Rhinoxenus cachorra Soares and Domingues, 2019

Soares, Geusivam B., Magalhães, Keila X., Silva, Ana Carolina, Carneiro, Jânio S., Barbosa, Lucineia L., Costa, Nayna G. S. & Domingues, Marcus V., 2019, Monogenoids (Polyonchoinea, Dactylogyridae) from Hydrolycus armatus (Characiformes, Cynodontidae) with the description of a new species of Rhinoxenus and the proposal of a new genus from the Xingu River, Pará, Brazil, Zootaxa 4700 (2), pp. 229-245 : 231-233

Rhinoxenus cachorra Soares and Domingues n. sp.

( Figs. 1–9 )

Type host: Hydrolycus armatus (Jardine & Schomburgk) .

Site: Nasal cavities.

Type locality: Volta Grande , Xingu River, municipality of Altamira, Pará State, Brazil (03°21’15,7’’S; 52°11’47,5’’W), collected on June 13, 2015 .

Prevalence: 100% of three hosts examined.

Mean intensity: 4.5 parasites per infected host.

Specimens deposited: Holotype, MPEG nº 168; 9 paratypes, MPEG n° 169–177; 3vouchers, MPEG n° 178– 180.

Etymology: The specific name is derived from the common name of the host, “cachorra,” used by the people of the Northeast Amazon, Brazil.

Zoobank Life Science Identifier: (LSID) for Rhinoxenus cachorra n. sp. is urn:lsid:zoobank.org:act:9B20D7DD-0B6F-4191-967A-75466A0FCA90

Comparative measurements: see Table 2 .

Description (based on ten specimens; five mounted in Hoyer and five mounted in Gomori’s trichrome): Body fusiform, total length excluding haptor 511 (475–550; n= 5), total width at level of germarium 141 (105–170; n=5) ( Fig. 1 ). Tegument smooth. Cephalic region broad; cephalic lobes inconspicuous; three bilateral pairs of head organs with rod-shaped secretion; cephalic glands not observed. Two pairs of eyespots; anterior eyes slightly farther apart than posterior pair; accessory chromatic granules absent. Mouth subterminal, midventral; pharynx muscular, ovate to subspherical, 31 (27–28; n= 6) long, 28 (24–32; n=6) wide; esophagus short. Two intestinal ceca, confluent posteriorly to gonads, lacking diverticula. Common genital pore opening midventral near level of cecal bifurcation; genital atrium muscular. Intercecal gonads, overlapping. Testis dorsal to germarium, fusiform, 37 (25–50; n=2) long, 28 (15–42; n=2) wide (observed only in paratypes). Vas deferens apparently looping left intestinal cecum; seminal vesicle sigmoid, representing a dilation in the vas deferens, with distal portion looping posteriorly before entering MCO base. Single prostatic reservoir, bifurcated, posterior to copulatory complex. Copulatory complex comprising MCO, accessory piece ( Fig. 2 ). MCO sclerotized, tubular, spiral, counterclockwise, with two coils, 139 (100–157; n=4) long, base with sclerotized cap, distal aperture acute; circular sclerotized tandem brim associated with MCO base. Accessory piece, articulated with MCO, comprising complex sheath with distal portion expanded, bifid. Germarium fusiform, 52 (40–80; n=4) long, 23 (22–25; n=4) wide. Eggs, Mehlis’ glands, ootype not observed. Vagina single, sclerotized, opening ventrally at the left body margin, at level of vitelline commissure; vaginal vestibule heavily sclerotized at distal portion; vaginal canal sclerotized, sigmoid. Seminal receptacle broad, anterior to germarium. Vitellaria well developed, coextensive with intestinal ceca. Haptor subtrapezoidal, 150 (125–175; n=4) long, 117 (100–137; n=4) wide. Anchors dissimilar. Ventral anchor 111 (107–115; n=5) long, with inconspicuous roots; base 36 (32–38; n=5) width, with sclerotized cap; shaft recurved near mid-length, point with fish-hook-like termination ( Fig. 8 ). Dorsal anchor 120 (114–130; n=4), with blunt proximal end covered by subtle sclerotized cap, straight shaft, tapered distal end ( Fig. 9 ). Ventral bar with ends ventrally bent toward to its posterior portion ( Figs 6–7 ). Dorsal bar absent. Hooks dissimilar in shape, comprising shank of two subunits; filamentous hook loop extended near to beginning of shank dilation; hook pair 2, 28 (25–32; n=10) long, with erect thumb, curved shaft, short point, proximal ½ of shank inflated ( Fig. 3 ); hook pairs 1, 3–7, 32 (30–35; n=7) long, with slightly depressed to straight thumb, slightly curved shaft, short point, proximal ¾ of shank inflated ( Figs. 4–5 ).

Remarks: Rhinoxenus cachorra n. sp. is similar to Rhinoxenus euryxenus Domingues & Boeger, 2005 mainly due to the morphology of the haptoral structures. Both species have a ventral anchor with inconspicuous roots and a sclerotized cap on the base of the anchor with projection for articulation to ventral bar; shaft recurved near the mid-length, point with fish-hook-like termination; a ventral bar with ends ventrally bent toward to its posterior portion. The new species differs from R. euryxenus by the presence of a spiraled MCO with two counterclockwise coils (from one and a half to two coils in R. euryxenus ), and an accessory piece with an expanded, bifurcated distal portion (cone-like in R. euryxenus ). Finally, these species differ on the morphology of the point of the ventral anchor and hook pair 2; R. euryxenus has the point of ventral anchor with saucer-like termination, and the hook pair 2 is robust, with an erect and robust thumb, whereas Rhinoxenus cachorra n. sp. has the point with hook-like termination, the hook pair 2 is not robust and its thumb, although erect, is also not robust.

Figures

FIGURES 1–9. Rhinoxenus cachorra n. sp. 1. Holotype whole-mount (ventral) (composite). 2. Copulatory complex. 3. Hook pair 2. 4. Hook pair 1. 5. Hook pair 3–7. 6. Ventral bar (view, ventral). 7. Ventral bar (view, dorsal). 8. Ventral anchor. 9. Dorsal anchor.