Susanlimae ianwhittingtoni gen . nov . , sp . nov . ( Monogenoidea : Dactylogyridae ) , a dweller of the gill rakers of Pseudeutropius moolenburghae ( Siluriformes : Schilbeidae ) from Sumatra

A new genus and species of Monogenoidea, Susanlimae ianwhittingtoni gen. nov., sp. nov., are proposed for dactylogyrids collected from the “Nuayang tipis”, Pseudeutropius moolenburghae Weber & de Beaufort, 1913, which inhabits freshwater in Sumatra. While clearly a member of a putative clade that includes Asian and African catfish parasites, S. ianwhittingtoni sp. nov. differs from most members of this clade by having a bifurcated haptor that embraces the gill rakers of its host. This haptoral morphology and mode of attachment also occur in species of Bifurcohaptor Jain, 1958. However, species of Susanlimae gen. nov. are easily distinguished by the comparative morphology of their haptoral armature. In Susanlimae gen. nov., the ventral and dorsal bars are single, elongated, and inverted u-shaped (ventral bar short and two short dorsal bars in Bifurcohaptor spp.); the dorsal anchor is robust with well-defined roots (reduced roots and elongate shaft in Bifurcohaptor spp.); and the ventral anchor has an elongated, deep root (inconspicuous in Bifurcohaptor spp.).

In the laboratory, the gills of each fish were removed and their parasites were collected from the sediment with the aid of probes and forceps under a dissecting scope.Some specimens were stained with Gomori's trichrome and mounted in Damar's gum for study of their soft anatomy; other specimens were cleared and mounted in Hoyer's mounting medium (prepared as in HUMASON 1979) for study of their hard structures.Illustrations were prepared using a camera lucida on an Olympus BX51 microscope equipped with phase contrast.Measurements, all in micrometers, were taken following the procedures of MIZELLE & KLUCKA (1953).In the descriptions, the mean is followed by the range and the number of structures measured (n), in parentheses; the length of the body includes the haptor (longitudinal axis of haptor).The length of the male copulatory organ (MCO) and bars represent their actual length measured with the software ImageJ (SCHNEIDER et al. 2012).The hooks are numbered according to MIZELLE (1936).The type specimens are deposited in the parasitological collections of the Instituto Oswaldo Cruz (Rio de Janeiro, Brazil) (CHIOC) and the Muséum national d'Histoire naturelle (Paris, France) (MNHN).Vitellaria in trunk, absent from regions of other reproductive organs.Haptor bifurcated, composed by bilateral "arms"; with dorsal, ventral anchor/bar complexes, seven pairs of similar hooks (5 pairs ventral, 2 pairs dorsal).Hook with shank comprising single subunit.Bars elongate, inverted U-shaped.Ventral anchor with elongate deep root.Superficial root of dorsal anchor provided with accessory sclerite (= cuneus).Parasites of the gill rakers of species of Siluriformes (Actinopterygii).
Etymology.The generic epithet is in honor of Dr. Lee Hong Susan Lim (1952-2014) (University of Malaya in Kuala Lumpur), a Malaysian parasitologist and a good friend of the first two authors.Dr. Lim is greatly responsible for most of our knowledge of the diversity of Monogenoidea from Asian Siluriformes.

