Crotonia brachyrostrum ( Hammer, 1966 )

Colloff, Matthew J., 2015, The Crotonia fauna of New Zealand revisited (Acari: Oribatida): taxonomy, phylogeny, ecological distribution and biogeography, Zootaxa 3947 (1), pp. 1-29 : 12-14

Crotonia brachyrostrum ( Hammer, 1966)

( Figs. 5 , 7 d)

Acronothrus brachyrostrum Hammer, 1966 , p. 31, Fig. 39.

Crotonia brachyrostrum ( Hammer, 1966) :— Luxton 1982, p. 247.

Dimensions. Females: mean length (n = 15) 932 Μm (range 853–995 Μm); mean breadth 501 Μm (range 480–530 Μm). Males: mean length (n = 19) 834 Μm (range 793–874 Μm); mean breadth 424 Μm (range 389–464 Μm). Mean ratio of length of prodorsum to total length: 0.32.

Female. Prodorsum: rostrum well-developed, with very prominent naso, lateral edges incurved; rostral setae (ro) 31 Μm, spiniform, smooth ( Fig. 5 a). Lamellar setae (le) 252 Μm, recurved, smooth, flagelliform. Lamellar apophyses 88 Μm, just over half as long as their mutual distance; extending anteriorly beyond apices of rostral setae. Interlamellar apophyses three times as long as broad; interlamellar setae (in) slender, 263 Μm, flagelliform, smooth; extending anteriorly as far as arc of lamellar setae. Prodorsal ridges extending half the distance between interlamellar and lamellar apophyses. Diameter of bothridium 40 Μm. Anteriolateral ridge of bothridium elongated, curved, sub-conical, with three lobed ridges ( Fig. 7 d). Inter-bothridial ridge and median field of muscle sigilla well-developed. Prodorsum porose.

Notogaster: ratio of length to breadth 1.36; broadest at level of setae e 2 ( Fig. 5 a). Dorsosejugal suture discrete, simple. With 13 pairs of smooth notogastral setae. Pre-notogastral shield rectangular, bearing setiform setae c 1 75 Μm long, and separated from notogastral shield by transverse hyaline strip. Apophyses of setae c 3 prominent, 28 Μm long, at least twice as long as broad; setae c 3 flagelliform, 309 Μm long, extending as far as bases of lamellar apophyses. Dorsal notogaster flat, almost at right angles to lateral plates, lateral margins more-or-less parallel. Notogastral shield discrete, porose; bordered laterally by narrow strip of small tubercles extending posteriorly as far as caudal cluster. Lateral hyaline strip (suprapleural scissure) relatively broad, well developed, bearing tubercles of setae cp, e 2 and f 1. Tubercles of setae f 2 long (31 Μm) prominent, projecting beyond lateral margin. Seta f 2 103 Μm long; cp 52 Μm; e 2 72 Μm. Seta d 2 short (26 Μm), setiform, their bases 175 Μm apart. Opisthonotal gland gla slightly anterior of f 2. Caudal apophyseal cluster bilateral, separate: 78 Μm apart; caudal margin between them transverse. Caudal region rounded, U-shaped. Setae f 1 93 Μm long, their apophyses projecting posteriolaterally, slightly separated from, and parallel with, those of h 1. Apophysis of seta h 2 72 Μm long, twice length of that of h 1, slightly incurved; seta h 2 100 Μm long; apophyses of setae h 3 ventral to, and parallel of, those of h 1.

Venter: epimeres porose ( Fig. 5 b); epimeral setae smooth, spiniform, sub-equal 26–37 Μm long; formula 3-1-3- 3. Genital plates sub-circular; posterior margin straight posteriolateral margin straight, angled obtusely to posterior margin; each plate 170 Μm long, 108 Μm broad with eight setiform setae; two pairs of aggenital setae, subequal in length to genital setae. Anal plate 52 Μm broad, 222 Μm long with three spiniform setae on posterior half of anal plate; three pairs of adanal setae ad 2-3 setiform, ad 1 spiniform, longer and thicker than others. Ventral margin of notogaster surrounding anal plates V-shaped. Setae of p series smooth, curved, setiform, p 3 31 Μm, p 2 41 Μm, p 1 36 Μm, on short tubercles; setae p 1 separated by distance twice the width of their tubercles.

