Balian E.V., L?v?que C., Segers H., Martens K. (Eds.) Freshwater Animal Diversity Assessment

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families, i.e. Emydidae and Geoemydidae. Their

adaptation towards a more or less complete life

outside of the water seems to be a rather fast process,

because in one genus, one can recognize true fresh-

water species, amphibious or semi-aquatic species

and terrestrial turtles. This condition is especially

conspicuous in the Neartic genus Terrapene (box

turtles), family Emydidae, the e xtreme being T. coa-

huila, which is fully aquatic, and T. ornata ,whichcan

live in very dry areas. Some other species that have

adopted a rather t errestrial life, however often in

forested and damp areas, belong to the family

Geoemydidae and are encountered in South-east Asia

(Heosemys, Geoemyda, Pyxidea, Cuora), an d in

Tropical America (Rhinoclemmys). Outside these

families, turtles that regularly leave their water home

andarecomfortableonlandbelongtothegenera

Pelomedusa (Pelomedusidae ), Kinosternon, Chelo-

nia, Glyptemys and some others. These can wander

long distances, especially by night, from one swamp

to another. Most other species only leave the water

either for basking (on logs, rocks, sandy shores: e.g.

Platysternon) or for laying eggs. Table 1 gives data

on the typical environment of the extant genera of

turtles.

Many turtles are opportunistic regarding their diet,

eating any available food, whether of animal or

vegetal origin, but they usually probe potential food

items by smelling before eating. Q uite often, during

growth, there is a shift from a rather carnivorous

feeding towards a vegetarian one. Preys mainly

consist of invertebrates (e.g. insects, mollusks), or

carrion: many turtles are unable to capture adult

vertebrates, except for some specialized taxa (e.g.

Chelidae like Chelus, Trionychidae, Macrochelys)

that are capable of ambushing ﬁshes. Vegetarian

turtles eat aquatic plants, grasses, leaves or fallen

fruits.

Species and generic diversity of freshwater turtles

A little more than 320 species of Turtles are

recognized today, depending on the taxonomy fol-

lowed (Pritchard, 1979; Ernst & Barbour, 1989;

Iverson, 1992; David, 1994; Spinks et al., 2004;

Bonin et al., 2006). A single family includes the true

terrestrial members, called Tortoises (18 genera, ca.

60 species), and two families include all the present

marine Turtles or true Turtles (6 genera, 7–8 species).

All others Chelonians are freshwater turtles and

belong to one of the other 11 families (Table 2). Three

families (Chelidae, Pelomedusidae and Podocnemid-

idae) belong to suborder Pleurodira, which is

considered to be the most primitive suborder not-

withstanding that several specialized features are

present. Pleurodira has a typical Gondwanan range,

occurring mainly in the Southern hemisphere. The

other families belong to Cryptodira; 3 families are

monotypic (Carettochelyidae, Dermatemydidae and

Platysternidae), with a limited distribution; 3 other

families include numerous species and have a wide

range, covering several biogeographical regions

(Trionychidae, and the related Emydidae and Geo-

emydidae). Finally, 2 families (Chelydridae and

Kinosternidae), with only 6 genera together, are

limited to the New World, with a mainly Nearctic

range (Vetter, 2005). Table 1 gives the list of the

genera considered in this review, with their respec-

tive number of sp ecie s.

Fig. 1 (a) Mesoclemmys nasuta (Pleurodira), (b) Mauremys

rivulata (Cryptodira)

594 Hydrobiologia (2008) 595:593–598

123

Table 1 Summary of the diversity, distribution and ecology of the extant genera of freshwater turtles

Suborder, family Genus Number of species Biogeographical region Typical environment

Pleurodira

Chelidae Chelodina 8 Australasian Rivers, swamps

Elseya 10 Australasian Rivers, swamps

Elusor 1 Australasian Rivers

Emydura 7 Australasian Rivers, swamps

Macrochelodina 5 Australasian Rivers

Pseudemydura 1 Australasian Swamps

Rheodytes 1 Australasian Rivers

Acanthochelys 4 Neotropical Small rivers, swamps

Chelus 1 Neotropical Swamps

Hydromedusa 2 Neotropical Small rivers

Mesoclemmys 10 Neotropical Rivers, swamps, ponds

Phrynops 4 Neotropical Rivers

Platemys 1 Neotropical Swamps, ponds,

Rhinemys 1 Neotropical Rivers (black waters)

