THALASSOZETES BARBARA N. SP. (ACARI, ORIBATIDA), A NEW INTERTIDAL SPECIES FROM THE COAST OF BARBADOS

The new intertidal oribatid mite species Thalassozetes barbara n. sp. is characterised by a specific gastronotic cuticular reticulate pattern, 14 pairs of very short and blunt notogastral setae and long lamellar ridges. The occurrence on the island of Barbados represents the first record of the genus Thalassozetes in the Atlantic Ocean.


INTRODUCTION
The Selenoribatidae represent a truly intertidal oribatid mite family. These mites dwell exclusively in the littoral zone of tropical and subtropical coasts (Schuster 1989, Procheş andMarshall 2001). This family includes seven genera, Arotrobates Luxton, 1992, Carinozetes Pfingstl and Schuster, 2012, Psednobates Luxton, 1992, Rhizophobates Karasawa and Aoki, 2005, Schusteria Grandjean, 1968, Selenoribates Strenzke, 1961and Thalassozetes Schuster, 1963, whereas all of these genera are not very species rich. Psednobates and Rhizophobates are monotypic and the most diverse genus Schusteria contains five species. However, a recent study (Pfingstl and Schuster 2012) demonstrated that certain taxa are much wider distributed than formerly supposed and that the diversity of Selenoribatidae may exceed known numbers considerably as there are still many uncharted geographic areas in respect of intertidal arthropods. The same may apply to the genus Thalassozetes. Since the description of the type species Thalassozetes riparius (Schuster 1963) from the Mediterranean Sea this genus has long been monotypic. Talker et al. (1981) reported Thalassozetes from the Philippines but these specimens have never been determined nor officially described as a new species. So, nearly thirty years later, Bayartogtokh and Chatterjee (2010) discovered the second named species, T. tenuisetosus in the Arabian Sea. Now, a third species was found on the Island of Barbados in the Caribbean Sea, revealing the presence of this genus in the Western Atlantic Ocean.
The present paper describes this new species in detail and discusses the taxonomy and the geographic distribution of the genus Thalassozetes.

MATERIALS AND METHODS
Patches of intertidal algae growing on rocks were collected on the Island of Barbados and afterwards put in a Berlese-Tullgren apparatus for the extraction of mites. For investigation in transmitted light all animals were stored in pure ethanol, then heated in lactic acid (80°C for about 20 minutes) and afterwards embedded in BERLESE mountant. Observations, photographs and drawings were made with an Olympus BH-2 Microscope equipped with a drawing attachment. Image stacks were obtained by an Olympus E1 digital camera and layered with the Combine ZP software. Inscriptions of drawings were done according to Grandjean (1966Grandjean ( , 1968.
Integument -Colour dark brown. Cuticle of notogaster with irregular circular depressions forming a reticulate pattern. Cerotegument thick and basically granular.
Notogaster - (Figs. 2A, 2C and 3A). Rounded in dorsal view, convex in lateral view. Dorsosejugal suture complete but medially weakly devel- oped. Median rectangular light spot adjacent to anterior border of notogaster. Cuticle in centre of notogaster with irregular small circular depressions forming an irregular reticulate overall pattern (Fig.  4A). This pattern fades into a uniform granulation in lateral areas of gastronotic region (Fig. 4B). A pair of concave and parallel ridges on anterior part of notogaster. Laterally of these ridges, elliptical cavities showing fine granular surface. Fourteen pairs of very short and blunt notogastral setae, c 1-2 , da, dm, dp, la, lm, lp, h 1-3 , p 1-3 (approximate length 2 -5µm); c 3 absent. Porose areas or distinct pores absent. Five pairs of notogastral lyrifissures present; ia next to notogastral ridges and nearly parallel to anterior notogastral border; im obliquely, next to seta c 2 ; lyrifissure ih next to seta lp; ips anterior to seta p 3 and ip between setae p 2 and p 1 . Orifice of opisthonotal gland (gla) posterior and close to lyrifissure im.
Lateral aspect - (Fig. 2C). Cerotegument generally finely granular, larger granules in areas surrounding acetabula. Pedotectum I small, pedotectum II absent. Lateral parts of sejugal furrow broad and deep, showing conspicuous granules. Next to lateral border of bothridium triangular protrusion orientated caudally. Lateral enantiophyse present, anterior projection triangular, well developed, posterior protrusion triangular and small. Discidium developed as strongly projecting triangular bulge between acetabula III and IV.
Ventral region of idiosoma -(Figs. 2B, 3B). Cuticle basically granular, larger granules and darker colouration next to acetabula, anterior and posterior of genital orifice and laterad of anal opening. Epimeral setation 1-0-1-1, seta 1b long reaching trochanter III, setae 3b and 4a short and thin. Internal borders of all epimera well visible, sternal apodemes II, sejugal and III well developed. A densely granulated median sternal cavity on epimeron I, lateral borders slightly concave. Three pairs of short and fine genital setae, arranged in longitudinal rows. Insertion of tendon β next to anterior corners of genital orifice. Aggenital setae absent. Anal valves triangular. Preanal organ triangular in ventral view. Two pairs of short anal setae, an 1-2 , arranged in a longitudinal row. Three pairs of short and simple adanal setae, ad 1-2 flanking anal orifice, ad 3 posterior of anal valves. Lyrifissure iad slightly oblique and adjacent to anterior corners of anal opening.

