Scapheremaeus baylyi, Colloff, Matthew J., 2010

Colloff, Matthew J., 2010, The hyperdiverse oribatid mite genus Scapheremaeus (Acari: Oribatida: Cymbaeremaeidae) in Australia, with descriptions of new species and consideration of biogeographical affinities, Zootaxa 2475, pp. 1-38 : 8-11

Scapheremaeus baylyi sp. nov.

( Figs. 3 , 4 )

Scapheremaeus sp.: Bayly, 1997, p. 169.

Dimensions. Holotype female: length 551, breadth 367; paratype female: length 580, breadths 343; paratype males: length 530, 535, breadth 313, 338. Ratio of length of prodorsum to total length (holotype): 0.22.

Prodorsum. Tuberculate laterally, with rugose pattern of poorly-defined inter-costular ridges with granular microsculpture ( Fig. 3 a). Rostrum pointed, rostral seta (ro) smooth, curved, ca. 30 long, positioned at apex of short rostral ridge. Lateral carinae absent. Lamellar seta bacilliform, 12, on small tubercle. Apical trans-costular ridge present. Costulae well developed, more-or-less parallel, bowed laterally, extending posteriorly as far as dorsosejugal furrow. Interlamellar seta absent. Sensillus club-shaped, darkly-pigmented; head ca. 17 broad, with tuberculate microsculpture, emerging on short stalk from small bothridium (diameter 20).

Notogaster. Length 412. Circumdorsal scissure entire, oval ( Fig. 3 a). Lenticulus elongate (50 long, 26 broad), constricted medially. No humeral process visible in dorsal view. Centrodorsal plate 377 long, 180 broad, oval, broadest at level between setae la and lm, with microsculpture consisting of irregular wavy ridges with coarse, granulate microsculpture. Thirteen pairs of smooth, bacilliform notogastral setae (ca. 15–20) on short tubercles; five pairs on centrodorsal plate, five pairs on dorsal circumnotogastral plate (h 3 absent), three pairs in p series on ventral circumnotogastral plate. Dorsal circumnotogastral plate covered with regularlyspaced parallel plications becoming V-shaped, irregular ventrally ( Fig. 4 ). Opening of gla positioned anteriolateral of seta lp. With four pairs of lyrifissures visible dorsally; ia positioned on ventral circumnotogastral plate in humeral region, posterior of seta c 2.

Ventral region. Epimeral setae setiform, subequal in length, formula 3-1-2-2 ( Fig. 3 b). Microsculpture of ventral plate irregularly ridged. Sub-hexagonal genital plates as broad as long, with six pairs of longitudinallyaligned genital setae (ca. 8–12) positioned close to, but not on, medial edges. Genital and anal plates striate. Anal setae spiniform, 12, positioned at least their length from median edge of anal plates. With three pairs of minute spiniform adanal setae. Ventral surface of circumnotogastral plate notched posteriomedially.

Lateral aspect. Mid-line of rostrum slightly slanted posterioventrally ( Fig. 3 c). Hysterosoma deep, 232; not dorsoventrally flattened. Exobothridial seta absent. Humeral process consisting of a short, obtusely-angled ridge. Centrodorsal ridge prominent, extending entire length of centrodorsal plate and 70 above lateral margin of circumdorsal scissure. Ventral circumnotogastral plate deep (58).

Legs. Heterotridactylous; covered in thin plaque-like cerotegument. Formula Leg II: 1-4-3(1)-3(1)-12(1); Leg IV: 1-2-1(1)-3(1)-10(1).

Material Examined. Holotype female, two paratype males and one paratype female, in 2–4 cm-deep temporary rock pools on granite outcrop, Cable Beach (35°07´S 117°54´E), Torndirrup National Park, Western Australia, coll. I.A.E. Bayly, 27.vii.1990.

Etymology. Scapheremaeus baylyi sp. nov. is named in honour of its collector, Dr Ian A.E. Bayly (School of Biological Sciences, Monash University), in recognition of his research contribution to the systematics and ecology of freshwater invertebrates.

Remarks. Scapheremaeus baylyi sp. nov. differs from other members of the genus by the following combination of characters: 1) the deep hysterosoma without the dorsoventral flattening typical of other Scapheremaeus spp. 2) parallel regular plicatures on dorsal circumnotogastral plate; 3) centrodorsal region with wavy, granulate ridges; 4) with 13 pairs of notogastral setae, having only two pairs of setae in the h series; 5) setae of p series on the ventral circumnotogastral plate.

Scapheremaeus baylyi sp. nov. has most of the characteristics of the Patella species-group ( Colloff, 2009), including short lamellar setae on short tubercles linked by a trans-costular ridge, the prodorsum without pronounced lateral carinae (though lateral ridges are present on S. rustenburgensis Engelbrecht, 1975 ), a complete circumdorsal scissure and a centrodorsal plate with ridged microsculpture. It differs in having only 13 pairs of notogastral setae, lacking diagonal humeral extensions of the circumdorsal scissure as found in S. demeteri Mahunka, 1983 , S. patella ( Berlese, 1886) and S. rustenburgensis (but not S. clavisetus Mahunka, 1978 ) and the setae of the p series are on the ventral circumnotogastral plate whereas the other members have them located on the dorsal circumnotogastral plate.

Scapheremaeus baylyi sp. nov. was found by Bayly (1997) in saline water in small, shallow temporary rock pools (‘gnammas’) on a coastal granite outcrop in southern Western Australia, where it co-occurred with a Trimalaconothrus sp. This habitat is similar to that of the aquatic ameronothrid Chudalupia meridionalis Wallwork, 1981 ( Bayly, 1982; 1998). Engelbrecht (1975) described Aquanothrus montanus from sandstone montane pools in South Africa. Norton et al. (1996) found an ameronothrid feeding on rotifers in temporary rock pools on the Colorado Plateau. These species appear to be cryptobiotic, surviving dry conditions by burrowing into sediment, and becoming active upon re-wetting. I consider Scapheremaeus baylyi sp. nov. is aquatic or semi-aquatic, though its capacity for cryptobiosis is not known. The expanded hysterosoma may be linked to its aquatic habitat. Many Scapheremaeus spp. that live in microhabitats subject to fluctuations in wetness and dryness and are markedly dorsoventrally flattened (see, for example, S. alisonae sp. nov. above; S. truncatus sp. nov. and S. zephyrus sp. nov., below). For arboreal species, dorsoventral flattening may be linked to conservation of body water by allowing them to remain entirely within the saturated 1–2 mm thick boundary layer adjacent to moist leaf surfaces ( Ferro & Southwick, 1984; cf. discussion below).

Figures

FIGURE 3. Scapheremaeus baylyi sp. nov. a) dorsal; b) ventral; c) lateral.

FIGURE 4. a) Scapheremaeus baylyi sp. nov., circumnotogastral plates, viewed ventrally (centrodorsal plate removed); b – e) tibiae I (right, antiaxial); b) Scapheremaeus allmani sp. nov., showing cerotegument; c) Scapheremaeus tuberculosus sp. nov.; d) Scapheremaeus alisonae sp. nov.; e) Scapheremaeus bulbosensillatus sp. nov.