1. RESEARCH NOTES 397
inal size distribution of particles. When these prob-
lems are solved, it will be possible to give answers to
the still completely open question about selective
ingestion of organic and/or inorganic particles by
bivalves.
The authors thank Dr Mathieu Pouhcek for help-
ful comments. This research was supported by the
National Fund of Scientific Research of Belgium to
J.-M. Defossez.
REFERENCES
1. EISMA, D , BOON, J., GROENEWEGEN, R.,
ITTEKKOT, V , KALF, J. & MOOK, W.G. 1983
Mitt GeoL PalaonL InsL Univ. Hamburg,
SCOPE/UNEP Sonderb, 55: 295-314
2. HYLLEBERG, J. & GALLUCI, V J 1975. Mar BioL,
32:167-178.
3. Ki0rboe, T. & Mehlenberg, F 1981. Mar EcoL
Prog. Ser, 5: 291-296.
4. Ki0rboe, T., Mahlenberg, F & Nohr, O 1980.
Ophelia, 19 (2): 193-205
5. Ki0rboe, T., M0hlenberg, F. & Nohr, O. 1981
Mar. BioL, 61:283-288.
6. Newell, R.LE. & Jordan, SJ. 1983. Mar. EcoL
Prog. Ser, 13: 47-53.
7.NEWELL, C.R^ SHUMWAY, S.E., Cucci, T L &
SELVTN, R. 1989. J Shellfish Res., 8:187-196.
8. RAZET, D., HERAL, M., PROU, J., LEGRAND, J &
SORNIN, J.-M. 1990. Halwtis, 20-143-161.
9 SHUMWAY, S.E., Cucci, T.L., NEWELL, R.C. &
YENTSCH, CM. 1985. J Exp. Mar BioL EcoL, 91
77-92.
J Moll. Stud. (1996), 62, 397-398 © The Malacologwal Society of London 1996
First discovery of Dicyemida (Mesozoa) in Caribbean cephalopods
Pablo E. Penchaszadeh, Jorge M. G6mez, Carlos Izsak and Rafael Rodriguez
Departmento de Estiuhos Ambientales, Umversidad Stmdn Boltar Apartado 89000, Caracas 1080, Venezuela
e-mail- ppenchas@usb. ve
Dicyenuds are minute ciliated worms that live as
parasites on cephalopods. They are multicellular but
they do not consist of tissues in the usual sense of the
word Dicyemids were discovered by Cavohni1
but
first described by Krohn.1
Van Benden3
was so
impressed with their structural simplicity that he
concluded they represent a distinct branch of the
animal kingdom, intermediate between the proto-
zoans and the metazoans. They live attached to the
surface of the excretory organs of the host More
than 40 species of benthic or epibenthic cephalopods
are currently reported to host dicyemids.4
Until
recently, dicyemids were believed to be limited to
the Northern Hemisphere; the first description of a
southern dicyemid species was Dicyema austrahs
Penchaszadeh, 1968 a parasite of the South Western
Atlantic endemic Octopus tehuelchus d'Orbigny.3
Immediately after this, more new species descrip-
tions came from Antarctica, New Zealand and
Argentina.*"*
In temperate and polar waters, adult benthic
cephalopods are generally 100% infected while in
the subtropical region the infection is reported to
range from 10% to 20%.4
Since the reports of
negative finding of dicyemids in cephalopods off
Oahu, Hawaii, and the Marshall Islands9
and in
waters off Suva, Fiji10
it has been believed that in the
tropics and off oceanic islands cephalopods do not
host dicyemids.*
There are nevertheless some previous records of
dicyemids in tropical localities. One is from a site
very close to the Tropic of Cancer Port Etienne,
Mauritania, West Africa, LaL 21°00'N11
; the other
record is from a truly tropical area: West Bengal
Bay, India.12
The nearest American localities to the tropical
Caribbean from where dicyemids were described are
the subtropical Florida Keys, USAU
in the north,
and the temperate Mar del Plata, Argentina3
-4
-14
in
the south.
Thirteen octopus identified as Octopus vulgans
Cuvier, 1797 from La Guaira (10°30'N) were exam-
ined for parasites and found to be heavily infected
by dicyemids. The coastal zone of Venezuela offers
several examples of upwelling phenomena, and the
area of La Guaira-Macuto is included m such a sys-
tem, with sea water temperatures several degrees
below the rest of the typical Caribbean Sea." This
could be related to the presence of mesozoans in the
local populations of Octopus. But what makes this
finding very striking is the high incidence of infection
(100% in adult cephalopods) and the presence of a
variety of mesozoan species, belonging to the genus
Dicyema and some new to science, still to be
described.
The presence of heavily infected populations of
cephalopods in Venezuela must encourage the
search in other tropical localities. From a number of
68 dicyemid species (there are presently 71 known
species), Hochberg4
estimated in 1990 a projected
total of about 200 species in the phylum. If we now
add the potential host cephalopods still to be exam-
ined in tropical areas, we could certainly consider-
ably increase that estimate.
byguestonMarch5,2013http://mollus.oxfordjournals.org/Downloadedfrom

2. 398 RESEARCH NOTES
REFERENCES
1. CAVOUNI, F. 1797. Memoria sulla Generazione
dei Pact et dei Granchi. Napoh.
2. KROHN, A. 1839 Nouzen aus dem Gebiete der
Natur- und HeUkunde, 11. 213-216.
