Phthiracarus pellucidus Ramsay, 1966

Liu, Dong & Zhang, Zhi-Qiang, 2016, Phthiracarus species (Acari: Oribatida: Phthiracaridae) from New Zealand, with description of a new species, redescription of Phthiracarus pellucidus and a key to 19 described species from the Australian Region, Journal of Natural History (J. Nat. Hist.) 50, pp. 1463-1472 : 1467-1470

Phthiracarus pellucidus Ramsay, 1966

( Figure 2 )

Redescription

Measurements. Prodorsum: length 195–232 width 125–140, height 77–100, setae: ss 25, ro 35, in 63, le 45, ex 25; notogaster: length 335–454, width 240–335, height 235–322; setae: c 1 80, c p 90, d 1 85, e 1 80, h 1 81, ps 1 80, ad 1 50, ad 2 40, ad 3 37, an 1 12, an 2 12; genito-aggenital plate 85 × 130, ano-adanal plate 65 × 145.

Integument. Colour yellowish. Entire surface of idiosoma punctate.

Prodorsum ( Figure 2A–B ). Median carina and posterior furrows absent; lateral carinae very weak, nearly invisible; sigillar fields invisible; sensilli (ss) short with rounded head; other prodorsal setae (in, le, ro, ex) thin, smooth and attenuate; comparative length: in> le> ro> ex = ss, mutual distance: in – in / ro – ro ≈ 5.4.

Notogaster ( Figure 2A ). Setae of notogaster (c 1 / c 1 – d 1 ≈ 0.7) thin, smooth and attenuate; setae c 2 further away from anterior margin, setae c 3 nearest; vestigial setae f 1 not observed; one pair of lyrifissures ia present.

Venter ( Figure 2A, C–D ). Setae h of mentum nearly as long as distance between them; seven pairs of genital setae (g) with formula: 4:3; ano-adanal plates each with five setae, comparative length: ad 1> ad 2> ad 3> an 1 = an 2.

Legs ( Figure 2E–F ). Setal counts for leg segments (without tarsi): I: 1–3–2(2)–5(1); II: 1–3–2(1)–3(1), III: 2–2–1(1)–2(1), IV: 2–1–0–2(1); setae d on femora I situated in the middle of segment, at the level of setae l’’; setae v’ on femora I absent; setae l’ on genua IV absent; setae a’’ on tarsi I and setae ft’’ on tarsi II curved distally; setae a’’ on tarsi II curved distally; setae s and pv’ on tarsi IV present; setae s on tarsi I and II present.

Material examined

Three adults ( NIGA, in alcohol, 72/211), New Zealand: Middle I ., Mercury Is., CL., from litter, 21 November 1972, leg . G .W. Ramsay.

Remarks

These specimens were collected by G .W . Ramsay who first described this species ( Ramsay 1966). Compared to the holotype, these specimens have longer notogastral setae.

Key to species of Phthiracarus known from the Australian Region

1. Dorsal and lateral regions fused on prodorsum........................................................................ ............................................................................................. P. curiosus Niedbała, 1998b (Hawaii)

– Dorsal and lateral regions not fused on prodorsum........................................................... 2

2. Sensilli long and narrow, their length more than 10 times their width.................... 3

– Sensilli short and wide, their length much less than 10 times their width.............. 7

3. Interlamellar setae situated anterior to lamellar setae........................................................... .............................. P. pygmaeus Balogh, 1958 (Melanesia, Polynesia, Hawaii, Australia)

– Interlamellar setae situated between lamellar setae........................................................... 4

4. Lateral carinae on prodorsum absent, lamellar setae minute, shorter than rostral setae.............................................................................. P. tubulus ( Hammer, 1972) (Polynesia)

– Lateral carinae on prodorsum present, lamellar setae considerably longer than rostral setae........................................................................................................................................... 5

5. Rostral setae positioned very close to each other, distance between rostral setae less than one-fifth the length between lamellar and interlamellar setae; four pairs of notogastral lyrifissures present; formula of genital setae: 6(4 + 2): 3........................ ................................................................. P. banksi Niedbała, 1987 ( New Zealand, Australia)

