Paradiplectanum, Domingues, Marcus V. & Boeger, Walter A., 2008

Domingues, Marcus V. & Boeger, Walter A., 2008, Phylogeny and revision of Diplectanidae Monticelli, 1903 (Platyhelminthes: Monogenoidea), Zootaxa 1698, pp. 1-40 : 20-22

Paradiplectanum n. gen.

Synonymy: Diplectanum Diesing, 1858 , partim

Diagnosis: Tegument smooth. Genital pore opening posterior to male copulatory organ (MCO). Genital atrium muscular. Vas deferens not observed. MCO tubular, simple; accessory piece present, non-articulated with the MCO. Prostatic reservoir simple. Accessory copulatory organ absent. Vaginal atrium sclerotized. Vaginal aperture marginal. Squamodiscs ventral, dorsal; anterior rows of rodlets with open rings; intermediate rows of rodlets with anterior lightly sclerotized blunt spinelet [28]. Superficial root of ventral anchor reduced. Parasites of marine perciform fishes ( Sillaginidae ).

Type-species: Paradiplectanum sillagonum ( Tripathi, 1957) n. comb. from

Sillago attenuatta McKay , Sillago sihama (Forsskål) (type host), and Sillago vincenti McKay.

Other species: Paradiplectanum blairense ( Gupta & Khanna, 1974) n. comb.

from Sillago indica McKay, Dutt & Sujatha , Sillago japonica Temminck & Schlegel , and Sillago sihama .

Remarks: Paradiplectanum is clearly apart of the Diplectanum complex (see comments above and Diplectanum diagnosis). Including the fact that members of Paradiplectanum n. gen. are parasitic on the gills of sillaginid fishes, features distinguishing the genus include the combined presence of (1) squamodiscs (ventral, dorsal) with intermediate rows of rodlets with lightly sclerotized blunt spinelet; (2) MCO not articulated with the accessory piece; and (3) vaginal atrium sclerotized.

There are four other diplectanid species occurring on sillaginid hosts: Diplectanum blairense Gupta & Khanna, 1974 , D. puriense Tripathi, 1957 , Monoplectanum australe Young, 1969 and M. youngi Hayward, 1996 . Paradiplectanum can be easily distinguished from Monoplectanum since species of the later genus possess a vaginal atrium muscular and a single ventral squamodisc. Comparison of P. sillagonum with D. blaiense suggests that these species are congeneric. The transfer of D. blaiense as a member of Paradiplectanum is based on voucher specimens in Hayward’s (1996) redescription of this species (type material was not deposited by the senior authors). However, the illustration of the species clearly shows that Hayward (1996) confused the posterior prostatic reservoir with the accessory piece. Diplectanum blaiense has all the diagnostic features attributed to Paradiplectanum . Diplectanum puriense , another parasite of a sillagid fish, does not represent a species of Paradiplectanum and can be distinguished from members of the new genus by having a male copulatory organ with nested tubes and lacking of accessory piece.

The generic epithet refers to the independent origin of members of this genus within Diplectaninae.

Rhabdosynochus Mizelle & Blatz, 1941

Synonymy: Cornutohaptor Mendoza-Franco, Violante-González & Vidal Martínez, 2006

Diagnosis: Tegument scaled. Genital pore opening posterior to male copulatory organ (MCO). Genital atrium muscular. Vas deferens intercaecal or looping left intestinal caecum. MCO tubular, coiled; accessory piece present, complex. Prostatic reservoir simple. Accessory copulatory organ absent. Vaginal atrium sclerotized. Vaginal aperture medial [29]. Accessory adhesive organ absent [30]. Superficial root of ventral anchor reduced. Parasites of marine perciform fishes ( Centropomidae ).

Type-species: R. rhabdosynochus Mizelle & Blatz, 1941 from Centropomus undecimalis (Bloch) .

Other species: R. hargisi Kritsky, Boeger & Robaldo, 2001 from Centropomus undecimalis ; R. hudsoni Kritsky, Boeger & Robaldo, 2001 from Centropomus undecimalis ; R. nigrescensi ( Mendoza-Franco, Violante-González & Vidal-Martínez, 2006) n. comb. from Centropomus nigrescens Günther.

Remarks: Oliver (1987) and Desdevises et al. (2001) considered Rhabdosynochinae a sister group of Lamellodiscinae and Diplectaninae based on the primarily homology of placodiscs and the other accessory adhesive organs (squamodiscs and lamellodiscs). However, Kritsky et al. (2001) suggest that these structures do not represent homologous features and considered that species of Rhabdosynochus , Murraytrema and Murraytrematoides share the character “absence of accessory adhesive organ”.

Our analysis suggests that the accessory adhesive organ was secondarily lost several times in the evolutionary history of Diplectaninae (character changes 29, 43, 51, 58, in fig. 7), including in the clade formed by Rhabdosynochus + Cornutohaptor , supporting the non-homology of the placodiscs with the lamellodiscs and squamodiscs. The recognition of Rhabdonynochinae as a junior synonymy of Diplectaninae is supported by the opening of the common genital pore subsequent to MCO [27], and ventral anchor with reduced superficial root [26].

Cornutohaptor is monotypic and consistently emerged as the sister group of Rhabdosynochus in clade “J” by sharing the secondary loss of the accessory adhesive organ. Cornutohaptor has no autapomorphies, suggesting its single species is congeneric with species of Rhabdosynochus . Both genera share the same morphology of the copulatory complex (non-articulated, coiled MCO, complex accessory piece) and hosts (centropomid fishes). Cornutohaptor nigrescensi is, thus, transferred to Rhabdosynochus as R. nigrescensi n. comb.