Tomocerus ocreatus Denis, 1948

Yu, Daoyuan, Man, Le Cong & Deharveng, Louis, 2016, Tomoceridae (Collembola, Entomobryomorpha) from the southern Annamitic cordillera: redescription of Tomocerus ocreatus Denis, 1948 and description of a new species of Tomocerina Yosii, 1955, European Journal of Taxonomy 176, pp. 1-14 : 3-7

Tomocerus ocreatus Denis, 1948

Figs 1A , 2 , 3

Diagnosis

Typical Tomocerus species with pale body colour, moderately long antennae and full set of 6+6 eyes. Head without distinct PAO; Th. II with relatively reduced number of macrochaetae; tenent hair clavate, moderately developed; unguis with 5–6 teeth; tenaculum unscaled, with numerous chaetae; manubrium without dorsal scales and blunt prominent chaetae; dental spines compound with numerous moderate sized denticles; no small dental spine between two distal large spines; mucro with 9–10 intermediate teeth.

Neotype

VIETNAM: ♀, on slide. Collected in Hon Giao, Bi Doup massif, northeast of Dalat , Lam Dong Province, 108°42’53”E, 12°11’11’’N, alt. 1630 m, 12 Jun. 2008, by Louis Deharveng & Anne Bedos (sample code Vn08-150). Deposited in MNHN (specimen Vn08-150_To1).

Description

Body length 3.6 mm. Ground colour uniformly yellowish white. Ant. III+IV, antero-ventral part of head, coxae and tibiotarsi with dark pigment. Eye patches black. Scales brown ( Fig. 1A ).

Body densely clothed by scales and various types of chaetae. Scales of typical morphology of Tomocerinae , with continuous longitudinal ridges on surface ( Lubbock 1873). Ordinary chaetae of different sizes. Microchaetae smooth and pointed. Macrochaetae and mesochaetae from slightly to strongly ciliated, some slightly ciliated mesochaetae appearing to be smooth under optical microscope. Most macrochaetae straight, rod-like and subcylindrical, some macrochaetae on posterior abdominal segments long, curved and acuminate. Mesochaetae acuminate, shorter and thinner than macrochaetae. S-chaetae subcylindrical, more hyaline than ordinary chaetae, as small as microchaetae except long ones on Abd. IV. Dorso-inner chaetae on dens modified as strong pointed spines. Pseudopores as small circular structures similar to chaetae sockets, distributed at least on Th. II to Abd. IV, coxae, and manubrium.

PAO not seen. Eyes 6+6. Antennae nearly as long as body. Antenna length ratio as I:II:III+IV= 1.0:1.7:15.4. Ant. I and Ant. II dorsally scaled, Ant. III+IV unscaled. Prelabral and labral chaetae (labral

formula) 4/5, 5, 4, the distal 4 chaetae stronger. Distal edge of labrum with four curved spine-like papillae ( Fig. 2A ), and a well developed ventro-distal brush. Mandibular head asymmetrical, the left one with 4 teeth (including a basal rounded one) and the right one with 5, left molar plate distally with a tapered tooth ( Fig. 2B ). Basal teeth of maxillary lamella 5 slightly longer than apical ones, without beard-like appendage ( Fig. 2C ). Maxillary outer lobe with trifurcate palp, one basal chaeta and 4 sublobal hairs ( Fig. 2D ). Both dorsal and ventral sides of head scaled. Cephalic dorsal macrochaetotaxy: anterior area: 2, 2; interocular area: 2, 6, central uneven macrochaeta absent; postocular area: 2+2; posterior area: 2. Posterior margin of head with about 20+20 small chaetae ( Fig. 2E ). Mentum with 5 chaetae, submentum with numerous chaetae.

