A new marine mite of the genus Litarachna Walter, 1925 from Guadeloupe, Caribbean Sea (Acari, Hydrachnidia, Pontarachnidae)

The water mite family Pontarachnidae Koenike, 1910, the only family of the true water mites (Hydrachnidia) occurring in the marine environment, consists of two genera, Pontarachna Philippi, 1840 and Litarachna Walter, 1925. Most of the known pontarachnid mites species were collected in the marine littoral zone (Smit 2003), but some species such as Litarachna lopezae and Pontarachna nemethi , are known only from mesophotic coral ecosystems (MCEs) and were collected at a depth of almost 70 m (Pešić et al . 2012, 2014). The most recent checklist of pontarachnid mites was published by Chatterjee et al . (2019), listing 53 species worldwide, 30 species of Pontarachna and 23 species of Litarachna. Recently, two more species, one from each genus were described from the Gulf of Antalya, Levantine Sea, Turkey (Pešić et al . 2019

to Koenike-fluid.The holotype of the new species will be deposited in Naturalis Biodiversity Center in Leiden (RMNH).
Diagnosis (Female unknown) -A pair of small platelets with coxoglandularia 4 and associated setae free in the integument between posterior apodemes of Cx-IV; posterior margin of Cx-IV with long medial posterior apodemes extending beyond anterior margin of the ring around gonopore; a ring around gonopore with two pairs of setae surrounded by 43-44 pairs of perigenital setae free in integument.

Description
Male -Idiosoma L 289, W223.Coxal field: L 133, W 204; Cx-I separated medially; suture lines Cx-II/III and Cx-III/IV incomplete; posterior margin of Cx-IV with two pairs of apodemes, the medial ones long, posteriorly extending beyond the anterior margin of sclerotized ring around gonopore (Fig. 1A).Sclerotized ring around gonopore L/W 27/25, with two pairs of setae, surrounded by 43-44 pairs of perigenital setae lying free in integument.Between the posterior apodemes of the fourth coxal plates a pair of glandularia-like structures and a pair of small platelets with coxoglandularia 4 and associated setae.Posterior to the genital field a pair of platelets with three pores (V3 [gland and seta sensu Wiles et al. 2002] fused with Lgl-3) and three pairs of wheel-like acetabula sensu Cook (1996).One of these wheel-like structures large with many radiating spokes, the most posterior ones small with relatively few radiating spokes.Excretory pore unsclerotized, near posterior end of idiosoma.
Etymology -Named after the island where the new species was found.
Discussion -The new species belongs to the Litarachna duboscqi species group (see Pešić et al. 2008 for discussion) characterized primarily by the incomplete, medially obliterated, suture line Cx-III/IV and ventral margin of P-4 with a large tubercle.
Due to the glandularium-like structure posterior to Cx-IV not fused with adjoining coxoglandularia 4, and the higher number of perigenital setae (> 20 pairs) in male, the new species resembles Litarachna sagamiensis Moto & Abé, 2013 from the Pacific coast of Japan and L. caribica from Curaçao.The latter species differs in the light fusion of the first coxal plates (unfused in guadeloupensis), and a moderate length of medial posterior apodemes of Cx-IV not extending beyond the sclerotized ring around gonopore (extending in guadeloupensis), the latter bearing four pairs of setae (two pairs in guadeloupensis).
Litarachna sagamiensis Moto & Abé, 2013 is similar to the new species in the unfused Cx-I, but can easily be separated from the male of new species in lower number of perigental setae (24-25, data taken from Moto & Abé 2013) and a comparatively longer medial posterior apodemes of Cx-IV reaching posterior margin of the sclerotized ring around gonopore (Moto & Abé 2013) Two other species known from the Caribbean Sea, L. degiustii and L. lopezae belong also to duboscqi-species group.Litarachna degiustii differs in the large fusion of the first coxal plates, the fusion of glandularium-like structure posterior of the fourth coxal plates with coxoglandularia 4, and the presence of four pairs of perigenital setae in the male (Cook 1958;Pešić et al. 2008).Litarachna lopezae can be separated by the fused Cx-I, a glandularium-like structure fused with Cx-IV, a peg-like seta at the base of P-4 ventral tubercle and the presence of four pairs of perigenital setae in the male (Pešić et al. 2014).
-This is the first report of a new pontarachnid mite species from Guadeloupe indicating both the lack of taxon-specific sampling efforts and the understudied species-rich meiofauna assemblages in the Caribbean Sea.