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Comunicación dada en: euromal - 8th European Congress of Malacological Studies (10-14 September 2017, Kraków, Poland)., The global decline of freshwater mussels can be partially attributed to their complex life cycle. Their survival from glochidium to adulthood is like a long obstacle race, with juvenile mortality as a key critical point. Mass mortality shortly after entering into a juvenile state has been reported in both wild and captive populations, thus weakening the effec - tive bivalve population. A similar phenomenon oc - curs during metamorphosis in natural and hatchery populations of juvenile marine bivalves. Based on a morphological analysis of newly formed juveniles of the freshwater species Margaritifera margaritifera (Margaritiferidae) and Unio mancus (Unionidae), we show that a second metamorphosis, consisting of drastic morphological changes, occurs that leads to suspension feeding in place of deposit feeding by the ciliated foot. We hypothesise that suspension feed - ing in these two species develops and improves grad - ually due to several morphological features including the contact between cilia of the inner gill posterior filaments,¬ the¬ inner¬ gill¬ reflection,¬ the¬ appearance¬ of¬ the ctenidial ventral groove and the formation of the pedal palps. Regardless of the presence of available food, a suspension feeding mode replaces deposit feeding, and juveniles unable to successfully transi - tion morphologically or adapt to the feeding changes perish.

The morphological development and the sequence of organogenesis from glochidium to the early juvenile stage of the freshwater pearl mussel, Hyriopsis bialatus, were observed. Larvae of H. bialatus were cultured in standard tissue culture medium (M199) supplemented with common carp (Cyprinus carpio) plasma and they showed transformation within 10 days. Larval samples were collected every 2 days during glochidia development and subjected to histological processing. Three types of cell masses were developed during this period: the ventral plate (the foot rudiment), lateral pits (the gill rudiment), and the oral plate or endodermic sac (the origin of the digestive tract). The ventral plate gave rise to two foot lobes which fused into a single lobe. The gills were developed from the lateral pits next to the ventral plate, forming a pair of gill buds that became elongated and turned into gill bars. The digestive tract began with the formation of mouth by invagination of the oral plate (or endodermic sac) and fo...

Larvae of the freshwater mussel Utterbackia imbecillis metamorphose to juveniles either during their attachment to a host fish, or in vitro in a culture medium. This transformation includes degeneration of larval structures and development of the juvenile morphology. Early in metamorphosis the cells comprising the larval mantle enlarge and project into the mantle cavity, forming a structure referred to as the mushroom body. Its cells, which are ultrastruc- turally very similar to digestive cells of adult bivalves, are involved in pinocytosis or phago- cytosis of the larval adductor muscle and of tissue from the host fish that is enclosed between the larval shells. Ingested material is passed from pinosomes to heterophagosomes which in turn fuse with heterolysosomes, where final degradation of ingested material occurs. Acid phos- phatase activity was detected in heterophagosomes and heterolysosomes of all animals exam- ined. In larvae that metamorphosed in vitro, the apical cytoplasm of the cells of the mushroom body, and the extracellular spaces among them, also exhibited acid phosphatase activity. Larvae reared on a host fish accumulated substantial deposits of lipids and glycogen within larval mantle cells during metamorphosis, whereas larvae reared in vitro did not. The larval mantle cells which constitute the mushroom body appear to be the primary sites of intracellular di- gestion of the larval adductor muscle and host tissue during metamorphosis.

The metamorphosis of the glochidium of the critically endangered Margaritifera auricularia in the gills of a host is studied here for the first time. Siberian sturgeon, Acipenser baeri, were infected with glochidia and regularly inspected using scanning and optical microscopy. The mature glochidia immediately attach to the epithelium of the sturgeon gill filaments, piercing the secondary lamellae and the connective tissues, blood cells, and vessels within the lamellae. Once the epithelium is pierced, overlapping host lamellae cover the glochidium and form a cyst. Metamorphosis takes place inside the cyst. Sixteen days after infection the glochidium becomes spherical in shape and the larval muscle is reabsorbed. The two adductor muscles of the juvenile are observed 34 days after infection at 16–20°C. Metamorphosis is complete in approximately 51 days at 18–22°C and in 65 days at 16–17°C. Released juveniles have a spherical shell with a thin rim of new shell material and a finely ciliated foot. Juvenile mean measurements are: length = 190 μm, width = 193 μm, and height = 210 μm. J. Morphol. 254:259–265, 2002. © 2002 Wiley-Liss, Inc.

