Duges caudatus is a Tenuipalpidae and not a Tydeidae (Acari)

A BSTRACT — Depending on the publication consulted, Dugès’ caudatus is a mite listed either in the Tenuipalpidae, or in the Tydeidae, or in both. The name varies accordingly and the species is called either Tenuipalpus caudatus (Dugès, 1834) or Tydeus caudatus (Dugès, 1834). A transect was conducted on laurustinus shrubs ( Viburnum tinus ) around Montpellier (France) to retrieve the species described by the French obstetrician. It results that Dugès’ caudatus is probably a Tenuipalpidae and not a Tydeidae. Tenuipalpus caudatus (Dugès, 1834) is redescribed from specimens collected in Montpellier and a neotype is deposited in Paris. The most frequent tydeid observed on Viburnum tinus in Montpellier was Tydeus goetzi Schruft, 1972, a redescription is also given. Tydeus caudatus (Dugès, 1834) is no longer a valid name.


INTRODUCTION
The "Historia Animalium" (Ancient Greek: Περὶ Τὰ Ζωα ΄Ιστορίαι) is one of the largest works of Aristotle and is sometimes translated into "Inquiry into Animals". Indeed, it was a real inquiry to guess what is Dugès' caudatus, what the French obstetrician and naturalist saw and described.

Antoine Louis Dugès
Antoine Louis Dugès (1797-1838) was a French obstetrician and naturalist who was born in Charleville-Mézières. He was appointed professor of obstetrics at the University of Montpellier where a room still bears his name. As a zoologist, he first studied worms (Dugès, 1928), then other organisms. He attempted to reconcile the ideas of Cuvier and Geoffroy Saint-Hilaire and published several laws (Dugès, 1832;McBirney and Cook, 2009). Dugès conducted osteological and myological studies of amphibians (Dugès, 1834a), and also performed extensive research involving mites (Dugès 1834b, c, d). A spider still bears his name, Spermophora senoculatus (Dugès, 1836). With Henri Milne Edwards, he was responsible of arachnids in the famous book edited by Baron Cuvier "Le règne animal distribué d'après son organisation" (the exact publication date is discussed by Cowan, 1976). In 1838, he published an influential work on comparative physiology, titled "Traité de physiologie comparée de l'homme et des animaux" and dedicated to E. Geoffroy Saint-Hilaire.

Montpellier samples
A first batch of 20 leaves of laurustinus (Viburnum tinus) collected by M. Bertrand in the park surrounding his laboratory at the University of Montpellier were received on 24 June 2002.

Transect samples
In addition to the leaves collected in Montpellier 19 series (Table 1) of 20 leaves were collected on September 2002, along a transect of North Spain and southern France Mediterranean forests (Table  2).

Sample treatment
Leaves were deposited in a plastic bag and labeled accordingly. Part of leafs were immediately surveyed using a dissecting microscope. Other leafs, protected in the plastic bag, were sent by post to the lab in Belgium where they were also surveyed using a dissecting microscope. Most mites were thus mounted in Hoyer's medium and identified under a light microscope. Some specimens were studied with a Scanning Electron Microscope (SEM).

Redescriptions
Redescriptions are based on pictures as explained in André and Ducarme (2003) and detailed in André et al. (2010). Notation system used by Beard et al. (2005) and Mesa et al. (2009) were applied on idiosoma, designations or nominations of setae on tydeid tarsus proposed by André (1981) were again used.

The type locality
Dugès' (1834b) did not give the type locality of his caudatus. In his memoir, Dugès dealt with 13 different species and described 10 of them (Table 1). The type locality was given for seven out of the ten described species; for all of them, it was the South of France or near Montpellier, "his" city. This strongly suggests that the type locality of Dugès' caudatus was probably the South of France as for most of the other species he described.
The host plant, Viburnum tinus, is a forest element of Mediterranean stock with a circum-Mediterranean distribution (Quézel et al., 1999). This is another observation pleading in favor of the South of France as the type locality of Dugès' caudatus.
However, we cannot formally exclude the possibility that caudatus was found in Paris. Indeed, Dugès was a student of E. Geoffroy Saint-Hilaire, professor of vertebrate zoology at the "Muséum d'histoire naturelle" and he said to have collected mites in Paris where he was graduated (Dugès, 1834b: 28). On the other hand, the host plant was already cultivated in Paris in that time (Boisduval, 1867).

Montpellier samples
Out of 20 leaves of laurustinus collected in Montpellier (series "0" in Table 3), nineteen leaves were inhabited by tydeid mites. Four species were found to coexist on the leaf undersurface: a Tenuipalpus, a slow-moving bright red mite; an Acarididae (four females) and two tydeid species. A tydeid species, very small, was represented by a single female.
All the other tydeid specimens belonged to the same species, Tydeus goetzi, and included only two females among numerous immatures. Out of the 30 specimens mounted, there were two females, three tritonymphs, 17 deutonymphs, seven protonymphs and a single larva. The real immature/adult ratio was certainly higher as small specimens were more difficult to detect and capture than females.

