The rediscovery of Gibbula nivosa

The best known marine snail endemism in the Maltese Islands is certainly Gibbula nivosa Adams, 1851 - in vernacular, this is the Maltese Topshell. This mollusc was previously known in a 'live setting' only from St. Thomas' Bay in Marsaskala, with the ever-increasing scarcity of live individuals leading some authors to speculate on its extinction.

A paper published last November, however, sets the record straight - G. nivosa is alive and kicking (albeit in a critically endangered manner) in two localities around the Maltese Islands. You can read the original abstract here and a synopsis here.

Gibbula nivosa Adams, 1851
on a 1979 stamp

A walk around the Colosseum

The Amphitheatrum Flavium, better known as the Colosseum, is an iconic Roman era building in the centre of Rome. Ravaged by natural phenomena and looters throughout the centuries, it still stands towering above the city, and offers a wonderful opportunity to admire the architectural and engineering prowess of the ancient Romans.

In 1643, far before the advent of Linnaean taxonomy, a gent by the name of Domenico Panaroli decided to publish an inventory of the plants found inside the Colosseum after noticing several exotic (mainly North African) species inside and around it, resulting in the tome Plantarum Amphytheatralium Catalogus. Nowadays, the list of species from the Colosseum has grown to 684 species of plants (Caneva, 2003).

A humidity-loving moss, bearing sporangia (fruiting bodies) on stalks

Adiantum capillusveneris L., also found in Malta

Cymbalaria muralis G. Gaertn., B. Mey. & Scherb.

Of course, the ample vegetation offers much cover for my favourite invertebrates - snails. The most common ones present in soil were Eobania vermiculata (Müller, 1774) and a species of Cernuella (I have not yet decided which this is out of the confusing trio of C. virgata (Da Costa, 1778), C. cisalpina (Rossmässler, 1837) and C. neglecta (Draparnaud, 1805)). Later on, a few specimens of Papillifera bidens (Linnaeus, 1758) and Xerotricha apicina (Lamarck, 1822) were encountered amongst the ruins.

Cernuella sp.

Xerotricha apicina (Lamarck, 1822)

On a totally unrelated note, here's one of the modern day inhabitants of the Colosseum:

References:

Caneva, G., 2003. The Colosseum's use and state of abandonment as analysed through its flora. International Biodeterioration & Biodegradation, 51: 211-219.
Panaroli, D., 1643. Jatrologismi sive medicae observationes quibus additus est in fine Plantarum Amphytheatralium Catalogus. Typis Dominici Marciani, Rome.

New section

The picture on the right hand column of this blog labelled 'On S. E. Asian gastropods' now leads to a new page, where I will be posting my work on snails from the region of South-East Asia.

Updates will also be listed accordingly on this main blog section.

Amphidromus sekincauensis Dharma, 2007 - South Sumatra

Scorpion, interrupted

I (unintentionally) interrupted this scorpion at Għajn Tuffieħa while it was feasting upon the remains of a fellow arthropod - a hapless woodlouse, which can be seen still attached to the scorpion's jaws in the lower picture. A few seconds after being discovered, the scorpion released the morsel and assumed a compact, defensive stance, remaining utterly immobile until yours truly decided to leave it in peace and restore its stony hideout to its original place.

Only this species of scorpion exists in Malta. It is the small Euscorpius sicanus (Koch, 1837), also found on other Mediterranean islands.

Dissertation - A student’s guide to the geology of the Maltese Islands

The citation and abstract to my B. Ed. (Hons) dissertation have been added to the links on the right-hand side of this blog. The page can also be accessed through here.

Burst of purple...

... or indigo, lilac, anyway - whatever you want to call it. Cheirolophus crassifolius (Bertoloni) is much better known as Widnet il-Baħar, and it has been designated as the national plant of Malta. It is an endemic species with a troubled taxonomic history and embellishes cliffs with its beautiful blooms during most of summer. A very hardy plant which withstands highly alkaline soil, it has also been used as an ornamental and is frequently seen in roundabouts, public gardens and roads, though it remains very rare in the wild.

To read about the Maltese national tree please click here.

The Maltese national tree

Tetraclinis articulata (Vahl, 1791) is a North African conifer from the Cypress family. It is also the national tree of Malta, and is known locally as 'is-siġra tal-għargħar'. Most specimens encountered in the wild grow on clay slopes and appear to thrive in quite arid habitats. The picture above shows a mature specimen from the Maqluba depression at Qrendi, while below a young individual from Għajn Tuffieħa bay can be seen.

The giant Maltese dormice

Insular gigantism is an evolutionary process that leads to individuals in a population becoming progressively larger in size than their ancestors.

