Dugesia gonocephala

Two specimens on the left, slowly sliding over the sandy bottom. The detail cutout below shows the pointed-triangular shape of the head. The eyes are in front of the 'ears'. D. lugubris also has the latter . The determination remains uncertain, see also below under "What's in a name".

On the top left of the photo you can see a smaller flatworm, probably a young specimen of the same species.

In the photo below left a specimen in an extremely arrow-shaped position, below right you can see how the flatworm, like most aquatic snails, can crawl upside down at the bottom of the water surface. The light zone in the middle: that is where the stomach is located, which can be bulged out, more about this on the Dugesia lugubris page.

If conditions are favorable, this flatworm can occur in large numbers. Small clumps of flatworms can be seen in some places in the Mosbeek. There they move slowly among the also common amphipods that slide over the bottom in a side-lying position and occasionally swim quickly away to another place.

Finally, two more photos of the flatworms at this location, both with the typical triangular head. The left photo can be enlarged.

Bibliography:

Angus, B. 2007 The study of turbellarians (Platyhelminthes) at the Queensland Museum. Memoirs of the Queensland Museum 53( 1 ): 157-185. Brisbane. ISSN 0079-8835.
Retrieved 29-04-204 from: https://www.biodiversitylibrary.org/partpdf/303988

Ball, I.R. 1974 A Contribution to the Phylogeny and Biogeography of the Freshwater Triclads (Platyhelminthes: Turbellaria)
Biology of the Turbellaria 15 339-401 Riser & Morse( Ed.) McGraw-Hill Inc. 1974
Read 28-04-2024

Dugès, A. 1830 Aperçu de quelques observations nouvelles sur les Planaires et plusieurs genres voisins.
Annales des Sciences naturelles. 1. Ser. Tom. 21: 72-91
Read 27-04-2024 at: https://www.biodiversitylibrary.org/page/32172479#page/89/mode/1up

Girard, C. 1850 A brief account of the fresh-water planariae of the United States
Read 27-04-S2024 at: https://www.biodiversitylibrary.org/item/35741#page/273/mode/1up

de Vries, J. 1984 On the species of the Dugesia gonocephala group (Platyhelminthes, Turbellaria, Tricladida) from Greece. Bijdragen tot de dierkunde , Volume 54 - Issue 1 p. 101- 126
Retrieved 26-04-2004 from: https://repository.naturalis.nl/pub/504437

What's in a name ?

This flatworm was named Planaria gonocephala by the physician and naturalist Antoine Louis Dugès in 1830. In the article about his observations (see Bibliography), he wrote "(Nobis)" after the name, which means something like 'invented by me'. He began his description of the species with: "Cet grande espèce est assez commune dans quelques ruisseaux d'eau très-pure;..." (this large species is quite common in some (babbling) brooks with very clean water).

Gono- angle, chephala a deflection of the head, thus: the 'angle-headed flatworm'. There is a lizard genus called Gonocephalus , the angle-headed lizards.

The name, Planaria gonocephala Dugès 1830, changed because the French physician and biologist Charles Frédéric Girard (1850), after a study of American flatworms, in which he found a species of worm that closely resembled P. gonocephala of Dugès, separated a group and gave the genus name Dugesia proposed (page 265), probably in honor of Dugès. The name was accepted and the new name became Dugesia gonocephala (Dugès) 1830, in brackets according to the rules.

Ian R. Ball (1974) proposed a separate family, the Dugesiidae (p. 344). Within the Dugesiidae he proposed the genus name Girardia, named after Girard. (Do not confuse this name with Giarda, a parasitic worm). These names are accepted.

The taxonomy of flatworms remains difficult, the reason given being that they are primitive animals. It has now been established that D. gonocephala is a supergenus with a group of species that can only be distinguished on the anatomy of the genitals! (de Vries, 1984). Within that group, D. gonocephala has been redefined in stricto sensu ('in the strict sense, more precisely defined')