Towards addressing the current state of confusion within the Hexabothriidae Price, 1942 (1908): Callorhynchocotyle Suriano & Incorvaia, 1982 (Monogenea: Hexabothriidae) re-visited, with the preliminary evaluation of novel parameters for measuring haptoral armature of hexabothriids

Abstract

The monogenean family, Hexabothriidae Price, 1942 (1908), currently consists of 15 valid genera parasitic on the gills ofchondrichthyan fishes. The hexabothriid literature is littered with inconsistencies, ambiguity and editorial errors whichhampers the progress and the development of investigations after the significant treatment of the family by Boeger &Kritsky (1989). A lack of consistency in the measurement protocol for the haptoral armature of hexabothriids is highlight-ed and discussed. The preliminary results of a new measurement protocol incorporating existing and novel parameterswere explored for the first time using statistical analyses. Character variables were investigated for their utility as poten-tially useful discriminators using univariate and multivariate analyses. The elimination of age-associated variance in suck-er sclerites was performed by ratio-transformation of the data to an age-dependant variable. Character variables with ahigh coefficient of variance after accounting for age were disqualified for use in the subsequent analyses. A coefficient ofvariance exceeding a conservative 10% limit was considered the result of measurement error resulting from the small sizesof these variables and therefore may also reflect the limitations of hardware and software in making small but accuratemeasurements. The proposed protocol is tested on representatives of Callorhynchocotyle and a Rajonchocotyle species totest the utility of character variables in separating species. Principle Component Analysis of the combination of the sucker-sclerites and the hamulus provided a preliminary level of robustness in separating Callorhynchocotyle species with theexception of Callorhynchocotyle hydrolagi for which there were insufficient data. Results confirm the importance of thehamulus in providing valuable diagnostic significance but the shape of the sucker sclerites as a function of total length anddiameter may also provide significant potential. Callorhynchocotyle is revisited with the addition of new specimens for 3of the species. The new data resulting from the measurement protocol are included in the redescription of Callorhynchoc-otyle marplatensis, Callorhynchocotyle callorhynchi and Callorhynchocotyle amatoi. Supplemental information is provided for C. hydrolagi and Callorhynchocotyle sagamiensis.

The surface topography of Callorhynchocotyle callorhynchi (Manter, 1955) (Monogenea: Hexabothriidae), a parasite of the holocephalan fish Callorhinchus capensis

“…Our SEM measurements of the oral sucker, eggs, appendix, haptor and suckers of C. callorhynchi correspond well with most of the previous morphometric data presented for this species (Manter 1955;Beverley-Burton and Chisholm 1990;Vaughan and Christison 2012). Nevertheless, our observations are not entirely in accordance with those of light microscopical studies and indicate the presence of some new characteristics for this species.…”

“…In taxonomic papers on C. callorhynchi, a 'papillate' surface of the lumen of the haptoral suckers has been indicated by Manter (1955), Boeger et al (1989), Beverley-Burton andChisholm (1990) and Vaughan and Christison (2012), which implies the presence of sensory structures, i.e. unciliate nerve receptors.…”

“…Polyopisthocotylean monogeneans of the family Hexabothriidae comprise 15 valid genera parasitic on the gills of chondrichthyan fishes, with most being recorded from elasmobranchs (sharks and rays) and one genus, Callorhynchocotyle Suriano & Incorvaia, 1992, being reported only from holocephalans (chimaeras) (Vaughan and Christison 2012;WoRMS 2015). In addition to having hosts with a more ancient lineage than the majority of polyopisthocotyleans, hexabothriids also differ in having an oral sucker (a plesiomorphic feature, according to and the main haptoral attachment organs functioning as suckers rather than clamps.…”

“…Nevertheless, these authors considered that, whereas host transfer (dispersion) appears important in the evolutionary history of hexabothriids, as indicated by the parasitism of holocephalans by species of Callorhynchocotyle, coevolution may be shown to be more prevalent when the occurrence of hexabothriids in all groups of elasmobranchs is known. Several of the most recent revisions of the taxonomic status of species of Callorhynchocotyle from chimaeras (both the Callorhinchidae and the Chimaeridae) provided diagnoses for the five known species of the genus Beverley-Burton and Chisholm 1990;Vaughan and Christison 2012). However, studies on the ultrastructural characteristics of hexabothriids are few (Lyons 1972;Agrawal et al 1996;Bullard et al 2001;Bullard and Dippenaar 2003;Poddubnaya et al 2015) and only the latter deals with a species of Callorhynchocotyle.…”

Hexabothriids of Devil Rays (Mobulidae): New Genus and Species from Gill ofMobula hypostomain the Northern Gulf of Mexico and Redescription of a Congener FromMobula rochebruneiin the Eastern Atlantic Ocean

“…Consulting the 11th edition (Lawrence, 1995), vasa efferentia is derived from vasa (¼ small vessels, ducts, or canals; p. 628) and efferent (¼ vessels conveying contents outward from an organ; p. 169-170). Unfortunately, the terms sperm duct and common sperm duct were not defined by Glennon et al (2005) or by Vaughan and Christison (2012), or for that matter by Lawrence (1989;1995), leaving the definitions of those terms introduced by Glennon et al (2005) indeterminate and open for interpretation. Unlike vasa efferentia, sperm ducts is ambiguous because it does not impart a relative location of the ducts or a direction of the sperm being conveyed within them.…”