Pattern of body chaetotaxy as in Fig. 2F . Bothriotricha 2, 1/0, 0, 1, 2, 0, 0 on Th. II–Abd. VI, respectively, as typical in Tomocerinae . Macrochaetae densely arranged along anterior margin of Th. II (not shown in figure). Th. II with a row of macrochaetae behind anterior margin. Number of macrochaetae or large mesochaetae in the posterior row as 3, 3/3, 3, 4, 2, 4 (3 dorsal+1 lateral) from Th. II to Abd. V. On Th. II no macrochaeta near the pseudopore contrary to most other tomocerids; on Abd. III s-microchaeta and accompanying microchaeta posterior to lateral macrochaeta; Abd. IV with one lateral macrochaeta and numerous long s-chaetae; on Abd. V inner macrochaeta smaller than others in posterior row; Abd. VI with numerous chaetae of moderate size. Most mesochaetae laterally and posteriorly on terga. Pseudopores near the axis of terga, 1, 1/1, 1, 1, 1, 0, 0 from Th. II to Abd. VI.

Legs with numerous ordinary chaetae. Trochantero-femoral organ with 1, 1 slender chaetae. Front, middle and hind tibiotarsus dorsally with 1, 1, 3 long prominent chaetae, ventrally with 4–5, 5, 6 blunt spine-like chaetae ( Fig. 2G ). Each tibiotarsus with a distal whorl of 11 chaetae, ventral 6 as ordinary chaetae, dorsal 5 modified: tenent hair clavate, as long as inner edge of unguis; 2 accessory chaetae extremely minute; 2 guard chaetae thin and long, slightly shorter than tenent hair ( Fig. 3A, B ). Unguis slender, with baso-internal ridging visible in lateral view; lateral teeth pointed, of moderate size. Inner edge of unguis with 5–6 teeth, the basal tooth smaller, the other subequal in size. Unguiculus about half as long as unguis, its inner edge with 1 tooth. Pretarsal chaetae 1+1, much larger than tenent-hair accessory chaetae ( Fig. 3B ).

Ventral tube with scales on both anterior and posterior faces, lateral flap unscaled, anterior face with about 15 chaetae on each side, posterior face with about 55 chaetae, each lateral flap with 45–47 chaetae. Rami of tenaculum with 4+4 teeth, anterior face with 13 small chaetae and without scale ( Fig. 3C ). Furca ratio manubrium: dens: mucro=2.9–3.1:4.1–4.4:1.0. Manubrium ventrally scaled, without chaetae, laterally with large round scales and 11 chaetae, proximal 2 chaetae small and slender, distal 9 distinctly stronger and serrated; dorsal scales absent; each dorsal chaetal stripe with about 90 chaetae in different sizes, without blunt chaetae; pseudopores 11–12 on each side ( Fig. 3D ); external corner chaeta as large as small mesochaetae in chaetal stripe ( Fig. 3E ). Dens basally without inner modified scale or outer strong chaetae. Dental spines formula as 3/4, II, distal spine strongest, about 0.1 times as long as dens; all spines with numerous denticles of moderate size ( Fig. 3F ). Dens dorsally with ordinary chaetae and feather-like chaetae as typical in Tomocerinae , ventrally with only scales. Mucro elongated, bearing numerous smooth chaetae with elongated sockets; both basal teeth with proximal lamellae, the outer tooth with a toothlet; apical and subapical tooth subequal; structure of dorsal lamellae of Tomocerus type, two dorsal lamellae running from subapical tooth, outer lamella ending in inner basal tooth, inner lamella ending freely at base of mucro; outer lamella with 9–10 subequal intermediate teeth ( Fig. 3G ).

Remarks

Denis (1948) provided accurate description for Tomocerus ocreatus . For instance, he described clearly the dental spines as “covered with secondary spines, more similar to scales than denticles”, and the figure showed that those scale-like denticles were of moderate size and covered at least basal half of each spine, on which account we rejected some records of non-type Tomocerus ocreatus (see below). But naturally, some later revealed characters were not mentioned by him. For instance, chaetotaxy had not been used for taxonomy in Tomocerinae before Yosii (1956). The limit of original description is a main reason for the misidentification of Tomocerus ocreatus in some subsequent records, and finally turned the species into a complex including a number of closely related forms from Vietnam to eastern Russia. To overcome the deep confusion about this species, a redescription of type specimen is necessary. Because the holotype and unique type specimen of Tomocerus ocreatus was lost, we propose to set up a neotype for the species from specimens of the type locality.

