Terrestrial invertebrates - Udine Cultura

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environments, invertebrates living in brackish-water areas are divided into three ecological categories: halobiontic, if they live exclusively in salty environments; halophilic, if they have a preference for these environments but may also be found elsewhere; and haloxenic, if they are normally unrelated to salty environments and are found there because they are indifferent to salinity (for example, in the case of species which visit flowers) or remain confined in ecotone areas with weak salinity. As is typical of extreme environments, specialised forms are often represented by few species but high numbers of individuals: a study conducted on beetles in one site of the Lagoon of Venice found that the haloxene and halophilic forms, together, amounted to 30% of all species, but almost 70% of individuals. The distinction between these categories is often difficult. There are also species which behave differently according to the population considered. In these cases, halophilia is not an ecological requirement, but due to competition driving the more adaptable species into difficult environments. Only terrestrial invertebrates are described in this chapter: the aquatic fauna of brackish water and freshwater environments have already been covered in other volumes of the Italian Habitats series (“Brackish Coastal Lakes” and “Pools, Ponds and Marshes”, respectively; see also the chapter on aquatic invertebrates in this volume). For each group, the fauna of the saline environments are discussed separately from those of non-saline environments. 94 ■ Between land and sea: annelids, crustaceans and springtails Isopod of the genus Sphaeroma Emerging land around lagoons, affected by tidal excursions, hosts some amphibious species belonging to typically marine groups. Examples are the annelids living in brackish mud, such as Hediste diversicolor and Timarete filigera, the nearest to dry land Amphipod of the genus Orchestia for the almost exclusively marine group of polychaetes. Representatives of marine groups of crustaceans that have acquired the capacity to pass more or less lengthy periods out of water can also be identified. Among the less “emancipated” are decapods, represented by the green crab (Carcinus aestuarii), a truly marine species which every now and then may be found on dry land, and flabellate isopods, represented by Sphaeroma species, which may even breed without returning to the sea. However, they remain dependent on the presence of damp ground, because their porous teguments mean that they can easily fall prey to dehydration. Slightly more constrained by the water but always very hygrophilous, are the few talitrid amphipods which frequent dry land. Examples are Talitrus saltator, which does not stray from the beaches, or species of the genus Orchestia, which venture further inland. The halophilic O. gammarellus is highly abundant in brackish areas: hundreds of them may be seen leaping away in all directions as soon as any object is lifted off the ground. Freshwater environments are frequented by its ally O. cavimana, which ascends watercourses to sites on the mainland. The large group of oniscoidean isopods (woodlice) behaves in the opposite manner: they are typically terrestrial animals, a few species of which frequent brackish environments, and a tiny minority (genus Tylos) even reach the tide mark on sandy beaches. Among the species of brackish environments, some are specialised, like Halophiloscia couchii and Armadilloniscus ellipticus, which cohabit with talitrids on the ground of the wettest glasswort communities and which give way, on higher ground and further inland, to less specialised forms, such as Armadillidum assimile, a ubiquitous dry-land species also found in damp non-saline environments. Among the collembolans (springtails), Anurida maritima is characteristic of sandbanks. This animal is only a couple of millimetres long, and occasionally becomes extremely conspicuous by forming swarms of thousands of specimens which, closely gathered together, cover the ground like large patches of indigo. 95
96 ■ Molluscs The malacological fauna of sandbanks is characterised by a quite small number of species but an often high density of individuals. In particular, two small gastropods are frequently found: Truncatella subcylindrica and Myosotella myosotis. Myosotella myosotis The former, as its name suggests, loses the first rings of its shell with age while retaining all the subsequent ones, which are of a constant diameter. The latter is a ubiquitous species, which can tolerate sudden changes in salinity and temperature. Its shell may vary considerably in shape, even on a small geographical scale, making it difficult at times to distinguish it from similar but rarer species, such as Auriculinella bidentata and Ovatella firminii, which are more demanding in their choice of environment. All these species live close to the tide line. Oxyloma elegans is characteristic of damp freshwater environments, which are also frequented by many inland species. This species is associated with riverbanks and freshwater reservoirs with dense riparian vegetation, where it is easily observed on the leaves of reeds, cattails, irises and other marsh plants. It is spread throughout mainland Italy and on the large islands, but is not closely linked to the coastal strip, as it may also be found above 1000 m. ■ Spiders Detailed information on the spiders of lagoon and river mouth ecosystems is mostly available for the northern Adriatic coast. In brackish-water areas, the ground-dwelling arachnid fauna is dominated by numerous species of lycosids or wolf spiders: among the Larinioides suspicax most abundant are Pardosa cribrata and P. luctinosa, the latter apparently stenoecious and loyal to brackish-water environments. Some hygrophilous species that are indifferent to salinity conditions are also frequent, such as Trochosa hispanica and various species of the genus Pirata. In the same environments, but on the vegetation, two salticids - Heliophanus flavipes and Sitticus caricis are particularly abundant: they lie in wait for their prey on plant stems, without using webs. Much more obvious than the small salticids are the araneids of the genus Larinioides (L. suspicax in particular), due both to their conspicuous size and large webs, which are stretched horizontally on herbaceous vegetation and made even more noticeable by the white silk case next to them - the spider’s hiding-place. On drier and sunnier grasslands, another eye-catching araneid is the Argiope lobata unmistakable Argiope lobata, of which the enormous females are most easily seen. This is a thermophilous species, without any specific bond with brackish water, but frequent along the coasts of the central and southern regions. The clubionids are very abundant in reed-beds. They are represented by many species of the genus Clubonia, in particular C. phragmitis and C. stagnatilis, and lycosids, among which Trochosa hispanica and Alopecosa pulverulenta are sometimes very abundant. In a study conducted at Valle Vecchia, near Caorle in the Veneto region, individuals of these two species accounted for more than two-thirds of all spider fauna. They are in any case both ubiquitous species, and the former has ever been observed to show a slight preference for scrub environments rather than open areas.The third quite abundant lycosid, Pardosa prativaga, also frequents reed-beds, probably not as its elective habitat, but suboptimal. A small salticid, Marpissa nivoyi, moves around on the ground - it is often associated with its congener M. radiata, which however prefers to stay on the vegetation. Mendoza canestrinii also lives among reed stems and, unlike the two previous ubiquitous species, shows an obvious preference for reed-beds, as does Antistea elegans, of the hahniid family, a hygrophilous species which may also be found in water-meadows and other types of damp environment. 97
Page 1: Terrestrial invertebrates MARCO ULI
Page 5 and 6: 100 ■ Heteropterans The typical h
Page 7 and 8: 104 the wet mud on the coastline, a
Page 9 and 10: 108 ■ Dipterans The dipterans of
Page 11 and 12: Terrestrial vertebrates MAURO BON
Page 13 and 14: 116 117 Great crested grebe (Podice
Page 15 and 16: diver (Gavia arctica) and red-throa
Page 17 and 18: 124 Recent artificial environments:
Page 19 and 20: 128 aquatic birds, especially dabbl
Page 21 and 22: 132 Lesser white-toothed shrew (Cro
Page 23 and 24: agriculture and livestock farms sur
Page 25 and 26: 140 These environments are protecte
Page 27 and 28: Teaching suggestions MARGHERITA SOL
Page 29 and 30: 148 How to identify molluscs More t
Page 31 and 32: 152 RELINI G., BERTRAND J., ZAMBONI
Page 33 and 34: 156 Gibbula - 49, 52 Heterocerus -
Page 35: The authors wish to thank the follo

Terrestrial invertebrates - Udine Cultura

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