Hypogastrura gracilis ( Folsom, 1899 )

Jiang, Jigang, Yin, Wenying, Chen, Jianxiu & Bernard, Ernest C., 2011, Redescription of Hypogastrura gracilis, synonymy of Ceratophysella quinidentis with C. duplicispinosa, and additional information on C. adexilis (Collembola: Hypogastruridae), Zootaxa 2822 (1), pp. 41-51 : 41-46

Hypogastrura gracilis ( Folsom, 1899)

Figs 1−3

Achorutes gracilis Folsom, 1899: 263

Type material. Female lectotype (on slide) and 4 paralectotypes (in alcohol), Japan , Yanaka, Tokyo, Japan , 14 November 1894, deposited in the Museum of Comparative Zoology , Harvard University, Cambridge, Massachusetts, USA .

Other material. 16 females and 6 males, China, Jiangsu Province , Lianyungang City, Huaguoshan Park, 6 November 2006, in soil under bricks and piles of decayed peanut plants, collected by Jian-xiu Chen et al.; collection number C9530, deposited in the Department of Biology , Nanjing University, China .

Redescription. Body length: up to 1.9 mm; color in ethanol violet to violet-black dorsally, pale to yellow ventrally and on tibiotarsi, furca and ventral tube. Tegumentary granulation fine and uniform, dorsum of Abd. V with 9–19 (usually 13–15) granules between setae p 1.

Body setae similar in length. Dorsal cephalic setae weakly differentiated ( Figs 1A, B ). Seta v 2 longer than v 1; setae p 1, p 3 and p 5 slightly blunt, and longer than p 2, p 4 and p 6 ( Fig. 1A ). Head ventrally with 6 proximal, 4 basomedial, 5 basolateral and 3 postlabial setae ( Fig. 2D ). Th. I with 3+3 setae. Th. II with 3 rows of setae; m 3 present (lectotype) or absent (Chinese specimens), m 2, m 5 or m 6 rarely absent, m 7 and p 4 sensilliform. Th. III with 3 rows of setae; m 2, m 5, p 3’ present, m 3 absent in lectotype; m3 present, m2, m5 absent in Chinese specimens; m 7 and p 4 sensilliform, ratio of sensillum p 4 to common seta p 5 2.1–3.0:1. Setae absent on thoracic sterna. Abd. I–III each with 3 rows of setae, but setae and their positions on Abd. I in lectotype partially obscured: 5+ 5 in anterior row, a 3 and a 5 absent; 3+ 3 in middle row, as m 3, m 4 and m 6 or m 7; 7+ 7 in posterior row, as p 1–7, p 5 sensilliform ( Fig. 1A ). Abd. IV with 3 rows of setae: 5+ 5 in anterior row; 3+ 3 in middle row, m 2 absent; 6+ 6 in posterior row, p 5 sensilliform, ratio of p 5 to common seta p 4 2.4–2.5: 1 in Chinese specimens, slightly less in lectotype ( Figs 1A, B ). Abd. V with 2 rows of setae, 5+ 5 in anterior row; 6+ 6 in posterior row, p 1:p 2 ratio 1.5:1; p 3 sensilliform ( Fig. 1 ).

Head without tubercles and spines. Labrum ( Figs 2A, B ) with granulation similar to that of body; 6 apical papillae, outer papillae rounded to conical, setal formula 4/5, 5, 4. Maxilla with lamella 1 longer and other lamellae shorter than maxillary teeth; short marginal filaments present on lamellae 2 and 3; dense and fine denticles present on lamella 1 and inner side of lamellae 4–6; lamella 5 with large process (conspicuous “shoulder”) ( Fig. 2C ). Maxillary outer lobe with 2 sublobal hairs ( Fig. 2F ). Labial palpus with 5 papillae (A–E), lateral process, guard setae a 1, b 1–4, d 2–4, e 1–6 present, d 1 and e 7 absent ( Fig. 2E ).

