Naim S. Ismail

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.

Heavy metal concentrations in common freshwater snails of Azraq Oasis, Jordan

Heavy metal concentrations in three freshwater snails, an aquatic plant, sediment, and water from Azraq Oasis pools in the Jordanian desert were measured by atomic absorption spectrophotometry. There were significant differences in metal accumulation among snail species. These snails are ranked according to their metal accumulation capacity in the order: Melanoides tuberculata > Melanopsis praemorsa > Theodoxus jordani. Although there were no significant differences among the size classes of these snails in metal concentrations, larger snails contained generally higher levels of metals than the smaller ones. The concentration factors for the selected snails exceeded 103, while it ranged from 0.1–10.2 × 103 for Typha angustata plants. Among sampling sites, metal concentrations in M. praemorsa, T. angustata, sediment, and water were not significantly different, except for Fe in M. praemorsa which was highest at station 3, and Cd and Cr which were highest in water and sediment of station 4. The seasonal variation in metal content was found to be species and metal-dependent.

Development, growth, and migration of Philophthalmus gralli (Trematoda) from Jordan in the eyes of chicks.

The growth of Philophthalmus gralli from Jordan was studied experimentally by inoculating 10 excysted metacercariae around the right eye of 47 day-old chicks. The growth rate was slow in the first three days during which flukes did not exceed 0.30 mm long. Then growth became rapid reaching 2.70 mm long on day 24. This was followed by a low growth rate during which the flukes grew from 2.70 mm to 2.90 mm on day 40. The flukes started to appear in the left eye on day 12 post-inoculation of metacercariae in the right eye. The recovery of flukes in the left eye increased from 5% on day 12 to 30% on day 32. The development of P. gralli from Jordan was the same as of other species of Philophthalmus. However, a sixth stage, post-maturation stage, is suggested in addition to the 5 developmental stages of Philophthalmus. The ratio of the transverse diameter of the ovary to that of testes in the post-maturation stage was 1:1.1-1:1.2.

Larval stages of digenetic trematodes ofMelanopsis praemorsa (L. 1758, Buccinum) (Thiaridae) snails from Yarmouk River, Jordan

Seven new types of cercariae are described from the freshwater snailMelanopsis praemorsa (L. 1758, Buccinum) collected from Yarmouk River, north Jordan, during 1982: two virgulate xiphidiocercariae, a microcotylous xiphidiocercaria belonging to the “Pusilla” sub-type, a brevifurcate lophocercous cercaria, a microcercous cercaria, and two pleurolophocercous cercariae. These cercariae are namedCercaria melanopsi I throughVII. Details are presented on the morphology and behavior of the cercariae as well as on their development within the snail. The relationships between these cercariae and adult trematodes reported from Jordan are discussed.

Larval stages of digenetic trematodes ofTheodoxus jordani (Sowerby 1836) snails from Yarmouk River, Jordan

Two types of cercariae are described from the freshwater prosobranchTheodoxus jordani (Sowerby 1836) collected from the Yarmouk River during 1982: a tail-less cercaria belonging to themutabile group and a microcercous cercaria belonging to theCercaria brachyura group. These two cercariae were given the namesCercaria theodoxi I andC. theodoxi II, respectively. Details are presented on the morphology and behaviour of the cercariae as well as on their development within the snail. The relationships between these cercariae and adult trematodes reported from Jordan are discussed.