. Annual report - Western Society of Malacologists. Mollusks; Mollusks. collection. Most of these features are chronic in the 2 first involved species. They have been classified in 3 decreasing degrees of seriousness: 1) chronic abnormalities represented by a lack of one or several parts of the body (oral veil, rhinophores, cerata; see fig. 5A, B, C & E) and presumably resulting from a serious and early injury (by pollution?) during larval life or metamorphosis, and therefore without possibility of readjustment; 2) chronic abnormalities represented only by a more or less acute malforma- ti
. Annual report - Western Society of Malacologists. Mollusks; Mollusks. collection. Most of these features are chronic in the 2 first involved species. They have been classified in 3 decreasing degrees of seriousness: 1) chronic abnormalities represented by a lack of one or several parts of the body (oral veil, rhinophores, cerata; see fig. 5A, B, C & E) and presumably resulting from a serious and early injury (by pollution?) during larval life or metamorphosis, and therefore without possibility of readjustment; 2) chronic abnormalities represented only by a more or less acute malforma- tion due to a wrong readjustment (slender axis of the tail, see fig. 5D; verrucosities on the visceral hump, see fig. 5H & I) following a slight injury (bite, etc.) inflicted to the animal after its metamorphosis; 3) temporary abnormalities recorded in juvenile speci- mens only (negative allometry) readjusted in a normal way during growth. As a conclusion to this ecological and biological account, it must be emphasized that interstitial opisthobranchs could be regarded as indicator organisms which characterize a clean sedimentary environment devoid of pollution. Indeed as soon as pollution occurs in an area, disappearance of the rare species as well as changes in the abundance of dominant species are recorded together with modifi- cations of their season cycles. LITERATURE CITED Arnaud , C. Poizat & Salvini-Plawen. 1986. Marine interstitial Gastropoda (including one freshwater interstitial species), in Stygofauna Mundi, L. Botosaneanu (Ed), Leiden, Brill/ W. Backhuys. Poizat C. 1981a. Signification ecologique de quel- ques Gasteropods Opisthobranches mesop- sammiques des cotes de Provence. Haliotis 11 : 201-212. Poizat C. 1981b. Gasteropodes mesopsammiques de la mer du Nord (Robin Hood's Bay, ) : Ecologieet distribution/, moll. Stud. 47 : 1-10. Poizat C. 1983a. Mesopsammic opisthobranchs from the Provencal coast Marseille, Bouches-du- Rhone, F
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