Trimusculotrema

Whittington, Ian D., 2010, Revision of Benedeniella Johnston, 1929 (Monogenea: Capsalidae), its assignment to Entobdellinae Bychowsky, 1957 and comments on subfamilial composition, Zootaxa 2519, pp. 1-30 : 21-22

Comments on Trimusculotrema species and affinities with entobdellines

Bullard et al. (2004) drew attention to strong morphological similarities between species of Listrocephalos which they assigned to the Entobdellinae and Trimusculotrema which at the time was assigned to the Benedeniinae after Whittington & Barton (1990). Common morphology included a circular papillate haptor lacking a marginal valve, reduced non-overlapping median haptoral sclerites, separate male and female [uterine] genital pores and a dorsal uterine pore. Despite these anatomical parallels, Bullard et al. (2004) wrestled with arguments about whether the structural similarities between these taxa were due to convergent evolution imposed by strong ecological constraints (e.g. similarities in ‘life-style’ resulting from inhabiting similar sites on similar host species) or a result of common ancestry (i.e. shared characters by phylogenetic descent). Bullard et al. (2004) were conservative and chose not to infer a close phylogenetic relationship between Trimusculotrema and Listrocephalos . The present study, part of a larger initiative to establish a phylogenetic framework for the Capsalidae using data from morphological and, where possible, molecular genetic assessments of many capsalid species, formally unites these taxa in the Entobdellinae together with Benedeniella species. Ongoing work based on comparative anatomy and molecular analyses will either support or refute the decision made here about the subfamilial status of Trimusculotrema based currently solely on morphology.

The anterior attachment organs of Trimusculotrema species differ from those of species in the other entobdelline genera, Benedeniella , Branchobdella , Entobdella , Listrocephalos , Neoentobdella and Pseudoentobdella , because no ventral grooves, rays, troughs or divided adhesive pads have been reported. Instead, Trimusculotrema species possess anterior attachment organs that appear to bear no ventral specialisations other than the observation by Whittington & Barton (1990) that the anterior region in Trimusculotrema uarnaki Whittington & Barton, 1990 was ‘rough’ but the posterior region was ‘relatively smooth’ (see their fig. 10). This feature of Trimusculotrema species deserves further study. Like species of all entobdelline genera except Branchobdella and Entobdella , Trimusculotrema species principally parasitise the skin surfaces of marine elasmobranchs.