Material Examined and Locality Data. Fifteen females, 19 males, under Nothofagus truncatus, Canaan Track, Caanan Downs Scenic Reserve, Abel Tasman National Park, Nelson, 40°52'S 172°54'E, 530 m., coll. M. Luxton, 15.v.1965.

Remarks. Crotonia brachyrostrum can be differentiated from other members of the genus based on the following combination of characters: 1) the smooth prodorsal and notogastral setae; 2) the elongated, curved, subconical anteriolateral ridge of the bothridium; 3) the relatively short apophyses of setae h 2, no longer than twice the length of those of h 1; 4) apophyses of setae f 1 are separated from those of h 1; 5) the U-shaped caudal region, broadening posteriorly, broadest at the level of setae e 2; 6) the prominent apophysis of seta f 2, as long as those of f 1 and almost as long as those of h 1; 7) setae c 1 and e 2 are sub-equal in length and longer than cp.

Crotonia brachyrostrum is morphologically most similar to C. norfolkensis Colloff, 2010 from Norfolk Island. Both C. norfolkensis and C. brachyrostrum have well-developed setae c 3; the apophyses of setae h 2 are relatively short, parallel or converging apically; apophyses of f 1 are separate and those of h 3 shorter than the others and not visible dorsally; the relatively short setae p 1; and setae e 2 are shorter than f 2. Crotonia brachyrostrum differs from C. norfolkensis in that the caudal region is rounded and U-shaped, rather than acute and sub-rectangular and the region between apophyses of setae h 2 is U-shaped rather than transverse; setae d 2 are longer and the anteriolateral ridge of the bothridium is elongated and sub-conical, rather than a blunt D-shaped lobe, and the epimeral setal formula is 3- 1-3-3 rather than 3-1-4-3.

Hammer (1966) differentiated C. brachyrostrum from C. cophinaria based on a shorter, broader rostrum in ventral view; a strongly-developed interbothridial ridge; a partial dorsosejugal suture; a much shorter seta c 3; the medial caudal margin is U-shaped rather than square and the apophyses of setae h 2 are straight and slightly converging rather than curved and diverging. The material of C. brachyrostrum examined here is consistent with Hammer’s description regarding the interbothridial ridge (it is weakly-developed or absent in C. cophinaria ) and caudal apophyses, but setae c 3 are longer, the dorsosejugal margin is complete and the shape of the caudal margin is variable. However, there are a number of additional characters that differentiate the two species. In C. brachyrostrum the caudal setae are smooth and seta f 1 is reflexed, as long as seta h 1 and h 3, and on thin, curved, tubular apophyses at least twice as long as broad. The apophysis of seta h 2 is only twice the length of that of h 1. In C. cophinaria , the caudal setae are barbed; seta f 1 is straight and half the length of seta h 1 and h 3 and a similar length and shape to seta h 2. The apophysis of seta h 2 is at least 5 × the length of that of h 1. In addition, the shape of the bothridial anteriolateral ridge is completely different between the two species ( Fig. 7 d, e) and females of C. cophinaria are much larger: 1100–1300 Μm long, 630–700 Μm broad, compared with female C. brachyrostrum : 790–875 Μm long, 390–465 Μm broad.

Luxton (1982) made C. brachyrostrum a junior synonym of C. cophinaria ( Michael, 1908) on the basis that “The differences from C. cophinaria noted by Hammer (1966) for C. brachyrostrum are readily encompassed by the obvious variability seen between individuals and do not appear to warrant separate specific status.” Luxton’s (1982) decision was not accepted by Colloff (2009a) because it was not based on an examination of type material and the morphological differences between the two are more than can be explained by intra-species variation. This view is confirmed by the additional characters listed above that can be used consistently to differentiate the two species.

Figures

FIGURE 5. Crotonia brachyrostrum (Hammer, 1966), female; a) dorsal; b) ventral. Scale bar = 200 µm.

FIGURE 7. Details of bothridia of a) Crotonia ramsayi sp. nov.; b) Crotonia unguifera (Michael, 1908); c) Crotonia caudalis (Hammer, 1966); d) Crotonia brachyrostrum (Hammer, 1966); e) Crotonia cophinaria (Michael, 1908). Scale bars = 20 µm.