3 BENEDEN, R. VAN 1876. Bull Acad. R Belg,
Cll SCL Ser. 2,41 1160-105; 42: 35-97.
4 HOCHBERG, F.G. 1990. Diseases of Marine Ani-
mals, 3: 47-202.
5. PENCHASZADEH, P E 1968. Neotropica, 14: 17-
131.
6. SHORT, R.B. & HOCHBERG, F.G. 1969. J. Parasu.,
55: 583-596.
7. SHORT, R.B. & POWELL, E.C. 1969. J Parasu.,
55. 794-799.
8. PENCHASZADEH, P E. 1969. Neotropica, 15.1-6.
9. MCCONNAUGHEY, B H 1949 Univ. Calif. PubL
Zoot., 55:1-34, pi. 1-7.
10. KOSHIDA, Y., HORIUCHI, S., TAJIKA, K. & RAJ,
U. 1986. ZooL Set, Tokyo, 3 (Abstract), p. 1108.
11. NOUVEL, H. 1934 Bull Soc. ZooL Fr, 59: 176-
186.
12. KALAVATI, C, NARASIMHAMURTI, C.C. &
SUSEELA, T. 1978 Proc Indian Acad. Sci (Aninu
Sci), STB: 161-167.
13. SHORT, R.B. 1961. /. Parasil., 47: 273-278.
14. PENCHASZADEH, P.E. & CHRISTIANSEN, H.E.
1970. Neotropica, 16. 119-123
15. OKUDA, T. 1974 Cuademos Azules; Conf. UN
Derecho del Mar, 15. 43-57.
/. Moll Stud. (1996), 62, 398-402 © The Malacological Society of London 1996
Observation of spawn in Melanopsis praemorsa (Prosobranchia: Melanopsidae)
A. Mouahid1
, M. Idaghdour2
, M. Ghamizi2
and H.
'Laboratoire de Biologie Animale, UMR 5555 du CNRS, Centre de Biologie et d'Ecologie Tropicale et Miditer-
ranlenne, Universitt, 52 Avenue de VUleneuve, 66860 Perpignan Cedex, France
'Laboratoire de Parasitologie, Faculti des Sciences Semlalia, BP15, Umversiti Cadi Ayyad, Marrakech,
Morocco
Melanopsis praemorsa (Linnaeus, 1758, Buccinum)
is a gastropod snail which belongs to the Proso-
branchia, to the superfamily Cerithioidea1
and to the
family Melanopsidae.3
This species is highly poly-
morphic; within the same population, the external
characteristics of the shell, the growth and the phe-
notypic enzyme profile vary.3
However, a direct evi-
dence of genetic difference at the species level is still
lacking" and these different morphs may belong to a
single, circum-Mediterranean superspecies.4
-3
M. praemorsa is distributed in the circum-Mediter-
ranean zone from Gibraltar to Mesopotamia.1
Closely related taxa, with a smooth shell as in M.
praemorsa sensu stricto and classified as Melanopsis
or Zemelanopsis have been identified in New-
Zealand and New Caledonia.54
M. praemorsa is adapted to live in many different
waterbodies: sources, nvers, streams, mouths of
rivers, dams, lakes, irrigation canals and basins,
oases and Moroccan traditional subterranean irriga-
tion systems called 'khettaras'. It may tolerate varia-
tions of flow (0.12 to 0.44 m/s), temperature (133 to
25.6°C), salinity (1.25 to 3.5%) and pH (7 to 8J).3
This snail has a generalist diet: it may eat different
plant food and occasionally dead organisms during
their decomposition.
Recently, in laboratory conditions, it has been
demonstrated that M. praemorsa stimulates the
growth of the schistosome vector snail Bulinus
wrigha and consequently enhances the cercanal pro-
duction of the trematode Schistosoma bovis1
and
that M. praemorsa stimulates the general .fitness of
healthy Bulinus truncatus.' A better knowledge of
the reproductive pattern of M. praemorsa, and par-
ticularly of the spawn of M. praemorsa infieldand
laboratory conditions was thus desirable in order to
estimate the possible importance of M. praemorsa in
the life history traits of the schistosome vector mol-
luscs and its bearing on the transmission of the dis-
ease.
The field study took place in two irrigation canals
situated in the Haouz region (South of Marrakech,
Morocco). These irrigation canals are fed by the
same dam, Lalla Takerkoust They have muddy-
sandy substrates with slowly flowing water. These
habitats are usually occupied with a high density of
snails. Fifty healthy sexually mature snails were col-
lected from each canal every month during one year.
Sex ratio was calculated after sex determination
based on external characters and, if necessary, on
dissections. Spawn was carefully searched for by fil-
tering the muddy-sandy substrates.
Several hundred adult M. praemorsa, more than
15 mm in diameter, with smooth and blackish shell
were collected from the irrigation canals (Fig. 1).
Snails were kept in the laboratory as groups of 100
individuals in large aquaria (560 x 40 x 14 cm); the
substratum was one-third in area clay and two-thirds
stones from ariver.They were fed with various food,
e.g. algae, lettuce, apple, carrot. The aquaria were
filled up to 7 cm with aerated water from a welL The
river stones and floating pieces of polystyrene were
byguestonMarch5,2013http://mollus.oxfordjournals.org/Downloadedfrom