Pelomedusidae Pelomedusa 1 Afrotropical (incl. Madagascar) Ponds, swamps

Pelusios 18 Afrotropical (incl. Madagascar) Lakes, quiet rivers

Podocnemididae Erymnochelys 1 Madagascar (Afrotropical) Lakes, quiet rivers

Peltocephalus 1 Neotropical Swamps, rivers

Podocnemis 6 Neotropical Rivers and tributaries

Cryptodira

Carettochelyidae Carettochelys 1 Australasian Rivers and tributaries

Chelydridae Chelydra 3 Nearctic, Neotropical Swamps, rivers

Macrochelys 1 Nearctic Lakes, quiet rivers

Dermatemydidae Dermatemys 1 Neotropical (North) Lakes, quiet rivers

Emydidae Actinemys 1 Nearctic Swamps, ponds, rivers

Chrysemys 1 Nearctic Rivers, Lakes

Clemmys 1 Nearctic Swamps, ponds, rivers

Deirochelys 1 Nearctic Swamps, rivers

Emydoidea 1 Nearctic Swamps, rivers

Emys 1 Palaearctic Swamps, ponds, rivers

Glyptemys 2 Nearctic Swamps, bogs, rivers

Graptemys 15 Nearctic Rivers, lakes

Malaclemys 1 Nearctic Brackish waters only

Pseudemys 3 Nearctic Rivers, lakes, ponds

Terrapene 6 Nearctic Swamps or terrestrial

Trachemys 15 Nearctic, Neotropical Rivers, lakes, ponds

Geoemydidae Batagur 1 Oriental Rivers and tributaries, estuaries

Callagur 1 Oriental Rivers and tributaries, lakes

Chinemys 2 Oriental, Palaearctic Rivers, swamps, ponds

Cuora 12 Oriental Rivers, swamps or terrestrial

Cyclemys 4 Oriental Rivers, swamps

Geoclemys 1 Oriental Rivers and tributaries

Geoemyda 3 Oriental Swamps or terrestrial

Hydrobiologia (2008) 595:593–598 595

123

Present distribution and main areas of endemicity

Most freshwater turtles live in the tropical and

subtropical zones, only few reach the Northern tem-

perate zone. Even in warm areas, their distribution is

quite unbalanced, and two hot spots, both of endemicity

and diversity, can be discerned in the Northern

hemisphere. One covers the Southeast of North

America (Emydidae), the other one is Southeast Asia,

more speciﬁcally the Indo-Malayan biogeographical

Table 1 continued

Suborder, family Genus Number of species Biogeographical region Typical environment

