MALACOLOGIA, 1969, 7(2-3): 211-294
A TAXONOMIC STUDY OF SOME SPECIES OF SEMISULCOSPIRA IN
JAPAN (MESOGASTROPODA: PLEUROCERIDAE)
George M. Davis
406th Medical Laboratory
U. S. Army Medical Command, Japan
APO San Francisco, California 96343
The purpose of this paper is to establish basic taxonomic concepts for 10
distinct species-group taxa of the freshwater snail genus Semisulcospira.
Over 30 species and subspecies of this genus had been named from Japan,
including the Ryukyu and Ogasawara Islands. In the current study, topotypes
of the most prominent of the previously described species were obtained. Two
taxa are described here as new, Semisulcospira habei habei and S. habei
Topotypes were analyzed in terms of the largest 10% of each population.
Data were collected on adult shell morphology, embyro shell characters and
intra-brood pouch development of embryo shells. Data were analyzed and
presented to permit the reader to understand natural variation in the para-
meters measured or counted. Data were correlated with the cytological findings
of Burch & Davis (1967) and Burch (1968) in order to establish species con-
The taxa are relegated to 2 species groups, the Semisulcospira libertina
group and the S. niponica groups. The former is characterized by having a
chromosome number of n=18 or 20, adult shells have 7 or more basal cords,
and there are numerous (100 or more) young in the female brood pouch
(modified palliai oviduct). S. libertina and S. reiniana are the main species
in the complex. S. kurodai is placed in the group because the taxon's chromo-
some number is n=18; the species is, however, considered transitional between
the 2 species groups as the adult shells average 5.1 basal cords and there are
35.5 ± 15.4 embryos per female brood pouch.
The Semisulcospira niponica species group is characterized by species
having low chromosome numbers, n=7 to 14; adult shells have 2 to 6 basal
cords and there are few embryos per brood pouch (an average of 25.2 ±9.8
maximum to 5.2 ± 3.4 minimum, depending on the species). Taxa included in
this group are endemic in Lake Biwa and its drainage; they are: S. niponica,
S. decipiens , S. reticulata, S. habei habei, S. habei yamaguchi, S. nakasekoae
and S. multigranosa .
A key to the species is provided to aid in the identification. The utility of
traits used in describing the taxa is discussed. Characters of basic im-
portance in defining the species are chromosome numbers, number of basal
cords on the adult shell, number of embryos carried by the female, ontogeny
of shell sculpture, number of ribs and nodes on the adult shell, embryo size
and shape, growth patterns of the embryos in the brood chamber, whorl size
attained by the embryo in the female, embryo sculpture and color patterns.
Several traits seem to be particularly subject to inter-population variation.
These are adult shell width, spire angle, length of body whorl, embryo micro-
sculpture, apical whorl measurements and adult color patterns. In the
Semisulcospira libertina species group the presence or absence of ribs and
embryo sculpture is subject to such variation. Spire angle is, however, useful
in differentiating between several species. The number of whorls and adult
shell length are subject to environmental control.
Semisulcospira habei yamaguchi, S. decipiens and S. multigranosa are sib-