A new acanthocolpid cercaria (Digenea) from Cantharus dorbignyi (Prosobranchia) in the Western Mediterranean

A new cercaria is recorded from the prosobranch snail Cantharus dorbignyi from the sublittoral region off the coast of Corsica. The redia, cercaria and metacercaria (the latter experimentally developed in the labrid fishes Symphodus ocellatus and S. rostratus) are described, along with the behaviour of naturally emitted cercariae. In view of the morphology of the larval stages, the parasite is thought likely to be an acanthocolpid. The morphology of the cercaria and metacercaria are compared with both known and suspected acanthocolpid cercariae and with adult acanthocolpids known to occur in the Mediterranean. Morphological and circumstantial evidence suggests that this cercaria may be a species of the genus Tormopsolus.     

Some rare larval trematodes of prosobranch snails, Semisulcospira spp., in the Lake Biwa drainage system, central Japan

A total of 17737 individuals of prosobranch snails, Semisulcospira spp., were collected from Lake Biwa and its tributaries, central Japan, from 1995 to 1999. They were examined for trematode larvae. One species of Aspidogastrea and 28 species of Digenea were detected. This paper briefly describes five of the 28 digeneans: a tetracotyle metacercaria from S. niponica, Cercaria A (cystophorous cercaria) from S. reticulata, Cercaria B (echinostomatid cercaria) from S. libertina, Cercaria C (magnacauda cercaria) from S. niponica and Cercaria D (mutabile cercarium) from S. nakasekoae. They were rare and every one of them was obtained from one snail only once.     

Studies on Cercariae from Kuwait Bay. XI. Description and surface topography of Cercaria kuwaitae XI sp.n. (Digenea: Echinostomatidae)

A new echinostome cercaria, Cercaria kuwaitae XI sp.n., from the prosobranch gastropod Cerithidea cingulata (Gmelin) from Kuwait Bay is described. The new cercaria is characterized by 23 collar spines and primary excretory tubules with distinct diverticula. The cercaria encysts in the snail host and is similar to those of Acanthoparyphium sp. The surface topography of the redia, cercaria and metacercarial cyst wall is studied by scanning electron microscopy. This is the first echinostome cercaria to be recorded in a gastropod from the Arabian Gulf region.     

Experimental data on the life-cycle of Petasiger grandivesicularis Ishii, 1935 (Trematoda: Echinostomatidae)

Larval stages of an echinostome were found in Planorbis planorbis in a brackish water lake on the Black Sea coast of Bulgaria. The cercaria is a large-tailed form with 19 collar spines. The life-cycle was completed in the laboratory using aquarium-reared fishes (Lebistes reticulatus, Puntius tetrazona tetrazona, P. pentazona pentazona, P. nigrofasciatus, Carassius auratus auratus and Xiphophorus helleri) as second intermediate hosts and canaries as definitive hosts. The redia, cercaria, metacercaria and experimentally reared adults are described. The species is determined as Petasiger grandivesicularis Ishii, 1935, and its cercaria is compared in detail with those of related forms. A key to the known large-tailed echinostome cercariae from the Palaearctic Region is presented.     

A new cercaria and metacercaria of Acanthoparyphium (Echinostomatidae) found in an intertidal snail Zeacumantus subcarinatus (Batillaridae) from New Zealand

A new 23-collar-spined cercaria and metacercaria are described from intertidal molluscs of the coast of New Zealand. The new cercaria found emerging from the mud snails Zeacumantus subcarinatus (Sowerby) (Prosobranchia: Batillariidae) is characterized mainly by the number and arrangement of the cephalic glands, the size of the suckers, and the size and number of the collar spines. The cercaria encysts in the cockle Austrovenus stutchburyi (Wood) (Bivalvia: Veneridae) which lives in sympatry with the first intermediate host throughout New Zealand. Laboratory infections of cockles by cercariae from naturally infected snails resulted in metacercariae identical to those found in naturally infected cockles. The main features of the cercaria and metacercaria are the presence of a reniform collar with 23 spines, two pairs of small cephalic glands at the oral sucker level, another two pairs of much longer ones posterior to the pharynx, and the excretory vesicle Y-shaped with the main collecting canals extending to the anterior level of the ventral sucker. Each of the main collecting canals had 10-11 pairs of bilateral diverticula between the anterior edge of the ventral sucker and anterior body end. A brief discussion of its possible life cycle and ecology is also provided.     

A comparative study of cercarial chaetotaxy in two species of Petasiger Dietz, 1909 (Digenea: Echinostomatidae)

The chaetotaxy of two types of cercariae found in naturally infected Planorbis planorbis in a brackish water lake in Bulgaria is described. The comparison of the sensory patterns shows the distinct species status of the cercariae of P. grandivesicularis and Petasiger sp. The morphology of the cercaria of Petasiger sp. is described and compared with that of known large-tailed Petasiger cercariae from the Palaearctic. It is suggested that the unidentified species of cercaria is probably a larval stage of P. pungens.     