Hardella 2 Oriental Rivers, lakes

Heosemys 4 Oriental Rivers, swamps or terrestrial

Hieremys 1 Oriental Rivers, swamps

Kachuga 3 Oriental Rivers and tributaries

Leucocephalon 1 Oriental Rivers, swamps

Malayemys 2 Oriental Rivers, swamps, ponds

Mauremys 6 Oriental, Palaearctic Rivers, swamps, ponds, wadis

Melanochelys 2 Oriental Rivers, swamps or terrestrial

Morenia 2 Oriental Rivers and tributaries, swamps

Notochelys 1 Oriental Rivers, swamps

Ocadia 1 Oriental Rivers, swamps, ponds

Orlitia 1 Oriental Rivers, lakes

Pangshura 5 Oriental Rivers, swamps

Pyxidea 1 Oriental Swamps or terrestrial

Rhinoclemmys 9 Neotropical Rivers, lakes, swamps or terrestrial

Sacalia 2 Oriental Rivers, swamps

Siebenrockiella 1 Oriental Rivers, swamps

Kinosternidae Claudius 1 Neotropical (North) Swamps, quiet rivers

Kinosternon 19 Nearctic, Neotropical Swamps, quiet rivers

Staurotypus 2 Neotropical (North) Lakes, quiet rivers

Sternotherus 4 Nearctic Swamps, quiet rivers

Platysternidae Platysternon 1 Oriental Small rivers in hilly areas

Trionychidae Amyda 1 Oriental Rivers and tributaries, lakes

Apalone 3 Nearctic Rivers and tributaries, lakes

Aspideretes 4 Oriental Rivers and tributaries, lakes

Chitra 3 Oriental Rivers and tributaries

Cyclanorbis 2 Afrotropical Rivers and tributaries, lakes

Cycloderma 2 Afrotropical Rivers and tributaries, lakes

Dogania 1 Oriental Rivers and tributaries, lakes

Lissemys 2 Oriental Rivers and tributaries, lakes

Nilssonia 1 Oriental Rivers and tributaries, lakes

Oscaria 1 Oriental, Palaearctic Rivers and tributaries, lakes

Palea 1 Oriental Rivers and tributaries, lakes

Pelochelys 2 Oriental Rivers and tributaries, estuaries

Pelodiscus 1 Oriental, Palaearctic Rivers and tributaries, swamps

Rafetus 1 Palaearctic Rivers and tributaries

Trionyx 1 Afrotropical, Palaearctic Rivers and tributaries, lakes

Total N = 79 N = 257

596 Hydrobiologia (2008) 595:593–598

123

realm (Geoemydidae and Trionychidae) (Vetter &

van Dijk, 2006). The relative paucity of turtles in

the Palaearctic region, especially compared with the

Nearctic, is most probably a consequence of the

Pleistocene glaciations, in conjunction with the East-

West orientation of geographical barriers (Mediterra-

nean basin, Himalayas) preventing climate-induced

range shifts and recolonization. In the Southern hemi-

sphere, one family (Chelidae) predominates, and is

almost equally represented in South America and in

Australasia, while the Pelomedusidae is the dominant

family of freshwater turtles in Africa. Endemicity at the

regional, or even local, scale is the rule for freshwater

turtles at the genus and, especially, species level; there

are relatively few genera or species that have a range

that spans more than one region. Figure 2 gives an

arrangement of the taxa of Table 1 classiﬁed according

to biogeographical regions.

Table 2 Distribution of extant species and genera of freshwater turtles, per Biogeographical region. (number of genera in

parentheses)

PA NA NT AT OL AU PAC ANT World

Chelidae 23 (7) 33 (7) 56 (14)

Pelomedusidae 19 (2) 19 (2)

Podocnemididae 7 (2) 1 (1) 8 (3)

Carettochelyidae 1 (1) 1 (1)

Chelydridae 2 (2) 2 (1) 4 (2)

Dermatemydidae 1 (1) 1 (1)

Emydidae 1 (1) 42 (11) 6 (1) 48 (12)

Geoemydidae 3 (1) 9 (1) 57 (23) 68 (24)

Kinosternidae 12 (2) 17 (3) 26 (4)

Platysternidae 1 (1) 1 (1)

Trionychidae 4 (4) 3 (1) 5 (3) 17 (10) 26 (15)

Total 8 (6) 59 (16) 65 (16) 25 (6) 72 (34) 34 (8) 0 (0) 0 (0) 257 (79)

PA, Palaearctic region; NA, Nearctic region; NT, Neotropical region; AT, Afrotropical region; OL, Oriental region; AU, Australasian

region; PAC, Paciﬁc region and Oceanic Islands; ANT, Antarctic region

Fig. 2 Distribution of

freshwater turtle species

and genera per

biogeographic region

(number of species /

number of genus). PA,

Palaearctic region; NA,

Nearctic region; NT,

Neotropical region, AT,

Afrotropical region; OL,

Oriental region; AU,

Australasian region; PAC,

Paciﬁc region and oceanic

islands; ANT, Antarctic

region

Hydrobiologia (2008) 595:593–598 597

123

Human related issues

Turtles (and tortoises) are very sensitive to modiﬁ-

cations of their environment, and are among the ﬁrst

vertebrates to disappear when a habitat is destroyed.

Another threat is increasing collection, for food, for

perceived medical purposes and for the pet trade.

