Litarachna communis Walter, 1925 (Acari: Hydrachnidiae: Pontarachnidae): taxonomic status, lectotype and paralectotype designation and redescription

Litarachna communis, the type species of the genus, was originally described by C. Walter (1925) based on specimens collected on the coast of Banyuls-sur-Mer in France. Walter did not specify the type designation and type depository of L. communis in the original description. Therefore, we looked for the specimens used in the original description of L. communis and successfully found 14 specimens on five glass slides (Nos. 2698-2702) deposited in the Natural History Museum of Basel. Comparative study of morphological characteristics between real specimens and the original descriptions by Walter (1925) was carried out in order to specify the material used in the descriptions of female, male, and nymph of L. communis. As a result, it was confirmed that the female on slide No. 2700, the male on slide No. 2701, and the nymph on slide No. 2702 were the specimens used in the original description of L. communis. Consequently, we designated the female on slide No. 2700 as the lectotype and the male on slide No. 2701 and the nymph on slide No. 2702 as the paralectotypes of L. communis. Redescriptions of the female, male, and nymph of L. communis were also given on the basis of the newly designated types to provide additional information on morphological characteristics of the species.


INTRODUCTION
The Pontarachnidae is the only family found in a marine habitat in the subcohort Hydrachnidiae (Krantz and Walter 2009) or in the phalanx Hydrachnidia (Krantz 1978). The family contains two genera, Pontarachna Philippi, 1840 andLitarachna Walter, 1925. The genus Litarachna consists of 26 species, which are mainly recorded from the intertidal zone on the coasts of the tropical and temper-ate Pacific, Atlantic and Indian Oceans (Smit 2002, Pešić 2013a,b, Pešić et al. 2012, 2013, Moto and Abé 2013. Litarachna communis Walter, 1925 is the type species of the genus and has been recorded thus far from the Mediterranean Coast. This species was originally described by Walter (1925) based on the specimens collected from algae on the coast of Banyuls-sur-Mer in France. In the original description, Walter mentioned most of the important taxonomic characteristics used for specific discrimina-tion of the female, the male, and the nymph and provided drawings of their body parts in detail. However, he did not specify the type designation and type depository of L. communis. In the course of the history of classification of organisms, taxonomic confusion caused by a lack of type designation has occurred repeatedly. Therefore, for several years we have been looking for specimens used in the original description of L. communis in order to designate the types of this species. In 2012, we fortunately obtained information on the depository of the specimens used in the original description of L. communis with the aid of European acarologists Dr. H. Smit, Dr. R. Gerecke, and Dr. V. Pešić. We also had an opportunity to examine the actual specimens of L. communis deposited in the Natural History Museum of Basel in Switzerland with the assistance of Dr. E. Stöckli and Dr. A. Hänggi of this museum. In the present study, we specify the female, the male and the nymph specimens used in the original description by Walter (1925) on the basis of a precise comparison of taxonomic characteristics between real specimens and the original description. In addition, we designate the lectotype and paralectotype of L. communis. Furthermore, we provide a redescription of L. communis based on the designated lecto-and paralectotypes in order to compensate for a deficiency in the original description.
Specimens on each slide were examined under a light microscope (Olympus, BX51). At first, the general condition of each glass slide was examined. Thereafter, the morphological characteristics of each specimen on the slide were examined in detail. Figures were drawn with the aid of a camera lucida (Olympus, U-DA), and measurements were made with an ocular micrometer.
Measurements are carried out only for the specimens in measurable condition. All measurements are given in micrometers (µm) in descriptions. The body parts were measured in the following format: (1) Idiosoma: Length -from the anteriormost margin of the first coxal plate to the terminal end of the idiosoma, width -at the widest point; (2) Segments of leg: Length -straight dorsal length from the proximal base to the distal end; (3) Segments of palp: Length -straight dorsal length from the proximal base to the distal end, height -at the proximal base and distal end of the segment; (4) Segments of chelicera: Length -straight ventral length from the proximal base to the distal end; (5) First to fourth coxal plates: Length -from the anterior-most margin of the first coxal plate to the posterior-most margin of the fourth coxal plate along the longitudinal axis, width -at the widest point; (6) Medial and lateral apodemes: Lengthfrom the posterior margin of the fourth coxal plate to the distal end of these apodemes; (7) Genital field: Length -from the anterior margin to the posterior margin along the longitudinal median axis, width -at the widest point; (8) Pre-and postgenital sclerites in the female: Width -at the widest point.

