The first Nearctic record of the genus Neocheiridium (Pseudoscorpiones: Cheiridiidae), with description of Neocheiridium gullahorum sp. n.

Abstract Background The genus Neocheiridium Beier, 1932 currently contains seven Neotropical (including Caribbean) and two Afrotropical species, with no Nearctic records. New information An undescribed species of Neocheiridium from South Carolina was discovered in the Ohio State University Acarology Collection and is described as Neocheiridium gullahorum, n. sp. (based on specimens of both sexes). A key to known world species of Neocheiridium is proposed.


Introduction
is the third largest genus in the family Cheiridiidae. The genus was first described by Max Beier in his monograph on the world pseudoscorpion fauna, with Cheiridium corticum Balzan, 1890 from Paraguay as type species (Beier 1932, Balzan 1890. Beier (1959) added one more species from Argentina and Vitali-di Castri (1962) described two new species from Chile. Beier (1978) then added a fifth species from Galapagos Islands. Subsequently, Mahnert (1982) described two Afrotropical species, making Neocheiridium a Gondwanan taxon, rather than a strictly Neotropical one and presented a key to the known species. Then Mahnert and Aguiar (1986) redescribed the type species, added two more Neotropical species (including N. strinatii from Caribbean islands) and amended the generic diagnosis (see Fig. 1 for the currently known American records).
No North American Neocheiridium species are hitherto known (Chamberlin 1924, Hoff 1958, Harvey 2013. Altogether, nine Neocheiridium species are known from the Neotropical and Afrotropical regions. In addition, an undescribed species of the genus has been reported from Boatswainbird Island (near Ascension Island) (Rowlands 2001) and there are unpublished records of one species from the Seychelles islands and one from Australia (Mark Harvey, pers. comm.). Currently known distribution of Neocheiridium species in the Americas. Some symbols indicate multiple nearby finding localities (based on Aguiar and Bührnheim 1998, Beier 1959, Beier 1978, Harvey 2013, Mahnert 2014, Mahnert and Aguiar 1986, Vitali-di Castri 1962, Von Schimonsky and Bichuette 2019, Vitali-di Castri 1967 The generic boundaries in the family Cheiridiidae may need revision (Mahnert 2014, Mahnert and Aguiar 1986, Judson 2000, but as currently understood, the genus Neocheiridium is characterised by subtriangular granular carapax with two small eyes, one procurved furrow and "shoulders", abdomen with only 10 (divided) tergites visible from above, rallum with four blades, the distalmost of which is expanded, palp chelal fingers shorter than hand, movable finger with only one trichobothrium, femur and patella of legs fused with suture between them hardly visible and usually body and pedipalp setae curved and covered with cerotegument (Beier 1932, Mahnert 1982, Mahnert 2014, Mahnert and Aguiar 1986. A new species of Neocheiridium is described below, based on specimens of both sexes from the Ohio State University Acarology collection, collected from South Carolina, USA. The finding locality (Hilton Head Island) is a low island near the South Carolina continental coast, with a humid subtropical climate (Köppen classification Cfa), having humid, warm summers and cool and rainy winters. The island has very sandy soil that does not hold water well, drying quickly without percipitation. It is a densely populated area with little natural vegetation remaining.

Materials and methods
All specimens were extracted from a soil and debris sample using standard Tullgren funnels. The material was kept in 70% ethanol.
Specimens were studied using a Leica S8AP0 dissecting microscope and a Leica DM6000B compound microscope. Line-drawings were prepared using a U-DA drawing tube attached to an Olympus CX31 compound microscope. The images were generated by combining stacks of images with different focal planes using software LAS V.4.5.0.
One specimen (female paratype) was cleared in 10% KOH and mounted on to a slide (in Hoyer's medium), the other specimens being studied in cavity slides in glycerol. The terminology used follows Harvey (1992). All measurements are given in millimetres. The measurements for female are given for holotype, followed by the female paratype in parentheses.

Abbreviations
The following abbreviations are used for pedipalp trichobothria: t -terminal exterior on movable finger, et -exterior terminal on fixed finger, est -exterior subterminal on fixed finger, esb -exterior subbasal on fixed finger, eb -exterior basal on fixed finger, it -interior terminal on fixed finger, isb -interior subbasal on fixed finger, ib -interior basal on fixed finger.

Description
Diagnosis: Neocheiridium species with sharp triangular teeth on the distal end of the palpal chela, becoming trapezoidal and gradually flatter towards the proximal end, metazonal depression open to posterior margin, 7 trichobothria on the fixed pedipalp finger and 1 on the movable finger. Palpal chelae length-width ratio with pedicel 2.4-2.6. Body length at least 1 mm, no more than 7 setae on the half-tergites, 4 teeth on the cheliceral fixed finger, female galea without apical branches, tubercles on tergites I-III similar to tubercles of other tergites, two pairs of setae between eyes and cucullus.

Etymology
The specific name derives from the word "gullah" used to describe the people and traditional culture of the type locality, with genitive plural ending -orum.

Discussion
The new species seems to be related to Neocheiridium triangulare Mahnert & Aguiar, 1986, described from Rio Urubu, Brazil and may be Neocheiridium galapagoense Beier, 1978 from the Galapagos Islands. These species share the sharp triangular teeth on the distal end of the palpal chela, becoming trapezoidal and gradually flatter towards the proximal end, the metazonal depression, open to posterior margin and 7 trichobothria on the fixed pedipalp finger and 1 on the movable finger. N. triangulare and N. galapagoense can be separated from the new species by having more slender palpal chelae (length-width ratio with pedicel 2.8-2.9 and 2.5-2.8, respectively, versus 2.4-2.6 in N. gullahorum) and smaller size (body length 0.76-0.97 and 0.90-0.95, respectively, versus 1.06-1.21 in N. gullahorum) (Mahnert and Aguiar 1986, Mahnert 2014. It also differs from N. galapagoense by having no more than 7 setae on the half-tergites (8-10 in N. galapagoense), more slender palpal distal teeth and 4 teeth on the cheliceral fixed finger (2 for N. galapagoense). Differences with N. triangulare include the lack af apical branches of the female galea, the lack of more strongly sclerotised rows of tubercles on tergites I-III, two pairs of setae between eyes and cucullus, the structure of female external genitalia and smaller number and shape of teeth on pedipalps.
Nothing is known of the ecology of the new species. However, considering its small known range and habitat degradation in the type locality due to recent real estate development there, it may be a vulnerable or endangered species.