. The area was highly en-
riched, and the pools typical of the habitat
with which aequalis and grandis are nor-
mally associated. One female was unusual-
ly large, 6.5 mm long, at the top end of the
range given by Angus (1992) for aequalis
and in the middle of the range for grandis\
it is, however, clearly aequalis. The occur-
rence of a few unusually large females of
aequalis may give rise to records of gran-
dis. Hansen (1881) recorded both grandis
and aquaticus, records overlooked by
Sharp (1900), as was originally noted by
Reuter (1901). Nielsen (1908) repeated
Hansen’s records. Mjoberg (1917) noted
only Helophorus aquaticus L., but with
reservation.
Helophorus brevipalpis Bedel. Bengtson
(1981) recorded this species, as guttulus,
from eight localities on Sandoy, Koltur,
Streymoy, Eysturoy, and Borðoy, with ear-
lier records adding Nólsoy. Angus (1985)
showed guttulus Motschulsky to be a Cau-
casian species, the Faroese species intend-