Pontarachna nemethi, sp. nov.
Creators: name: Pešić, Vladimir
name: Chatterjee, Tapas
name: Schizas, Nikolaos V.
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Trombidiformes
Pontarachnidae
Pontarachna
Pontarachna nemethi

description: Pontarachna nemethi sp. nov.
(Figs. 1–2)
Type series. Holotype male (NHMB), dissected and slide mounted in Hoyer's fluid, El Seco (18°7.331N; 65°11.605W), east of Vieques Island, Puerto Rico, collected by the Rebreather Tri-Mix Diving team of UPRM, January 17, 2010. Paratypes: three males, five females, two deutonymphs, same data as holotype, one male, two females and one deutonymph dissected and slide mounted (NHMB).
Diagnosis. (Adults). Idiosoma L <300 µm; first coxal plates fused; medial posterior apodemes of fourth coxae narrow and of moderate length, not extending to posterior margin of genital field; posterior to the genital field two pairs of wheel-like acetabula (sensu Cook 1996) (Fig. 1b), these on a common platelet on their respective sides. Male: Sclerotized area of genital field with 10–12 pairs of setae. Female: Postgenital sclerite with a pair of wheellike acetabula (sensu Cook 1996) and 2–4 pairs of pores (Fig. 2b).
Description. Male (holotype, in parentheses measurements of the paratype): Idiosoma L/W 250 (266)/216 (216). Coxal field L/W 135 (140)/194 (208). First coxal plates fused medially. Suture lines of Cx-II/III incomplete, suture line of Cx-III/IV extending onto narrow medial posterior apodemes of Cx-IV. Medial posterior apodemes of Cx-IV of moderate length, not extending to posterior margin of genital field (Fig. 1a). Lateral posterior apodemes of Cx-IV short and broad. Genital field (Fig. 1c) L/W 26 (29)/32 (33) consisting of a sclerotized area with 7–8 (10–12) pairs of setae (regularly visible as setae pores). Due to the oblique position of the genital field in holotype, resulting in a difference of shape of the genital field between holotype and examined paratype specimen (compare Figs. 1a and 1c), and because the specimens have been fixed in ethanol, some pores could have been unobserved. Ejaculatory complex (Fig. 1d) L 47. Posterior to the genital field two pairs of wheel-like acetabula (sensu Cook 1996), these on a platelet on their respective sides. Excretory pore unsclerotized, near the posterior idiosoma margin. Palp: total L 149 (151), dL: P-1, 19 (19); P-2, 35 (35); P-3, 32 (31); P-4, 49 (51); P-5, 14 (15); dL P-2/P-4 ratio 0.71 (0.69); palp chaetotaxy as shown in Figs. 1g –h; capitulum vL 72 (79); chelicere styliform as in Fig. 1f. Legs: dL of I-Leg-2-6 (Fig. 1e): 29 (29), 37 (37), 36 (37), 49 (52), 65 (69); claws with ventral and dorsal clawlets; III–Leg-5, IV-Leg-4 and IV-Leg-5 with one swimming setae, respectively.
Female (n = 2): Similar to male, except for the shape of the genital field and postgenital area. Idiosoma L/W 280–290/234. Coxal field L 135–142, W 207–208; medial posterior apodemes of fourth coxae not extending to posterior margin of genital field (Fig. 2a). Genital field L 50; pregenital and postgenital sclerite 28–31 and 35–38 wide respectively. Postgenital sclerite with a pair of wheel-like acetabula (sensu Cook 1996) and 2–4 pairs of pores (Fig. 2a, b). Posterior to the genital field two pairs of wheel-like acetabula, these on a platelet on their respective sides. Palp: total L 152–168, dL: P-1, 19–21; P-2, 37–40; P-3, 35–36; P-4, 46–55; P-5, 15–16; dL P-2/P-4 ratio 0.8 (0.73); palp as in male; capitulum vL 78–82. Legs: dL of I-Leg-2-6 (Fig. 1i): 32, 39, 37–39, 51–52, 66–67.
Deutonymph (collected together with adults of Pontarachna nemethi and suspected to represent this species): Similar to adults, but lacking a genital field and Cx-I separated medially (Fig. 1j). Idiosoma L/W 180/150; palp (Fig. 1k) total L 110, dL: P-1, 12; P-2, 25; P-3, 23; P-4, 38; P-5, 12; dL P-2/P-4 ratio 0.66; dL of I-Leg: 23, 22, 27, 25, 37, 49.
Etymology. The species is named after Michael Nemeth, a Tri-Mix Rebreather diver who collected many mesophotic samples for the third author during the DeepCres research program.
Remarks. Pontarachna nemethi sp. nov. can easily be distinguished as adults from all other members of the genus Pontarachna by the possession of fused first coxae, a character which has not been reported for this genus previously. It is worth noting that in Litarachna four species have fused first coxal plates, two of these, i.e., L. degiustii Cook, 1958 and L. caribica Pešiċ, Chatterjee & Schizas, 2008, are known only from the Caribbean Sea (Cook 1958; Pešiċ et al. 2008).
Additional diagnostic characters of the new species include: medial posterior apodemes of fourth coxae narrow and of moderate length, not extending to posterior margin of genital field, the sclerotized area around the genital field in male with 7–12 pairs of setae, and postgenital sclerite in female with a pair wheel-like acetabula and 2–4 pairs of pores.
Distribution. Only known from the type locality.
Habitat. The mites were collected from 52–67 m depth. The greatest depth at which pontarachnid mites have been recorded previously was reported by Mari & Morselli (1983) who found Litarachna communis Walter occurring down to a depth of 25 m, although most specimens were found between 3 and 5 m. The finding of new species from a mesophotic coral ecosystem near Vieques Island of Puerto Rico remarkably extended the potential area of the world ocean occupied by the Pontarachnidae. We do not know the exact microhabitat (loose rubble or sediment) of Pontarachna nemethi sp. nov. or if it is associated with a specific macroalgae/sponge/coral species because these substrata have not been separated in the present collection.
description: Published as part of Pešić, Vladimir, Chatterjee, Tapas & Schizas, Nikolaos V., 2012, A new species of Pontarachna (Acari, Hydrachnidia, Pontarachnidae) from a mesophotic coral ecosystem off Vieques Island, Puerto Rico, Caribbean Sea, pp. 63-67 in Zootaxa 3440 on pages 64-66, DOI: 10.11646/zootaxa.3440.1.3, http://zenodo.org/record/282142