Characteristics of the seasonal development of Schistogonimus rarus (Trematoda: Prosthogonimidae). An essay on quantitative estimation of the trematode in the ecosystem of the Malye Chany lake (south of Western Siberia)

Quantitative estimation of the trematode Schistogonimus rarus at the stage of cercaria is carried out in the ecosystem of the Malye Chany lake, south of Western Siberia, on the base of long-term data obtained in 1995-2002. Average daily emission of the S. rarus cercaria was shown to be significantly higher in larger mollusc hosts (p < 0.01), by the results of laboratory investigations. Moreover, significant decrease of the average daily emission of the S. rarus cercaria from June to July is established (p < 0.01). It was revealed, that emission of the S. rarus cercaria in the south of Western Siberia (both in natural and laboratory conditions) lasts no more than 50 days and is finished in August. The infestation rate of the mollusc host Bithynia troschelii by the S. rarus parthenites varied from 0.28 to 1.44 % in different years and correlated with the water temperature at first ten days of June (r = 0.75). Flow of the S. rarus cercaria (specimens per square meter) was estimated on the base of the quantitative characteristics of the cercaria emission, data on the infestation rate of the host population, and data on the host abundance. The flow of the cercaria varied from 6000 (in 1998) up to 330000 (in 2000) per season and correlated with the water temperature in third ten days of June (r = 0.71).     

Identification and description of Bucephalus minimus (Digenea: Bucephalidae) life cycle in Portugal: morphological, histopathological, and molecular data

The cercaria of Bucephalus minimus infects the digestive gland and gonads of its first intermediate host, the edible cockle, Cerastoderma edule. Light microscopy (LM) and scanning electron microscopy (SEM) of the cercaria showed a tail formed by a central stem, with 2 long contractile arms presenting distinct morphological surfaces. The encysted metacercaria naturally infected the flathead grey mullet, Mugil cephalus. The cysts found in the heart, liver, and spleen were shown to be identical by the internal transcribed spacer (ITS 1) sequence and morphological features and were associated with encapsulation, recruitment of cell infiltrates, and presence of melanomacrophages and adipose tissue. To establish the life cycle, we compared the ITS1 sequence in an adult from the known definitive host, Dicentrarchus labrax; encysted metacercariae from the liver, heart, and spleen of M. cephalus; and a cercaria from C. edule. With this comparison, we determined that they had a 100% similarity. Therefore, the ITSI sequence data clearly indicate that these 3 parasitic stages belong to the same species, i.e., B. minimus.     

Two species of heterophyid larval digeneans from a thiarid gastropod Thiara tuberculata (Müller) from India.

Two species of heterophyid cercariae, cercaria of Haplorchis taichui and Haplorchis pumilio are obtained from Thiara tuberculata from Visakhapatnam, India. This is the first report of cercariae of both the parasites from India. The characteristic features of H. taichui cercaria are the presence of two sets--one set of lateral and other dorsoventral cuadal finfolds, 15 acicular spines in three alternating rows and seven pairs of lobed penetration glands arranged in two longitudinal rows. H. pumilio cercaria is characterized by the presence of two sets of caudal finfolds, 15 acicular spines in three alternating rows and seven pairs of voluminous unicellular penetration glands.     

A review of the currently recognised opecoelid cercariae,including the identification and emergence ecology of Cercaria capricornia XII (Digenea: Opecoelidae) from Nassarius olivaceus (Gastropoda: Nassariidae) in Central Queensland,Australia

A new opecoelid cercaria, Cercaria capricornia XII, is reported from Nassarius olivaceus in Capricornia, Central Queensland, Australia. Combined molecular and morphological data indicate that this cercaria is a member of the subfamily Opecoelinae. Cercaria capricornia XII is the first known opecoeline cercaria reported from a nassariid gastropod. Cercaria capricornia XII can be distinguished from other opecoelid cercariae by the combination of the presence of a 2-pointed stylet, body length and width, and the size of the tail. The emergence pattern for C. capricornia XII in captivity was erratic; rapid emergences of thousands of cercariae were interspersed by periods that sometimes exceeded a month in which no emergence occurred. There was no detectable pattern to or stimulus of the emergence. The molluscan host range of opecoelids is analysed in detail. Gastropods from the Buccinoidea, Cerithioidea and Rissooidea are hosts to both opecoeline and plagioporine cercariae, but the dominant subfamily infecting the Cerithioidea and Rissooidea is the Plagioporinae. The dominant marine host gastropod superfamily for opecoeline cercariae is the Buccinoidea; the family Nassariidae is contained in the Buccinoidea. The range of gastropod superfamilies known as hosts of plagioporines is much broader than that for opecoelines, which may be explained by the relative size of the two opecoelid families and perhaps by indications that the Plagioporinae is polyphyletic.     

