Ultrastructure of the seminal receptacle and the dimorphic sperm in the commensal bivalve Mysella bidentata (Veneroida; Galeommatoidea; Montacutidae)

Jespersen, Å. and Lützen, J. 2001 . Ultrastructure of the seminal receptacle and the dimorphic sperm in the commensal bivalve Mysella bidentata (Veneroida: Galeommatoidea: Montacutidae). — Acta Zoologica (Stockholm) 82 : 107–115
The seminal receptacle and the euspermatozoa and paraspermatozoa of Mysella bidentata were examined at an ultrastructural level and the results were compared with earlier findings of the same and other species of the Montacutidae. The euspermatozoon has a slender 13 µm long nucleus and a 1.1 µm long bullet-shaped acrosome. The acrosome of the paraspermatozoon is almost identical in ultrastructure to that of the euspermatozoa but is longer (1.9 µm) and more slender and is bent at an angle to the diminutive nucleus (1.1 µm long). The unpaired seminal receptacle is lined by a heavily ciliated epithelium and a non-ciliated epithelium with short and broad microvilli. Euspermatozoa only are stored in the receptacle. They are densely packed and orientated with their heads towards the non-ciliated epithelium. In this position they develop numerous extremely fine microvilli from the acrosome which apparently serve to attach them to the epithelial microvillar surface. Stored sperm may presumably remain functional for at least six months. A possible function of paraspermatozoa could be to clump sperm into sperm bags to keep them in suspension.     

Spermatogenesis in the endosymbiont-bearing bivalve Loripes lucinalis (Veneroida: Lucinidae)

In the endosymbiont-bearing bivalve Loripes lucinalis, spermatogenesis is similar to that described for numerous bivalve species and leads to the formation of an aquasperm. The head and midpiece measure 10.5 ± 1.5 μm in length. The head is made up of a cylindrical nucleus slightly tapered apically and capped by a short conical acrosome. The nucleus lacks both an anterior and posterior nuclear invagination. The acrosome is 1.0 ± 0.1 μm long and consists of an acrosomal cone containing a diffuse subacrosomal material and an apical electron-lucent vacuole. There is no axial rod. The midpiece is made up of four mitochondrial spheres that surround the distal and proximal centrioles. The base of the distal centriole is joined to the plasmic membrane by the pericentriolar complex made up of nine radial arms. A cytoplasmic collar is observed that sheaths the flagellum as it emerges from the distal centriole. The spermatozoa present in mature acini are grouped into characteristic rings, which may have a nutritive function, with the acrosome oriented toward the centre of these ring formations. Also present within the gonad are somatic cells that seem to play a nutritive role in relation to the germinal cells. These nutritive cells undergo a cycle of development and lysis that corresponds to the spermatogenic cycle of the bivalve. These cells are large and rich in glycogen and lipid inclusions. In-depth examination of nutritive cells and gametes reveals that the male gonad is devoid of microorganisms in either a vegetative or cryptic form, suggesting that a vertical transmission through paternal gonadal inheritance is a very unlikely means of symbiont transmission in L. lucinalis. © 1996 Wiley-Liss, Inc.     

Morphology, structure of dimorphic sperm, and reproduction in the hermaphroditic commensal bivalve Pseudopythina tsurumaru (Galeommatoidea: Kellidae)

In Japan Pseudopythina tsurumaru is an up to 10.8 mm-long commensal of the burrowing sea cucumber Protankyra bidentata, whereas in Hong Kong the same species is smaller and associated with the crab Hexapus anfractus, itself a commensal of P. bidentata. Japanese P. tsurumaru is a hermaphrodite tending towards protogyny maturing to a female when > or = 7 mm, and entering the hermaphroditic condition when > or = 9 mm long. In addition to normal euspermatozoa, the species produces 30-32 microm long and 7 x 8 microm broad spindle-shaped paraspermatozoa provided with a conical acrosome, a nucleus, and a bundle of approximately 15-16 flagella issuing from the head region. Paired pouch-formed seminal receptacles normally occur in bivalves > or = 6 mm. Bulk sperm transfer presumably takes place by way of spermatozeugmata formed by the two types of sperm cells. Exogenous euspermatozoa attach to particular nonepithelial cells that occupy the interior of the receptacles. These cells, together with their associated sperm, are probably released as syncytial sperm-carrying bodies into the suprabranchial chamber, where the ova are fertilized.     