This process occurs when a population is isolated - for example, on a part of land which detaches from the mainland, beoming an island - and therefore divorced from its previous ecosystem, with all the biotic and abiotic factors which this entails.

In the new environment, the successful species may become free from a considerable number of predators (which may not have enough resources in the new ecosystem, therefore decreasing or becoming extinct) and also competitors (which may not be so successful in the new ecosystem).

In Malta, during the Pleistocene, this process can be seen to have occurred with several species of reptiles and mammals. The extinct giant lizard Lacerta siculimelitensis Böhme & Zammit-Maempel, 1982, still has congeners of smaller size living around the Mediterranean.

Two very interesting 'giants' from Maltese Pleistocene deposits are Leithia melitensis (Adams, 1863) and Leithia cartei (Adams, 1867). Fossils of these two animals were found from Middle Pleistocene deposits in Mnajdra, Mqabba and Wied Inċita, and a jaw from the National Museum of Natural History is pictured above. The genus is from the rodent family Gliridae (the dormice), which does not exist anymore on the islands of Malta. The size of the former was about twice that of the recent species Eliomys quercinus L., 1766, a specimen of which can be seen below. L. cartei was only slightly smaller than L. melitensis - indeed, differentiation based solely on size may give errors (Petruso, 2004).

There is also another genus of Maltese Pleistocene dormice, which consisted of animals smaller than Leithia but still large by 'modern' standards. This genus, Maltamys, consists of two species - Maltamys wiedincitensis Zammit Maempel & de Bruijn, 1982 and Maltamys gollcheri de Bruijn, 1966.

Zammit Maempel & de Bruijn (1982) are of the opinion that both Maltamys and Leithia are derived from Eliomys, due to similarity in anatomical features. However, more recent publications (Petruso, 2002; Petruso, 2004) state that convergent evolution is more probable, meaning that Maltamys and Leithia are more distantly related than previously thought.

Some material of the mentioned four fossil species has since been found in other Mediterranean countries, but all type material comes from Malta.

In a future post we shall look at an evolutionary pattern which is the diametrical opposite of insular gigantism - insular dwarfism.

References:

Böhme, W. & Zammit Maempel, G., 1982. Lacerta siculimelitensis sp. n. (Sauria: Lacertidae), a giant lizard from the Late Pleistocene of Malta. Amphibia-Reptilia, 3 (2-3): 257-268.
Bruijn, H. de, 1966. On the Pleistocene Gliridae (Mammalia, Rodentia) from Malta and Mallorca. Proceedings Koninklijke Nederlandse Akademie van Wetenschappen, B 69 (1): 480-496.
Petruso D., 2002. Il contributo dei micromammiferi alla Stratigrafia e Paleogeografia del Quaternario continentale siciliano. Ph. D. thesis, University of Napoli.
Petruso, D., 2004. New data on Pleistocene endemic Sicilian-Maltese dormice (Gliridae, Mammalia). 18th Senckenberg Conference 2004 in Weimar.
Zammit Maempel, G. & Bruijn, H. de, 1982. The Plio/ Pleistocene Gliridae from the Mediterranean Islands reconsidered. Palaeontology, B 85 (1): 113-128.

Picture of Eliomys quercinus L., 1766 from http://upload.wikimedia.org/wikipedia/commons/d/d5/Eliomys_quercinus02.jpg

A meeting of old and new

Sphincterochila candidissima (Draparnaud, 1801) is a very noticeable denizen of seaside cliffs and coralline karsts of the central Mediterranean. Right now (in addition to a period in late October-November) this species is highly active in Malta, with most reproduction and egg-laying taking place in time before the imminent summer season forces the animals to aestivate.

The snails are white for optimum reflection of heat, and construct hardy epiphragms (aperture coverings) from mucus and calcite dust, which prevent considerable water loss by evaporation.

The photograph shows a live mature individual, resting next to the long-dead shell of a presumed ancestor. The latter is embedded in a Holocene rupestral deposit. The specimens come from a small population at Rdum tal-Madonna, Mellieħa.

New project uploaded

A small website required for a University assignment has been uploaded at the link pasted below:

Maltese Endemic Landsnails

Virtually all photographs included are appearing on the web for the first time.

The website expires this year, so I will upload the content here as soon as that occurs.

Three wild Asteraceae, in bloom

Helichrysum melitense - Dwejra, 21.VI.2008


Bellis annua - Clapham Junction, 19.XII.2009

Anthemis urvilleana - Magħlaq, 26.III.2009

Variations on a theme, Part I

The sea snail Columbella rustica (Linné, 1758) is a very common inhabitant of Maltese rock pools and shallow platforms. It has a large range, extending from the Mediterranean down to the coasts of Angola and the eastern Atlantic islands.

