Polycladus Blanchard 1845
Creators: name: Almeida, Ana Laura
name: Álvarez-Presas, Marta
name: Carbayo, Fernando
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Platyhelminthes
Tricladida
Geoplanidae
Polycladus

description: POLYCLADUS BLANCHARD, 1845
Type species: Polycladus gayi Blanchard, 1845, fixed by monotypy by Ogren & Kawakatsu (1990).
New diagnosis: Polycladini with mouth and gonopore in the posterior-quarter of the body. Copulatory apparatus with a well-developed penis papilla. Female genital canal with dorsal entrance into the genital antrum.
Distribution: As for that of the tribe.
Remarks on the new tribe Polycladini: In the molecular phylogenies, Polycladus is represented by an unidentified specimen. This specimen is retrieved as a sister to Gusana in all analyses. Apart from the unidentified Polycladus sp. (in: Carbayo et al., 2013), only Polycladus gayi is formally described. The diagnosis of the genus was revised by Graff (1896) and Ogren & Kawakatsu (1990). The most remarkable features of Polycladus are the large size of the body and a body width of 40% of the body length. Only some species of Obama (Geoplanini) resemble Polycladus in this aspect, but their bodies do not reach such a width. Therefore, Polycladus does not fit into any tribe, except Polycladini. Polycladus also presents two additional exclusive traits, as discussed below, namely, a transverse subneural parenchymal muscle and a longitudinal transneural parenchymal muscle.
Several works have dealt with Polycladus gayi (see: Barahona-Segovia et al., 2020 and references therein), but actually only Graff (1899) and Schmidt (1902) have reported details of its internal morphology. The most conspicuous characteristic of this genus is the extraordinarily wide (2.4 times as long as wide in P. gayi) and flattened body (Graff, 1899), along with marginal eyes only (Graff, 1899; Schmidt, 1902). The musculature of the species is not clearly understood. Graff (1899) detailed illustrations of the cutaneous and parenchymal muscles (Graff, 1899: plate 30, figs 3, 4). The cutaneous musculature is described as comprising three muscle layers, namely, a layer of circular muscle, a layer of diagonal fibres and a third innermost layer of longitudinal muscle. The parenchymal musculature shown in Graff’s drawing of a transverse section of the body (plate 30, fig. 3) is depicted as being comprised of ‘obere Transversalmuskeln’, ‘mittlere Transversalmuskeln’ and ‘ ventrale Transversalmuskeln’. The two latter muscles are crossed by fibres of ‘ventrale Longitudinalmuskeln’. In another drawing of a sagittal section (plate 30, fig. 4), only ‘dorsale Longitudinalmuskeln’ and ‘dorsoventrale Muskeln’ are depicted. The ‘dorsale Longitudinalmuskeln’ are represented with dashed lines, suggesting that they might not be longitudinal but diagonal. Although Graff (1899) stated that the parenchymal musculature in land planarians consists of longitudinal, transverse and dorsoventral fibres, all Geoplaninae (except Timyma) present a dorsal parenchymal layer of diagonal muscle. In our experience, the orientation of the fibres of the cutaneous and parenchymal muscle layers in Geoplaninae is best discerned, if not only, on horizontal sections (for an example, see Figs 14C, 18B, 25B, C of this paper).
Summing up, apart from the dorsoventral muscle fibres, the parenchymal musculature in Polycladus gayi comprises a dorsal layer of decussate fibres (‘dorsale Longitudinalmuskeln’), a transverse supraintestinal muscle (‘obere Transversalmuskeln’), a transverse subintestinal muscle (‘mittlere Transversalmuskeln’), a transverse subneural muscle (‘ ventrale Transversalmuskeln’) and a longitudinal transneural muscle (‘ventrale Longitudinalmuskeln’), which is intermingledwithfibresofthesubintestinalandsubneural muscles. The transverse subneural parenchymal muscle and the parenchymal transneural layer of longitudinal muscle are unique among the Geoplaninae.
description: Published as part of Almeida, Ana Laura, Álvarez-Presas, Marta & Carbayo, Fernando, 2023, The discovery of new Chilean taxa revolutionizes the systematics of Geoplaninae Neotropical land planarians (Platyhelminthes: Tricladida), pp. 837-898 in Zoological Journal of the Linnean Society 197 (4) on pages 876-877, DOI: 10.1093/zoolinnean/zlac072, http://zenodo.org/record/7813977