Rhinoxenus euryxenus, Domingues & Boeger, 2005

Domingues, Marcus V. & Boeger, Walter A., 2005, Neotropical Monogenoidea. 47. Phylogeny and coevolution of species of Rhinoxenus (Platyhelminthes, Monogenoidea, Dactylogyridae) and their Characiformes hosts (Teleostei, Ostariophysi) with description of four new species, Zoosystema 27 (3), pp. 441-467 : 454-456

Rhinoxenus euryxenus n. sp.

( Fig. 4 )

TYPE MATERIAL. — Holotype ( CHIOC 36293 ); 7 paratypes ( CHIOC 36294 a-g; INPA 435 a-c; MNHN 168 HG-T1 209-209 bis).

ETYMOLOGY. — The specific ephitet is from Greek (eury = broad + xen/o = guest) and refers to the wide occurrence of this parasite within Serrasalminae .

TYPE HOST AND LOCALITY. — Nasal cavities of Serrasalmus marginatus (Characidae) , Baía da Medalha, Rio Paraná, Matogrosso do Sul, Brazil, 18. VI.1996.

OTHER MATERIAL EXAMINED. — Brazil. Rio Uatumã, lago Tapana, Santa Anna, Amazonas, from Serrasalmus gouldingi (Characidae) , 2-3.XI.1989, voucher specimens ( CHIOC 36297). — Rio Miranda, Passo do Lontra, Mato Grosso do Sul, from Serrasalmus marginatus (Characidae) , 31.XI.1996, voucher specimens ( CHIOC 36299). — Baía da Medalha, Rio Paraná, Matogrosso do Sul, from Serrasalmus marginatus (Characidae) , 18-19. VI.1996, voucher specimens ( INPA 436 a-b; MNHN 169 HG-T 1 210-210 bis; USNPC 95237). — Rio Iatapu, lago Maracanã, Manaus, Amazonas, from Serrasalmus rhombeus (Characidae) , 2.XI.1989, voucher specimens ( CHIOC 36296; INPA 437 a-b; MNHN 170 HG-T 1 211; USNPC 95238). — Rio Paraná, near Porto Rico, Paraná, from Serrasalmus spilopleura (Characidae) , 1992, voucher specimens ( CHIOC 36298). — Rio Capucapu, near the confluence of the Rio Jatapu, Cachoeira das Garças, Amazonas, from Serrasalmus striolatus (Characidae) , 31.XI.1989, voucher specimens ( CHIOC 36295); same locality, from Leporinus agassizii (Anostomidae) , 31.XI.1989, voucher specimens ( INPA 438 a-b).

COMPARATIVE MEASUREMENTS. — See Tables 7 and 8.

DESCRIPTION

Body fusiform, 607 (480-720; n = 10) long; greatest width 176 (150-210; n = 9) at body midlength. Cephalic lobes poorly developed; three pairs of cephalic organs; cephalic glands posterolateral to pharynx. Eyes equidistant; members of anterior pair smaller than those of posterior pair; eye granules elongate. Pharynx spherical, 42 (35-54; n = 11) in diameter. Haptor subtrapezoidal, 96 (64-115; n = 11) long, 115 (86-140; n = 11) wide. Ventral anchor with inconspicuous roots; base with sclerotized cap articulated with ventral bar; shaft recurved near midlength; point with saucer-like termination. Dorsal anchor with blunt proximal end covered by conspicuous sclerotized cap, straight shaft, tapered distal end. Ventral bar with expanded ends, irregularly sclerotized. Hook pair 2 robust, lying in small lobes on posterior trunk, with thumb erect, robust, shaft short, evenly short curved point; proximal 3/4 of shank inflated; FH loop extending to near beginning of shank dilation. Hooks pairs 1, 3-7 with erect thumb, delicate evenly curved shaft, short point; proximal 4/5 of shank long inflated; FH loop extending to near beginning of shank dilatation. Male copulatory organ a coiled tube with approximately 1.5 to 2 rings; copulatory ligament twisted. Testis elongate, 120 (n = 1) long, 25 (n = 1) wide; seminal vesicle fusiform; prostate in two dorsolateral fields. Germarium elongate, 63 (56-70; n = 2) long, 32 (29-37; n = 2) wide. Ootype, uterus not observed. Vagina sclerotized, distal portion with loop; vestibule sclerotized, cup-shaped, often everted ( Fig. 4B ). Seminal receptacle elongate. Vitellaria coextensive with cecae; vitelline commissure anterior to germarium. Egg not observed.

REMARKS

Rhinoxenus euryxenus n. sp. closely resembles R. piranhus based on the morphology of MCO and point of the ventral anchor. The new species, however, differs from R. piranhus by possessing ventral anchors with shafts strongly recurved near midlength (relatively straight shaft in R. piranhus ) and lacking the small terminal protuberances on the ventral bar as described by Kritsky et al. (1988: fig. 4) for R. piranhus . Rhinoxenus euryxenus n. sp. appears ubiquitous to fishes belonging to Serrasalmus . The occurrence of R. euryxenus n. sp. on Leporinus agassizii (Anostomidae) is considered accidental.

Figures

FIG. 4. — Rhinoxenus euryxenus n. sp.; A, holotype (ventral); B, vagina; C, male copulatory organ (MCO); D, hook from pairs 1, 3-7; E, hook from pair 2; F, ventral bar; G, ventral anchor; H, dorsal anchor. Scale bars: A, 100 μm; B-E, 10 μm; F-H, 50 μm.