DISCUSSION
Despite its apparently unique morphology, S. ianwhittingtoni shares many features with other dactylogyrid parasites of siluriform fishes from Asia and Africa.For instance, the ventral anchors are significantly smaller than the dorsal anchors, each dorsal anchor has an accessory sclerite (= cuneus) associated with its superficial root, and the ventral bar tends to be Vshaped or composed of two smaller bars, articulated or not.These features are common in species of several genera, such as Thaparocleidus Jain, 1952, Cornudiscoides Kulkarni, 1969 (Fig. 10), Bifurcohaptor Jain, 1958 (Fig. 11), Mizelleus Jain, 1957, Bychowskyella Achmerow, 1952, Quadriacanthus Paperna, 1961, Malayanodiscoides Lim & Furtado, 1986, Notopterodiscoides Lim & Furtado, 1986, Pseudancylodiscoides Yamaguti, 1963, and Paraquadriacanthus Ergens, 1988.Together with other characteristics, they may represent synapomorphies providing support for the shared ancestry of these genera.LIM et al. (2001) for example, regarded the dactylogyrids mentioned above, together with other species lacking the aforementioned combination of characters, as members of Ancylodiscoidinae Gussev, 1961.In this study, however, we accept the hypotheses of KRITSKY ZOOLOGIA 32 (6): 532-537, December 2015& BOEGER (1989) and ŠIMKOVÁ et al. (2003) and refrain from recognizing Ancylodiscoidinae (as well as Ancyrocephalinae) as valid, since this group is not monophyletic according to published phylogenies.
Unlike most species of Monogenoidea of catfishes, S. ianwhittingtoni attaches to its host by embracing the gill rakers and penetrating the epithelium with anchors and hooks located at the distal extremities of the bifurcated haptor (haptoral arms) (Figs. 8,9).A similar kind of attachment is found in species of Bifurcohaptor, but in the latter the attachment is to the gill filament rather than the gill rakers (KEARN & BIJUKUMAR 1997).Bifurcohaptor indicus Jain, 1958 (and likely all other spe-  KEARN & BIJUKUMAR (1997).However, comparative analysis of the hard parts involved in the attachment in S. ianwhittingtoni and B. indicus indicates that this mode of attachment likely originated from independent evolutionary events (see Figs. 11,12).In the new species, both ventral and dorsal bars are inverted V or U-shaped, the ventral anchor depicts an unusually long deep root, while the dorsal anchor is robust with conspicuous roots.In species of Bifurcohaptor, the dorsal bar is small and robust; the ventral bar is split into two separate parts, each positioned by each ventral anchor and located distally in the haptoral arms; and the dorsal anchor is greatly elongated, almost as long as each respective haptoral arm, lacking conspicuous roots.
Even though haptors adapted to embrace the gill filaments or gill rakers are unusual among the Monogenoidea, species of other genera of Polyonchoinea have similar functional morphology, including those of Dactylogyridae and Diplectanidae.The single species of Furcohaptor, F. cynoglossi Bijukumar & Kearn, 1996 (Fig. 13), parasite of the gill filaments of the flatfishes Cynoglossus macrostomus Norman, 1928 andCynoglossus puncticeps (Richardson, 1846), has haptoral arms the haptoral armature is reduced.The genus was originally assigned to the Ancyrocephalinae, but is most likely a member of Diplectanidae.This hypothesis is supported by the morphology of the anchor and divided bar, greatly resembling those of Diplectanidae; by the presence of a male copulatory organ directed posteriorly; and the morphology of the head area and head organs.
A definitive transfer of Furcohaptor to Diplectanidae may not happen until analysis of molecular data and description of the internal organs (not provided in the original description of the species) (BIJUKUMAR & KEARN 1996).In F. cynoglossi, the haptoral arms are elongate and the hard structures (hooks, bars, and anchors) are located solely at the distal portion of these arms.Another diplectanid, Aetheolabes goldiensis Boeger & Kritsky, 2009 (Fig. 14), a parasite of the freshwater Sciaenidae Plagioscion sp.(and its likely congeneric Diplectanum umbrinum Tripathi, 1959 -see BOEGER & KRITSKY 2009) also presents an embracing haptor.In species of Aetholebes Boeger & Kritsky, 2009 the ventral bar is short, robust, and located at the base of the haptoral arms; the dorsal bars are long, almost as long as the haptoral arms, and articulate proximally; and the anchors are located distally within the arms.As Susanlimae gen.nov.and Aetholebes are members of distinct families within the Polyonchoinea, the general similarities in haptor morphology are simply the result of convergent evolution.ACKNOWLEDGMENTSFish specimens were donated for parasite inspection by the "Catfish Asia Project" (supported by the European Commission) of L. Pouyaud and J. Slembrouck.WAB is a research fellow of the Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil.This is publication ISE-M 2015-226 SUD.
ABSTRACT.A new genus and species of Monogenoidea, Susanlimae ianwhittingtoni gen.nov., sp.nov., are proposed for dactylogyrids collected from the "Nuayang tipis", Pseudeutropius moolenburghae Weber & de Beaufort, 1913, which inhabits freshwater in Sumatra.While clearly a member of a putative clade that includes Asian and African catfish parasites, S. ianwhittingtoni sp.nov.differs from most members of this clade by having a bifurcated haptor that embraces the gill rakers of its host.This haptoral morphology and mode of attachment also occur in species of Bifurcohaptor Jain, 1958.However, species of Susanlimae gen.nov.are easily distinguished by the comparative morphology of their haptoral armature.In Susanlimae gen.nov., the ventral and dorsal bars are single, elongated, and inverted u-shaped (ventral bar short and two short dorsal bars in Bifurcohaptor spp. long, robust, with slightly tapering ends.Eggs not observed.Type host.Pseudeutropius moolenburghae Weber & de Beaufort, 1913 (Siluriformes: Schilbeidae) Site of infection.Gill rakers.Type locality.Batang Hari river, near the Village de Kubu Kandang, Sous-district Pemayung, Province Jambi, Indonesia.Latitude: 1°36'17.51"S,Longitude: 103°19'16.65"E.Date: May 2005.Specimens deposited.CHIOC 38202 a (holotype); 5 paratypes CHIOC 38202 b,c, MNHN HEL545, HEL546.One paratype kept in the private collection of AP.