Cercaria sevillana n sp,a new cercaria (Digenea: Microphallidae) from Nassarius reticulatus (L) (Mollusca: Prosobranchia) in Portugal

Cercaria sevillana n. sp. (Digenea: Microphallidae) was discovered infecting the gonads and digestive gland of the prosobranch Nassarius reticulatus (L.) (Nassariidae) collected from the Ria de Aveiro, Portugal. Cercariae were obtained by natural emission and were studied under a differential interference contrast microscope and scanning electron microscope (SEM). C. sevillana n. sp. is identical to the cercaria found by Dolgikh (1965) in the same mollusc host from the Black Sea, but erroneously named C. misenensis Palombi, 1940, which is a parasite of Cerithium rupestre Risso, 1826 (Cerithiidae). Cercaria sevillana n. sp. can be distinguished from C. misenensis by its tail being shorter than the cercarial body, as well as by differences in the pattern of penetration glands the size and shape of the stylet and excretory vesicle, and its behavioural pattern. An unusual structure of the tail of this new cercaria was observed by SEM; it is characterised by the presence of annular folded membranes arranged as overlapping flounces around its central axis. This resembles the traditional skirts of the women of Seville. Such a morphological feature of the tail has not been previously observed, but may be a feature of many microphallid cercariae.     

Population dynamics of Melanoides tuberculata (Thiaridae) snails in a desert spring,United Arab Emirates and infection with larval trematodes

A dense population of Melanoides tuberculata was found at a brackish (5.93–6.98%) desert spring in the United Arab Emirates. A total of 232–300 snails were measured and examined for larval trematodes during the period January 1990 to January 1991. The relative abundance of various size classes of the snail has shown that the mass release of young snails occurred twice a year, in April–May and September–October. Seven different forms of cercariae were found: A xiphidiocercaria, a brevifurcate cercaria, two pleurolophocercous cercariae, two gymnocephalous cercariae, and the cercaria of Philophthalmus gralli. The overall infection rate of this snail was 73.6% and ranged from 51.3 during February–March 1990 to 91.7% during January 1991. The xiphidiocercaria and the P. gralli cercaria were the most abundant and were found in 21.1% and 29.7%, respectively, of the examined snails. A relatively high rate (9.5%) of double infection was found. Cases of triple infection were also encountered.     

Argentophilic and scanning electron microscopic observations of the tegumentary papillae of Echinostoma revolutum (Trematoda) cercariae

Argentophilic staining and scanning electron microscopy (SEM) were used to study the tegumentary papillae of Echinostoma revolutum cercariae. The most abundant papilla was uniciliate and arranged bilaterally on the body and tail of the cercaria. The distribution of these papillae was similar to that seen in other 37-collar spined echinostome cercariae. SEM revealed a total of 18 multiciliate papillae--16 on the anterior end and 2 at the middle of the body. These papillae contained up to 18 cilia per papilla and have not been reported previously from any cercaria.     

Localization of photoreceptors in the cercariae of Proterometra macrostoma (Trematoda: Azygiidae)

The swimming behavior of the cercaria of the digenetic trematode Proterometra macrostoma changes in response to light. However, this cercaria does not possess obvious eyes or eyespots. Using behavioral assays, we were able to show that both intact and distome-removed cercariae swim significantly greater vertical distances under dim, red light than under brighter, white light. Electrophysiological experiments confirmed this result and further showed that the transverse band of the tail, known to control cercariae swimming behavior, was necessary and sufficient for the display of the light-dependent swimming behavior. Together, these data show that the distome is not required for light-dependent swimming behavior in P. macrostoma cercariae and indirectly demonstrates the presence of photoreceptors in the transverse band of the cercaria tail.     

Four trematode cercariae from the New Zealand intertidal snail Zeacumantus subcarinatus (Batillariidae)

Abstract

The cercariae and sporocysts (or rediae) of four trematode species are described from the intertidal snail Zeacumantus subcarinatus: a distome xiphidiocercaria assigned to the genus Renicola (family Renicolidae); a monostome xiphidiocercaria belonging either to the genus Microphallus or Megalophallus (family Microphallidae); a magnacercous cercaria of the genus Galactosomum (family Hetero‐phyidae); and a cercaria of the genus Philophthalmus (family Philophthalmidae). The morphological features of these cercariae are compared to previously described cercariae of the same genera. In addition, since the philophthalmid cercaria encysts readily on artificial substrates in the laboratory, the metacercaria of this species is also described. These cercariae are part of a diverse community of at least six digenean species parasitising the snail Z. subcarinatus that, together, have a major impact on the ecology and evolution of this snail.     

