Vitzthumegistidae, fam. nov.: trigynaspid mites on terrestrial hermit crabs (Anactinotrichida: Mesostigmata: Trigynaspida)

A new family of cercomegistoid mesostigmatid mites, Vitzthumegistidae, including the species of Vitzthumegistus paguroxenus (Andre, 1937b) (= Physalozercon paguroxenus Andre, 1937b); V. latronis (Vitzthum, 1937) (= Cyclothorax latronis Vitzthum, 1937); and V. andrei (a nomen novum for Cyclothorax carcinicola von Frauenfeld, 1868, sensu Vitzthum, 1928), has been proposed. This family differs from the Cercomegistidae by the following characters: a holodorsal shield, absence of presternal shield, weakly sclerotized or vestigial (neither paired nor fragmented) sternal shield in the female, a smooth anterior and lateral margin of gnathotectum, and heavily branched (polyramous) hypostomal setae 1 (hs1) in the adult. The Vitzthumegistidae fam. nov. becomes biologically a unique group within the Trigynaspida, in which the members exhibit associations with paguroid hermit crabs (Crustacea: Decapoda: Paguroidea) in the Indo-Pacific region. A key to species of the Vitzthumegistus is provided.


INTRODUCTION
The psychosemanticist will specialize in the havoc wrought by verbal artillery upon the fortress of reason. Their job will be to cope with the psychic trauma caused by linguistic meaninglessness, to prevent the language from degenerating into gibberish, and to save the sanity of persons threatened by the onset of polysyllabic monstrosititis.
-James Thurber (The New Yorker, May 28, 1955 Issue, p.28) In his article, Kim (2008: 34) took a taxonomic action, invalidating the family name Physalozerconidae sensu Kethley (1977: 135) (Trigynaspida: Antennophoriae) out of the realm of the Mesostigmata. His action was based on the reasoning that the sole genus within the family, Physalozercon sensu Berlese (1903), has no nominal species as the known type species, "P. raffrayi (Wasmann, 1902)", was based on "Antennophorus raffrayi", a nomen nudum mentioned in Wasmann (1901Wasmann ( , 1902. In the endnote #2, Kim (2008: 34) also noted that Physalozercon paguroxenus André, 1937b, the only species added to the Physalozercon since Berlese (1903), was transferred to the Vitzthumegistus sensu Kethley, 1977 (Trigynaspida: Cercomegistiae: Cercomegistidae) by Kethley (1977: 139). While the taxonomic action of Kim (2008) was a bona fide intention to give minimized changes and confusion to the taxonomic and classification system of the Mesostigmata by recognizing the Vitzthumegistus sensu Kethley (1977: 139), the normal course of action could be the recognition of André's (1937b) P. paguroxenus as the type species for the Physalozercon by subsequent mono- Kim C.-M. typy (ICZN, 1999: Art. 67.2.2;69.3), and the recognition of this species at a family level. Such action, however, would certainly raise "taxonomic and nomenclatural" confusion regarding the concepts on the Physalozercon since, in a clear and strict sense, the description of Physalozercon paguroxenus André, 1937b was based on a misidentification, and the species cannot belong to the Physalozercon sensu Berlese (1903). In fact, while the Physalozercon of Berlese belongs to the infraorder Antennophoriae, the Physalozercon paguroxenus André, 1937b must belong to the infraorder Cercomegistiae. Accordingly, it is not difficult to note that recognizing the Physalozercon sensu André (1937b) (non Berlese, 1903) for the Vitzthumegistus sensu Kethley (1977) and raising the genus to the cercomegistoid Physalozerconidae fam. nov. (non Physalozerconidae Kethley, 1977) within the Cercomegistiae, which was previously used within the Antennophoriae with completely different family or infraordinal concept, can cause taxonomic, homonymic confusion. A further course of action to fix this problem would therefore be necessary.
Although the name Vitzthumegistus sensu Kethley (1977) was not made available, and so the name is not entering to synonymy, it should be noted that Kethley's unrevealed intention to group the above three species into a single genus is meaningful in terms of taxonomy as I see that these three species constitute a morphologically and biologically (in terms of the group's host association) unique clade separated from the other genera of Cercomegistidae, allowing its status as a distinct family within the Cercomegistiae. In addition, by following Johnston (1960), Kethley (1977) correctly recognized that two male specimens reported as the Cyclothorax carcinicola von Frauenfeld, 1868 by Vitzthum (1928: 194) are the cercomegistoid trigynaspids, and offered a new replacement name, V. andrei. Furthermore, the name Vitzthumegistus is also used in the acarology's most-widely used general textbook of Krantz & Walter (2009) as a distinct genus, different from other known cercomegistoids.
In this standpoint, I would re-recognize the grouping and names of aforementioned three species proposed by Kethley (1977), and would offer a description for the Vitzthumegistus (= gen. et nomen novum for Physalozercon sensu André, 1937b), along with offering of the name V. andrei, a nomen novum for the so-called Cyclothorax carcinicola von Frauenfeld, 1868, by Vitzthum (1928), in order to make these names available, to save the names and taxonomy, and to avoid any further confusion. Since André (1937b) did not give the generic description for the Physalozercon, I would consider the Vitzthumegistus a new genus (as with Kethley, 1977) and a new replacement name (nomen novum) for the Physalozercon sensu André (1937b), and the Vitzthumegistus is the type genus for the Vitzthumegistidae fam. nov. (Trigynaspida: Cercomegistiae: Cercomegistoidea) describing herein.

