RESEARCH NOTES 397

inal size distribution of particles. When these prob-lems are solved, it will be possible to give answers tothe still completely open question about selectiveingestion of organic and/or inorganic particles bybivalves.

The authors thank Dr Mathieu Pouhcek for help-ful comments. This research was supported by theNational Fund of Scientific Research of Belgium toJ.-M. Defossez.

REFERENCES

1. EISMA, D , BOON, J., GROENEWEGEN, R.,ITTEKKOT, V , KALF, J. & MOOK, W.G. 1983Mitt 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 EcoLProg. Ser, 5: 291-296.

4. Ki0rboe, T., Mahlenberg, F & Nohr, O 1980.Ophelia, 19 (2): 193-205

5. Ki0rboe, T., M0hlenberg, F. & Nohr, O. 1981Mar. BioL, 61:283-288.

6. Newell, R.LE. & Jordan, SJ. 1983. Mar. EcoLProg. 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, 9177-92.

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 RodriguezDepartmento de Estiuhos Ambientales, Umversidad Stmdn Boltar Apartado 89000, Caracas 1080, Venezuela

e-mail- ppenchas@usb. ve

Dicyenuds are minute ciliated worms that live asparasites on cephalopods. They are multicellular butthey do not consist of tissues in the usual sense of theword Dicyemids were discovered by Cavohni1 butfirst described by Krohn.1 Van Benden3 was soimpressed with their structural simplicity that heconcluded they represent a distinct branch of theanimal kingdom, intermediate between the proto-zoans and the metazoans. They live attached to thesurface of the excretory organs of the host Morethan 40 species of benthic or epibenthic cephalopodsare currently reported to host dicyemids.4 Untilrecently, dicyemids were believed to be limited tothe Northern Hemisphere; the first description of asouthern dicyemid species was Dicyema austrahsPenchaszadeh, 1968 a parasite of the South WesternAtlantic endemic Octopus tehuelchus d'Orbigny.3

Immediately after this, more new species descrip-tions came from Antarctica, New Zealand andArgentina.*"*

In temperate and polar waters, adult benthiccephalopods are generally 100% infected while inthe subtropical region the infection is reported torange from 10% to 20%.4 Since the reports ofnegative finding of dicyemids in cephalopods offOahu, Hawaii, and the Marshall Islands9 and inwaters off Suva, Fiji10 it has been believed that in thetropics and off oceanic islands cephalopods do nothost dicyemids.*

There are nevertheless some previous records ofdicyemids in tropical localities. One is from a sitevery close to the Tropic of Cancer Port Etienne,

Mauritania, West Africa, LaL 21°00'N11; the otherrecord is from a truly tropical area: West BengalBay, India.12

The nearest American localities to the tropicalCaribbean from where dicyemids were described arethe subtropical Florida Keys, USAU in the north,and the temperate Mar del Plata, Argentina3-4-14 inthe south.

Thirteen octopus identified as Octopus vulgansCuvier, 1797 from La Guaira (10°30'N) were exam-ined for parasites and found to be heavily infectedby dicyemids. The coastal zone of Venezuela offersseveral examples of upwelling phenomena, and thearea of La Guaira-Macuto is included m such a sys-tem, with sea water temperatures several degreesbelow the rest of the typical Caribbean Sea." Thiscould be related to the presence of mesozoans in thelocal populations of Octopus. But what makes thisfinding very striking is the high incidence of infection(100% in adult cephalopods) and the presence of avariety of mesozoan species, belonging to the genusDicyema and some new to science, still to bedescribed.

The presence of heavily infected populations ofcephalopods in Venezuela must encourage thesearch in other tropical localities. From a number of68 dicyemid species (there are presently 71 knownspecies), Hochberg4 estimated in 1990 a projectedtotal of about 200 species in the phylum. If we nowadd the potential host cephalopods still to be exam-ined in tropical areas, we could certainly consider-ably increase that estimate.

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REFERENCES

1. CAVOUNI, F. 1797. Memoria sulla Generazionedei Pact et dei Granchi. Napoh.

2. KROHN, A. 1839 Nouzen aus dem Gebiete derNatur- 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 (AninuSci), STB: 161-167.

13. SHORT, R.B. 1961. / . Parasil., 47: 273-278.14. PENCHASZADEH, P.E. & CHRISTIANSEN, H.E.

1970. Neotropica, 16. 119-12315. 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 thefamily Melanopsidae.3 This species is highly poly-morphic; within the same population, the externalcharacteristics 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 stilllacking" and these different morphs may belong to asingle, 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 Melanopsisor Zemelanopsis have been identified in New-Zealand and New Caledonia.54

M. praemorsa is adapted to live in many differentwaterbodies: sources, nvers, streams, mouths ofrivers, 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 to25.6°C), salinity (1.25 to 3.5%) and pH (7 to 8J).3

This snail has a generalist diet: it may eat differentplant food and occasionally dead organisms duringtheir decomposition.

Recently, in laboratory conditions, it has beendemonstrated that M. praemorsa stimulates thegrowth of the schistosome vector snail Bulinuswrigha and consequently enhances the cercanal pro-duction of the trematode Schistosoma bovis1 and

that M. praemorsa stimulates the general .fitness ofhealthy Bulinus truncatus.' A better knowledge ofthe reproductive pattern of M. praemorsa, and par-ticularly of the spawn of M. praemorsa in field andlaboratory conditions was thus desirable in order toestimate the possible importance of M. praemorsa inthe 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 canalssituated in the Haouz region (South of Marrakech,Morocco). These irrigation canals are fed by thesame dam, Lalla Takerkoust They have muddy-sandy substrates with slowly flowing water. Thesehabitats are usually occupied with a high density ofsnails. Fifty healthy sexually mature snails were col-lected from each canal every month during one year.Sex ratio was calculated after sex determinationbased on external characters and, if necessary, ondissections. Spawn was carefully searched for by fil-tering the muddy-sandy substrates.

Several hundred adult M. praemorsa, more than15 mm in diameter, with smooth and blackish shellwere collected from the irrigation canals (Fig. 1).Snails were kept in the laboratory as groups of 100individuals in large aquaria (560 x 40 x 14 cm); thesubstratum was one-third in area clay and two-thirdsstones from a river. They were fed with various food,e.g. algae, lettuce, apple, carrot. The aquaria werefilled up to 7 cm with aerated water from a welL Theriver stones and floating pieces of polystyrene were

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