Atopogyrodactylus, Kritsky & Boeger & Patella, 2020

Kritsky, Delane C., Boeger, Walter A. & Patella, Luciana, 2020, Neotropical Monogenoidea. 63. Atopogyrodactylus praecipuus gen. et sp. n. (Gyrodactylidae), an oviparous gyrodactylid from the external surface of a bristlenose catfish Ancistrus sp. (Siluriformes: Loricariidae) from the Rondônian Amazon, Brazil, Zootaxa 4732 (1), pp. 169-176 : 170-171

Atopogyrodactylus n. gen.

Type species: Atopogyrodactylus praecipuus n. sp.

Type host: Bristlenose catfish, Ancistrus sp. ( Loricariidae ).

Etymology: The Greek root atop/o (= odd or strange) is appended to “ gyrodactylus ” to indicate the unusual relationship between the haptoral sclerites of the type species compared to that of other gyrodactylid species.

ZooBank registration: The Life Science Identifier (LSID) for Atopogyrodactylus n. gen. is urn:lsid:zoobank.org:act:20356315-EE59-452A-8101-F3238D145CE6 .

Diagnosis: Body elongate, fusiform, comprising body proper (cephalic region, trunk, and peduncle), and haptor. Tegument thin, smooth. Cephalic lobes 2, terminal; each containing spike sensilla, portion of head organ. Cephalic glands comprising 2 bilateral groups of gland cells posterolateral to pharynx. Eyespots absent. Mouth subterminal, midventral. Pharynx comprising 2 tandem bulbs; proximal bulb glandular, muscular; distal bulb muscular with 8 digitiform projections occasionally protruding through mouth. Intestinal ceca 2, lacking diverticula, terminating blindly in posterior trunk or peduncle. Worms oviparous, protandrous. Gonads tandem, intercecal. Testis postgermarial (when present), reduced in adult specimens and usually becoming nonfunctional as female reproductive system develops. Two tandem seminal vesicles posterior to male copulatory organ (MCO). Copulatory sac absent. MCO allantoid, unarmed, variably bent or coiled, appearing muscular. Accessory copulatory sclerite present. Vas deferens, prostate, prostatic reservoir not observed. Germarium (in adults) submedial, with internal fertilization chamber usually filled with sperm; oviduct variably coiled, originating from dorsal surface of germarium; ootype distal to elongate oviduct, surrounded by large Mehlis’ gland. Uterus containing single egg (or empty); uterine pore dextroventral, submarginal at level of MCO. Vagina absent. Egg with short flared proximal filament embedded in amorphous droplet. Numerous vitelline follicles in postgermarial field of trunk, pregermarial follicles few or absent; vitelline ducts forming inverted U or backward h. Haptor ventrally concave, originating from ventral side of expanded posterior end of peduncle, armed with pair of ventral anchors, 16 identical hinged hooks, and slightly concave ventral plate overlying anchor pair; anchors with points usually directed dorsolaterally; bars absent. Hooks evenly spaced along lateral and posterior margins of haptor, with extrahamular distribution (see Kritsky & Mizelle 1968). Parasitic on external surface of neotropical catfishes assigned to the Loricariidae .

Remarks: Atopogyrodactylus n. gen. most closely resembles Nothogyrodactylus Kritsky & Boeger, 1991 by species of both genera having one or more accessory copulatory sclerites associated with an allantoid MCO and the apparent absence of a copulatory sac enclosing the MCO. Species of these genera are known only from bristlenose catfishes, Ancistrus spp. ( Table 1 ). Atopogyrodactylus differs from Nothogyrodactylus by its species lacking haptoral bars (present in Nothogyrodactylus spp.) and by having a ventral plate overlying the atypical gyrodactylid anchors in the haptor (ventral plate absent, anchors typically gyrodactylid in Nothogyrodactylus spp.).

Two other genera containing oviparous gyrodactylids, Onychogyrodactylus Kritsky, Vianna, & Boeger, 2007 and Aglaiogyrodactylus Kritsky, Vianna, & Boeger, 2007 , are characterized by species possessing accessory copulatory sclerites, but unlike the species of Atopogyrodactylus and Nothogyrodactylus , the accessory copulatory sclerites and MCO lie separately or together within copulatory sacs ( Kritsky et al. 2007). Finally, the monotypic Phanerothecioides Kritsky, Vianna, & Boeger, 2007 includes a species, Phanerothecioides agostinhoi Kritsky, Vianna, Boeger, 2007 , that lacks haptoral bars (as does Atopogyrodactylus praecipuus n. sp.). This species differs from A. praecipuus by lacking the haptoral plate and by having a poorly developed copulatory sac enclosing the MCO (copulatory sac absent in A. praecipuus ). The character “presence of a ventral plate overlying the anchors” in A. praecipuus n. sp. separates Atopogyrodactylus from all other gyrodactylid genera containing oviparous species.

The haptor of A. praecipuus resembles those of the viviparous species assigned to Archigyrodactylus Mizelle & Kritsky, 1967 , by having anchors without well-developed basal roots, a plate-like structure ventrally overlying the anchors, and by lacking sclerotized haptoral bars (see Mizelle & Kritsky 1967). It is unlikely that these features of the haptor in species of the two genera are homologs, as members of the respective genera possess different modes of reproduction and occur in different aquatic environments. Species of Archigyrodactylus are known only from marine embiotocid and atherinopsid fishes of the eastern Pacific Ocean.