MATERIALS AND METHODS
Notations for idiosomal chaetotaxy follow the Hirschmann (1957) system re-clarified in Karg & Schorlemmer (2011: 5), and terminologies for idiosoma follow Kim (2004). An Olympus model BX51 compound microscope with 100X/1.35 (oil) UPlanApo objective lens with differential interference contrast (DIC) was used to examine the specimens. Lindquist et al. (2009a) treated the non-Linnean category "cohort" as a rank between the ranks of order and family. In this article, however, I recognize the cohort as a rank between the class and order; and the infraorder as a rank between the suborder and superfamily by following the taxonomic hierarchy shown in the Appendix 10 in Lincoln et al. (1982: 279). This treatment is not de novo, and has been applied to many taxonomic groups of zoology, including, but not limited to, the Crustacea. The infraorders Antennophoriae and Cercomegistiae used in this article are equivalent to the Antennophorina and Cercomegistina, respectively, as used in Kim (2004) and Lindquist et al. (2009a); and such usage of naming is intended to avoid the use of the suffix -ina, designated for the rank of "subtribe" in zoological nomenclature (ICZN, 1999: Art. 29.2; also see Kim, 2006: 19).
Type series -Syntype: Two males (slide number: V1207, V1208; each mounted on a thin square cover slip).
Type locality -INDONESIA: Northeast coast of Sumatra Island, Beach of Perbaungan.
Remarks -The Vitzthum Collection in Zoologische Staatssammlung (ZSM) has two additional microscope slides (slide number: V1214, V1215), which carry the mite specimens from Coenobita sp. collected by Johannes Carolus van der Meer Mohr  in March, 1933 at the same type locality (Beach of Perbaungan) in Sumatra Island. Slide V1214, in poor condition, contains three female specimens mounted together on a thin square cover slip, and slide V1215 carries a single male mounted on a thin square cover slip. Slide V1215 lacks gnathosoma, anterior dorsum, and legs I; and through the V1214, I was able to confirm the presence of three-tined palptarsal claws and polyramous hs1 setae. However, these four specimens in V1214 and V1215 slides were not included in the original description of Vitzthum (1928), and cannot be treated as name-bearing types. For the minimal change of name, I followed the same specific epithet, andrei, that Kethley (1977: 139) proposed in honor of Marc André (10 February, 1900-28 May, 1966. Immatures and biology are unknown.

DISCUSSION
The newly recognized genus Vitzthumegistus carries eight setae on femora IV, no postanal seta, long setae av4 and pv4 on a well-developed ventral intercalary Kim C.-M. sclerite on a circumsegmental fissure between basiand telotarsi IV, six setae on palp genua, threetined palptarsal claw (apotele), dentate chelicerae, dendritic cheliceral excrescences, and almost fused tritosternal laciniae, which collectively display the typical characteristics of the Cercomegistoidea of the Trigynaspida (Kim, 2004). In addition to these characters, the Vitzthumegistus carries a holodorsal shield, almost finely dentate cheliceral digits, no free presternal shield, weakly sclerotized entire (i.e., neither paired nor fragmented) sternal shield in the female, smooth anterior and lateral margin of gnathotectum, heavily branched (polyramous) hypostomal setae 1 (hs1), and no claws on tarsi I in the adult. In comparison, the members of Cercomegistidae carry two dorsal shields, paired presternal shields, serrate anterolateral gnathotectal margin (often with anterior projections), and simple or weakly barbed hypostomal setae 1 (hs1). While Kethley (1977: 139) correctly grouped these species together under a single genus and assigned the genus to the Cercomegistidae, due to the major differences described above, the Vitzthumegistus cannot be placed into the Cercomegistidae.
Within the Cercomegistoidea, presence of a holodorsal shield in the adult is found in the Asternoseiidae and Saltiseiidae, but the anterolateral gnathotectal margin in these two families is not smooth, but serrate. The smooth gnathotectal margin is found in the Seiodidae, but seiodids carry two distinct dorsal shields (i.e., podonotal and opisthonotal shields), which are also found in other cercomegistoid families (i.e., Cercomegistidae, Pyrosejidae). In addition, seiodids have tarsi I with claws, and have completely free tritosternal laciniae. In other words, the combination of characters found in the members of Vitzthumegistus is not found in any single family in the Cercomegistoidea, and I raise the genus Vitzthumegistus to a new family-group within the Cercomegistoidea of the Trigynaspida. In their key to the families of Mesostigmata, Lindquist et al. (2009b: 158) treated the Vitzthumegistus as a separate unit, different from other known cercomegistids. Within the Trigynaspida, in which the members often display a variety of host associations (see Kim, 2004: 161 for details), the Vitzthumegistidae fam. nov. become a unique group, in which the members exhibit associations with paguroid hermit crabs (Crustacea: Decapoda: Paguroidea) in the Indo-Western Pacific (Oriental) region (i.e., Pentecost Island (Île Pentecôte), Vanuatu; Sumatra, Indonesia). Since immatures have not yet been reported from host hermit crabs, the biology of Vitzthumegistus remains an intriguing mystery.

Key to species of the genus Vitzthumegistus
(Based on adult)