Fine structure of Lasaea subviridis and Mysella tumida sperm (Bivalvia,Galeommatacea)

Summary Lasaea subviridis and Mysella tumida sperm resemble the primitive spermatozoan type, but exhibit several unique morphological features. L. subviridis sperm heads vary in shape and size owing to differing degrees of nuclear condensation. A fully mature, heterogenous acrosomal vesicle with an associated axial rod is present. Up to 50% of L. subviridis sperm in developing gonads have conspicuously angled flagella that propel the sperm cells in irregular helical paths. This may represent a penultimate stage in sperm development because the remainder of the sperm cells have posteriorly-directed flagella and swim in a nonhelical anterior direction. A trend toward a reduction in both nuclear condensation and swimming ability may be a long-term consequence of increasing degrees of localized, but non-internal self-fertilization in marine invertebrates that brood. Mysella tumida sperm are monomorphic and possess numerous microvilli (30–60 nm in diameter and up to 5.7 m in length) that resemble stereocilia and radiate from the cell membrane surrounding the basal body. In this species, the sperm cell does not have an axial rod, and the complex acrosomal vesicle contains five distinct zones of varying electron opacity. One of these zones is a transverse, electron-opaque band that is apparently composed of rolled-up membrane. Following acrosomal breakdown, this membrane unfolds to cover the anterior tip of the sperm cell. Although both L. subviridis and M. tumida are hermaphroditic, the relative size of their male investments is conspicuously different. Approximately 40–50% of the M. tumida gonadal volume is testis compared with about 5% of that in L. subviridis.     

Sperm dimorphism and spermatozeugmata in the commensal bivalve Pseudopythina macrophthalmensis (Galeommatoidea, Kelliidae)

The bivalve Pseudopythina macrophthalmensis (Galeommatoidea) is a commensal with the crab Macrophthalmus convexus (Ocypodidae) in Okinawa Prefecture, Japan. It is a protandric hermaphrodite which incubates the 65-μm large ova in the suprabranchial cavity. The species produces two types of sperm, which were studied with the electron microscope. The euspermatozoon has an elongate 2.8-μm-long, pointed acrosome, a slender 12- to 13-μm-long nucleus and a middlepiece containing several closely packed mitochondria arranged as a 5.5- to 6.0-μm-long sheath around the basis of the flagellum. The paraspermato- zoon is vermiform, 220-μm-long and up to 5-μm-broad. Anteriorly there is a ca 7-μm-long bullet-shaped acrosome followed by a subcylindrical 3.0- to 4.7-μm-long nucleus. Adjacent to the nucleus occurs a bundle of 26–42 40-μm-long flagella. The cytoplasm is packed with spherical lipid droplets and ovoid granules of unknown composition. Sperm of both types aggregate to form spermatozeugmata, which were found in the posterior mantle cavity or in paired seminal receptacles. Within the receptacles the euspermatozoa dissociate themselves from the spermatozeugma and become attached to the epithelial lining of the receptacle whereas the paraspermatozoa presumably disintegrate. The possible significance of the two types of sperm is discussed in the light of their presumed functions in gastropods. Accepted: 9 November 2000     

Comparative study of the morphology of the female seminal receptacles of Ilia nucleus and Persephona mediterranea (Decapoda,Brachyura, Leucosiidae)

Because of the poor knowledge of the morphology of the female reproductive organs of most brachyuran crabs, this study investigated two Atlantic representatives of the family Leucosiidae, Ilia nucleus (Linnaeus, 1758) and Persephona mediterranea (Herbst, 1794), using histological methods and magnetic resonance imaging (MRI). While the vagina conforms to the concave type, the arrangement of the two chambers of the seminal receptacle differs strongly from that of other eubrachyuran sperm storage organs. Both chambers are oriented laterally within the crab's body. This is in contrast to the dorso-ventral orientation described in most other known brachyuran crabs. The lateral chamber is covered by cuticle, whereas the medial chamber is covered by a holocrine glandular epithelium. The oviduct connection is located ventrally, posterior to the vagina. The oviduct orifice is characterized by a transition from the epithelium lining the oviduct to the seminal receptacle's holocrine glandular epithelium. Moreover, muscle fibres are attached to the oviduct orifice and to the sternal cuticle. This musculature can be interpreted as an important feature in the fertilization and egg-laying process by supporting and controlling the inflow of eggs into the seminal receptacle lumen. The results of this study are compared to the morphology of the seminal receptacle of another leucosiid crab, Ebalia tumefacta (Montagu, 1808), and to those of other known eubrachyuran crabs.     