The transect samples
The identifications of mites collected along the transect are summarized in Table 3.
However, the question is not knowing if the Tydeidae are common on the laurustinus leaves, but knowing what species Dugès saw and described in his memoir. In 1834, Renucci made his famous experiment on scabies in Paris (Renucci, 1835;Ghesquier-Pourcin, 2009). While basic microscope technology and optics were available to Dugès, it is much more recently that techniques in sample illumination were developed to generate the high quality images seen today. For example, Köhler il- lumination was discovered only in 1893. Nevertheless, several other French scientists made similar observations, mites running on the leaf undersurface of the same host plant, the laurustinus: Boisduval (1867), Donnadieu (1875), and Girard (1880).
First of all, the Latin binomen (Tetranychus caudatus) as well as the French name (Tétranyque à queue) designate a Tetranychoidea. Characters used in the comparison between Dugès' original description and current observations are listed in Table 4. Triophtydeinae were not retained, the presence of three eyespots is observed even with a dissecting microscope and is not reported by Dugès (1834b -character 8). Pronematinae were also not retained as the absence of apotele I is easy to see (character 12). Remain two species that are both frequent on laurustinus in Montpellier ( Figures 1B, C). The presence of numerous eggs in gravid females of the genus Tydeus would have been reported by Dugès (1834b), yet the French physician wrote that there was only one egg in gravid females (character 1). This observation accords with the biology of Tenuipalpus (see for instance, Pontier et al. 2000). The genus has a clear constriction at the level of trochanter III, a peculiarity noted by Dugès (character 10). This corresponds to the anterior margin of opisthosoma abruptly narrowing in Tenuipalpus and already reported by Baker (1945). The opisthoma The symbol "?" means that the character was not described by Dugès or the criterion does not apply.
Characters concern mites observed in France and Western Europe. See the text for discussion. prolongs into four foliaceus setae which forms the "tail" also reported by Dugès (characters 4 to 6). Again, the "tail" recalls that observed in Tenuipalpus and already reported by Baker (1945). Characters 7 (habitat) and 2 (size) are not decisive even if they apply more to a Tenuipalpus than a Tydeus.
Arguments in favor of Tydeidae are the color (character 3) and the speed (character 13). Yet, the food content directly affects the color of Tenuipalpidae which is variable (Morishita, 1954;Haramoto, 1969). Last, Tenuipalpidae observed in Western Europe are stationary when feeding and move slowly when disturbed. This contrasts with the speed observed in Tydeidae which are fast running species. Table 4, it is concluded that Dugès' caudatus is probably a Tenuipalpidae and not a Tydeidae. Dugès' original description is thus completed in the next section, from specimens collected in Montpellier.
Prodorsal shield ( Fig. 2A, C) with longitudinal cells on a median crest except for a small posterior portion with irregular and transverse cells, lateral part with transverse striae and minute pores, anterolateral shield with two ocelli, posterolateral corners of prodorsum angulate. Prodorsal setae, (v2) and (s1) minute, slightly serrate; s2 on a small tubercle behind a anterolateral projection and broadly lanceolate.
Opisthoma with a strong median crest prolonged anteriorly by another crescent-like crest. Cells on the crest with well-defined borders and rounded contours, with more or less transverse striae along the median crest. A second projection over trochanter III. A pair of opisthosomal pores distinct, (po). Setae minute (e1, d3), or foliaceous (c1, d1, c3), "tail" composed of four pairs of foliaceous setae (e2, f1, f2 and h1) plus one pair of flagelliform setae (h2).
Tarsi III and IV (Fig. 5) with an antixial dorsal flagelliform seta arising from a tubercle, ft, two serrate prorals arising also from tubercles, (p), and two plumose ventral setae (u). Tarsi I and II with a paraxial dorsal flagelliform seta arising from a tubercle, ft', this elbowed element seems to form a pair with a squamous seta arising from a tubercle, ft". Under this dorsal pair, also arising from their own tubercle, a pair of typical eupathidia, (p). Between the prorals, the solenidion ω , also on a tubercle. Last, the two pairs of setae, (tc) and (u). All the apoteles with 3 bifid elements (ol', om and ol") equipped with tenent hairs (Fig. 4D).

Redescription of Tydeus goetzi Schruft, 1972
The most frequent tydeid found in trichomes of laurustinus from Montpellier was T. goetzi. The original description did not give information on striae and is completed here. Figure 6A gives a whole view with the three distinct clavate setae at the tip of the opisthoma, the "spätelformig" setae of Schruft (1972). Serrate setae with a radial symmetry are clearly distinct from clavate setae, characterized by a radial symmetry at the base and a bilateral symmetry in the distal part (Fig. 6B).
Striae form circular patterns at the base of clavate setae and delineate two distinct angles at the tip of anal lips (Fig. 6B).
Compact striation pattern on genital lips. Dorsal setae on genu III and tibiae III and IV are blunt distally.

CONCLUSIONS
The Tydeidae and Tenuipalpidae are two distinct and well-defined families of Prostigmata. The Tydeidae belong to the superfamily Tydeoidea, superchort Eupodides, while the Tenuipalpidae are members of the superfamily Tetranychoidea, supercohort Eleutherengonides (Walter et al., 2009). Dugès' caudatus cannot belong to different families depending on the publication. Dugès (1834b) did not mention a type. Although Tenuipalpus caudatus is the type species of the genus and the family, there is no depository listed in recent catalogs (Mesa et al., 2009). Accordingly, a neotype is designated and deposited in Paris (Muséum national d'Histoire naturelle). This deposition will clarify the taxonomic status of the species described by Dugès (1834b) and will prevent the species from being listed in different and unrelated families, namely the Tydeidae and Tenuipalpidae. It will also clarify the type locality of the species, Montpellier, where Dugès made most of his observations. Voucher specimens are also deposited in Brussels (Institut royal des Sciences naturelles de Belgique).
Accordingly, Tydeus caudatus is thus a name that does not conform to the rules of the International Code of Zoological Nomenclature and therefore is not available for use as a valid name. This accords with Oudemans' (1937) statement that Tydeus caudatus is a nomen nudum although, according to the Dutch acarologist, Dugès' species was considered a synonym of Tydeus spathulatus. This conclu-sion does not apply to the Tydeidae described by Kuznetsov (1979) under the name Venilia caudata.