Neoechinorhynchus (Hebesoma) colastinense, Arredondo & Gil de Pertierra, 2012

Arredondo, Nathalia J. & Gil de Pertierra, Alicia A., 2012, A new species of Neoechinorhynchus (Eoacanthocephala: Neoechinorhynchidae) from Pachyurus bonariensis (Perciformes: Sciaenidae) from the Paraná River basin in Argentina, with comments on two other species of the genus, Revue suisse de Zoologie 119 (4), pp. 425-439 : 427-432

Neoechinorhynchus (Hebesoma) colastinense n. sp.

Figs 1-8, 10, 13, 16, 19

TYPE MATERIAL: Holotype MANC-Pa No. 517/1 (male); allotype MANC-Pa No. 517/2 (female) and paratypes, MANC-Pa No. 517/3 (4 females) and MHNG INVE 79181 (1 male and 2 females) from Pachyurus bonariensis ; Colastiné River , Santa Fe Province, Argentina.

ETYMOLOGY: The species is named after the type locality and means “from Colastiné.”

DESCRIPTION

General (based on 10 specimens: 2 males, 7 gravid females and 1 juvenile female with ovarian balls used for SEM): Eoacanthocephala, Neoechinorhynchidae , with the characters of the genus Neoechinorhynchus and subgenus Hebesoma Van Cleave, 1928 (sensu Salgado-Maldonado, 1978; Amin, 2002). Fresh individuals white. Worms small. Trunk cylindrical, elongated, swollen anteriorly, curved ventrally, with 5 dorsal and one ventral giant nuclei, dorsal and ventral body wall similar in thickness (Figs 1, 2). Entire epidermal surface porous (Fig. 19). Sexual dimorphism usually inconspicuous. Proboscis spherical, wider than long (Fig. 3), with prominent apical organ (Fig. 10). Proboscis hooks in 3 circles of 6 hooks each. Hooks in anterior circle largest, alternating in two levels, separated from more posterior circles of hooks but sometimes surpassing the hooks of the middle and posterior circles, with simple roots directed posteriorly. Hooks of the middle and posterior circles much smaller than those of the anterior circle, with orbicular roots (Figs 3, 13). Neck relatively long, broader at base (Figs 1, 10, 16). Proboscis receptacle long, single-walled, extending for a short distance into the trunk when specimens are relaxed (Figs 1, 10); cerebral ganglion pyramidal-shaped situated near posterior end of receptacle (Figs 4, 10). Lemnisci subequal, digitiform, longer than proboscis receptacle, double-nucleated lemnisci usually slightly longer than single-nucleated lemnisci (Figs 1, 2, 4). Genital pore terminal in males and slightly subterminal in females (Figs 1, 2, 5).

Male: Trunk 2.6-3.2 mm (n = 2) long, 0.6-0.7 mm wide, LWR 5:1 (Fig. 2). Proboscis 90-110 (n = 2) long, 120-130 wide. Length of proboscis hooks in anterior circle 80-95 (85; n = 4), in middle circle 40-45 (n = 2), in posterior circle 15-20 (n = 2); roots not measured. Apical organ 100 long (n = 1), 60 wide. Neck 285-300 (n = 2) long. Proboscis receptacle 350-360 (n = 2) long, 145-150 wide; cerebral ganglion 100-105 (n = 2) long, 35-70 wide. Lemnisci 815-1110 (975; n = 4) long, 150-200 (165) wide. Reproductive system approximately fills the trunk, testes overlap lemnisci, 2.1- 2.5 mm (n = 2) in length, occupying 78-81% (79%) of total length. Testes oval, in tandem, overlapping, about equal in size but anterior testis slightly larger, 450-560 (n = 2) long, 300 wide, than posterior 365-530 (n = 2) long, 290-320 wide. Cement gland ovoid, about same size as testes, overlapping posterior testes, 480-535 (n = 2) long, 315-340 wide, with ovoid cement reservoir 280-300 (n = 2) long, 200-245 wide. Saefftigen’s pouch 450-485 (n = 2) long, 120-165 wide. Penis 60-90 (n = 2) long, 30-50 wide. Bursa 420-460 (n = 2) long, 210 wide, with two bursal pockets (Fig. 2).