Basal chromodorid sperm ultrastructure (Nudibranchia, Gastropoda, Mollusca)

The relationship between three genera considered basal in the Chromodorididae (Cadlina, Tyrinna, Cadlinella) has not yet been resolved by traditional morphological means. Here we examined the sperm ultrastructure of Tyrinna nobilis, Tyrinna evelinae, Cadlina flavomaculata and Cadlina cf. nigrobranchiata, with the expectation of finding phylogenetically informative characters. No Tyrinna or Cadlina species showed sperm similarities to Cadlinella. Both Cadlina species and Tyrinna nobilis (but not T. evelinae) exhibited coarse striations in the acrosomal pedestal. The putative fibers that occurred between the coarse striations of the pedestal are condensed into a layer in Cadlina and Tyrinna, but not in other species that also have coarse striations (Gymnodoris), and may constitute evidence for a close relationship. Tyrinna evelinae possessed fine acrosomal striations, which was shared with other Chromodorididae, Actinocyclidae and the cryptobranchs Rostanga and Aphelodoris. We also examined the sperm ultrastructure of ‘Chromodoris’ ambiguus, an animal which has shown molecular affinities to species of Cadlina, and not Chromodoris. The sperm of ‘C.’ ambiguus did not exhibit the typical Cadlina characteristics, but also showed important differences to other investigated Chromodoris species.     

Spermatogenesis and sperm ultrastructure in the polychaete genusOphryotrocha (Dorvilleidae)

The details of spermatogenesis and spermiogenesis are described forOphryotrocha puerilis. The ultrastructure of mature sperm is shown forO. puerilis, O. hartmanni, O. gracilis, O. diadema, O. labronica, andO. notoglandulata. Clusters of sixteen cells each are proliferated by two stem cells in each setigerous segment ofO. puerilis representing the very early stages of both oogenesis and spermatogenesis. In each spermatocyte-I cluster, the cells are interconnected by cytoplasmic bridges. Early, clusters are enveloped by peritoneal sheath cells. These transient gonad walls break down prior to meiosis. The meiotic processes may start in the clusters with the cells still interconnected, or during breakdown of the original cluster, giving rise to smaller subclusters of both spermatocytes I and spermatocytes II with various numbers of cells. Finally, spermatid tetrads are present. As spermiogenesis progresses, the tetrads disintegrate. Golgi vesicles in both spermatocytes and spermatids contain electron-dense material, presumably preacrosomal. The acrosome is formed by such vesicles. In the six species studied here, the acrosomes appear to be of a similar overall structure but are of different shape. Centrioles are usually located beneath the acrosome. The distal centriole forms the basal body of a flagellum-like cytoplasmic process. The microtubules of these flagellar equivalents do not show a normal ciliar arrangement. The flagellar equivalent appears to be non-motile. InO. hartmanni and inO. notoglandulata, a flagellar equivalent is missing. Microtubules originating from the proximal end of the distal centriole stretch to the nuclear envelope. This feature appears to be especially conspicuous inO. puerilis and inO. labronica. InO. labronica and inO. notoglandulata, bundles of microtubules paralleling the cell perimeter appear to stabilise the sperm. Various numbers of mitochondria are either randomly distributed around the nucleus or accumulate on one side, often directly under the acrosome. Parts of the present paper were presented at the 2^nd International Polychaete Conference, Copenhagen 1986 and at the 3^rd International Polychaete Conference, Long Beach, Ca. 1989.     