Life cycle of Genarchopsis goppo (Trematoda: Derogenidae) from Nara, Japan.

A cystophorous cercaria obtained from Semisulcospira libertina (Gould) from Tobihino, Nara, Honshu, Japan, was used to experimentally infect a freshwater goby Rhinogobius sp. OR via the copepods Mesocyclops leuckarti (Claus), Thermocyclops hyalinus (Rehberg), and Eucyclops sarrulatus (Fisher). It was shown to grow into Genarchopsis goppo Ozaki, 1925. The parasite was found to occur as a natural infection in the stomach of Rhinogobius sp. OR and Odontobutis obscura (Temminck and Schlegel) from Tobihino.     

甲醛胁迫下四种盆栽植物的生理动态反应

选择巢蕨(Neottopteris nidus)、巴西铁(Dralaena fragrans)、虎尾兰(Sansevieria trifasciata)和黑美人(Aglaonema commutatum)4种室内盆栽植物作为典型的试验材料,以15 mg·m-33甲醛分别进行熏蒸处理,测定单位干物质甲醛的吸收量、相对电导率、丙二醛含量和叶绿素含量等,以研究这些植物在甲醛胁迫下的生理动态反应。结果表明:在甲醛胁迫的4 d时间内,巢蕨和巴西铁的单位干物质甲醛吸收量均在第3天达到峰值,而黑美人和虎尾兰则一直在缓慢增加,其中以巢蕨吸收的量最多,巴西铁单位干物质甲醛吸收量最少; 4种植物的相对电导率、丙二醛的含量均随甲醛胁迫时间的增加而增加,以巢蕨的相对电导率最高,虎尾兰最低,但巴西铁的丙二醛的含量最高,巢蕨最低; 4种植物的叶绿素含量均随甲醛胁迫时间的增加而降低,其中黑美人降低幅度最高,虎尾兰最低。     

Genetic variability among cercariae of the Schistosomatidae (Trematoda: Digenea) causing swimmer's itch in Europe

Ribosomal DNA sequences of the internal transcribed spacer 1 (ITS1) were obtained from schistosome cercariae responsible for swimmer's itch in Europe. Two types of ITS1 (1100 and 1400), which differ by the number of repeated patterns were found among cercariae shedded by Lymnaea ovata and L. auricularia (Lymnaeidae). A phylogenetic analysis of the ITS1 region showed that sequences of each type form two well-defined clades. An adult of Trichobilharzia regenti isolated from the nasal vessels of Anas platyrhynchos (Anatidae) was found to correspond to the cercaria type 1400. The sequencing of several ITS1 clones from a single cercaria of each type, as well as a specific PCR-based test suggested that both ITS1 types do not co-occur within a single individual.     

Cercaria patellae Lebour, 1911 developing inPatella vulgata is the cercaria ofEchinostephilla patellae (Lebour, 1911) n. comb. (Digenea,Philophthalmidae)

The echinostome cercaria,Cercaria patellae Lebour, 1911, which develops in the limpetPatella vulgata (Prosobranchia, Diotocardia, Patellidae), was investigated by light and scanning microscopy. The highest prevalence of limpets with rediae/cercariae occurred on bare rocks on the upper part of the shore. The prevalence was higher in larger snails and in those which had an orange foot-sole. The cercariae penetrated into other gastropods,Aplysia punctata (Opisthobranchia, Cephalaspidea, Aplysiidae),Acanthodoris pilosa (Opisthobranchia, Nudibranchiata, Lamellidorididae) andP. vulgata. No differences in size were found between metacercariae which naturally infected onlyP. vulgata and five-day-old metacercariae from experimental infections. Inin vitro experiments excystation of metacercariae from natural infections took place as a passive process after a double treatment with pepsin and trypsin which caused the dissolution of the cyst wall. After metacercariae from natural infections were fed to one-day-old chickens, the young adults developed. Detailed morphometrical data on rediae, cercariae and metacercariae are compared with previously published measurements of living specimens. Chaetotaxy demonstrated a distinct distribution of tegumental papillae of cercariae, resembling that of the Echinostomatidae or Philophthalmidae. Scanning electron microscopy of adults revealed short, blunt spines anteriorly, while flattened serrated spines occurred on the posterior tegument. Morphometry revealed no major differences to previously published data. Considering all ecological data and comparing the morphological data with those of previous publications by different authors, we conclude thatC. patellae Lebour, 1911, the cercaria in the limpet, is a developmental stage of a digenean in the intestine of the oystercatcherHaematopus ostralegus and should be referred toEchinostephilla patellae (Lebour, 1911) n. comb.