Hypogastrura gravesi Wray, 1971

Bernard, Ernest C., 2015, Redescriptions of Hypogastruridae and Onychiuridae (Collembola) described by David L. Wray, Zootaxa 3918 (3), pp. 301-338 : 310-313

Hypogastrura gravesi Wray, 1971

Figs. 1 B, 6, 7

Hypogastrura gravesi Wray 1971: 147 .

Hypogastrura (Ceratophysella) gravesi Christiansen & Bellinger 1980: 142 ; 1998: 139.

Specimens examined. Lectotype juvenile male and 25 paratype juveniles (by present designation), USA, North Carolina, Macon County, February 1970, R. C. Graves, coll.; 1 female, USA, North Carolina, Swain County, Great Smoky Mountains National Park, Ravensford, wetland pitfall #24, N667946.010 E721059.060, 1 –8 August 2001, E. Bernard & P. Jennings, colls.; 1 female, USA, North Carolina, Jackson County, Waterrock Knob, pitfall #4 along creek, rhododendron, 646552N 66458E, 6–20 June 2002, J. Robertson, coll.; 1 female, USA, North Carolina, Swain County, Great Smoky Mountains National Park, Ravensford, upland forest north of stream, 14 July 2004, E. Bernard, A. Mayor, J. Moulton, T. Conatser, colls.

All of the 26 slide-mounted “ type series” specimens are juveniles. One of these specimens, which appears to be a juvenile male, is labeled “ type ” and so is considered the lectotype, with the other 25 being paralectotypes. Three recently collected females fit the general description of H. gravesi and were used to more precisely describe the species.

Redescription. Body length of juveniles 0.81–1.18 mm, females 1.23, 1.57 mm [up to 1.0 mm]. In ethanol dorsum with violet pigmentation distributed in mosaic pattern ( Fig. 1 B) [dirty white background with purplish pigment distributed in specks and blots over whole body]. Anal spines amber. Granulation very fine, granule width 1.1–1.5 Μm; Yosii’s ‘a’ number 10‒16. Most body setae long, pointed, minutely serrate ( Figs. 6 A, B, H‒J), not spiniform, longest on Abd. III–VI. All head setae present except for variable absence of one or more sd-setae. Sensilliform setae (s-setae) p4 and m6 on Th. II–III and p5 on Abd. I about half the length of p3; s-setae on Abd.

II–V similar in length to neighboring p-setae in adult ( Fig. 6 B), slightly shorter in late-stage juvenile ( Fig. 6 A). Microsensilla on thoracic terga not seen. Anterior setae of thoracic terga similar in length; seta m2 on Th. II present or absent. Insertions of setae p1 and p2 on Th. II–III on same level. Abdominal tergites I‒III lacking seta a3; m3 and m4 present. Seta p2 slightly shorter than or same length as p1 on Abd. IV and V. Seta p4 on Abd. IV anterior to s-seta m 6 in female ( Fig. 6 B), in line with other p-setae in juvenile ( Fig. 6 A). Plurichaetosis weak, with occasional doubling of setae.

Antennal segment IV with single-lobed apical vesicle, apex of segment with several rounded, minutely granulated lobes surrounding vesicle aperture ( Fig. 7 F); microsensillum minute, subapical organite capitate ( Fig. 7 D); four or five curved sensilla present; most dorsal setae slender, thin-walled, sensillum-like, with rounded tips; most ventral setae pointed, not sensillum-like ( Figs. 7 C, D). Ventral side of Ant. IV with sensory field of 40–50 fine short, slender setae bifurcated at their tips, and with two hooked sensilliform setae, one subapical and the other at the anterior edge of the sensory field setae. Sense organ of Ant. III with two small, weakly lobed inner sensilla in shallow pits flanked by two long sensilla that may be doubled ( Figs. 7 D, E); Microsensillum peg-like. Eversible sac not seen. Antennal segment I with 7 setae, Ant. II with 12–13 setae.

Ocelli 8+8, all ocelli of approximately equal size. Postantennal organ ( Figs. 7 A, B) slightly wider than nearest ocelli, with 4 lobes, anterior lobes longer than posterior lobes; accessory tubercle present but small, not surrounded by posterior lobes. Labrum rounded-trapezoid, upper surface coarsely tuberculate, anterior edge weakly four-lobed ( Fig. 6 C), with 5, 5, 4 setae and 4 prelabral setae. Head of maxilla with lamellae 1 and 2 slightly exceeding capitulum teeth, lamella 4 elongated and reaching tips of teeth. Outer lobe of maxilla with terminal hair, basal seta and two sublobal hairs ( Fig. 6 E). Labial palpus with six proximal setae and all guard setae except d1 ( Figs. 6 F, G), lateral papilla present. Guard setae b3, b4, d3 and d4 foliate, e1 and e3–6 tapering, lengths equal to or longer than sensilla A–E; a1, b1, b2, d2 and e2 pointed.