Structure of sperm,spermatozeugmata and ‘lateral organs’ in the bivalve Arthritica (Galeommatoidea: Leptonidae)

The position and structure of paired ‘lateral organs’ in the foot of Arthritica semen and Arthritica bifurca might indicate a chemosensory function. In both species part of the organ is also glandular. In A. semen the glandular epithelium is detached piecemeal and, probably by means of the foot, is moved to and grafted upon the gills of the same individual. The transferred epithelia appear as disk‐shaped actively secretory ‘gill bodies’ which, attached to the abfrontal side of the inner demibranch, replace the ordinary unciliated gill epithelium. The secretion is liberated into the suprabranchial chamber, which serves as a marsupium, but its function is uncertain. Arthritica semen is a protandric hermaphrodite and produces very large ova that undergo a direct development that results in a non‐planktonic lecithotrophic crawling juvenile stage. The sperm cells have filiform nuclei that are straight in the euspermatozoa and more or less helicoidal in what is considered to represent paraspermatozoa. By a process of aggregation, spermatozeugmata are formed which consist exclusively either of euspermatozoa or paraspermatozoa. Spermatozoa are stored in the oviduct in A. semen but in paired seminal receptacles in A. bifurca.     

Mating and role of seminal receptacles in the reproductive biology of the spider crab Maja squinado (Decapoda, Majidae)

The reproductive biology of the spider crab Maja squinado was analyzed based on monthly samples from an 18-month study carried out in Galicia (NW Spain) and laboratory experiments holding primiparous and multiparous females in captivity with and without males. The seminal receptacles of adult females were analyzed and their relationship with the presence and developmental stage of the eggs and the gonad maturity stage was determined. Gonad maturation in primiparous females began one or two months after the pubertal moult. Females having gonads in an advanced stage of development made their appearance in December and the first spawning took place in mid-winter or early spring. The percentage of ovigerous females from March to September was ∼75%. As the incubation period progressed, the ovaries became mature again in order to carry out the next spawning. Under experimental conditions the breeding cycle started earlier in multiparous females, during their second yearly cycle, than in primiparous ones. After mating, female spider crabs store sperm in seminal receptacles and this sperm is used in the fertilization of eggs immediately prior to spawning. The analyses of seminal receptacles consisted of the estimation of fullness and the number of differentiated sperm masses. The number of masses ranged between 0 and 6 in field samples (median for females with stored sperm=1) and was positively correlated with fullness. Differences in colour and volume of individual masses showed that, at least in some cases, females carried out successive matings with long intervals in between. This storage mechanism allowed females to fertilize successive broods without remating (as was also shown under experimental conditions). Juvenile females from shallow waters did not have developed seminal receptacles which indicated that mating was not possible until the onset of maturity. Postpubertal females in shallow waters (August to October), including animals participating in aggregations, always showed empty receptacles. The seasonality of receptacle fullness showed that mating involved hard-shelled females and occurred in deep water during the autumn migration from juvenile habitats or in the wintering habitats, during the last stages of gonad maturation (November to February). After fertilization ovigerous females continued to store sperm, but the volume was lower than in non-ovigerous females. Mating may occur in ovigerous females, particularly in the final period of incubation, because in females with broods almost ready to hatch, both new and older sperm masses were seen in the receptacles (distinguished by colour and size). The fullness of the receptacles decreased both in ovigerous and non-ovigerous females in the final phase of the annual breeding cycle (August–October), however, some sperm was still available. In the laboratory, mating was observed, and no courtship nor postcopulatory guarding was recorded. The analysis of receptacles from laboratory experiments indicated that primiparous and multiparous females showed differences in the seasonality of mating in the first phase of the breeding cycle (September–January), related to differences in the timing of gonad maturation and hatching. Mating occurred in the final stages of gonad maturation, a short time before hatching, and matings were detected in ovigerous females. Multiple matings were also evident, to a greater extent than in the field, probably due to the higher availability of males. Females underwent over four successive spawnings in the laboratory without having to recopulate, and the incubation lasted on the average from 40 to 58 days (∼18 and 16°C respectively) and the mean duration between hatching and the next spawning was 3.4 days. It is estimated that most females carry out three successive spawnings during the annual cycle.     

New findings on sperm ultrastructure in thrips (Thysanoptera, Insecta)