According to the last IUCN classiﬁcation (IUCN,

2006), 159 species, or ca. 60%, of freshwater turtles

are accounted as being more or less threat ened. Data

are deﬁcient for 10 species including 5 probable

hybrids, 1 species is at low-risk but conservation

dependant (Podocnemis expansa, a large river turtle

of South America), 11 are considered as of least

concern, 40 as vulnerable, 38 as near threatened, 36

as endangered, 20 as critically endangered, 1 as

extinct in the wild (Aspideretes nigrica ns, a large soft

shell turtle restricted to a tank in Bangladesh) and 2

as extinct (Pelusios seychellensis and Cuora yunnan-

ensis, although a specimen o f the later has recently

been observed in a market). About one third of these

threatened species are South-east Asian, China being

a major consumer of turtles. It is revealing that

among the species listed as endangered or critically

endangered there are at lea st ﬁve, resp. two species,

which were quite abundant in the pet trade no more

than twenty years ago: Chinemys reevesii, Geoemyda

spengleri, Heosemys spinosa, Pyxidea mouhotii,

Platysternon megacephalum and Cuora galbinifrons

and Cuora trifasciata, respectively), all from South-

east Asia.

Acknowledgements I thank Estelle Balian for her patience

and support, and Peter Paul van Dijk for his fruitful comments

as reviewer.

References

Bonin, F., B. Devaux & A. Dupre

, 2006. Turtles of the World.

Transl. Pritchard, The Johns Hopkins University Press, P.

C. H. Baltimore.

David, P., 1994. Liste des reptiles actuels du monde I.

Chelonii. Dumerilia 1: 7–127.

Ernst, C. H. & R. W. Barbour, 1989. Turtles of the world.

Washington, Smithsonian Inst. press.

IUCN, 2006. 2006 IUCN Red List of Threatened Species.

http://www.iucnredlist.org, downloaded on 6 November

2007.

Iverson, J. B., 1992. Revised Checklist with Distribution Maps

of the Turtles of the World. Richmond, Indiana, privately

printed.

Pritchard, P. C. H., 1979. Encyclopedia of Turtles. T.F.H.

Publications Co., Neptune City, New Jersey.

Spinks, P. Q., H. B. Shaffer, J. B. Iverson & W. P. McCord, 2004.

Phylogenetic hypothesis for the turtle family Geoemydidae.

Molecular Phylogenetics and Evolution 32: 164–182.

Vetter, H., 2005. Terralog, Turtles of the World, Vol. 3. Central

and South America. Frankfurt am Main and Rodgau,

Chimaira and Aqualog.

Vetter, H. & P. P. van Dijk, 2006. Terralog, Turtles of the

World, Vol. 4. East and South Asia. Frankfurt am Main

and Rodgau, Chimaira and Aqualog.

598 Hydrobiologia (2008) 595:593–598

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FRESHWATER ANIMAL DIVERSITY ASSESSMENT

Global diversity of snakes (Serpentes; Reptilia)

in freshwater

Olivier S. G. Pauwels Æ Van Wallach Æ Patrick David

 Springer Science+Business Media B.V. 2007

Abstract A list of the snake species inhabitin g

freshwaters is provided. It includes 153 species,

which represents about 5% of all known snakes.

These freshwater snakes belong to 44 genera distrib-

uted among the families Acrochordidae, Boidae,

Colubridae, Elapidae, Homalopsidae and Viperidae.

The highest diversities in freshwater snakes are found

in the Oriental (64 species) and Neotropical (39

species) Regions. Conservation actions are needed

for several overcollected species with a limited

distribution.

Keywords Snakes  Serpentes  Freshwater 

Biodiversity

Introduction

With about 3000 species known so far, snakes are a

successful group of predatory vertebrates that occupy

a wide range of environments in tropical and

temperate areas, from deserts and mountain summits

to oceans. Many snake species live close to water and

often venture into it; probably all can swim, but only

a limited number can be consider ed strictly aquatic.

