Four new species of virgulate xiphidiocercariae infecting the freshwater snail, Bithynia (Digoniostoma) pulchella (Benson, 1836) in Malabar, Kerala

The present paper describes four new species of virgulate xiphidiocercariae infecting the freshwater gastropod, Bithynia (Digoniostoma) pulchella (Benson, 1836) collected from Malabar, Kerala. Cercaria sp. XXII Malabar n. sp. has a spinose body and tail; four pairs of penetration glands; short, narrow oesophagus; a pair of short, unequal caeca; bicornuate excretory vesicle and 18 pairs of flame cells. Cercaria sp. XXIII Malabar n. sp. is characterized by an oval, spinose body; aspinose tail; dagger-shaped stylet; medially fused virgula; globular pharynx; short oesophagus; three pairs of penetration glands; bicornuate, ‘V’-shaped excretory bladder, and 18 pairs of flame cells. Cercaria sp. XXIV Malabar n. sp. has a spinose body and tail, medially fused virgula, muscular pharynx, short prepharynx and oesophagus; four pairs of penetration glands; bicornuate, ‘V’-shaped excretory bladder, and 12 pairs of flame cells. Cercaria sp. XXV Malabar n. sp. has a spinose body, aspinose tail, sac-like virgula; globular pharynx, narrow oesophagus; short caeca; four pairs of penetration glands; transversely elongated, bicornuate excretory bladder, and 12 pairs of flame cells. All four cercariae developed in sporocysts within the digestive gland of B. (D.) pulchella. Morphology and morphometry of the cercariae are compared with related species to establish their systematic position