Terminology
Terms on glandularia, platelets, setae, and acetabula were partly referred to Tuzovskij (1987) and Wiles et al. (2002). Right or left is referred to on the basis of a dorsal view. The number of paired setae, glandularia, and platelets on the right and left sides of the idiosoma is referred to only the one side. In addition to general terminology for Hydrachnidiae, the following terms are also employed for morphological notations.
Posteromedial and posterolateral apodemes: Posteromedial and posterolateral projections on the posterior margin of the fourth coxal plate; sclerotized ring: A sclerotized plate surrounding the gonopore in the male; genital sclerites: Two sclerotized plates placed anteriorly (pregenital) and posteriorly (postgenital) to the gonopore in the female; genital setae: Setae on the sclerotized ring in the male; perigenital setae: Setae around the genital field in the male; ventral glandularium: A ventral 202 large gland with a slit-like opening; wheel-like acetabulum (Cook 1996): A wheel-like structure with radiating sulci.

Taxonomic status of
Remarks -Litarachna communis is quite similar to L. divergens Walter, 1925 andL. denhami Lohmann, 1909 in lacking a ventral tubercle on P-2 and P-4 and in the absence of a peg-like seta on P-4. However, according to Viets (1957), L. communis is distinguished from L. divergens by the ratio of the dorsal length of P-5 to that of P-4, the arrangement of perigenital setae in the male, and the location of the genital field in the female, and from L. denhami by the ratio of the dorsal length of P-2 to that of P-4. The ratios of the dorsal length of P-4 to that of P-2 in L. communis and L. divergens are almost the same, while the ratio in L. denhami is larger than those in L. communis and L. divergens. In addition, P-5 is longer than half of P-4 in L. communis, while P-5 is shorter than in L. divergens. Furthermore, the genital field of the female in L. communis is located between right and left apodemes of the first coxal plates, while in L. divergens it is located more posteriorly.

Designation of the lectotype and paralectotypes
In the original description of L. communis, Walter (1925) described the female, male, and nymph in this sequence based on the examination of three specimens in total. However, he did not designate a type series in the original publication. We discovered 14 specimens of L. communis in total on the five glass slides (Nos. 2698-2702) (Figures 1a-e) deposited in the Natural History Museum of Basel. Therefore, all these specimens should be considered as syntypes of L. communis under Article 73.2 of the International Code of Zoological Nomenclature (International Commission on Zoological Nomenclature 1999). In order to designate the lectotype as well as the paralectotype of L. communis, we specified the female, male, and nymph used in the original description of L. communis by Walter (1925). The female must be designated as the lectotype and the others as the paralectotype.
In the original description of Walter (1925) the material was collected from the Baie du Troc, Banyuls-sur-Mer, on April 10, 1924. The taxonomic information, as it is recorded on the label of each glass slide, is as follows. Among the five glass slides mentioned above, three of them (Nos. 2700-2702) contained specimens collected from the same place on the same date in the original description. Furthermore, only 203 Moto A. and Abé H. Considering the collecting locality and condition of the specimens, it is highly probable that the female, male, and nymph used in the original description of L. communis are the specimens mounted on slides No. 2700, No. 2701, and No. 2702 In order to ensure that the specimens on the slides Nos. 2700-2702 are the specimens used in the original description by Walter (1925), we made a precise comparison between morphological characteristics observed in the specimens and those given in the original description.
The result of the morphological comparison was summarized in Appendixes 1-3. The taxonomic characters observed in the specimens accorded well with those shown in the original descriptions and figures 18-25 in Walter (1925) except for the following points: 1) Lpl-2 and Ost-2 were not mentioned in the original description, although the platelet and the seta were present on the epidermal cuticle of the observed material. The differences were probably caused by the difficulty of precise observation at that time.
2) The direction of the tip of the PLA in the original figures 18 and 24 by Walter (1925) was somewhat different from that observed in the material. Walter (1925) probably made a picture of the PLA before complete mounting of the material. 3) The palpal chaetotaxy in the original description was different from that in the actual specimens. This discrepancy was probably caused by the difficulty of observation of the fine setae or sockets on dorsal margins of palpi. 4) Chelicerae in the original figure 21 were not broken, whereas those in the observed material were partly broken ( Figure 2). It is highly probable that Walter (1925) made a picture of them before their damage through dissection. 5) Walter (1925) mentioned in the original description that a lot of setae on legs were bipectinate. On the contrary, setae on the legs in his original figure 23 were not bipectinate. According to the present examination of the material, most of the setae on legs were not bipectinate but spiniform. Consequently, Walter (1925) probably made the wrong conclusion that most of the setae on legs were bipectinate based only on the limited observation of a bipectinate seta on the genu of the first leg.
Considering the result of the morphological comparisons mentioned above as well as the collecting locality and the condition of specimens on the slides, specimens on slides No. 2700-No. 2702 were collected and arranged by C. Walter himself and used in the description of L. communis. Therefore, it should be concluded that the female on slide No. 2700, the male on slide No. 2701, and the nymph on slide No. 2702 are the specimens used in the original description of L. communis by Walter (1925).
In conclusion, we designate the female on slide However, we do not designate the specimens on the slides No. 2698 and No. 2699 as the paralectotypes, because these specimens were not actually used in the specific description by Walter (1925) and were severely deteriorated to the extent that mor-205 phological characteristics used for specific identification could not be examined.
When Walter (1925) made an original description of L. communis, he examined the following additional specimens to obtain distributional data on this species: Two females collected from the algae Gigartina helminthocortes in the Mediterranean Sea, and three males, five females, and one nymph probably collected from the same locality as the former two females. Considering the collecting locality, substrates, and number of individuals in each sex, these specimens surely correspond to those mounted on slides No. 2698 and No. 2699.
Apart from the specimens mentioned above, Walter (1925) also briefly noted the existence of other specimens of L. communis in the last part of the description, in which three males, five females, and one nymph were collected from the algae Cystosira found at 1-3 m depth in Rovigno near Punta Muccia in Italy by Dr. Vatova in 1925. Unfortunately, we could not find these specimens in the collections deposited in the Natural History Museum of Basel.
Legs (Figures 4a-d) -Length and chaetotaxy are given in Tables 1 and 2, respectively. Two swimming setae located on tibia of Leg-IV. A pair of bacilliform setae located on dorsal margin of tarsi in all 208  Idiosoma -450 long and 400 wide.
Dorsum -Unobservable. Probably same form as the female.
Chelicerae -Broken and composed of claw and basal segments.
Legs -Length and chaetotaxy are given in Table  3 and 4, respectively. One swimming seta located on tibia of Leg-IV. A pair of bacilliform setae located on dorsal margin of tarsi in all legs.
Legs -Length and chaetotaxy are given in Tables 5 and 6, respectively. A pair of bacilliform setae located on dorsal margin of tarsi in all legs. Swimming setae absent.