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Etymology -The species name refers to the name of my spouse Barbara, who always supported me and my interest in research. She has tolerated my passion for the little mites for many years and moreover she accompanied me on my research trip to the beautiful island of Barbados, where the new species was found. The name is given as noun in apposition.

DISCUSSION
The diagnosis of the genus Thalassozetes has been solely based on the morphological features of the type species T. riparius for a long time. With the description of the second species T. tenuisetosus (Bayartogtokh and Chatterjee 2010) this diagnosis was slightly widened and included for example the possession of two setae on epimeron IV, 13-15 pairs of notogastral setae and 2-3 adanal setae. The new species T. barbara clearly shows the typical characteristics of the genus, whereas it conforms in most morphological features to T. riparius. These two species share anterior gastronotic ridges, the epimeral cavity on epimeron I and the short knoblike famulus on tarsus I (Table 1). Therefore these species are supposed to be closer related to each other than to T. tenuisetosus. In the genus diagnosis given by Bayartogtokh and Chatterjee (2010) morphological features of Rhizophobates shimojanai, Schusteria melanomerus and S. ugraseni were also included, as Subías (2004Subías ( , update 2013, prior to this, had transferred these species to Thalassozetes. Pfingstl and Schuster (2012) already stated that this taxonomic act was not justified because these species clearly diverge from the Thalassozetes specific morphology and therefore should be retained in their original genera. Accordingly the possession of 15 pairs of gastronotic setae and two pairs of adanal setae, shown in the respective species, are not typical for the genus Thalassozetes and should be removed from the diagnosis. Grandjean (1968) compared the genera Thalassozetes, Selenoribates and Schusteria and stated that anterior notogastral foveae separated by longitudinal ridges are only shown in Selenoribates species. Meanwhile Pfingstl and Schuster (2012) demonstrated that similar structures are present in the selenoribatid genus Carinozetes and now T. barbara also exhibits this morphological feature. This trait may have evolved convergently within these respective taxa and may represent an adaptation to the intertidal lifestyle, whereas neither a functional nor an ecological correlation could yet be detected. However, another trait which is clearly related to the littoral environment is the strongly granular surface of selenoribatid mites. Pfingstl and Schuster (2012) demonstrated that the obvious granulation of certain body surfaces in Carinozetes species retains a layer of air during tidal inundation and allows the animals to breathe underwater. Although there are no in vitro observations of T. barbara, it is assumable that the strongly granulated areas surrounding the acetabula and certain other body regions are involved in the formation of a respiratory plastron system.
The known distribution pattern of the genus Thalassozetes is based on only a few scattered and distant records. Schuster (1977) reported T. riparius from the Adriatic coast and the Black Sea, Talker et al. (1981) found an undetermined Thalassozetes species on the Philippines in the Indo-Pacific and T. tenuisetosus was recorded from the Indian coast in the Arabian Sea. The discovery of T. barbara from the island of Barbados is the first record of a Thalassozetes species from the Atlantic Ocean. The large distributional gaps among all of the records indicate the incompleteness of sampling activities and a much wider distribution of Thalassozetes species along coasts of the Atlantic, Caribbean and Indo-Pacific Ocean should be assumed.