The glochidium larvae of freshwater mussels of the family Unionidae need to find suitable hosts to attach themselves and metamorphose into free-living juveniles. The specificity of the host-parasite relationship was investigated for the Iberian Unio tumidiformis Castro, 1885 by means of experimental infections and also by analyzing naturally infected fish. The process of encapsulation of glochidia was studied using scanning electron microscopy. Unio tumidiformis has proven to be an unusual host-specific unionid mussel, apparently parasitizing only fish of the genus Squalius Bonaparte, 1837. Successful encapsulation or complete metamorphosis was observed in five fish taxa: S. aradensis (Coelho, Bogutskaya, Rodrigues et Collares-Pereira), S. caroliterti (Doadrio), S. pyrenaicus (Günther), S. torgalensis (Coelho, Bogutskaya, Rodrigues et Collares-Pereira) and S. alburnoides (Steindachner) complex (only for the nuclear hybrids with at least one copy of the S. pyrenaicus genome). Complete metamorphose was achieved in 6 to 14 days at mean temperatures ranging from 21.8 to 26.1 °C. The current study provides support for cell migration being the main force of cyst formation and shows the influence of potential host's genome in response to the infection process to determine the success of the metamorphosis ©Institute of Parasitology, Biology Centre ASCR.

To metamorphose into juveniles and subsequently mature into adults, the glochidia larvae of freshwater mussels in the order Unionoida must temporarily parasitize the gills, fins, or other external structures of fish. Once attached to the fish, the glochidium is encapsulated by host fish epithelial tissue. The migration of epithelial cells of the bluegill sunfish Lepomis macrochirus over glochidia of Utterbackia imbecillis was examined by time-lapse video microscopy, and the morphology was examined by scanning electron microscopy. Initially, the leading edge epithelial cells migrating over the larvae became rounded and the cells moved as a sheet until the attached glochidium was completely covered. Cyst formation on host fish that had been repeatedly exposed to mussel larvae was significantly delayed and morphologically irregular compared to that on naive fish. Cyst formation on other species of fish that are less successful as hosts was examined. In general, it took longer for glochidia to become encapsulated on these less suitable potential hosts. The delay and irregularities in cyst formation on resistant fish and nonhost fish species may result in increased mortality and reduced success of metamorphosis of glochidia.

7 páginas, 4 figuras, The metamorphosis of the glochidiumof the critically endangered Margaritifera auricularia in the gills of a host is studied here for the first time. Siberian sturgeon, Acipenser baeri, were infected with glochidia and regularly inspected using scanning and optical microscopy. The mature glochidia immediately attach to the epithelium of the sturgeon gill filaments, piercing the secondary lamellae and the connective tissues, blood cells, and vessels within the lamellae. Once the epithelium is pierced, overlapping host lamellae cover the glochidium and form a cyst. Metamorphosis takes place inside the cyst. Sixteen days after infection the glochidium becomes spherical in shape and the larval muscle is reabsorbed. The two adductor muscles of the juvenile are observed 34 days after infection at 16–20°C. Metamorphosis is complete in approximately 51 days at 18–22°C and in 65 days at 16–17°C. Released juveniles have a spherical shell with a thin rim of new shell material and a finely ciliated foot. Juvenile mean measurements are: length 190 m, width 193 m, and height 210 m. J. Morphol. 254: 259–265, 2002. © 2002 Wiley-Liss, Inc., Demografía, hábitat y ciclo vital de Margaritifera auricularia and the Fauna Ibérica Project (DGES PB95-0235)

The glochidium ofMargaritifera auriculariais described for the first time by using light microscopy, scanning electron microscopy and histological techniques. The larval mantle is formed by only two layers of cells; the inner one being much thicker, with microvilli. All cell masses of the glochidium are temporary aggregations that are the rudiments of organs of the subsequent juveniles which will be released after metamorphosis in the host tissues. In the glochidium there are three main masses of cells: (i) the muscle, which is in an anterior position; (ii) the oral plate in the centre of the larva; and (iii) the more ventrally and posteriorly situated ventral plate, or foot rudiment, flanged with lateral pits all bearing dense cilia. No rudimentary organs such as the pericardium, the kidney, the heart or nerve ganglia have developed. There are no visible hooks in the valve margins, but by using light microscopy we observed minute teeth covered by a rim of the periostracum. Near the margin of the shell there are two pairs of sensory hair tufts only observable by scanning electron microscopy. The glochidium ofM. auriculariais the largest of the family Margaritiferidae and intermediate between the glochidium of the known species of this family and those of Unionidae.