Rhinoxenus Kritsky, Boeger & Thatcher, 1988

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 : 443-444

Genus Rhinoxenus Kritsky, Boeger & Thatcher, 1988

TYPE SPECIES. — Rhinoxenus piranhus Kritsky, Boeger & Thatcher, 1988 , from Pygocentrus nattereri Kner, 1858 (Characidae) .

OTHER SPECIES INCLUDED. — Rhinoxenus arietinus Kritsky, Boeger & Thatcher, 1988 from Leporinus agassizii Steindachner, 1876 , L. elongatus Valenciennes, 1849 , L. friderici friderici (Bloch, 1794) , L. lacustris Amaral Campos, 1945 , L. obtusidens (Valenciennes, 1836) , Schizodon altoparanae Garavello & Britski, 1990 , S. borellii (Boulenger, 1990) , S. fasciatus Spix & Agassiz, 1829 , Schizodon sp. and Rhytiodus argenteofuscus Kner, 1858 (Anostomidae) ; R. bulbovaginatus Boeger, Domingues & Pavanelli, 1995 from Salminus brasiliensis (Cuvier, 1816) (Characidae) ; R. nyttus Kritsky, Boeger & Thatcher, 1988 from Schizodon fasciatus and Schizodon sp. (Anostomidae) ; R. piranhus from Prystobricon sp., Serrasalmus marginatus Valenciennes, 1836 and S. spilopleura Kner, 1858 (Characidae) ; R. anaclaudiae n. sp., from Triportheus cf. nematurus , Triportheus sp. and Brycon sp. (Characidae) ; R. curimbatae n. sp., from Prochilodus cf. lineatus (Prochilodontidae) ; R. euryxenus n. sp. from Serrasalmus gouldingi Fink & Machado Allison, 1992 , S. marginatus , S. rhombeus (Linnaeus, 1766) , S. spliopleura , S. striolatus Steindachner, 1908 (Characidae) , Leporinus agassizii (Anostomidae) ; R. guianensis n. sp., from Curimata cyprinoides (Linnaeus, 1766) (Curimatidae) ; and several undeterminate Rhinoxenus species from Hydrolicus scomberoides (Cuvier, 1816) (Cynodontidae) .

EMENDED DIAGNOSIS. — Dactylogyridae . Body divid- ed into cephalic region, trunk, haptor (peduncle absent). Tegument smooth. Cephalic lobes, head organs, cephalic glands present. Eyes four. Pharynx muscular, glandular; intestinal ceca two, confluent in posterior trunk, lacking diverticula. Gonads overlapping; testis dorsal to germarium. Common genital pore near bifurcation of intestinal caeca. Vas deferens looping left intestinal cecum; seminal vesicle a dilation of vas deferens. Copulatory complex comprising a sclerotized male copulatory organ (MCO), accessory piece; MCO a coiled tube with counterclockwise rings ( Kritsky et al. 1985, 1988), with conical base surrounded by two circular sclerotized tandem brims; proximal brim articulated to copulatory ligament of accessory piece. Copulatory ligament lying within rings of MCO; distal portion of the accessory piece expanded. Vagina sclerotized, sinistral, proximal portion of vagina with one or more loops. Seminal receptacle present. Vitellaria follicular. Haptor with 14 hooks, having ancyrocephaline distribution ( Mizelle 1936); hook comprising shank of two subunits; pair of ventral anchors, a pair of spike-like dorsal anchors; ventral bar; dorsal bar absent. Parasites of the nasal cavity of the Neotropical characiform fishes.

REMARKS

The general features of the internal morphology of Rhinoxenus species are well documented by Kritsky et al. (1988) and Boeger et al. (1995). Diagnostic features of the genus include: 1) presence of dorsal anchor modified into a spike-like sclerite; 2) absence of dorsal bar; 3) presence of hook from pair 2 located in two bilateral lobes of the trunk; and 4) two circular sclerotized tandem brims on the base of the MCO. The original diagnosis of Rhinoxenus does not include the two circular tandem sclerotized brims associated with the base of the MCO. These structures have been reported in species of Dawestrema ( Kritsky et al. 1985) and of Cacatuocotyle (Boeger et al. 1997) but probably represent independent evolutionary events. Thus, the presence of these brims is considered a synapomorphy for Rhinoxenus . Kritsky et al. (1988) report that species of Rhinoxenus present all hooks with shank inflated proximally. Rhinoxenus curimbatae n. sp. is the only species of the genus that does not present this character. However, the absence of the shank inflation seems to be a second autapomorphic loss.