THE NAUTILUS 112(l):6-33, 1998
Page 6
Additions and Corrections to the Taxonomy of the genus
Peasiella Nevill, 1885 (Gastropoda: Littorinidae)
Da\id G. Reid
Department of ZooIogN
The Natural Histon Museum
Lxmdon S\V7 5BD,' UK
D.reidCS'nhm.ac.nk
Yiu-Ming Mak'
Department of Ecology and
Biotliversity
The University of Hong Kong
Hong Kong
ABSTRACT
Peasiella is a genus of the Littonmdae with nnnute, trochoidal
shells, found onlv in the Indo-West Pacific region. A prexious
monograph recognized slx Recent species. As a result of new
anatomical information (reproductive anatomy, egg capsules,
radulae) two of these are dixided into five and two species,
respectively, to make a total of 11 species in the genus. Three
of these are descnhed as new. Additional notes on distribution,
variation and nomenclature are provided on otlier species.
Characters of the radula and pallial oxiduct are relatively uni-
form throughout the genus, hut penial shapes are often diag-
nostic. Shell shape and sculpture show extreme mtraspecific
x-ariabilitx'
INTRODUCTION
Pca.sicllo is one of the more poorly knoxvii genera of the
Littorinidae. In common xxith all members of the ,sub-
family Littorininae, its species occur t)n hard substrates
in the httoral zone. Although easily accessible and often
abundant, they are infre(juently collected oxving to their
small size and crvptic habit in rock crexaces and among
oyster and barnacle shells. All knoxvn species occur in
the Indo-West Pacific province and most are entirely
tropical, although several extend into the temperate
zones of southern Africa and the northxx'esteni Pacific.
Among Utt(jrinids, they are readily recognized by their
small (1-7 mm diameter), trochoidal or depressed shells,
lacking spines, with open umbihcus and multispiral oper-
culmn. These characters are superficially similar to those
of trochids (but lacking the nacreous interior of that
group), with which they were often contused by eark
authors (see review of taxonoinic histon-bv Reid,
1989a). Other littorinids with trochoidal sliells include
the genera Bciiihicimu and m.scllop.sis irom Australia
and New Zealand (Reid, 1988), and Tcctiiniis and C.i'u-
chritis from the Indo-West Pacific and western Atlantic
(Ro.sevvater, 1972; Reid, 1989b; Reid & Celler, 1997).
' Present address: 1.3/F, Canton Road Covemment Offices, Ag-
riculture and Fisheries I^epartinent, Hong Kong
For long these small littorinids were neglected ta.\o-
nomicallv. The most recent monograph of e.xtant and
some fossil Pca.sicllo species was that by Reid (1989a);
before this the onlv compilations were a fist by Nevill
(1885) and a monograph bv Trvon (1887). The anatomy
(male and female reproductive tracts, paraspermatozoa,
egg capsule, alimentary tract, head-foot pigmentation),
radula, protoconch and teleoconch were described in de-
tail bx' Reitl (1989a). As a result, the genus xxas defined
not onlv bv shell and opercular characters, but iilso by
the uni(jue combination of the elongate penis with single
mamilliform peni;il gland and closed vas deferens, to-
gether xvith the double-looped form of the pidfial ovi-
duct, and other anatomical features. These same char-
acters were included in a phvlogenetic an;ilysis of the
morphology of the genera and subgenera of the Litto-
rinidae (Reid, 1989b). However, since none of the coded
anatomical characters appeared to be apomoqihic xxithin
the famil), the (juK' formal svnapomorphies of the genus
in this analysis were the trochoidal shell shape and mul-
tispiral operculimi, and neither of these xx'as unitjue.
Nexertheless, the close moiphological similarities among
its members leaves little doubt that the genus is a mono-
phvletic one; the arrangement of the loops of the p;dli;d
oxiduct is one unitjue character, but oxving to difficulties
of coding such structures it did not appear as such in
the formal auiilvsis. As a result of Reid's (1989b) phylo-
genetic analysis, it was clear that Peasiella was a member
of the derived subfamilv Littorininae, and probably a
relatively basal member, although its precise relation-
ships xxith such genera as Maimvarin^ia, Ccnchhtis and
Tcctariiis were not resolved. A recent molecular study
included a species of Peasiella. vxith members of Tcctar-
iiis. Ccncliriti.\ and Sodiliftorina. but did not find any
close relationships xxith these other genera (Reiil & C;ell-
er, 1997).
In th(-previous systematic account ni Peasiella species
(Reid, 1989al, anatomical details were provided for all
the six species then recognized. Hovxexer, the amount
of material available vxas limited; for example, for P.
'isseli' onlx one preseived male was dissected, and tor /'
'iiifraciKtalii' oulx seven. As a result, it was loiuluded
BioStor
