Chaetodellus, Mašán & Halliday, 2013

Mašán, Peter & Halliday, Bruce, 2013, A new genus and species of soil mite (Acari: Pachylaelapidae: Pachylaelapinae) from the Canary Islands, Journal of Natural History (J. Nat. Hist.) 48 (7 - 8), pp. 403-412 : 405-409

Chaetodellus gen. nov.

( Figure 1 )

Type species Chaetodellus comatus sp. nov.

Diagnosis (female)

Dorsal idiosoma ( Figure 1A, G ). Dorsal shield oval-shaped, completely covering idiosoma, margins encroaching slightly onto ventral idiosoma; with 29 pairs of smooth pointed setae; setae strongly differentiated in length, j1 and J5 minute; J1 widely separated, markedly anterolateral to J2; z6 markedly anterolateral to j6. Shield with approximately 12 pairs of pore-like structures, some of them enlarged, suboval to slit-like.

Ventral idiosoma ( Figure 1B ). Presternal shields absent. Peritremes and peritrematal shields well-developed, peritrematal shields fused to exopodal shields, produced posteriorly well behind coxae IV. Genitoventral shield relatively large, trapezoidal, with straight posterior margin and three pairs of setae (st5, Jv1 and Zv2). Metapodal shields absent or fused with peritrematal–exopodal–parapodal complex (but this complex with no outlines of the fusion). Anal shield free, wide, subtriangular, bearing three short setae (one pair of paranals and one postanal). All ventral idiosomal setae smooth and pointed. Unsclerotized integument with five pairs of setae (r6, Jv2−Jv4 and Zv3).

Spermathecal apparatus ( Figure 1F ). Sperm access system with tubular components opening onto coxae III; tubular components long, fine for whole length, slightly and regularly broadened towards the coxa.

Legs. Legs normal in length, shorter than idiosoma. Tarsus II with all distal setae fine and pointed, not modified into spurs ( Figure 1E ). Chaetotaxy I-II-III-IV: coxa 2-2-2-1, trochanter 6-5-5-5, femur 13-11-6-6, genu 12 (2-5 / 3-2)-11-7-7, tibia 12-10-7-7; tarsi II–IV with 18 setae.

Gnathosoma . Corniculi short, horn-like. Palp segments without projections. Epistome with wide base and medial projection on distal margin; lateral margins of base rounded and denticulate, central projection with short narrow neck and furcate apex with large and small denticles ( Figure 1D ).

Etymology

The name of the new genus is derived from the Greek chaeto -, referring to the long dorsal shield setae, in combination with the diminutive suffix - ellus, as used in the names of other pachylaelapine taxa. Gender masculine.

Notes on the genus

The new genus is diagnosed by the following combination of characters: (1) dorsal shield expanded to encroach slightly onto the ventral surface of the idiosoma; (2) dorsal shield with 29 pairs of setae, which vary widely in length; (3) vertical setae j1 minute; (4) clunal setae J5 minute; (5) dorsocentral setae J 1 in unusual position markedly anterolateral to J2; (6) dorsal setae z 6 in unusual position markedly anterolateral to j6; (7) strongly reduced number of setae on unsclerotized ventral integument, R setae absent; (8) genitoventral shield with three pairs of setae including Zv2; (9) tarsus II with uniform fine, pointed setae, without modified spur-like setae; (10) separate metapodal shields absent; and (11) sperm access system with long spermathecal tubes opened onto coxae III. Some of these character states occur in other genera of Pachylaelapinae , but infrequently, and not in combination (especially the combination of characters in points 4 and 8 is unique among the all known pachylaelapid genera). For example Neopachylaelaps and Pachyglobolaelaps have 29 pairs of dorsal shield setae; seta J1 is anterolateral to J 2 in Pachyglobolaelaps and Sphaerolaelaps ; spur-like distal setae are also absent from tarsi II in Elaphrolaelaps, Pachysphaerolaelaps , Paralaelaps and Sphaerolaelaps ; dorsal shield setae J5 are minute in Neopachylaelaps, Olopachys , Pachydellus , Pachyglobolaelaps and Pachylaelaps . The combination of a tubular sperm access system and minute setae J5 is found in the genus Pachyglobolaelaps , which also has dorsal setae of widely varying lengths. The new genus may be easily distinguished from the other related genera by the characters introduced in the identification key below.

Elaphrolaelaps nepalensis Samšiňák and Daniel, 1978 has some features in common with the new genus – 29 pairs of dorsal shield setae, dorsal shield setae strongly differentiated in length, setae j1 and J5 minute, dorsal shield expanded onto the ventral idiosoma, and tarsus II without spur-like setae. However, the ventral idiosoma of E. nepalensis differs markedly from that of Chaetodellus – Zv2 is not on the genitoventral shield, the unsclerotized ventral integument has eight or nine pairs of setae, and the peritrematal shields are strongly expanded posteriorly to reach the posterior margin of the genitoventral shield.

