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First record of Armadilloniscus candidus Budde-
Lund, 1885 in the coastal areas of the Iberian
Peninsula (Crustacea: Oniscidea: Detonidae)
Lluc GARCIA and Jairo ROBLA
SHNB
SOCIETAT D’HISTÒRIA
NATURAL DE LES BALEARS
Garcia, L. and Robla, J. 2021. First record of Armadilloniscus candidus Budde-Lund,
1885 in the coastal areas of the Iberian Peninsula (Crustacea: Oniscidea: Detonidae).
Boll. Soc. Hist. Nat. Balears, 64: 39-46. ISSN 0212-260X. e-ISSN 2444-8192. Palma
(Illes Balears).
Armadilloniscus Uljanin, 1875 is a genus of halophilic woodlice that strictly occurs
in coastal habitats. Two species are known in the coastal areas of the western
Mediterranean and only one species, A. ellipticus, was previously recorded in the
Iberian Peninsula and the Balearic Islands. Another species, A. candidus, is reported
for the first time in Asturias and the Iberian Peninsula. This species could have
arrived to the Atlantic coast attached to floating objects, like logs, trunks or plants.
The record shows the capability of A. candidus to adapt to coastal areas of the
Atlantic. Until now, this species was only documented in the Atlantic by two single
records from the French coast and the Azores islands. Ecological data are provided of
this species in the Iberian Peninsula. Finally, figures of the habitus and of the
morphological characteristics are provided, that allow the identification of the two
species of Armadilloniscus present in the Iberian coastal areas.
Keywords: Armadilloniscus, Oniscidea, halophilic terrestrial isopods, Iberian
Peninsula, Atlantic coasts.
PRIMERA CITA D’Armadilloniscus candidus BUDDE-LUND, 1885 A
AMBIENTS COSTANERS DE LA PENÍNSULA IBÈRICA (CRUSTACEA:
ONISCIDEA: DETONIDAE). Armadilloniscus Uljanin, 1875 és un gènere
d'isòpodes terrestres halòfils que ocupen hàbitats estrictament litorals. A les costes de
la Mediterrània occidental es coneixen dues espècies d'aquest gènere i sols una
d'elles ha estat enregistrada a la península Ibèrica i a les Balears: A. ellipticus. L'altra
espècie, A. candidus, se cita per primera vegada a les costes d'Astúries i de la
península Ibèrica. Aquesta espècie pot arribar fins a les costes atlàntiques adherida a
objectes flotants com fustes, troncs o plantes. Aquest registre demostra la capacitat
d’A. candidus per colonitzar el litoral atlàntic, que fins ara sols estava documentada
per dos únics registres a la costa atlántica francesa i a les illes Açores. Es
proporcionen dades ecològiques addicionals d’aquesta espècie a la península Ibèrica.
Finalment, es proporcionen figures de l’hàbitus i de les característiques
morfològiques que permeten identificar les dues espècies d’Armadilloniscus presents
a les costes ibèriques.
Paraules clau: Armadilloniscus, Oniscidea, isòpodes terrestres halòfils, península
Ibèrica, costes atlàntiques.
Lluc Garcia, Balearic Museum of Natural Sciences/Interdisciplinary Ecology Group
University of Balearic Islands llucgarciaisopoda@gmail.com ; Jairo ROBLA,
Department of Conservation Biology, Doñana Biological Station - CSIC. C/ Américo
Vespucio, 26, 41092, Sevilla (Spain). E-mail: jairoroblasuarez@gmail.com.
Recepció del manuscrit: 23-06-2021; revisió acceptada:06-07-2021; publicació online: 07-07-2021.
40 Boll. Soc. Hist. Nat. Balears, 64 (2021)
Introduction
Armadilloniscus Uljanin, 1875 is a
woodlouse genus belonging to the family
Detonidae Bude-Lund, 1904 that includes
31 species well distributed worldwide
(Boyko et al., 2008). All species are strictly
coastal and have halophilic habits (Taiti &
Ferrara, 1989; Schmalfuss, 2003).
Armadilloniscus species live closely to the
sea, on sandy or rocky beaches using both
stones and plant remains as a refuge
(Vandel, 1962; Taiti & Ferrara, 1989).