Sperm ultrastructure of several species in each of the two suborders of Thysanoptera Tubulifera and Terebrantia shows a distinctive and unusual architecture. Members of the whole order share a bizarre axoneme consisting of 27 microtubular elements derived from the amalgamation of 3 (9+0) axonemes present in each spermatid at the beginning of spermiogenesis. The reciprocal shifting of these axonemes along the length of the sperm, together with their possible shortening and overlapping for short distances, could explain why in some species it is never possible to observe the complete set of 27 microtubular elements in any one cross section. Tubuliferan sperm have a small elliptical (in cross section) acrosome extending the length of the sperm. In Bolothrips insularis and Compsothrips albosignatus this structure is larger and is associated with an external, flattened vesicle throughout its length. Terebrantian sperm lack an acrosome, but display for half their length a dense body running parallel to the nucleus. The sperm, in members of this suborder, are also characterized by possession of a small mitochondrion and by the unusual bilobed outline of cross sections through the anterior sperm region, with the nucleus located in one of the two lobes. Structures serving to anchor sperm to the inner surface of the cyst cell have been observed at their anterior tips in the testes of tubuliferans. In B. insularis, an anterior appendage is formed in immature sperm and is maintained in the mature spermatozoon parallel to its long axis in the most anterior region. Such an anchoring structure has not been observed in sperm of the terebrantian species examined, probably because the testis of terebrantians contains only a single cyst of developing gametes.     

Spermatophore development and sperm ultrastructure inCraterostigmus tasmanianus (Chilopoda,Craterostigmomorpha)

 Spermatophore development and ultrastructure of the mature sperm of Craterostigmus tasmanianus were studied using light and electron microscopy. In C. tasmanianus, as in the Scolopendromorpha, the spermatophore develops within the vas deferens. The latter consists of three parts, each with a different morphology. The first may be involved in guiding the sperm to roll up into typical ring-like structures, while the other two, which show an evident secretory activity, secrete the acellular wall of the spermatophores. The ultrastructure of mature spermatozoa showed that a very close similarity exists between Craterostigmomorpha and Lithobiomorpha, especially regarding the organization of the connecting piece. Based on this similarity, we consider the Craterostigmomorpha together with the Scolopendromorpha, Geophilomorpha and Lithobiomorpha (=Pleurostigmophora) to be the sister group of the Scutigeromorpha. Accepted: 2 June 1996     

Morphological comparison of the buccal apparatus in two bivalve commensal Teleostei, Encheliophis dubius and Onuxodon fowleri (Ophidiiformes, Carapidae)

Onuxodon fowleri and Encheliophis dubius are two Carapidae species that live in bivalve hosts and their diet is made of the same type of prey. The aim of this study is to compare their cephalic morphology to see whether: (1) the head anatomy of both species is related to the constraints of their way of life and (2) there are differences between these species and commensal carapids that shelter in other invertebrates. The components of their skeletons and muscles are similar, but differ in size and are arranged differently. In O. fowleri, the buccal cavity is smaller than in E. dubius, the jaws (bearing very large anterior teeth) are larger, the quadrato- mandibular joint lies further to the rear and the fibres of muscle bundles A₃α, A₂α and A₂β are more vertical and insert higher on the neurocranium. The buccal system of O. fowleri appears better suited for ingesting food by biting and grasping. That of E. dubius seems better adapted to a feeding mechanism where sucking would have a more important role. The E. dubius head morphology is more similar to the cephalic anatomy of non-bivalve commensal species than to O. fowleri features. Diet constraints may have greater influence than the different host constraints on the head construction. A simulated backwards rotation of the posterior part of the E. dubius suspensorium around the posterior joint between the hyomandibular and the neurocranium brings the jaws and the cheeks to coincide with those of O. fowleri. This model could be indicative of how structure modifications and their influences on annex pieces could in part have a role in the biodiversity. Accepted: 10 December 1999     

Functional morphology of the female reproductive system of a crab with highly extensible seminal receptacles and extreme sperm storage capacity

We studied the functional morphology of the female reproductive system of the purple stone crab Danielethus crenulatus . The most remarkable feature is the relative storage capacity and extensibility of the seminal receptacles. These receptacles are a pair of simple sacs that lack internal structures dividing the internal lumen. Differences in seminal receptacle size and contents are accompanied by conspicuous changes in receptacle lining at a tissue level. Full seminal receptacles contain discrete sperm masses formed by hardened fluid and densely packed spermatophores. Different sperm masses are likely from different mates and their stratified disposition within the seminal receptacles is compatible with rival sperm displacement and last sperm precedence. Additionally, the anatomical structure of the vulva and vagina suggest active female control over copula. We discuss our results in the general context of sperm storage in brachyurans and the implications for the mating system of this species.     

