Can morphometrics help us predict the diet of land planarians?

Abstract

The use of morphometrics for taxonomy and to predict the diet of organisms based on related species has been applied to several groups. In this study, for the first time, we used morphometric data of land planarians to find patterns that could differentiate genera and feeding habits. We examined body shape, pharynx shape, mouth position and the thickness of the cutaneous musculature in 135 species of land planarians. Mouth position was explained, in part, by the position of the dorsal insertion of the pharynx, and transverse circularity by the relative thickness of the cutaneous musculature. The character that best separated genera and diet was the thickness of the cutaneous musculature. A principal components analysis recovered some patterns previously revealed by molecular phylogenetics, with some closely related genera appearing close to each other in the biplot. The same analysis also showed two clearly distinct groups, one of species that feed on woodlice and the other of species that feed on soft-bodied prey. We conclude that morphometrics can help to narrow down the potential prey of geoplaninid land planarians and aid taxonomic studies.

Records of the land planarian Polycladus gayi (Tricladida, Geoplanidae) preying on black snails Macrocyclis peruvianus (Gastropoda, Macrocyclidae)

“…The morphometrics of land planarians, such as the position of the dorsal insertion of the pharynx, and the thickness of the cutaneous musculature can help identify potential prey of geoplaninid land planarians and answer ecological questions (Boll & Leal‐Zanchet, 2022). The organization and thickness of the cutaneous musculature layers in P. gayi were briefly characterized by Graff (1899) and more were provided by Grau (2010), where the cutaneous musculature is described as relatively thick, especially regarding the transversal and longitudinal layers, when compared to other broad and flat neotropical land planarians (Boll & Leal‐Zanchet, 2022). Under laboratory conditions, many land planarians have a specialist diet, and species with very wide bodies usually only feed on terrestrial gastropods (Boll & Leal‐Zanchet, 2016), and this could be the case for P. gayi .…”

Morphometric differentiation of Landouria smimensis along altitudinal gradient

“…High rainfall makes the soil more fertile so that it supplies more abundant food sources [27]. The difference in size is also presumably due to the influence of different L. smimensis feed sources, that shell size can be affected by the food available in nature [17]. There is also a study that showed the size of freshwater gastropods was influenced by intraspecific competition or density abundance with limited food sources [28].…”

“…Several studies mentioned the importance of knowing the morphological differences in various types of land snails. Shell morphology can be characteristic of their food sources [17]. Each location has different characteristics.…”

Truly a hyperparasite, or simply an epibiont on a parasite? The case of Cyclocotyla bellones (Monogenea, Diclidophoridae)

“…Clearly, feeding on an arthropod and piercing its strong cuticle would require major changes in this part of the body. A parallel case is found in land planarians (Tricladida, Geoplanidae), which have species feeding on either soft body preys or on arthropods: considerable differences in anatomy are found between the two groups [ 10 ]. Nothing similar was found in monogeneans dwelling on crustaceans, especially in Cy.…”