Their flattened body shape and clinger
ability (Schmalfuss, 1984) are a strategy to
adapt to the unstable environment in which
they live. It allows them to cling tightly to
the substrate, either on the lower surface of
stones, wood or other remains deposited by
the waves (Vandel, 1962). In this way they
can resist the battering of the waves,
submersion and periods of marine transport
on floating objects to which they adhere.
Only two species of Armadilloniscus occur
in coastal areas of the western European
Mediterranean: Armadilloniscus ellipticus
(Harger, 1878) and Armadilloniscus
candidus Budde-Lund, 1885. Other
Mediterranean species such as
Armadilloniscus aegaeus Schmalfuss,
1981, Armadilloniscus aestuarii Verhoeff,
1930, Armadilloniscus bulgaricus
Frankenberger, 1941 and Armadilloniscus
letourneuxi Simon, 1885 seem confined to
the coasts of the central and eastern
Mediterranean Sea and the Black Sea.
Nevertheless, the last two species are
probably synonymous of A. ellipticus (Taiti
& Ferrara, 1989; Schmalfuss, 2003), the
most common species in the Mediterranean.
The identity of another Mediterranean
species, Armadilloniscus minutus Uljanin,
1875, remains undefined (Schmalfuss,
2003).
A. ellipticus has been reported in the
Mediterranean coasts of France, Italy,
Greece, the former Yugoslavia, Slovenia,
Croatia, Morocco, Tunisia, Spain
(including the Balearic Islands) and the
islands of Corsica and Malta (Vandel,
1962; Schmalfuss, 2003; Khemaissia et al.,
2013; Séchet & Noël, 2015; Noël, 2016;
Noël & Séchet, 2017). In addition, it was
found in the Ukrainian, Romanian,
Bulgarian and Russian coastal areas of the
Black Sea (Giurginca & Ćurčić, 2003;
Gongalsky et al., 2011; Linetskii et al.,
2020). It seems to be an expansive species
because, although it has a Mediterranean
origin (Vandel, 1962; Noël, 2016), it has
also been found in Hawaiian Islands,
Malaysia, Japan, Korea, China, Madagascar
and the Atlantic coast of North America
(Vandel, 1962; Schmalfuss, 2003). It was
also reported from the Azores and Madeira
(Vandel, 1956; 1960; 1962; Schmalfuss,
2003) and the French Atlantic Island of Île-
d'Aix (Noël, 2016). In the Iberian Peninsula
and neighbouring islands, this species has
been previously registered as
Armadilloniscus litoralis Budde-Lund,
1885, in Girona and Eivissa island (Cruz,
1991), Mallorca (Garcia and Cruz, 1996),
the Chafarinas Islands (Pons et al., 1999)
and as A. ellipticus in Mallorca and sa
Dragonera islands (Garcia, 2008, 2009) and
Cádiz (Cifuentes, 2021). The synonymy
between A. litoralis and A. ellipticus has
been established by Garthwait et al.,
(1992). The other species, A. candidus, was
only known from the Mediterranean coastal
areas of France, Italy, Algeria, Tunisia,
Malta (Vandel, 1962; Taiti & Ferrara, 1996;
Schmalfuss, 2003; Messina et al., 2012;
Séchet & Noël, 2015; de Matthaeis et al.,
2019) and the Azores in the Atlantic
(Vandel, 1956). The record from the Azores
(Vandel, 1956; 1962) was the only record
in the Atlantic until recently, when A.
L. Garcia and J. Robla, First record of Armadilloniscus candidus in the Iberian Peninsula (Crustacea) 41
candidus was found on the Atlantic coast of
France (Cherpitel et al., 2019).
The main goal of this work is to provide
the first record of Armadilloniscus candidus
for the Iberian Peninsula, specifically in
Asturias. Additionally, morphological and
ecological data are provided and its
presence on the European Atlantic coasts is
discussed.
Material and methods
Surveys were carried out in the northern
Iberian Peninsula (Asturias, Spain) (Fig.
1A) in 2020. Several coastal localities were
visited to collect specimens under stones,
dead wood, and deposits of plants (Fig.
1B). Specimens (Fig. 1C-1D) were hand
collected and then fixed and preserved in
75% ethanol. Specimens are kept in the first
author’s collection. Armadilloniscus
candidus specimens were photographed in
situ with a Xiaomi Redmi Note 7 mobile
device with a macro-lens.