One can regard the truly aquatic snakes as those

foraging in water and which are unable to survive

without aquatic prey and frequent to constant

submersion. Subtle external anatomical characters

betray aquatic habits in freshwater snakes. These

morphological specializations include position of

nostrils on the snout top, allowing the snake to breath

at the surface without being seen by birds and other

predators; a banded pattern, useful for camouﬂage;

valvular nostrils; dorsolaterally oriented eyes; keeled

scales; etc. However none of these characters are

common to all freshwater snakes, and some of these

characters, like a banded pattern, are shared with

many strictly terrestrial as well as with many

exclusively marine species. Many freshwater species

Guest editors: E. V. Balian, C. Le

que, H. Segers, &

K. Martens

Freshwater Animal Diversity Assessment

O. S. G. Pauwels

Monitoring and Assessment of Biodiversity Program,

National Zoological Park, Smithsonian Institution,

Gamba, Gabon

O. S. G. Pauwels (&)

Institut Royal des Sciences Naturelles de Belgique,

Rue Vautier 29, Brussels 1000, Belgium

e-mail: osgpauwels@yahoo.fr

V. Wallach

Museum of Comparative Zoology, Harvard University,

Cambridge, MA 02138, USA

e-mail: vwallach@oeb.harvard.edu

P. David

partement Syste

matique et Evolution, USM 602

Taxonomie-collection—Reptiles & Amphibiens, Case

postale 30, Muse

um National d’Histoire Naturelle, 25 rue

Cuvier, F-75231 Paris Cedex 05, France

e-mail: pdavid@mnhn.fr

123

Hydrobiologia (2008) 595:599–605

DOI 10.1007/s10750-007-9118-x

belong to genera also including marine or terrestrial

species. Only the combination of morphology and

natural history data can reveal if a species is a

freshwater dweller, and much work remains to be

done in these ﬁelds. Hereafter we brieﬂy present the

results of a thorough study of the literature and our

experience in the ﬁeld to provide a list as accurate as

possible of the freshwater snakes of the World. The

list must be regarded as provisional, since biological

information which could conﬁrm freshwater habits is

lacking for many genera and species (Fig. 1).

Species diversity and distribution

Details on freshwater snake systematics, distribution

and natural history are to be found in the works of,

a.o., Anonymous (no date) (World), Boulenger (1913)

(Palaearctic), Manthey & Gr ossmann (1997), Pauwels

et al. (2001), Cogger et al. (1987), Murphy & Voris

(2005), Vogel et al. (2004), Voris et al. (2002)

(Australasian and Oriental), do Amaral (1978), Cei

(1993) and Roze (1996) (Nearctic and Neotropical).

Familial and subfamilial allocations of colubroid

genera mostly follow Lawson et al. (2005) (Fig. 2).

Australasian Region

Among the most specialized aquatic snakes are the

acrochordids, containing three speci es found in

brackish and/or freshwater. Their morphological

adaptations towards aquatic life are so radical (a.o.

absence of enlarged ventral scales) that these snakes

are unadapted for terrestrial locomotion. One fresh-

water Acrochordus species (A. arafurae) lives in the

Australasian Region. Laticauda crockeri, endemic to

Rennell Island (Sol omon Archipelago), is the only

known freshwater member of this marine elapid

genus. The freshwaters of the region are also home to

four homalopsid snakes: Enhydris polylepis, Cantoria

annulata, Cerberus rynchops and Heurnia ventro-

maculata. The Australasian Region shares one

freshwater snake species with the Oriental Region:

Cerberus rynchops, which actually mainl y lives in

brackish and sea water. The Australasian freshwater

snake diversity is as poor as that of the Palearctic

Region, and about nine times less rich than that of the

neighbouring Oriental Region.

Afrotropical Region

Relatively few aquatic snakes live in the Afrotropical

Region’s continental waters. They are distributed

among the families Colubridae and Elapidae. Several

genera are specialized towards aquatic life and

contain exclusively freshwater species: Afronatrix,

Grayia (sensu lato, including Xenurophis), Helophis,

Hydraethiops (including two species, one, H. laevis,

being know n so far by only three specimens) and

Limnophis (Colubridae), Boulengerina and Lycodon-

omorphus (including a.o. L. bicolor, endemic to Lake

Tanganyika) (Elapidae). Madagascar houses only two

freshwater species, both endemic to the island,

Liopholidophis lateralis and L. sexlineatus.Itis

interesting to note the extreme colour and habitus

Fig. 1 Enhydris jagori

(photo credit: Olivier S.G.

