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JOURNAL OF CRUSTACEAN BIOLOGY, 34(1), 47-53, 2014

CURRENT DISTRIBUTION OF TWO SPECIES OF TYLOS (ISOPODA: ONISCIDEA) IN
THE CENTRAL MEDITERRANEAN AND THE INFLUENCE OF BEACH SAND
GRAIN-SIZE PARAMETERS

Giuseppe Montesanto 1,∗, Alan Deidun 2, Arnold Sciberras 2,
Jeffrey Sciberras 2, and Bianca Maria Lombardo 1

1 Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Sezione di Biologia Animale “Marcello La Greca,”
Università di Catania, Catania, Italy

2 IOI-MOC, University of Malta, Msida, Malta MSD 2080

ABSTRACT

The psammophilic genus Tylos Audouin, 1826 is represented within the Mediterranean basin as two species: T. ponticus Grebnicki, 1874,
and T. europaeus Arcangeli, 1938, according to Taiti and Ferrara (1996). It is impossible to define precisely the current distribution of the
two species, mainly because, in literature, both taxa have been described as subspecies of T. latreillii or even, in some cases, as T. latreillii
sensu lato. The current study surveyed populations of Tylos spp. on sandy beaches along the coastline of Sicily, circum-Sicilian islands and
the Maltese archipelago. The aims of this study are to fully and correctly identify all the sampled populations, pursuant to characterizing the
current distribution of the two species, which occupy similar ecological niches, and to investigate any possible granulometric preferences
by the two species. Data acquisition proceeded along three tiers: in situ sampling, manually and through the deployment of pitfall trap
constellations, literature review and by analyzing preserved specimens of Tylos held within the ‘Caruso’ collection (University of Catania,
Catania, Italy). Generally, T. europaeus showed a preference for fine sand, whilst T. ponticus showed a preference for fine-medium sand,
although, statistically, differences in the distribution of the two species could not be explained in terms of median grain size. The two
species were never recorded on the same beach. The degree of inter-specific morphological differentiation was also evaluated through a
detailed morphological study of sampled Tylos spp.

KEY WORDS: distribution, Isopoda, morphology, Oniscidea, sediment grain size, Tylos

DOI: 10.1163/1937240X-00002206

INTRODUCTION According to Schmalfuss (2003), within the Mediter-
ranean basin, there are currently two species belonging to the
Tylos Audouin, 1826 represents a cosmopolitan, semi-ter- psammophilic genus Tylos: T. ponticus Grebnicki, 1874; and
restrial oniscid isopod genus, typical of the upper zones T. europaeus. In the literature, however, many different syn-
of sandy shores where back-beaches are adequate, espe- onyms for Tylos in the Mediterranean have been proposed in
cially along the Atlantic coasts of Europe and the Mediter- the past.
ranean, where oniscid isopods and talitrid amphipods con-
stitute an important component of the eulittoral and supralit- Within Sicily and the circum-Sicilian islands, the existing
toral (McLachlan and Brown, 2006). Some species of Tylos, reports of Tylos (Caruso, 1973a, b, 1974; Caruso and
e.g., T. europaeus Arcangeli, 1938, are considered by some Lombardo, 1982; Caruso et al., 1987; Caruso and Lombardo,
authors (Goncalves et al., 2005) as a useful bioindicator of 1995) list all such samples under “Tylos latreillei.” Deidun
environmental quality in sandy shores, since oscillations in et al. (2003) and Deidun and Schembri (2008) both list T.
population dynamics, reproductive strategies, and productiv- europaeus as one of the most abundant macrofaunal species
ity of these species might reflect environmental changes. on the beach of Ramla l-Hamra in Gozo, whilst Deidun
et al. (2011) elaborate on the distribution of Tylos spp.
Several studies have been conducted on the population in the Maltese Islands and on the population dynamics of
dynamics (Hammer et al., 1969; Hayes, 1974; Goncalves T. europaeus. The latter authors list the occurrence of T.
et al., 2005), zonation (Kensley, 1974; Hayes, 1977; Fal- sardous, besides T. europaeus, in the Maltese Islands, but
laci et al., 1996), burrowing behaviour (Brown and Trueman, the former species is currently recognized as T. ponticus
1996), spatial distribution (Odendaal et al., 1999), bioecol- (Schmalfuss and Vergara, 2000). It is now generally assumed
ogy (Kensley, 1974; Fallaci et al., 1996), field orientation that the synonym T. latreilii = T. ponticus, whilst whether
(Ugolini et al., 1995), surface activity (Colombini et al., the synonym T. sardous = T. europaeus is still debatable (see
1996; Fallaci et al., 1996) and reproduction (Suzuki et al., also the remarks reported in: Taiti and Ferrara, 1996).
2013) of different species of Tylos.
It is impossible from the literature to define precisely the
current distribution of T. europaeus and T. ponticus; both

∗ Corresponding author; e-mail: g.montesanto@unict.it DOI:10.1163/1937240X-00002206

© The Crustacean Society, 2014. Published by Brill NV, Leiden