Morphological variation and abnormality of the type series
The idiosoma was 450 -520 long and 400 -430 wide in the female ( Walter (1925) described most of the taxonomic characters of L. communis in detail, but incorrectly mentioned the numbers of wheel-like acetabula and perigenital setae. In this study, three pairs of wheellike acetabula and 102 perigenital setae were found in L. communis. According to Tuzovskij (1987), every pontarachnid species have five pairs of idiosomal lyrifissures. However, we could observe only one pair of lyrifissures in the male and female, but none in the nymph. The specimens mounted on the slides can be observable only from ventral side. Therefore, it is probable that we overlooked the dorsal lyrifissures.

DISCUSSION
The number of perigenital setae in the paralectotype male did not correspond with the specimens reported from the Black Sea by Tuzovskij (1978). The paralectotype has 102 perigenital setae, whereas the Black Sea specimen has about 150 perigenital setae. In addition, Tuzovskij (1987) mentioned that a platelet "humeralis ventralis (Hv)" was present on a coxal plate in L. communis in Tuzovskij (1978). However, the lectotype and paralectotypes of L. communis have two setae instead of the platelet on the coxal plate. Therefore, L. communis sensu Tuzovskij (1978) is considered to be another species. The number of perigenital setae considerably varies within a species and the existence of the platelet Hv is not yet examined in many pontarachnid species. Consequently, the specific identification for the Black Sea specimen is not available in the present circumstances.
Comparison of taxonomic characteristics in the female of Litarachna communis between the original description by Walter (1925) and observation of the actual specimen (No. 2700) in the present study. In addition to the abbreviations used in the description, the following additional abbreviations are also employed. R: right, L: left, Leg-I (II, III, IV) -1 (2, 3, 4, 5, 6): Trochanter (to tarsus) of the first (to the fourth) leg. Measurements are given in micrometers (µm). For the paired appendage, if the measured value and the number of setae in the right appendage are different from those in the left appendage, those in the left appendage are given in parentheses. The characteristic is shown in bold in the case that a discrepancy between the original description and the present observation is recognized.