Tag Archives: invasiv species

THE RACE: As the (Flat)worm Turns


Dr. Tom Daniel, senior botanist, demonstrating impressive intrepidity in a Sao Tome river. GG VII A.  Stanbridge phot.

In the earliest blogs we discussed how islands are ideal for studying certain evolutionary processes and patterns; some of these phenomena like gigantism and dwarfism (below) are actually characteristic of islands. And, the results of these processes are much easier to see on islands because of their smaller size (versus, say, continents) and the smaller size of the plant and animal populations that inhabit them.

begon giant

Worlds largest (left, Sao Tome) and smallest (right, Principe) Begonia. (RCD construct).

Invasive species are organisms that somehow become accidentally established in areas where they did not exist before; they can be hugely damaging to ecosystems especially on islands, that are made up of plant and animal species that have co-evolved in isolation over perhaps millions of years. In the absence of natural predators (checks and balances), invader populations can become numerous and spread rapidly, and this can have a devastating effect by exhausting the resources these species utilize in the local environment. Invasive animal species populations can burgeon hugely, and then frequently die off; by then, the damage is usually done.

good plan

(Phot. Miko Nadel, GG VII)

A few years ago, we received a photo of a brightly colored worm-like creature on São Tomé (above), taken by one of our graduate students, Miko Nadel, a lichenologist from San Francisco State University. This striped creature turned out to be a terrestrial flatworm, a member of a primitive phylum of invertebrates called the platyhelminthes. Those of us lucky enough to study biology backwhen students were given actual organisms to observe rather than plastic models or video clips will remember “planarians,” aquatic flatworms (below) noted for their amazing ability to regenerate.

Dugesia planarian

Planarian (Dugesia) . Stock photo, Google photos.

planarian regen. U Heidelberg
Flatworm regeneration. (Univ. Heidelberg photo.

Terrestrial flatworms, also known as geoplanids have no anatomical or physiological mechanisms for retaining water and are thus very much tied to moist environments. They are voracious predators upon other soil invertebrates such as earthworms, slugs and, most importantly for us, snails. Geoplanids secrete a mucus that begins to digest and dissolve their prey externally (below), and all geoplanid species known feed using an extendable digestive tube or pharynx.

new geoattackGeoplanid attacking a snail. (R. Lima, phots)


As above, at Macambrara, Sao Tome. [Phot S. Mikulane]

Once aware of these, we began to notice more of them as did our ecologist colleague, Dr. Ricardo Lima, and we all became rather concerned. Why? Readers may recall that about half to 60% of all of the species of terrestrial mollusks (snails) of both São Tomé and Príncipe are endemic; i.e., they are found nowhere else in the world.

x new

[RCD construct-multiple photographers]

In fact, these snails have been isolated on the island and evolving for such a long period that scientists currently recognize six different genera and a unique snail family there! Given what we know about invasive species, if these geoplanids are indeed a new arrival then the unique snail fauna of the islands may well be in significant danger.



Another geoplanid [phot. F. Azevedo]

In 2012, we sent the original specimen to Dr. Ronald Sluys of Naturalis Biodiversity Centre in Leiden, Holland, one of the few specialists on flatworms. In the meantime, Dr. Ricardo Lima (below) has been conducting ecological research on the São Tomé forests for several years and has been able to collect many more geoplanids and send them to Dr. Sluys.

When the GG IX team visited Dr. Lima at Monte Café, São Tomé last year, he showed us pictures of a number of very different looking morphs of flatworms that he had collected and sent to Dr. Sluys. Were these different species or just variations on one or two species (morphs)?

various geos

Various geoplanids from Sao Tome [phots R. Lima, F. Azevedo, M. Nadel, R. Rocha]

Ron Sluys has been supervising a graduate student from the University of Kassel, Germany who is doing his MSc degree based on this material. His name is Matthias Neumann and as I write, he is on the island of São Tomé with Dr. Lima, studying the flat worms in situ and collecting more! We were able to fund his expedition with the Academy’s Gulf of Guinea Fund (see “Partners”, below).


Matthias Neumann and partner in the bush on Sao Tome. [R. Lima phot]

Matthias’ preliminary work suggests that there are indeed a number of species of geoplanids on the island: at least five new, undescribed species of the genus Othelosoma, and another previously known species, Bipalium kewense. B. kewense is an extremely widespread species, presumably carried about in the roots of plants; evidently it preys on earthworms rather than snails.

So far, little is known of these strange creatures. Neumann says that at least two of the undescribed species of Othelosoma are snail predators but even so, the presence of a number of species on the island rather than one dominant, rapidly spreading one might be taken as somewhat reassuring. If there are a number of closely related members of the same flatworm genus, it is more likely that the common ancestor of these species arrived a long time ago, speciated, and thus co-evolved with the endemic snail fauna. If this is so, than we would expect an ecological predator/prey balance in this system. If the flatworm fauna is in fact a radiation from a given colonizer, then it would mirror the status of the earthworm fauna as we understand it (below). So far, we are uncertain whether geoplanids are present on Príncipe.












We are in the planning stages for GG XI; see the next blog.

The Parting Shot:









A local teacher assists us in a binoculars demonstration on Sao Tome, GG IX. Dr. Luis Mendes in background.  [phot. A. Stanbridge]


The research expeditions and the primary school education program are supported by tax-deductable donations to the “California Academy of Sciences Gulf of Guinea Fund”* We are grateful for ongoing governmental support, especially to Arlindo de Ceita Carvalho, Director General, Victor Bomfim, and Salvador Sousa Pontes of the Ministry of Environment, Republic of São Tomé and Príncipe for their continuing authorization to collect and export specimens for study, and to Ned Seligman, Roberta dos Santos and Quintino Quade of STePUP of Sao Tome http://www.stepup.st/, our “home away from home”. GG VIII, IX , X and upcoming GG XI have been funded by a generous grant from The William K. Bowes Jr. Foundation, and substantial donations from Mrs. W.H.V.“D.A.” Brooke, Thomas B. Livermore, Rod C. M. Hall, Timothy M. Muller, Prof. and Mrs. Evan C. Evans, Mr. and Mrs. John L. Sullivan Jr., Clarence G. Donahue, Mr. and Mrs. John Sears, and a heartening number of “Coolies”, and members of the Docent Council of the California Academy of Sciences. Once again we are deeply grateful for the support of the Omali Lodge (São Tomé) and Roça Belo Monte (Príncipe) for both logistics and lodging and for partially sponsoring our education efforts for GG VII and GG VIII.

*California Academy of Sciences
55 Music Concourse Dr.
San Francisco, CA 94118