Stylochoidea Poche, 1926

Litvaitis, Marian K., Bolaños, D. Marcela & Quiroga, Sigmer Y., 2019, Systematic congruence in Polycladida (Platyhelminthes, Rhabditophora): are DNA and morphology telling the same story?, Zoological Journal of the Linnean Society 186, pp. 865-891 : 874-875

Superfamily Stylochoidea Poche, 1926

Historically, the taxonomic composition of Stylochoidea has been controversial, because the placement of Hoploplanidae has been equivocal. Laidlaw (1903), Bock (1913), Marcus & Marcus (1966) and Faubel (1983) assigned the family to Leptoplanoidea , whereas Prudhoe (1985) included it in Planoceroidea and Poche (1926) placed it in Stylochoidea . The currently accepted classification follows Poche’s (1926) placement ( Tyler et al., 2006 –2018). Our results, and those of Aguado et al. (2017), Bahia et al. (2017) and Tsunashima et al. (2017), support the inclusion of Hoploplana species in Stylochoidea ( Table 1).

In an attempt to define Stylochoidea (sensu Poche, 1926), Bahia et al. (2017) proposed ‘a rounded body shape, presence of nuchal tentacles, presence of cerebral and nuchal (and sometimes marginal) eyespots’ as synapomorphies. However, these synapomorphies do not define the superfamily as a whole. Specifically, some families (e.g. Latocestidae ) do not possess nuchal tentacles, and the trait may be variable even in individual genera (e.g. Leptostylochus ). Furthermore, the elongate shape of Latocestus defies the proposed rounded body shape.

Monogeneric families, families with very few species or families that appear only in one classification system have been omitted. Comparisons with Aguado et al. (2017) and Tsunashima et al. (2017) are found in the Discussion.

Abbreviation: N/A, not assessed.

AmongAcotylea, larvaearefoundonlyinStylochoidea [known exceptions are Notoplana australis ( Schmarda, 1859) and Stylochoplana maculata Quatrefage, 1845 ( Leptoplanoidea )] (Rawlinson et al., 2008; Lapraz et al., 2013). Hence, it might be tempting to use their presence to unite species in this superfamily inclusive of Hoploplana inquilina (Wheeler, 1894) . However, because we identified Stylochoidea (sensu Poche, 1926) as the most basal lineage in Acotylea, it is likely that larvae are a symplesiomorphy retained from the polyclad ancestor, rather than a synapomorphy of the superfamily. Consequently, we cannot identify a valid morphological or developmental synapomorphy for the entire superfamily, despite the molecular support of the clade.