Pauwels)

600 Hydrobiologia (2008) 595:599–605

123

resemblance between the harmless Grayia ornata and

the Boulengerina cobras, with which they share most

of their distribution. In contrast with the Australasian

Region, Afrotropical brackish waters do not house

any specialized man grove-dwelling species, although

mangroves are widespread there. Besides the strictly

freshwater Afrotropical taxa, a number of mostly

terrestrial snakes use aquatic systems as hunting

ﬁelds, at least occasionally, including: Dromophis

lineatus, Natriciteres spp. (Colubridae), Naja spp.,

Pseudohaje goldii (Elapidae) and Python spp. (Pyth-

onidae). None of the Afrotropical freshwater snake

species is shared with another Region.

Nearctic Region

Nearctic freshwater snakes belong to the Colubridae,

Elapidae and Viperidae. The colubrid genera Faran-

cia, Nerodia, Regina and Seminatrix include only

freshwater dwellers. The natricine genus Thamnophis

includes 34 species, of which only four are fre shwater

dwellers. The Nearctic Region is home to a single

venomous freshwater species, the pitviper Agkistrodon

piscivorus. No Nearctic aquatic species is shared with

the Neotropical Region. The diversity is relatively low

and comparable to that of the Afrotropical Region.

Neotropical Region

The most remarkable Neotropical freshwater snakes

are the anacondas (Boidae: Eunectes spp.), with

E. murinus being one of the world’s longest snake s,

with ofﬁcial records of specimens above 8 m long.

The venomous New World elapid genus Micrurus

includes 70 species; a single species (M. surinamen-

sis) being aquatic. All other Neotropical freshwater

snakes belong to 11 xenodontine colubrid genera.

Some of these genera exclusively contain aquatic

species (e.g., Helicops); in others aquatic species are

the exception (e.g., Echinanthera). None of the New

World freshwater snake species is shared with the

Old World. The Neotropical freshwater snake diver-

sity is the world’s second highest, although still much

lower than the Oriental one.

Fig. 2 Distribution of freshwater snake species and genera per

biogeographic region (species number/genus number). PA:

Palaearctic Region, NA: Nearctic Region, NT: Neotropical

Region, AT: Afrotropical Region, OL: Oriental Region, AU:

Australasian Region, PAC: Paciﬁc Region and oceanic islands,

ANT: Antartic Region

Hydrobiologia (2008) 595:599–605 601

123

Oriental Region

Among the two acrochordids inhabiting the Oriental

Region, only Acrochordus javanicus penetrates fresh-

waters. The genus Hydrablabes is composed of two

freshwater species, both endemic to Borneo. The

genera Opisthotropis and Parahelicops, sometimes

considered to be synonymous but here regarded as two

distinct genera, comprise a total of 16 speci es from the

Oriental Region, and one (O. kikuzatoi) from Japan.

Many are restricted to unpolluted fast streams in

undisturbed montane forest. All four Sinonatrix

species, a genus endemic to the Oriental Region, are

living in freshwater. The genus Xenochrophis

includes 11 species, all freshwater dwellers and

belonging to the Oriental Region, except one,

X. vittatus, whose distribution extends east to Sulaw-

esi, and is thus shared with the Australasian Region .

Besides sea snakes, the most aquatic snakes are the

Homalopsidae, which include 10 genera and 33

species, living in sea, mangroves or freshwater. They

are mainly distributed in the Oriental Region, but

some inhabit the Australasian Region. Enhydris

pakistanica occurs at the limit between the Oriental

and the Palaearctic Regions. Only one of the two

known Cerberus inhabits freshwaters, and this species

(C. microlepis) is endemic to Lake Buh i, Luzon,

Philippine Islands. The most morphol ogically pecu-

liar homalopsid is the genus Erpeton, characterized by

two soft nasal appendices, the role of which is still

unclear. The marine elapid snake Hydrophis torquatus

diadema often penetrates into Tonle Sap Lake in

Cambodia (Ineich, 1996). The ‘‘sea snake’’ Hydrophis

semperi seems endemi c to the freshwater lake Taal in

the Philippines. Hydrophis siba uensis is know n from

Sibau River in Borneo. No information on the biology

of the monotypic genera Anoplohydrus, Fimbrios and

Iguanognathus (Colubridae; future morphological

studies might attribute Anoplohydrus to homalopsids)

are currently available, which would allow to list them

with certainty among the fre shwater snakes.