Key to world genera and subgenera of Pachylaelapinae (females)

1. Tarsus II without thick spur-like setae.................................... 2 Tarsus II with at least distal seta pl1 modified, thick and spur-like, pl2 may also be so modified...................................................... 7

2. Dorsal shield with about 80 pairs of setae........................................................................... Pachysphaerolaelaps Mašán, 2007 Dorsal shield with at most 37 pairs of setae............................... 3

3. Some dorsal shield setae modified, elongated and thickened, with club-like tips.......................................... Sphaerolaelaps Berlese, 1903 All dorsal shield setae uniform, smooth and pointed...................... 4

4. Unsclerotized idiosomal integument strongly hypertrichous................................................................ Paralaelaps Trägårdh, 1908 Unsclerotized integument never hypertrichous, with 5−21 pairs of setae.... 5

5. Genitoventral shield with three pairs of setae (st5, Jv1, Zv2).................................................................... Chaetodellus gen. nov. Genitoventral shield with two pairs of setae (Zv2 off the shield)............ 6

6. Sternal shield with deep incision in posterior margin, at least to the level between setae st1 and st2........ Elaphrolaelaps (Incisosternum) Elsen, 1974 Sternal shield with no posterior incision................................................................. Elaphrolaelaps (Elaphrolaelaps) Berlese, 1910

7. Anal and genitoventral shields fused to form a genitoventrianal shield bearing three to five pairs of pre-anal setae and three circumanal setae............. 8 Anal shield free, subtriangular, bearing only three circumanal setae........ 9

8. Setae J5 minute (shorter than 10 µm), subconical; sperm access system with tubular components opened onto coxae IV...................................................................... Olopachys (Olopachys) Berlese, 1910 Setae J 5 not reduced in length, needle-like; sperm access system with saccular components opened onto coxae IV.......................................................................... Olopachys (Olopachylaella) Mašán, 2007

9. Tarsus II with one distal seta (pl1) modified, thick and spur-like.......... 10 Tarsus II with two distal setae (pl1, pl2) modified, thick and spur-like..... 13

10. Idiosoma subglobular; dorsal shield strongly vaulted, expanded ventrally and covering margins of ventral surface; setae J5 inserted with some other marginal dorsal shield setae on ventral expansion of the shield; unsclerotized idiosomal integument with seven pairs of setae........................................................................ Pachyglobolaelaps Mašán, 2007 Idiosoma dorsoventrally flattened; dorsal shield flat or slightly convex, covering only dorsal surface; setae J5 inserted dorsally; unsclerotized integument with more than seven pairs of setae (usually 10–15 pairs)................. 11

11. Setae J5 minute (shorter than 10 µm), subconical; tubular components of sperm access system concealed in coxae III (in P. sculptus group, extra-coxal section very short and with opening slightly protruding above inner surface of the coxa)........................................ Pachydellus Mašán, 2007 Setae J 5 not reduced in length, needle-like; tubular components of sperm access system otherwise formed, with long and fine tubes simply opened onto coxae III............................................................... 12

12. Long-legged forms, legs I and IV markedly longer than dorsal shield; genu IV with eight setae (2-4 / 1-1) and tibia IV with nine setae (2-3 / 2-2)........................................................ Pachylaelapsoides Mašán, 2007 Short-legged forms, legs I and IV shorter than dorsal shield; genu IV (1-4 / 1-1) and tibia IV (1-3 / 2-1) with seven setae............ Onchodellus Berlese, 1904

13. Dorsal shield with 29 pairs of setae (S1 absent); chaetotaxy of some leg segments deficient: femur I with 12 setae (2-5 / 3-2), genu I and tibia I with 11 setae (2-5 / 2-2), genu III with six setae (1-4 / 0-1); R setae on unsclerotized integument absent........................... Neopachylaelaps Mašán, 2007 Dorsal shield with 30 pairs of setae (S1 present); leg chaetotaxy normal: femur I (2-5 / 4-2) and genu I (2-6 / 3-2) with 13 setae, tibia I with 12 setae (2-5 / 3-2), genu III with seven setae (1-4 / 1-1); at least one R seta on unsclerotized integument present..................................................... 14

14. Setae J5 not reduced in length, needle-like; posterolateral margins of dorsal shield with one pair of slit-like hypertrophied gland pores (gdS4)........................................ Pachylaelaps (Longipachylaelaps) Mašán, 2007 Setae J 5 minute (shorter than 10 µm), subconical; posterolateral margins of dorsal shield with two pairs of slit-like hypertrophied gland pores (gdZ1, gdS4)............................ Pachylaelaps (Pachylaelaps) Berlese, 1888

Figures

Figure 1. Chaetodellus spp., females. (A–F). Chaetodellus comatus sp. nov. (A) Dorsal shield; (B) ventral idiosoma; (C) sternal shield, anterior portion; (D) epistome; (E) tarsus II, distal section; (F) tubes of sperm access system opened onto coxae III. (G) Chaetodellus meganalis, dorsal shield. Scale bars: 100 µm (A, B, F, G), 50 µm (C, D) and 25 µm (E).