Antennae ( Figs 2G–I ) 0.60–0.80 and 0.12–0.15 times length of cephalic diagonal and body length, respectively. Ant. IV with simple or weakly lobed subapical bulb; subapical vesicle (os) and microsensillum (ms) present; 3 dorsoexternal and 1 dorsointernal sensilla, curved and somewhat blunt, ventrally with 2 shorter sensilla near apex. Antenna III organ with 2 short rods in separate foveae and 2 guard sensilla. Ventral microsensillum present on Ant. III. Ant. II with 13 setae. Ant. I with 7 setae, without seta p. Eyes 8+8; eye patch with 3 setae, Oc 2 longer than Oc 1 and Oc 3 ( Fig. 2J ).

Postantennal organ subequal to nearest eye in diameter, composed of 4 lobes; anterior 2 lobes larger than posterior lobes, accessory tubercle absent ( Fig. 2J ).

Unguis well developed, with 1 inner tooth at 2/3 distance of its inner edge from base and 2 small lateral teeth near the apex ( Fig. 3A ). Unguiculus with broad basal lamella, tip of apical filament reaching 2/3–4/5 distance of inner edge of unguis. Legs I–III respectively with 1, 2, 3 setae on subcoxa 1; 0, 3, 3 on subcoxa 2; 3, 8, 7 on coxa; 7, 7, 7 on trochanter; 12, 13, 12 on femur; and 19, 19, 18 on tibiotarsus including 2, 3, 3 clavate tenent hairs ( Figs 3A–D ): on tibiotarsus I, setae A1 and A2 clavate; on tibiotarsi II and III, A1, A2, and A7 clavate; seta m present.

Ventral tube with 4+4 setae ( Fig. 3E ). Tenaculum with 3 teeth on each ramus, no seta on corpus. Manubrium with about 10+10 posterior setae. Dens posteriorly with fine granules and 7 setae ( Figs 3F, G ), length ratio of outer basal seta to inner basal seta 1.6–2.5:1 (average 2:1). Mucro with narrow outer lamella, without inner lamella; length ratio of dens to mucro 3.0–3.5:1 (average 3:1). Two anal spines on Abd. VI slightly curved, conical, slightly shorter than basal papillae. Adult female and male genital plates with 21–27 and 30–45 setae, respectively ( Figs 3H, I ).

Remarks. Five cotypes of this species were borrowed from the Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, and one specimen was mounted for microscopic observation.

Folsom (1899) described Hypogastrura gracilis from Tokyo, but the description is incomplete by current standards. Although the species was redescribed by Yosii (1960), knowledge of its characters still was considered insufficient to place it in a key to Palaearctic Hypogastruridae ( Thibaud et al. 2004) . Korean specimens were described by Park & Park (2006), but without a detailed analysis of the chaetotaxy. Neither of these redescriptions was based on type specimens.

Examination of a type specimen of H. gracilis established that the unguis possesses distal lateral teeth, a character not reported by Folsom (1899). The examination also confirmed the characters reported by earlier authors, although some of the setae were obscured or not found due to intestinal contents and crystalline formations in the body, especially in the region of Abd. I–III. Nevertheless, it is clear that the Chinese specimens should be assigned to this species. Hypogastrura gracilis is a member of the H. viatica species group ( Yosii 1960) on the basis of multiple clubbed tenent hairs (usually 2,3,3–4) on the tibiotarsi. In the key of Thibaud et al. (2004) this species will trace to H. viatica (Tullberg) . However, the macrochaetae of Th. I–Abd. IV of H. gracilis are all short and of approximately equal length; whereas, many of the p-row setae of H. viatica are much longer than the a-row setae ( Jordana et al. 1997, Yosii 1960). Also, H. gracilis possesses 7 dental setae (6 on H. viatica ). Dental seta number separates H. gracilis from all other H. viatica -group species except H. barguzini Babenko in Babenko et al. (1994) and H. purpurescens (Lubbock) . Hypogastrura barguzini differs from H. gracilis in having m-row setae on Abd. V (lacking in H. gracilis ) and having body sensilla shorter than the common setae (longer in H. gracilis ). In H. purpurescens , the metatibiotarsus has 2 clavate tenent hairs (A1, B2), whereas H. gracilis has 3 (A1, A2, A7).

