Neotegorhynchus, Lisitsyna & Xi & Orosová & Barčák & Oros, 2022

Lisitsyna, Olga, Xi, Bing-Wen, Orosová, Martina, Barčák, Daniel & Oros, Mikuláš, 2022, The erection of a new genus, Neotegorhynchus n. g. (Palaeacanthocephala Illiosentidae), with a redescription of Neotegorhynchus cyprini n. comb. from Cyprinus carpio from the Yangtze River basin, China, Zootaxa 5150 (1), pp. 83-96 : 86-87

Neotegorhynchus n. g.

Etymology: Generic name is derived from “Neo” to indicate the similarity to the genus Tegorhynchus Van Cleave, 1921 .

Type species: Neotegorhynchus cyprini (Yin et Wu, 1984) n. comb.

Generic diagnosis: Palaeacanthocephala , Illiosentidae . Trunk fusiform, with anterior trunk spines forming complete rings. Genital spines absent in both sexes. Females larger than males. Proboscis long, cylindrical, often curved ventrally. Proboscis with 12–14 longitudinal rows of hooks, 19–23 in each row. Size of hooks decreasing towards base of proboscis, basal two or three hooks in each row smallest. Ventral hooks larger than dorsal. Proboscis receptacle often goblet-shaped, its anterior third dilated, posterior part cylindrical. Proboscis receptacle doublewalled; inner wall attached to base of proboscis, outer wall beginning posterior to neck-trunk junction. Cerebral ganglion at border of anterior and middle thirds of proboscis receptacle. Neck short. Lemnisci ribbon-shaped, long, form numerous loops anterior to testes in males, extend into posterior part of body in females. Testes oval, located one after another without interval. Eight cement glands, length of gland complex not exceeding length of posterior testis. Cement reservoir spherical. Female genital tract short, muscular vaginal sphincter absent. Giant genital muscles are fan-shaped cells, each of which has one nucleus and is not attached to the front wall of the body. Eggs spindle-shaped, with polar prolongations of middle shell. Caudal end of female in form of dome on muscular base. En copula it is covered and retained by muscular part of male bursa of the complementary form. Genital pore terminal in both sexes. Parasites of freshwater fish.

Remarks: The family Illiosentidae includes 14 genera ( Smales 2015). The main features that differentiate the genera within the family are the presence or absence of genital spines, the location of somatic spines on the body, the position of the cerebral ganglion, the size and location of the posterior hooks on the proboscis and the position of the genital pore ( Smales 2015). Based on the arrangement of somatic spines in the anterior part of the body only, the absence of genital spines and the posterior hooks of the proboscis being smaller than the previous ones, Neotegorhynchus n. g. is similar to Indorhynchus Golvan, 1969 ; Metarhadinorhynchus Yamaguti, 1959 ; Pseudorhаdinorhynchus Achmerov et Dombrovskaja-Achmerova, 1941 ; Dentitruncus Sinzar, 1955 ; and Tegorhynchus Van Cleave, 1921 . The newly erected genus differs from representatives of the genus Indorhynchus by having a longer proboscis (900‒1800 versus 790) and less proboscis armature (12‒14 longitudinal rows of hooks versus 22 in Indorhynchus ) ( Golvan 1969). Neotegorhynchus n. g. differs from representatives of the genus Metarhadinorhynchus in the position of the cerebral ganglion (in the anterior third of the proboscis receptacle versus the middle part in Metarhadinorhynchus ) and the position of the genital pore of females (terminal versus subterminal in Metarhadinorhynchus ) ( Yamaguti 1959; Golvan 1969). Neotegorhynchus n. g. differs from representatives of the genus Pseudorhadinorhynchus in the position of the cerebral ganglion (in the anterior third of the proboscis receptacle versus at the bottom of it in Pseudorhadinorhynchus ) (Achmerov et Dombrovskaja-Achmerova 1941; Golvan 1969). The new genus Neotegorhynchus n. g. is closest to the genera Dentitruncus and Tegorhynchus sensu Monks et al. (1997) based on the proboscis armature and morphology of hooks, the absence of genital spines and the uneven attachment of the inner and outer walls of the proboscis receptacle; however, it has significant differences from members of these genera.

The genus Dentitruncus includes a single species, D. truttae Sinzar, 1955 . Neotegorhynchus n. g. has 12–14 longitudinal rows of hooks versus 18 in D. truttae . Also, the hooks of the basal row on the proboscis of the new genus are the smallest and do not form a ring, while the hooks of the basal row of D. truttae are longer than the hooks of the previous row and form a ring. The ventral hooks of Neotegorhynchus n. g. are larger than the dorsal, while the ventral and dorsal hooks of D. truttae are the same size. The cerebral ganglion in the new genus is located on the border of the anterior and middle third of the proboscis receptacle versus at the bottom of the proboscis receptacle in D. truttae . Also, the tegumental spines of Neotegorhynchus n. g. are arranged in a single field of the same width on the ventral and dorsal sides versus the field of tegumental spines longer ventral than dorsal in D. truttae (Siznar 1955; Manilla et al. 1976).

Currently, two species are assigned to the genus Tegorhynchus — T. brevis Van Cleave, 1921 , and T. holospinosus Amin et Sey, 1996 —both parasitic in marine fish ( Van Cleave 1921; Amin & Sey 1996; Monks et al. 1997), the only species Neotegorhynchus n. g. found in freshwater fish. Neotegorhynchus n. g. differs from both species of Tegorhynchus in the terminal position of the genital pore of females versus slightly dorsal by Tegorhynchus , the cerebral ganglion at the border of the anterior and middle thirds of the proboscis receptacle versus at the level of the neck in Tegorhynchus , and the spherical cement reservoir versus conical in Tegorhynchus ( Van Cleave 1921, 1940; Van Cleave & Lincicome 1940; Monks et al. 1997).

Neotegorhynchus n. g. differs from all the genera of the family Illiosentidae in the structure of the reproductive system of both sexes: a vagina lacking a muscular sphincter; terminally pointed protruding tail end of female in the form of a dome with a muscular base; female genital muscles are fan-shaped cells, each of which has one nucleus and is not attached to the front wall of the body; the muscular lip of the bursa of males repeats the domed shape of the posterior end of females, which en copula allows the lip of the bursa to seal to the posterior end of the female ( Fig.1J ).

Figures

FIGURE 1. Line drawing of Neotegorhynchus cyprini n. comb from Cyprinus carpio from China. A—total view of male, neotype; B—proboscis of male; C—hooks of a longitudinal row, ventral; D—hooks of a longitudinal row, dorsal; E—somatic spine; F—eggs; H—posterior ends of both sexes en copulation; J—posterior end of female. Scale bars: A—1 mm; B, H, J—500 μm; C, D, F—100 μm; E—20 μm.