The objectif in the present study is description of a new species of Sphincteristomum Oshmarin, Mamaev & Parukhin 1961, named Sphincteristomum mediterraneae, which is described in Oran bay, Algeria. It parasitizes the intestine of naturally infected Pagellus erythrinus, Teleostei, Sparidae. The Pagellus erythrinus is in important food fish in the Mediterranean. This genus belongs to the family Apocreadiidae, sub family Schistorchiinae, characterized by an obvious oral muscular sphincter, into a large oral sucker, a disc-shaped acetabulum under the intestinal bifurcation, an ocular pigment scattered in the forebody, a sequence ovary and two testes in tandem and a I-shaped excretory bladder. In the new species, the digestive apparatus displays a hexagonal peculiar aperture, followed by a longitudinal slit, a waved pharynx, two long and broad caeca, with a thick internal wall of endothelial cells. Each caecum has a sub terminal anus. The female genital apparatus displays a transversally elongated ovary, under the acetabulum. On the side of the ovary, there is a small Mehlis gland. Under the ovary, there are two transverse converging vitelloducts. Lateral and extracaecal vitelline follicles, are spread near the caeca. They converge in the hindbody. The relatively short uterus is preovarian, mainly. It contains few large yellow eggs. Its distal part is creased transversally, just before ending in genital atrium. The male genital apparatus shows two lobed heart-shaped testes, post ovarian, in tandem. From the anterior edge of each testis, two spermiducts climb up and converge into a naked, curved or sinuous seminal vesicle, followed by a short prostate surrounded by few prostatic cells, and a narrow ejaculatory duct, opening in genital atrium. The genital pore is close to the acetabulum and the intestinal bifurcation. No cirrus pouch. The excretory system shows a relatively short tubular I-shaped bladder, reaching the inferior level of the second testis. Two thin excretory arms are seen until the forebody of the worms. The terminal excretory pore is closed by a small sphincter. In the same P. eryrthrinus, immature worms devoid of genitalia, young worms with genitalia devoid of eggs and ovigerous worms, live together with senile specimens. These last ones show still, oral sucker, diffuse vitelline follicles and very small and scattered ocular pigment.