Female: Trunk 3.3-4.3 mm (3.9; n = 7) long, 0.6-0.8 mm (0.7) wide, LWR 5-6:1 (Fig. 1). Proboscis 115-140 (130; n = 4) long, 160-170 (165) wide. Length of proboscis hooks in anterior circle 100-115 (105; n = 7), in middle circle 40-55 (45; n =7), in posterior circle 20-45 (35; n = 7); length of hook roots in anterior circle 50-60 (55; n = 6), in middle circle 10-20 (15; n = 6), in posterior circle 5-15 (10; n = 6). Apical organ 95-120 (105; n = 5) long, 55-85 (75) wide. Neck 36-475 (440; n = 3) long, 205- 210 (n = 2) wide. Proboscis receptacle 435-475 (455; n = 7) long, 140-170 (155) wide; cerebral ganglion 95-150 (120; n = 7) long, 45-60 (55) wide. Lemnisci 775-1245 (1065; n = 14) long, 145-190 (175) wide (Figs 1, 4). Reproductive system length 1.15- 1.35 mm (1.25; n = 7), occupying 27-39% (32%) of total trunk length. Uterine bell 300-600 (435; n = 6) long, 50-100 (75) wide; uterus elongated 580-700 (660; n = 7) long, 80-115 (100) wide; vagina 160-200 (185; n = 7) long, 55-65 (60) wide (Figs 1, 5). Eggs elongated, outer membrane 40-65 (60; n = 10) long, 10-20 (15) wide; fertilization membrane with polar prolongations 40-55 (50; n = 10) long, 10-15 (11) wide; acanthor 30-40 (35; n = 10) long, 8-13 (9) wide; larval hooks 2-4 (3; n = 13) long (Figs 6-8).

DIFFERENTIAL DIAGNOSIS: The new species is characterized by the following combination of features: a cylindrical trunk, elongated and swollen anteriorly; a spherical proboscis with a prominent apical organ; an anterior circle of hooks very large, sometimes overlapping the middle and posterior circles of hooks; a relatively long neck; a male reproductive system occupying 78-81% (79%) of the total trunk length; a female reproductive system occupying 27%-39% (32%) of the trunk length; and elongated eggs with polar prolongations of fertilization membrane.

The eggs dispersed in the trunk cavity show different developmental stages of the polar prolongations of the fertilization membrane, from eggs without prolongations to eggs with prolongations not fully developed (Figs 6, 7). All the eggs measured in this description, which were those ripe and spontaneously laid during the fixation of adults, had such prolongations (Fig. 8).

Neoechinorhynchus (H.) colastinense sp. n. differs from all the South American neoechinorhynchids because it belongs to the subgenus Hebesoma (egg with polar prolongations of the fertilization membrane) (sensu Salgado-Maldonado, 1978; Amin, 2002), and by the large percentage of trunk cavity occupied by the female reproductive system (32%).

Only twelve of the more than ninety species of Neoechinorhynchus were placed on the subgenus Hebesoma , including species parasites of fishes and turtles from North America, Asia and India ( Amin, 2002; Amin & Muzzall, 2009). Using Aminś key (see Amin, 2002), it is possible to discriminate the new species from the following North American species belonging to Hebesoma from fishes: N. (H.) agilis (Rudolphi, 1819) (with holarctic distribution), N. (H.) carinatus Buckner & Buckner, 1993 , N. (H.) didelphis Amin, 2001 , N. (H.) doryphorus Van Cleave & Bangham, 1949 , N. (H.) idahoensis Amin & Heckmann, 1992 , N. (H.) pungitius Dechtiar, 1971 , and N. (H.) rostratus Amin & Bullock, 1998 . Neoechinorhynchus (H.) colastinense sp. n. differs from N. (H.) agilis by having a shorter trunk length (2.6-4.3 versus up to 11.2) and the number of giant hypodermal nuclei (5 dorsal and one ventral versus 6 dorsal and two ventral); from N. (H.) carinatus and N. (H.) doryphorus by the length of the anterior circle of hooks (same length versus lateral anterior hooks longer than other hooks in the same circle); from N. (H.) didelphis by having a single uterine bell and the lack of neck girdle; from N. (H.) idahoensis by the length of hooks in anterior and middle circles (anterior circle of hooks much larger than the middle circle versus anterior and middle circles of similar length); from N. (H.) pungitius by having a larger proboscis in males and females (90-110 long, 120-130 wide and 115-140 long, 160-170 wide versus 57-90 long, 79-95 wide and 63-90 long, 84-118 wide), and the polar prolongations of fertilization membrane not extending to the outer shell; and from N. (H.) rostratus by having hooks rooted in all circles (versus only the anterior circle rooted). The new species differs from N. (H.) tenellus (Van Cleave, 1913) , recently placed in Hebesoma (sensu Amin & Muzzall, 2009), mainly by having a longer neck (versus short), and a greater percentage of the trunk cavity occupied by the female reproductive system (32% versus 12%, respectively).