Cucullanus marajoara n . sp . ( Nematoda : Cucullanidae ) , a parasite of Colomesus psittacus ( Osteichthyes : Tetraodontiformes ) in the Marajó , Brazil Cucullanus marajoara n . sp . ( Nematoda : Cucullanidae ) , um parasito de Colomesus psittacus ( Osteichthyes : Tetraodontiformes ) no Marajó , Br

Cucullanus marajoara n. sp. (Cucullanidae) is reported to parasitize Colomesus psittacus (Tetraodontiformes), which is a fish species from the Marajó Archipelago, state of Pará, estuarine region of the Brazilian Amazon. The new species differs from similar species by the presence of a protruding upper lip on the cloacal opening, the distribution of the cloacal papillae: five pre-cloacal papillae pairs and 5 are ventral and located posteriorly to the pre-cloacal sucker and an unpaired papilla is located on the upper cloacal lip and five post-cloacal pairs, and a pair of lateral phasmids located between papillae pairs. Additionally, Cucullanus marajoara n. sp. is compared to other species of this genus described in Brazil, particularly Cucullanus ageneiosus and Cucullanus oswaldocruzi, which both occur in the same zoogeographic region of this study but parasitize fish of a different order (Siluriformes). Cucullanus dodsworthi and Cucullanus brevicaudatus are the only described species parasitizing fish of the order Tetradontiformes in Brazil, and the new species differs from these species by the distribution of the cloacal papillae and the host habitat. The description of Cucullanus marajoara n. sp. adds data to the biodiversity of described parasites that parasitize Tetradontiformes of the estuarine ichthyofauna in the Brazilian Amazon.

Colomesus psittacus commonly enters the fish traps along the shore, but they are not harvested because they produce a tetradoxina toxic to humans (SANTANA et al., 2010).The fishermen discard the fish outside of the traps.Because they were available abundantly and not part of the local source of food, we decided to investigate the parasite fauna of the species.During this study, a new species of Cucullanus was found; it is described herein and compared with other members of the genus recorded from the same zoogeographical region and the same group of hosts (Tetraodontiformes).

Materials and Methods
Twenty specimens of C. psittacus were caught by fishermen in the municipality of Soure (0°53'39" S, 48° 7'39" W), Marajó Archipelago, Pará state (Brazil).The fish were obtained from riverine fishermen who discarded them from their catch and were transported on ice to the Laboratório de Histologia e Embriologia Animal, Instituto da Saúde e Produção, Universidade Federal Rural da Amazônia, Campus Belém, Pará state, Brazil.The weight (g) and total length (cm) of the specimens were measured.After biometric analysis, the animals were necropsied to search for helminths.The digestive tract was isolated in petri dishes containing physiological solution and analyzed under a stereomicroscope (Leica -ES2).The collected helminths were fixed in an alcohol-formaldehyde-acetic acid (AFA) solution (930 mL of 70% ethanol, 50 mL of commercial formalin, and 20 mL of glacial acetic acid) stored at room temperature.Subsequently, the specimens were dehydrated in an ethanol series, clarified with Aman's lactophenol, and examined by light field microscopy using a Leica DM2500 microscope with a clear camera for scientific imaging and morphometric analysis.
Ten male specimens and ten female specimens were used for the morphometric analysis of the helminths.The measurements were made in millimeters as the means, with the ranges shown in parentheses.For scanning electron microscopy, the helminth specimens were washed in distilled water, postfixed in 1% osmium tetroxide, dehydrated to the critical point of CO 2 , metallized with gold + palladium, and analyzed using a TESCAN scanning electron microscope (VEGA 3) in the Laboratório de Microscópia Eletrônica de Varredura da Universidade Federal Rural da Amazônia.There are more than 100 putative species in the genus, so the suggestions of (YOOYEN et al., 2011;LACERDA et al., 2015), that morphological and morphometric comparisons should be made only among the different species that parasitize the same taxonomic group of hosts from the same zoogeographical region in which the host was found.The host fishes scientific name is in accordance with FishBase (FROESE & PAULY, 2018).

Survey data
Of the 20 specimens of C. psittacus collected in the Soure municipality, 90% (18 infected fish/ 20 examined fish) were parasitized by nematodes of the genus Cucullanus, which we compared in their morphology and morphometric with other members of the genus recorded for the zoogeographic region and the same group of hosts, and we proposed the species Cucullanus marajoara n. sp.
(Based on light microscopy and scanning electron microscopy examination: Figs.1-3) Medium-sized nematode, opaque white when alive.Females are larger than males, and the morphology of the anterior region is similar in both genders (Figures 1a and 2a).A thick cuticle forms a lateral cervical flap in some specimens, and the presence of thin transverse striae are observed along the body.The cephalic end is rounded, and an oral aperture in the form of a dorsoventral cleft is surrounded by a cuticular ring and delimited by a row of small teeth (Figures 2a-b).Presence of four external cephalic papillae, four internal papillae, and a pair of dorsolateral amphids (Figures 2a-b).The claviform muscular oesophagus is divided into two distinct and well-developed regions, and a well sclerotized anterior region forming an oral pseudocapsule (oesophastome) with a nerve ring is located in this region (Figure 1a).The posterior region of the oesophagus is expanded and opens into the intestine by a strong valve.The diverticulum of the oesophagus and intestinal cecum are absent.Deirids at level of the middle glandular oesophagus, and the excretory pore is located below the oesophagus (Figures 1a, 2c-d).
Cucullanus brevicaudatus, a parasite of B. capriscus (Tetraodontiformes: Balistidae), differs from the new species by the host family, habitat (marine), morphology of the gubernaculum well sclerotised, thin distally, enlarged and with small ornament proximally, tail size, and distribution of the caudal papillae (six pairs of precloacal papillae, one pair of adcloacal papillae, and three pairs of posterior papillae).
Cuculllanus marajoara n. sp.differs from other similar species that parasitize hosts of order Siluriformes by the host species and habitat, with the exceptions of C. oswaldocruzi, which is a parasite of the freshwater fish Paulicea luetkeni (Syn.Zungaro zungaro) found in the Curuá river, and C. ageneiosus, which is a parasite of the estuarine fish Ageneiosus ucayalensis; both of these species occur in Pará in the same zoogeographic region as the new species.Morphologically, Cucullanus marajoara n. sp.differs from these two species by the distribution of the cloacal papillae, including the presence of five precloacal pairs (the first pair is located anterior to the precloacal sucker, whereas pairs No. 2, 3, 4, and 5 are ventral and located posterior to the precloacal sucker) and five postcloacal pairs (pairs No. 6, 8, and 10 are ventral, pair No. 7 is lateral, and pair No. 9 is dorsal).The location of the phasmids between pairs No. 8 and 10 is a diagnostic feature of the new species and differs from C. ageneiosus, in which the phasmids are located immediately posterior to the tenth pair of papillae.In addition to belonging to a different host group, C. oswaldocruzi and C. ageneiosus do not present a protuberant cloacal upper lip and do not have an odd papilla on this lip, as has been observed in Cucullanus marajoara n. sp.