Crotonia ovata Olszanowski, 2000

Colloff, Matthew J., 2009, New species of Crotonia (Acari: Oribatida) from Tasmania Rainforest, and the habitat preferences of Crotoniidae, Zootaxa 2027, pp. 43-54 : 49-52

Crotonia ovata Olszanowski, 2000 .

( Figs. 3 , 4 )

Crotonia ovata Olszanowski, 2000 : p. 240.

Holonothrus ryszardi Łochyńska, 2008 b: p. 123.

Male.

Dimensions: mean body length of males (n = 6) 1060 (range 1011–1148); mean breadth 436 (range 396–488); mean length of females (n = 6); 1267 (range 1203–1356); mean breadth 488 (range 450–602); mean ratio of length of prodorsum to total length (both sexes): 0.32. The following supplementary description is based on the male, with details of artefactual change to the caudal region ( Fig. 4 b) based on a female specimen.

Prodorsum: as illustrated by Olszanowski (2000) except the trans-bothridial ridge may be less rounded ( Fig. 3 a); rostrum with well-developed naso, the microsculpture of the region posterior to the bothridia consists of sparse scattered tubercles, and interlamellar setae extend beyond apices of rostral setae. Bases of lamellar setal apophyses conspicuously expanded laterally.

Notogaster: ratio of length to breadth 1.16. Anterior notogaster not simple as illustrated by Olszanowski (2000), but with pre-notogastral shield, separated from notogastral shield by transverse hyaline strip on which tubercles of setae c 1 are positioned, visible on well-cleared specimens ( Fig. 3 a). Microsculpture of caudal region and that of the lateral strips consists of tubercles not alveloli. Median of the strips is a narrow zone of smooth cuticle. The centrodorsal region is microporose. The suprapleural suture is not fully visible in dorsal view, being positioned ventral of the lateral margin of the notogastral shield in lateral view ( Fig. 4 a). Below the suprapleural suture, the microsculpture of the cuticle consists of scattered tubercles, and the caudal margin of the notogaster descends almost vertically.

Some specimens have undergone shrinkage caused by post-mortem muscle contraction. In these, there is an artefactual change in the morphology of the caudal notogastral region ( Fig. 4 b). The caudal notogastral region becomes narrowed and concave, the margins curled dorsally and there is a consequent relocation of the apophyses of setae h 1 and h 2 to positions whereby they point dorsally rather than posteriorly or posteriolaterally.

Ven t er: epimeral microsculpture punctate, but with tuberculate margins. Sparsely tuberculate microsculpture in perigenital region and on adanal plates ( Fig. 3 b). Epimeral setal formula 3-1-3-3, seta 3c on well-developed tubercle (these setae covered in debris and not visible on the holotype specimen). Material examined: holotype female, Hellyer River Gorge (in ANIC). Non-type material: six males, two females from Mt. Michael; four females from Mt. Victoria.

Remarks. The above description, of the male of C. ovata , is intended to supplement Olszanowski’s (2000) description of the female. There is no significant morphological difference between the sexes apart from size.

Łochyńska (2008b) described Holonothrus ryszardi and placed the species in Holonothrus even though the notogastral setation was tri-deficient, i.e. missing setae c 2, d 1 and e 1. Holonothrus virungensis Norton & Olszanowski, 1989 , H. ecuadorensis Kuty, 2006 and H. nortoni Olszanowski, 2000 lack d 1 and e 1, but no other members of the genus are known to be trideficient (i.e. also lack c 2). The placement of ryszardi in Holonothrus appears to be predicated on the presence of two pairs of anal setae, mentioned by Łochyńska (2008b) in the description and illustrated in her Fig. 9. However, the scanning electron micrograph of the ventral surface (her Fig. 25) clearly shows three pairs of anal setae, characteristic of Crotonia . The trideficient notogastral setation is also consistent with this species being a member of the genus Crotonia .

The immatures described by Łochyńska (2008b) and assigned to H. ryszardi have a few character states consistent with immatures of Crotonia , including the deutonymphal epimeral setal formula of 3-1-2-2, consistent with that for C. ovata Olszanowski, 2000 , rather than 4-1/2-2/3-3 for those Holonothrus spp. described to date. Also the lateral notogastral setae emerge from small tubercles or apophyses that develop at the posterior ends of punctate cuticular plaques, whereas in Holonothrus these setae emerge from alveoli typically positioned in the centre or anteriolateral portion of the plaques. The apparent presence of four setae in epimere I in the tritonymph is more typical of Holonothrus , but this may be erroneous. It is important to note that the immatures were from samples that contain as many as four species of Holonothrus and three of Crotonia (including those described herein). Under these circumstances, matching immatures to adults correctly is less than straightforward.

If one accepts the placement of H. ryszardi within Crotonia , then the next question is its differentiation from previously-described species. In fact, it shows striking similarity to C. ovata in the following character states: 1) the prodorsal ridges are the same length, curved and strongly divergent apically; 2) the transbothridial ridge is well-developed and distinctively bi-lobed; 3) the lengths and relative positions of notogastral setae of the c series, d 2, e 2 and f 2 are almost an exact match; 4) the apices of the lamellar apophyses do not extend beyond the rostrum. This is an unusual feature in Crotonia (even accounting for the artefactual effect of any tilt of the specimen) and is confined to some members of the Cophinaria species group ( C. cophinaria , C. lanceolata , C. perforata , C. brassicae and C. reticulata ). In Holonothrus it is unusual for the lamellar apophyses to extend as far as the rostrum. Typically, they extend no more than half the distance between their bases and the rostrum (exceptions being H. ecuadorensis Kuty, 2006 , H. glaesarius Łochyńska, 2008 , H. gracilis Olszanowski, 1997 and H. venetiolanus Olszanowski, 1999 ).

Holonothrus ryszardi Łochyńska, 2008 is hereby designated the junior subjective synonym of Crotonia ovata Olszanowski, 2000 .

Figures

FIGURE 3. Crotonia ovata Olszanowski, 2000, male a) dorsal; b) ventral.

FIGURE 4. Crotonia ovata Olszanowski, 2000, a) male, lateral view; b) caudal region of a female specimen from Mt. Victoria showing artefactual alteration in morphology (cf. text for details).