THE NAUTILUS 105(1):7-15, 1991
Page 7
Littorina naticoides, New Species, with Notes on the Other
Smooth-shelled Littorina Species from the Northwestern Pacific
David G. Reid
Department of Zoology
The Natural History Museum
London SW7 5BD. U.K.
Alexander N. Golikov
Zoological Institute
Academy of Sciences of the L'.S.S.R.
Leningrad 199034, U.S.S.R.
ABSTRACT
A new species. Littorina (Neritrerna) naticoides. is described
from the northwestern Bering Sea, Kamchatka and Kurile Is-
lands. It is believed to be the sister species of L. aleutica and
the\ can be distinguished by penial and shell characters The
two are allopatric, L. aleutica showing an oceanic distribution
and L. naticoides a more continental one, but their ranges are
known to approach to u ithin 2.50 km of each other Five Lit-
torina species from the northwestern Pacific have smooth-shelled
forms, which can be difficult to distinguish. These are L. {N.)
naticoides, L. (N.) aleutica. L. (N.) sitkana. L. (N.) suhrotun-
data and L. (Littorina) kasatka. The diagnostic features of
their shells and reproductive anatomy are reviewed.
Key words: Littorina; Pacific; biogeography.
INTRODUCTION
Systematic studies of the family Littorinidae have been
revolutionised by two developments over the past two
decades. Firstly, anatomical features have been found to
be more reliable than traditional shell characters for
identification of species, and, secondly, there has been a
growing appreciation of the wide range of shell variation
shown by some species, and an understanding of its bi-
ological significance. The first use of anatomical char-
acters to discriminate between sibling species (with sim-
ilar or identical shells) was in the genus Littorina. (The
generic name is here used in the strict sense, as defined
by the cladistic analysis of Reid, 1989a). The most in-
formative of these new characters have proved to be the
shape of the penis, type of egg capsules and development
(Sacchi & Rastelli, 1966; Heller, 1975; Hannaford Ellis,
1979; Murray, 1979) and also the form of the pallial
oviduct (Reid, 1989a, 1990a). In all cases, studies of elec-
trophoretically detectable genetic variation have sup-
ported the status of the sibling species initially recognized
by anatomical differences (Ward, 1990). Although some-
times only one or other sex can be unequivocally iden-
tified by anatomical characters, there are no known cases
of morphologically inseparable Littorina species.
Extreme intraspecific variation in coloration, sculpture
and shape of the shell is a well-known feature of Lit-
torina. and contributes to the difficulties of identification.
Shell variation is especially marked in those species which
show direct development, for here the lack of a widely-
dispersed larval phase enhances the potential for adap-
tation to local environments. Selective factors influencing
morphological and color variation between populations
are believed to include predation, wave action and dam-
age by mobile boulders (e.g., review by Raffaelli, 1982;
Janson, 1982, 1983; Johannesson, 1986; Seeley, 1986).
Other factors such as growth rate can also contribute to
non-genetic shell variation (Kemp & Bertness, 1984).
The genus Littorina is restricted to the northern hemi-
sphere, and most species occur on temperate and cold
temperate shores (Reid, 1990b). So far, modern system-
atic revisions using anatomical details have only been
done in Europe and the northeastern Pacific. Littorina
species are also abundant in the northwestern Pacific,
and the most recent review of the littoral molluscs of the
Siberian region (Golikov & Kusakin, 1978) recognized
six species: L. squalida Broderip & Sowerby, 1829; L.
brevicnla (Philippi, 1848); L. rnandshurica Schrenck,
1861; L. aleutica Dall, 1872; L. sitkana Philippi, 1846;
L. kurila Middendorff, 1848. The identifications were
based only on characters of the shells. The first anatom-
ical work on northwestern Pacific Littorina was done as
part of a cladistic analysis of the 20 species then recog-
nized in the genus (Reid, 1990a). This largely supported
the classification of Golikov and Kusakin (although L.
kurila was synonymized with L. sitkana), but the ana-
tomical material used did not include any from the Soviet
Union.
As part of a wider study of the systematics and dis-
tribution of Littorina species (Reid, in prep), it has re-
cently been possible to examine the extensive collection
of preserved material from the Siberian coast held in the
Zoological Institute, Leningrad. Preliminary results in-
dicate that L. squalida. L. brevicnla and L. rnandshurica
can each be readily identified by shell characters, as
described and illustrated by Golikov and Kusakin (1978)
and Reid (1990a). The remaining three of the species
listed above were distinguished by Golikov and Kusakin
(1978) primarily by their shell sculpture: L. sitkana hav-
ing spiral ribs, L. kurila being smooth or almost so, and
L. aleutica having rows of nodules. This division now
seems to be an artificial one. Differences in reproductive
BioStor