Characters of H. gracilis from China conform well with the lectotype in the possession of 6 anterior papillae on the labrum (more pronounced and rounded on lectotype, conical on Chinese specimens), dens with seven setae, and mucro with small outer lamella. However, several apparent chaetotaxic differences, based on the redescription of Yosii (1960), led us to conclude initially that the Chinese specimens were a separate species closely related to H. gracilis . These differences include the apparent lack of m-setae on Abd. I−III (present on Chinese specimens) and absence of seta m 4 on Th. II (present on Chinese specimens). In the lectotype and Chinese specimens, the m-setae are advanced so far anteriorly that they could be interpreted as a-setae. The basic chaetotaxic plan as illustrated by Yosii (1960, p. 259, “key figure”) indicated a complete m-row for Abd. I−II. In most species of Hypogastrura s. l. as illustrated by Yosii, the m-row in these segments is usually reduced or absent. Most recent authors have accepted the presence of a reduced m-row consisting of m 3 and m 4 ( Babenko et al. 1994, Jordana et al. 1997), but Christiansen & Bellinger (1998) illustrated Abd. III as having only a- and p-setal rows. For convention the Babenko-Jordana interpretation is accepted here, even though m 3 and m 4 are located in the precise positions they would be if they were setae a 3 and a 5 slightly displaced posteriorly.

Identification of Korean specimens as H. gracilis ( Park & Park 2006) is not entirely certain. The lectotype and Chinese specimens of H. gracilis have 1+1 distal lateral teeth on the unguis, setae a 3 and m 3 on Th. III, and sensilliform seta p 5 on Abd. IV. The Korean specimens were not described as having lateral ungual teeth; lacked setae a 3 and m 3 on Th. III; and possessed seta p 4 on Abd. IV as a sensillum. However, the other characters described for Korean H. gracilis fit the species well. The lateral ungual teeth may be minute and very difficult to detect initially unless the unguis is seen in dorsal or ventral view (see Fig. 2A ). Furthermore, hypogastrurid body setae can vary from specimen to specimen and even between left and right sides. Occasional extra or missing setae are frequent, which may account for the p 4 position of the Abd. IV sensillum and the variation in Th. III chaetotaxy in the Korean specimens, and for chaetotaxic differences with the specimens redescribed by Yosii (1960).

Figures

FIGURE 1. Hypogastrura gracilis: A, Dorsal chaetotaxy of specimen from Jiangsu province, China; B, Partial dorsal chaetotaxy of lectotype. S = sensilliform seta.

FIGURE 2. Hypogastrura gracilis: A, Labrum of lectotype; B, Labrum of Chinese specimen; C, Maxilla of Chinese specimen: a, inner view, b, ventral view; D, Ventral cephalic chaetotaxy, Chinese specimen; E, Labial palpus, Chinese specimen; F, outer maxillary lobe, Chinese specimen; G–H, Dorsal view of antenna and ventral view of Ant. IV, respectively, Chinese specimen; I, Dorsal view of antenna, lectotype; J, Postantennal organ and eye patch, Chinese specimen.

FIGURE 3. Hypogastrura gracilis: A, Distal part of tibiotarsi, lectotype: a, tibiotarsus I, b, tibiotarsus II, c, tibiotarsus III; B– D, Tibiotarsus I, tibiotarsus II, hind leg, respectively, Chinese specimen; E, Ventral tube; F, Dens and mucro, lectotype; G, Furca, Chinese specimen: a, dorsal view of left side, b, lateral view of mucro; H– I, Female and male genital plates, respectively, Chinese specimens.