– Rostral setae positioned normally, distance between rostral setae more than one-third the length between lamellar and interlamellar setae; two pairs of notogastral lyrifissures ia and im present; formula of genital setae: 7(4 + 3): 2.. .............................................................................................................................. 6

6. Vestigial setae f 1 located anterior to setae h 1, setae v’ on femora I absent................. ........................................... P. crispus Hammer, 1972 (Polynesia, Hawaii, New Caledonia)

– Vestigial setae f 1 located posterior to setae h 1, setae v’ on femora I present............. ...................................................................................... P. fraternus Niedbała, 1998a (Polynesia)

7. Notogastral setae long and flagellate, setae c 1 longer than distance between setae c 1 and d 1 ................................................................................................................................................ 8

– Notogastral setae short and not flagellate, setae c 1 shorter than distance between setae c 1 and d 1 .. .................................................................................................................................. 9

8. Two pairs of notogastral lyrifissures present.. P. reductus Niedbała, 1998b (Hawaii)

– Four pairs of notogastral lyrifissures present... P. swiftae Niedbała, 1998b (Hawaii)

9. Four or five pairs of adanal setae present................................................................................... .......................................................................... P. probus Niedbała & Colloff, 1997 ( Australia)

– Three pairs of adanal setae present........................................................................................ 10

10. Three or four pairs of notogastral lyrifissures present.. .................................................. 11

– One or two pairs of notogastral lyrifissures present........................................................ 12

11. Three pairs of notogastral lyrifissures present; prodorsal, notogastral and anoadanal setae long..................................................... P. obscurus Niedbała, 1986 ( Australia)

– Four pairs of notogastral lyrifissures present; prodorsal, notogastral and ano-adanal setae minute...................................................................... P. minutus sp. nov. ( New Zealand)

12. One pair of notogastral lyrifissures present; seven pairs of genital setae present.... ............................................................. P. pellucidus Ramsay, 1966 ( New Zealand, Australia)

– Two pairs of notogastral lyrifissures present; nine pairs of genital setae present.. 13

13. Setae ad 1 and ad 3 arranged in one row with anal setae...................................................... ................................................................... P. anonymus Grandjean, 1933 (Hawaii, Australia)

– Setae ad 1 and ad 3 arranged not in one row with anal setae...................................... 14

14. Lateral carinae on prodorsum present ................................................................................... 15 – Lateral carinae on prodorsum absent ................................................................................... 16

15. Setae ps arranged in one row; genua IV without setae...................................................................... ................ P. paucus Niedbała, 1991 ( Papua New Guinea, Micronesia, Polynesia, Australia)

– Only setae ps 2 – ps 4 in one row, setae ps 1 situated highly at level of setae h 3; genua IV with one pair of setae....................... ..................... P. plenus Niedbała, 1998b (Hawaii)

16. Distal ends of heads of sensilli rounded, setae ad 1 and ad 2 on ano-adanal plate vestigial................................................................................................................................................ 17

– Distal ends of heads of sensilli pointed, setae ad 1 and ad 2 well developed.. 18

17. Setae ps 3 situated ventral to level of setae ps 2. P. perlucidus Niedbała, 1994 (Hawaii)

– Setae ps 3 situated nearly at same level of setae ps 2 ............................................................... ................................................................................................. P. insularis Jacot, 1935 (Polynesia)

18. Interlamellar setae more than twice longer than lamellar setae, setae l on tibiae IV present...................................................................... P. persimilis Niedbała, 1998a (Polynesia)

– Interlamellar setae less than twice longer than lamellar setae, setae l on tibiae IV absent................................................... P. inacessus Niedbała, 1998a (Polynesia, Australia)

Note: We suspect that P. perlucidus Niedbała, 1994 is a junior synonym of P. insularis Jacot, 1935 , although we did not check the type specimens. These two species are different from each other only in the insertion of setae ps 2 and ps3, which is a feature subject to individual variation.

Figures

Figure 2. Phthiracarus pellucidus Ramsay, 1966: (A) lateral view of body (legs removed); (B) prodorsum, dorsal view; (C) right side of ventral plate; (D) mentum of subcapitulum; (E) femur I; (F) tibia IV. Scale bars: A = 100 μm; B–F = 50 μm.