Tibiotarsi I–III with 19, 19, 18 setae, respectively, proximal whorl on tibiotarsus III with 7 setae ( Figs. 7 G–I). Clavate tenent hairs absent. Unguis with three small dorso-basal teeth; more apical dorsal tooth of varying position usually present; lateral teeth minute; inner tooth usually strong ( Figs. 7 G–J). Unguiculus with rounded lamella and apical filament reaching inner tooth of unguis.

Ventral tube with 4+4 setae. Tenaculum with 4+4 teeth, without setae. Length of dens 2–2.5 times length of mucro; dens strongly tuberculate dorsally with the largest tubercles distally, with seven smooth setae ( Figs. 7 K, L). Mucro laterally arched, tuberculate basally, outer lamella rounded. Anal spines blunt, rounded or truncated apically ( Figs. 6 H, I), half to three-fourths length of inner hind unguis.

Remarks. Hypogastrura gravesi is a member of the H. trybomi group. Christiansen & Bellinger (1998) considered the blunt anal spines of H. gravesi to probably be an ecomorphic condition, and reported that they had seen such spines only on immature specimens, a condition fitting all of Wray’s specimens. However, the collection of adults that also possessed blunt anal spines strengthens the argument that H. gravesi is a valid species. As redescribed here H. gravesi best fits the trybomi -group ( Christiansen & Bellinger 1980, 1998; Thibaud et al. 2004) in having pointed tenent hairs, fine body granulation, and a narrow mucro with rounded lamella. Further collections from the southern Appalachians, successful culture, and molecular comparison with other local Hypogastrura spp. would definitively determine the validity of this blunt-spined taxon.

The obliquely truncated anal spines sometimes seen in H. gravesi ( Fig. 2 I) are similar to the anal spines of the European C. luteospina Stach, 1920 ( Babenko 1994; Stach 1920, 1949; Thibaud et al. 2004), but that species otherwise possesses typical Ceratophysella characters.

Figures

FIGURE 2. Ceratophysella hermosa. A) Dorsal chaetotaxy, specimen from Goshen Prong, Sevier County, Tennessee. B) Dorsal chaetotaxy of head, mesonotum and Abd. IV ‒ VI, another Goshen Prong specimen. C) Dorsal chaetotaxy of head, mesonotum and Abd. IV ‒ VI, lectotype; mesonotum reconstructed from fragments. D) Lateral sensillum-like seta and microsensillum of mesonotum, Goshen Prong specimen. E) Lateral sensillum-like seta of metanotum, Goshen Prong specimen.

FIGURE 6. Hypogastrura gravesi. A) Paratype (juvenile), dorsal chaetotaxy. B) Adult specimen from Ravensford, Swain County, North Carolina, dorsal chaetotaxy. C) Labrum, holotype. D) Maxilla, Ravensford specimen. E) Maxillary palpus, Ravensford specimen. F) Labial palpus, Ravensford specimen. G) Labial palpus, holotype. H) Anal spines, holotype. I) Anal spines, paratype. J) Macrochaetae of posterior abdominal segments.

FIGURE 7. Hypogastrura gravesi. A) Left and right postantennal organs (PAO) and anterior eyes of specimen from Ravensford, Swain County, North Carolina. B) Left-side PAO and anterior eyes of holotype. C) Ventral view of fourth antennal segment, Ravensford specimen. D) Dorsal view of third and fourth antennal segments, Ravensford specimen. E) Partial third and fourth antennal segments, holotype; in Figs. C ‒ E typical pointed setae black, sensilliform setae with rounded tips outlined, sensilla stippled. F) Terminal protuberances of fourth antennal segment, specimen from Waterrock Knob, Swain County, North Carolina. G ‒ I, Ravensford specimen. G) Fore tibiotarsus. H) Middle tibiotarsus and apex of femur. I) Hind tibiotarsus. J) Foot complex, holotype. K, L) Dentes and mucrones. K) Ravensford specimen. L) Holotype.

FIGURE 1. A) Ceratophysella hermosa, dorsal habitus of ethanol-preserved specimen from Jackson, County, North Carolina. B) Hypogastrura gravesi, dorsal habitus of ethanol-preserved specimen from Sevier County, Tennessee. C) C. hermosa, upright dorsal cephalic spines (d 5, sd 5). D) H. ireneae, labrum in lateral view. A: antenna; M: mandible. Arrow indicates labrum base. Scale bars: A, B = 500 µm; C = 100 µm; D = 20 µm.