Fig. 1. A. Geographical situation of the Armadilloniscus candidus population detected in Asturias. B.
Rocky shore with algae of Conejera beach (Selorio, Villaviciosa). C. Typical layout of an immature
Armadilloniscus candidus in its habitat. D. Same for an adult.
Fig. 1. A. Situació geogràfica de les poblacions detectades a Astúries d’Armadilloniscus candidus. B.
Costa rocosa amb algues de la platja de Conejera (Selorio, Villaviciosa). C. Aspecte típic d’un
immadur d’Armadilloniscus candidus al seu hàbitat. D. El mateix per a un adult.
42 Boll. Soc. Hist. Nat. Balears, 64 (2021)
Photographs of preserved specimens of
A. candidus and A. ellipticus were taken
with a digital microscope (Dino-Lite). First
pleopods and genital papilla of males were
dissected and mounted on glass slides using
Faure's liquid. Photographs of the dissected
appendices were taken with a digital
camera (Nikon Coolpix) connected to an
optical microscope. Drawings were
prepared using a camera lucida connected
to an Olympus CH-30 microscope.
Photographs were edited with GIMP
2.10.12. Maps were generated with ArcGis
Desktop 10.8.1.
Results
Armadilloniscus candidus Budde-Lund,
1885
Material examined. Spain - Asturias:
Conejera beach, Selorio (Villaviciosa): 4♂
+ 6♀ + 3 inmature, 3-IX-2020, 3masl.
Conejera beach, Selorio (Villaviciosa): 1♀
+ 1 inmature, 19-IX-2020, 3 masl. Conejera
beach, Selorio (Villaviciosa): 1♂ + 1♀ + 1
inmature, 24-IX-2020, 3masl. (30T 308988
4822659).
Fig. 2. A. Armadilloniscus candidus, female from Asturias (scale: 1 mm). B. First male pleopods of
A. candidus from Asturias (scale: 0.1 mm). C. Armadilloniscus ellipticus, female from Balearic
Islands (scale: 1 mm). D. First male pleopods of A. ellipticus from Balearic Islands (scale: 0.1 mm).
Fig. 2. A. Armadilloniscus candidus, femella d'Astúries (escala: 1 mm). B. Primers pleopodis d'un
mascle d'A. candidus d'Astúries (escala: 0.1 mm). C. Armadilloniscus ellipticus, femella de les Illes
Balears (escala: 1 mm). D. Primers pleopodis d’un mascle d'A. ellipticus de les Illes Balears (escala:
0.1 mm).
L. Garcia and J. Robla, First record of Armadilloniscus candidus in the Iberian Peninsula (Crustacea) 43
Fig. 3. A-C. Armadilloniscus candidus: A. First male pleopod. B. Second male pleopod. C. Genital
papilla. D-E. Armadilloniscus ellipticus: D. First male pleopod. E. Genital papilla.
Fig. 3. A-C. Armadilloniscus candidus: A. Primer pleopodi del mascle. B. Segon pleopodi del mascle.
C. Apòfisi genital. D-E. Armadilloniscus ellipticus: D. Primer pleopodi del mascle. E. Apòfisi genital.
Morphological remarks. According to
Vandel (1962) and Taiti & Ferrara (1989),
the identification of Armadilloniscus
species is mainly based on morphology and
tergal sculpture. Contrary to most terrestrial
isopoda, Armadilloniscus species have,
with exceptions, homogeneous sexual
characteristics. Diagnostical characters
mentioned by Vandel (1962) to distinguish
both species lead to a certain confusion in
the Asturian specimens. The main somatic
difference between the two Armadilloniscus
species is the shape of the uropods
basipodites, semicircular in A. ellipticus
and quadrangular in A. candidus. In the
studied specimens this difference is not so
clear (Fig. 2A-2C). On the contrary, the
examination of the first male pleopods of
both species (Fig. 2B-2D and 3A-3D),
especially the shape of the endopodite of
the first pleopod (Taiti & Ferrara, 1996)
and the genital papilla (Fig. 3C-3E), allows
an easy identification. The most useful
characteristics to identify and differentiate
both species have been illustrated to
facilitate future reviews (Figs. 2 and 3).
Live specimens appear completely white
(Fig. 1C-D) but under magnification darker
due to a slightly pigmented epimera (Fig.