Palaearctic Region

In Europe, only two strictly aquatic snakes occur,

both being harmless colubrids: Natrix maura, found

in Europe and north Africa, and N. tessellata, which

has a wide Eurasian distribution. Besides the latter

species, Palaearctic Asia is home to four other

natricine freshwater snakes. Two of them (Sinonatrix

annularis and Xenochrophis piscator [including

X. sanctijohannis]) are shared with the Oriental

Region. The distributio ns of some of the species of

Opisthotropis extend to the limits betwee n the

Oriental and the Palaearctic Regions. None of the

Palaearctic freshwater species or genera are shared

with the Afrotropical Region.

A total of 153 freshwater snake species, i.e., circa

5% of all currently known snakes, is found in the

Australasian, Afrotropical, Nearctic, Neotropical,

Oriental and Palaearctic Regions (see Table 1). No

snakes are known from the Antarctic Region. The most

specialized species towards aquatic life are the elapid

sea snakes, of which two genera contain species living

eshwater, and Homalopsidae. All homalopsids

show strong morphological adaptations to aquatic life

(all notably have dorsolaterally oriented eyes and

valvular nostrils) and contain marine as well as

brackish and freshwater species. Most of the remaining

freshwater snakes belong to the colubrid Natricinae

and Xenodontinae, but these subfamilies contain

terrestrial as well as freshwater species. Freshwater

snakes are found in various groups in six families:

Acrochordidae, Boidae, Colubridae, Elapidae, Homa-

lopsidae and Viperidae. Except the Acrochordidae and

Homalopsidae, no freshwater species belong to strictly

aquatic snake families. Among the 44 genera including

freshwater species, 13 (29.5%) include non-freshwater

species, i.e. terrestrial or marine (compare total

number of species in each genus versus number of

freshwater species per Region in Table 1).

Human related issues

Few works on freshwater snake –human interactions

are available, but ﬁeld studies might reveal locally

important links. For instance, some homalopsids are

intensively collected for food or skin trade, as is

happening in Tonle Sap Lake in Cambodia, where

they are also used to feed crocodiles in neighbouring

breeding farms; this overcollection notably puts at

risk Enhydris longicauda, endemic to the lake (Stuart

et al., 2000). In China, snakes like Sinonatrix annu-

laris, some Enhydris spp. and Homalopsis are sold in

large numbers in food markets and restaurants (Zhou

& Jiang, 2005). Fuchs & Fuchs (2003) documented the

602 Hydrobiologia (2008) 595:599–605

123

Table 1 Global distribution of freshwater snake species per Region

Taxa/Region PA NA NT AT OL AU WORLD

ACROCHORDIDAE

Acrochordus (3) 1 1 2

BOIDAE

Boinae

Eunectes (4) 4 4

COLUBRIDAE

Colubrinae

Grayia (4) 4 4

Natricinae

Afronatrix (1) 1 1

Atretium (2) 22

Hydrablabes (2) 2 2

Hydraethiops (2) 2 2

Limnophis (1) 1 1

Natrix (4) 2 2

Nerodia (10) 10 10

Opisthotropis (15) 1 14 15

Parahelicops (2) 2 2

Regina (4) 4 4

Seminatrix (1) 1 1

Sinonatrix (4) 1 4 4

Thamnophis (34) 4 4

Xenochrophis (11) 1 11 1 11

Pseudoxyrhophiinae

Liopholidophis (9) 2 2

Xenodontinae

Coniophanes (12) 1 1

Echinanthera (6) 1 1

Farancia (2) 2 2

Gomesophis (1) 1 1

Helicops (17) 17 17

Helophis (1) 1 1

Hydrodynastes (2) 2 2

Hydromorphus (2) 2 2

Hydrops (3) 3 3

Liophis (44) 1 1

Pseudoeryx (1) 1 1

Sordellina (1) 1 1

Tetranorhinus (4) 4 4

Thermophis (1) 1 1

ELAPIDAE

Boodontinae

Lycodonomorphus (6) 6 6

Elapinae

Boulengerina (2) 2 2

Hydrobiologia (2008) 595:599–605 603

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