Iron Oxidation and Deposition in the Biofilm Covering Montacuta ferruginosa (Mollusca,Bivalvia)

The shell of the bivalve Montacuta ferruginosa is covered with a rust-colored biofilm. This biofilm includes filamentous bacteria and protozoa encrusted with a mineral, rich in ferric ion and phosphate. The aim of this research was to study two possible microbial iron precipitation pathways in the biofilm, namely, microbial iron oxidation and microbial degradation of organic Fe(III) complexes. The iron-oxidizing activity was assayed spectrophotometrically by monitoring the formation of the dye Wurster blue in biofilm extracts. Iron-oxidizing activity was effectively detected in extracts obtained by oxalic acid treatment of biofilm fragments. Extracts obtained without oxalic acid treatment, heated extracts, or extracts supplemented with HgCl 2 did not show any activity. This suggests that an iron-oxidizing factor (IOF), possibly an enzyme, coprecipitated with the mineral. Additional information gathered by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel-filtration chromatography, and UV spectrophotometry indicate that the IOF would be a small peptide or glycopeptide (1,350 Da). Microbial degradation of organic Fe(III) complexes was assayed with biofilm fragments incubated in a medium containing ferric citrate. Analysis of the supernatants after various intervals revealed that the complex was degraded by living microorganisms much faster than in the heat-killed negative controls. We conclude that ferric iron precipitation in the biofilm may proceed by way of microbial Fe(II) oxidation as well as microbial degradation of organic Fe(III) complexes.     

Spermiogenesis and sperm ultrastructure in ten species of Loricariidae (Siluriformes, Teleostei)

The current study describes the ultrastructural characteristics of spermatogenesis, spermiogenesis, and spermatozoa in specimens of siluriform taxa Neoplecostominae, Hypoptopomatinae, Otothyrinae, Loricariinae, and Hypostominae. Our data show that the characteristics of spermatogenesis and spermiogenesis and spermatozoa ultrastructure of Neoplecostominae are more common to Hypoptopomatinae and Otothyrinae than to Loricariinae and Hypostominae. Furthermore, Loricariinae and Hypostominae have more characteristics in common than with any other group of Loricariidae. These data reinforce the phylogenetic hypotheses of relationships among the subfamilies of Loricariidae. Considering the available data in Loricarioidei, Loricariidae presents ultrastructural characteristics of spermatogenesis and spermiogenesis that are also observed in Astroblepidae, its sister group. However, the most of the characteristics of spermatozoa ultrastructure found in Astroblepidae are also observed in Scoloplacidae, the sister group of a clade composed of Astroblepidae and Loricariidae.     

On sperm ultrastructure,spermiogenesis and the spermatophore of Heterolaophonte minuta (Copepoda,Harpacticoida)

Summary The spermatophore, mature spermatozoon and spermiogenesis of Heterolaophonte minuta have been investigated by light and electron microscopy. The spermatophore contains three different secretions which are responsible for the discharge of the contents of the spermatophore, the formation of the fertilization tube and the storage of the spermatozoa. The spermatozoon represents a type new for the Copepoda. It is a filiform cell about 25 m in length, ellipsoid in transverse section and tapered at the posterior end. The elongated nucleus contains chromatin fibrils and does not possess a nuclear envelope. Posterior to the nucleus, six mitochondria are placed one after the other. The posterior part of the spermatozoon contains parallel pseudomembranes. The gamete is not helically twisted and is without a flagellum and centrioles. The most remarkable feature of the spermatozoon is an osmiophilic cap in front of the nucleus. This cap corresponds to the acrosome of the spermatozoon. Early stages of spermiogenesis take place in the testis, where the spermatids are incorporated into accessory cells. The origin of the chromatin fibrils and the glycocalyx, as well as the breakdown of the nuclear envelope and centrioles, represent the final steps of spermiogenesis which occur in the vas deferens.     

Parasitizing of trematodes provokes warts on the hinge plate of the bivalve mollusk <Emphasis Type="Italic">Macoma balthica</Emphasis> Linnaeus, 1758 (Veneroida,Tellinidae)

The hypothesis on non-random correlation between abnormalities in the structure of hinge plate and infection of mollusks Macoma balthica with trematodes of the family Gymnophallidae has been tested on the basis of material from the Barents Sea. Significant correlation between the presence of warts and infection was established upon intraand interpopulation comparison. The hypothesis states that parasitizing of trematodes in the extrapallial cavity of mollusks influences the mantle functioning and provokes abnormalities in the hinge plate structure.