Proctoeces maculatus is a trematode from the Proctoeces genus. The parasite affects different types of marine mussels and initiates a host-parasite relationship. In addition, the parasite has been isolated from mollusks such as Scrobicularia spana suggesting that parasite has both vertebrate and invertebrate hosts (White 457). Proctoeces maculatus was first described in the year 1901 as a distinct species by Loos as a trematode that causes parasitic infection in the marine fish families like Sparidae and Labridae (Stunkard and Uzmann 184). In addition it was isolated from the marine fish species Mytilus edulis.
For a long time classification of the trematode has been a controversy among the research community due to the various morphological forms of the species that have been identified. Regardless of this, researchers have come to identify characteristic morphological patterns that have led to clear identification of the Proctoeces maculates as a distinct species in the Proctoeces genus (Shigeru and Egusa 1250).
Studies have elaborated the morphology of the trematode. It was observed that Proctoeces maculates a cuticula that is devoid of any fortifications. It has dominant and massive suckers. At the position of the exterior testis, there is a distinct dual morphology (bifurcation) of the vessels involved in excretion processes. The crura and the stem have on their outer surfaces, a thin lining composed of epithelial cells.
The epithelium has a characteristic even appearance when the wall is bloated. Proctoeces maculates’ genital pore occurs at the position lying between the pharynx and the acetabulum. The genital pore has a characteristic lateral orientation. The testes occur together with varying orientations (Lang and Dennis 70). They occur obliquely, contiguously or completely delineated from each other. The sperm ducts are connected to the cirrus sac and they originate from the anterior location from which they stretch resulting in a common canal that then feeds into the cirrus sac. The canal exits at the posterior end of the cirrus sac as spiraled seminal vesicle that has spermatozoa.
The canal is then channeled into another canal that is reinforced with a broad muscular wall. Highly specialized cells involved in secretion occur throughout the whole structure. These have chromatic granules at the end of the canal which is connected to the cirrus sac. After the cirrus sac there is a protrusion of the canal into an extended duct commonly called the hermaphroditic atrial canal (Lang and Dennis 69). There is a thin lumen between the cirrus sac and the canal with thick walls. This lumen acts as a collector of discharges from the secretory cells. Proctoeces maculates has an ovary that is located just before the testis. It is located in the posterior end of the parasite specifically in the anterior portion.
The posterior face is the site of origin of the oviduct. The oviduct has a characteristic ventral-medial orientation as it joins the fertilization area. Laurer’s canal protrudes from the region of fertilization in a dorsal-anterior manner and ends just above the ovary. The Mehlis’ gland has a connection to the ovary via the universal vitelline canal. To allow for egg formation, the oviduct enlarges at the end of the vitelline canal to form the ootype, the site for formation of the eggs (Lang and Dennis 67).
The uterus is posterior to the termination of the body. At this position there are spiraling ducts on both sides in tandem with the median trunk that lines the underside of the cirrus sac and empties into the central position of the hermaphroditic duct just before the genital pore. The eggs have a myriad of appearances either due to malformations or natural variation in sizes (La Rue 307).
The life cycle of Proctoeces maculates has been studied but with conflicting outcomes of the final host of the trematode. Some studies have shown that the final host of the parasite is the marine fishes while others show that the final host is the bivalve organisms such as Scrobicularia spana. Despite these findings, there is a consensus that Proctoeces maculates establish itself as a parasite in the fish species Mytilus edulis, where it results in infection that may eventually lead to death. The life cycle starts with eggs being produced by adult trematodes all through winter after which the adults succumb to death. The eggs hatch releasing miracidia. The miracidia in turn develop to form sporocysts.
The sporocysts are mainly found in large mussels and little or no sporocysts are found in the small mussels and this has been attributed to sexual immaturity of these small mussels. The sporocysts develop into the Cercariae in the first intermediate host. The Cercariae represents the larval stage of Proctoeces maculates. At this stage the parasite is unable to infect as it is immature. This stage occurs mainly during winter and is responsible for the low rates of infection observed during this period (Oliva, Valdivia and Cárdenas 737).
Reproduction of Proctoeces maculatus is greatly affected by its location in terms of tidal positions namely high, low, and floating subtidal locations. Production of Cercariae occurs mostly in the intertidal and subtidal periods. The cercarie at this point may either remain in the same host or migrate to a different host where it develops into an adult. The adult release the eggs completing the cycle. The purpose of the research is to find out the prevalence (absent or present) and intensity of the parasite infecting Mytilus edulis from the different locations.
Works Cited
La Rue, Gregory. “The classification of digenetic Trematoda: A review and new system. Experimental Parasitology 6.1 (1957): 306-309.
Lang, William and Emmet, Dennis. “Morphology and seasonal incidence of infection of Proctoeces maculatus (Looss, 1901) Odhner, 1911 (Trematoda) in Mytilus edulis.” OPHELIA 15.1 (1976): 65-75.
Oliva, Marcelo, Valdivia, Isabel and Cárdenas, Leyla. “Molecular and experimental evidence refuse the life cycle of Proctoeces lintoni (Fellodistomidae) in Chile.” Parasitology Research 106.1 (2010):737–740.
Shigeru, Shimura and Syuzo, Egusa. “A new digenetic trematode Proctoeces ichiharai.” Bulletin of the Japanese Society of Scientific Fisheries 45.10 (1979): 1249-1253.
Stunkard, Horace and Uzmann, Joseph. “The life-cycle of the digenetic trematode, Proctoeces maculatus (Looss, 1901) Odhner, 1911 [Syn. P. subtenuis (Linton, 1907) Hanson, 1950], and description of Cercaria adranocerca n. Sp.” Ibid 116.1 (1959): 184-193.
White, Carrey. “On the ecology of the adult digenetic trematode Proctoeces subtenuis from a lamellibranch host Scrobicularia spana.’’ Journal of Marine Biology 52.2 (1972): 457-467.