2A). The pigmentation of A. ellipticus is
darker both in vivo and preserved
specimens (Fig. 2C).
Ecological remarks. All specimens were
found in a coastal area adhered to the lower
surface of large stones which were covered
44 Boll. Soc. Hist. Nat. Balears, 64 (2021)
sporadically with water during high tide,
resulting in a very humid microhabitat. In
the study area, accumulations of algae
(mainly Codium spp. and Gelidium spp.)
were present, but no logs, trunks or deposits
of seagrass species (Zostera spp.) (Fig. 1B).
It is interesting to remark that although
several consecutive surveys were made,
some days no specimens of A. candidus
were found.
Discussion
Woodlice are a group of isopods highly
adaptable to a diversity of habitats. Vandel
(1962) created some categories that allowed
to include terrestrial isopods in groups
according to their different ecological
characteristics. One of the least diverse
groups are coastal and halophilic
woodlouse species, those exclusive to the
supralittoral area (Vandel, 1962). Most of
them feed on organic matter accumulations
from plants and wood (Vandel, 1962; Taiti
& Ferrara, 1989). Due to sampling
difficulties and the little interest in coastal
environments, the distribution of many of
the coastal woodlouse species is patched,
making it difficult to establish their real
range. Armadilloniscus is a good example.
A. ellipticus is a species widely distributed
along the Mediterranean, but Iberian
records are still scarce. A. candidus is an
even less known species, recorded from
fewer countries and had not yet been found
in the Iberian Peninsula until this study.
This report expands the catalogues of
terrestrial isopoda species of Asturias and
the Iberian Peninsula.
A. candidus, like A. ellipticus, is a
Mediterranean species with only two
previous records for Atlantic coastal areas
and islands (Vandel, 1968; Cherpitel et al.,
2019). Even less is known about its
biology. Most data agree on its coastal
habitats, living under large stones, wood,
logs and particularly, deposits of marine
seagrass species of the genus Zostera spp.
and Posidonia (Vandel, 1962; Taiti &
Ferrara, 1989; Garcia, 2008; Noël &
Séchet, 2017). A. candidus specimens have
been collected in Asturias under large
stones among accumulations of Atlantic
algae (Codium spp. and Gelidium spp.
among others). No seagrass species, present
in most Mediterranean areas, were found.
However, the study area is part of the
Villaviciosa estuary, one of the few areas of
distribution of the two Asturian Zostera
species (Diaz, 2003). The findings reflect
the ability of A. candidus to adapt to
Atlantic environments. In addition, Vandel
(1962) commented that coastal and
halophile woodlice are highly expansive.
Attached to logs, fragments of wood and
plants, these species can travel across the
ocean and colonize new shores (Vandel,
1962). By this means, A. ellipticus is
supposed to have spread throughout the
world. Something similar could be applied
to A. candidus. Direct arrival from the
Mediterranean or the Azores is unlikely due
to ocean currents. The Asturian population
may have arisen from other unknown
populations along the European Atlantic
coast. Thus, the Mediterranean origin of
this species should be reviewed in the
future, perhaps with the support of
molecular data. More surveys and studies
are needed to clarify the origin of these
populations, means of dispersal and the
distribution of this species. A. candidus was
not found on every sampling day in the
study area. Variations in the abundance and
detectability of this species could probably
be explained by fluctuations in temperature
and precipitation, which have shown to
have influence on isopod populations from
coastal areas (Messina et al., 2016).
L. Garcia and J. Robla, First record of Armadilloniscus candidus in the Iberian Peninsula (Crustacea) 45
In summary, Armadilloniscus candidus
is reported for the first time in the Iberian
Peninsula, specifically in Asturias, thus
expanding its known distribution in
southwestern Europe. In addition, the report
confirms the capability of A. candidus to
adapt to Atlantic conditions and improves
the ecological and morphological
knowledge of this species in the Iberian
Peninsula.
Acknowledgments
We would like to thank to Álvaro
Alonso and Omar Sánchez for helping us
sample the localities. We would like to
express our gratitude to Jorge Rodríguez
Pérez for editing and processing the
pictures of alive specimens, to David
Cabanillas for his help and to André
Burgers for reviewing the English text and
providing valuable comments about the
manuscript.
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