The shell is highly variable, even within relatively short distances in this range, since it relies directly on the habitat. Specimens from the northwest of Malta tend to be mostly small and dark, while others from the sandy beaches of eastern Malta are light coloured and much larger (photograph below). This can be explained by natural selection - yellow specimens are better camouflaged against the sand, while mechanical damage to the shells by waves is not a pressing problem in a soft substrate such as sand. The small compact individuals from rocky shores, on the other hand, are exposed to very rough currents, which may dislodge and batter the shells onto rocks, therefore a smaller surface area works better in this regard. The darker colour also conceals shells in the algae better than light ones.

In addition to population-scale differences, there is also some variability on the individual level. The above photograph, on the extreme left, shows a 'freak' elongated specimen with convex whorls. A 'turriculated' variety from the same area is figured below (photo by Constantine Mifsud).

Part III: The Biogeography of the Maltese Islands

The species found in the Maltese Islands give a clear picture of the origin and previous connections to the surrounding lands.

The shelled slug Testacella riedeli is the only terrestrial gastropod showing strong affinities with North African fauna (Giusti et al., 1995), however, this group of fauna is also derived from South European forms, which survived on landmasses fragmenting from South Europe and colliding into North Africa in the Early Miocene. The majority of animals and plants are closely related to Sicilian organisms, with fossils excluding the possibility that these were imported through human agency.

As an archipelago, Malta probably started to become exposed during the Messinian Salinity Crisis in the late Miocene. The virtual absence of macrofossils in some areas of the UCL suggests a supralittoral (or intertidal) landmass (Pedley et al., 1976). Subsequently, the archipelago was probably submerged and exposed several times with fluctuating sea levels and tectonic activity up to the Pleistocene. Pliocene deposits are absent on the Maltese Islands, suggesting aerial erosion.

The earliest suggestions for links with Sicily can be seen in the Quaternary deposits of Ghar Dalam, which contain fauna similar to that in mainland Europe such as species of Ursus, Palaeoloxodon, Cervus, Hippopotamus and other large mammals. Subsequent isolation of Malta can be deduced by the progressive dwarfing of some of these mammals in a process known as insular dwarfism (Zammit-Maempel, 1989) and the reverse process (insular gigantism) in the lizard Lacerta siculimelitensis (Boehme & Zammit-Maempel, 1982).

More information on the origin of the Maltese Islands is evident by looking at the clausiliid snails (Thake, 1985). Lampedusa originated from a Sicilian ancestor and invaded the land presently containing Malta and Lampedusa island in the Late Miocene. This is supprted by the fact that the island of Lampedusa harbours a species similar to the Maltese Lampedusa, namely L. lopadusae. On isolation of the islands during the Pliocene, the Lampedusa sp. in Malta differentiated into L. imitatrix which later also gave rise to L. melitensis.

Subsequently, either the sea-level fell again or the landmass rose so that Malta became connected to Sicily again. The Lampedusa-like ancestor on Sicily had meanwhile evolved into Muticaria macrostoma, which took the opportunity to invade the islands again. Being more competitive than Lampedusa sp., it managed to take over the areas occupied by Lampedusa, which it pushed to a restricted area on the southern coast of Malta. Interestingly, the island of Filfla was probably already detached from the Maltese mainland since Muticaria does not occur there, but a form of L. imitatrix thrives. Muticaria evolved into local forms following subsequent isolation of the Maltese mainland.

Plants are also mostly allied with South Europe forms, for example, Iris sicula and Ophrys oxyrrhyncos are endemic to Malta and Sicily. A relatively weaker North African link is also shown in plants such as Crucianella rupestris and Hypericum aegypticum.

References:

Boehme, W. & Zammit Maempel, G. (1982) Lacerta siculimelitensis sp. n. (Sauria: Lacertidae), a giant lizard from the Late Pleistocene of Malta. Amphibia-Reptilia, 3 (2-3), pp. 257-268.
Giusti, F., Manganelli, G. & Schembri, P. J. (1995). The non-marine molluscs of the Maltese Islands. pp. 1-608, Torino.
Pedley, H. M., House, M. R., & Waugh, B. (1976), The Geology of Malta and Gozo. Proceedings of the Geologists’ Association, 87, pp. 325-341.
Thake, M. A. (1985). The biogeography of the Maltese Islands, illustrated by the Clausiliidae. Journal of Biogeography, 12, pp. 269-287.
Zammit Maempel, G. (1977). An Outline of Maltese Geology. pp. 1-44, Progress Press, Malta.
Zammit Maempel, G. (1989). Ghar Dalam – Cave and Deposits. pp. 1-74, PEG, Malta.