Prevalence, morphology, and molecular analysis of Serrasentis sagittifer (Acanthocephala: Palaeacanthocephala: Rhadinorhynchidae), a parasite of the gilthead sea bream Sparus aurata (Sparidae).
Seventy specimens of the gilthead sea bream Sparus aurata of the Red Sea were collected during the period from March to November 2013; they were dissected and examined for parasitic acanthocephalans. Only 40 (57.14%) specimens were found to be naturally infected with Serrasentis sagittifer belonging to family Rhadinorhynchidae. The infection was recorded in the intestine, pyloric ceca, and the external surfaces of some internal organs of the infected fish. Seasonally, the prevalence of infection was increased to 77.14% during summer season and decreased to 37.14% during winter. Light and scanning electron microscopic investigation revealed that the adult worm was elongated (with broad anterior and narrow posterior ends) and measured 6.9-8.6 (7.6 ± 0.2) × 0.57-0.73 (0.63 ± 0.02) mm for male and 10.2-12.1 (11.5 ± 0.2) × 0.71-0.82 (0.76 ± 0.02) mm for female. Proboscis was long and cylindrical with a length of 0.97-1.6 mm (1.2 ± 0.2) for male and 1.12-1.17 mm (1.14 ± 0.02) for female. It was covered with numerous uniform spines arranged longitudinally as 9-11 rows each equipped by 15-18 spines. Spines were triangular, arrow-shaped, strong, and covered with cuticular theca; they decreased in size from the apex to the base of the proboscis. The proboscis is followed by a short spineless neck region followed by the body proper which is supported by multiple combs of spines (16-20) on its ventral surface. Molecular analysis of 18S rDNA sequence for the parasite demonstrated a close identity (>83%) between the present acanthocephalan and other previously described species within class Palaeacanthocephala with 98% identity with the previously recorded S. sagittifer (acc. no. JX014227) which is supported by the morphological data and the presence of trunk spines arranged within rows (comb-like) and the presence of four cement glands in the males. So, according to the records of morphological and molecular analyses, the present parasite is classified as S. sagittifer belonging to class Palaeacanthocephala and family Rhadinorhynchidae with a new host record from the gilthead sea bream S. aurata of the Red Sea.