Denis (1948) described Tomocerus ocreatus on one specimen, from “plateau du Lang Biang, 2400 m. alt., forêt tropicale”. It is not the Lang Bian peak itself that reaches 2400 m but the Chu Yang Sin massif north of the Lang Bian (= Dalat) plateau, the Lang Bian peak being only 2197 m in altitude. The Chu Yang Sin massif was and still is of very difficult access, and was certainly not the place where the collector, Dawydoff, operated. There are two main patches of subtropical forests around Dalat: a small one on the Lang Bian peak, and a much larger one 25 km northeast on the Bi Doup massif, which reaches 2287 m and is less easy to access. In any case, it is most likely on the slopes of one of these massifs that Tomocerus ocreatus was collected. On this account, we propose to designate a specimen that we obtained from litter sample in the Bi Doup mountain as the neotype.

The neotype is highly identical with the original description in almost all described characters, including the body colour, the length of antennae, the structure of claws and the morphology and arrangement of dental spines. The only difference is that in the neotype specimen the numbers of ungual teeth, dental spines and mucronal teeth are slightly larger than in the original one. It could happen in Tomoceridae that within the same species larger individuals have a few more teeth and dental spines than smaller ones, so the slight difference mentioned above can be treated as intraspecific considering the neotype specimen is slightly larger than the lost holotype (3.6 mm versus 3.3 mm).

Regarding previous non-type records of Tomocerus ocreatus, Stach (1964, 1965 ) redescribed two different forms of Tomocerus ocreatus from southeastern China and northern Vietnam, respectively, and also claimed that the Japanese record of “ Tomocerus minor ” by Uchida (1953) was actually Tomocerus ocreatus ; Yosii described a Japanese species Tomocerus kawamurai (Yosii, 1954) and then synonymized it with Tomocerus ocreatus ( Yosii 1956, 1967); Chiba (1968) recognized three forms in Japanese Tomocerus ocreatus ; Lee (1975) made descriptive notes on Korean specimens; Martynova (1977) recorded Tomocerus ocreatus in Sakhalin and made some descriptive notes on it. These redescriptions had subtle to considerable differences to each other, and were never identical to the original description. The Chinese “ ocreatus ” recorded in Hangzhou (“Hangchow”), Zhejiang Province by Stach (1964) has brownish body colour and distinctly short antenna about half the length of body; the northern Vietnamese record from Lao Cai Province by the same author ( Stach 1965) bears a small dental spine between two large distal spines, and the denticles on spines are finer than those in the original description, therefore it is more similar to Tomocerus folsomi Denis, 1929 from Yunnan Province, China; the Japanese “ ocreatus ” described by Yosii (1967) has dorsal scales and 2+2 blunt principal chaetae on manubrium which are absent in the true Tomocerus ocreatus ; other records ( Chiba 1968; Lee 1975; Martynova 1977) all have dental spines with one or two whorls of crownlike denticles near the base which is not the morphology of the true ocreatus form. But these remarkable differences were treated as intraspecific variations when other characters showed high similarity. Inferred from the present morphological review and the molecular study on Chinese ocreatus complex ( Zhang et al. 2014), the aforementioned non-type “ ocreatus ” may each represent an independent species in the complex, and so far the true Tomocerus ocreatus is known as only endemic to southern Annamitic range in Vietnam.

Figures

Fig. 1. Appearance of Tomocerus ocreatus Denis, 1948 and Tomocerina annamitica sp. nov. in alcohol. A. Tomocerus ocreatus (lateral view). B. Tomocerina annamitica sp. nov. (lateral view). Scale bar: 1 mm.

Fig. 2. Tomocerus ocreatus Denis, 1948. A. Labrum (dorsal view). B. Mandibular head (dorsal view). C. Lamella 5 of maxillary head (dorsal view). D. Maxillary outer lobe (ventral view). E. Cephalic dorsal chaetotaxy (circles = sockets of chaetae, same as below; 1 = anterior area; 2 = interocular area; 3 = postocular area; 4 = posterior area). F. Dorsal chaetotaxy of Th. II–Abd. VI (circle with a slash = pseudopore, same as below). G. Right tibiotarsi (lateral view). Scale bars: A, B, G = 100 μm; C = 10 μm; D = 50 μm; E, F = 500 μm.

Fig. 3. Tomocerus ocreatus Denis, 1948. A. Diagram of tibiotarsal distal chaetae (distal view; t = tenent hair; a = accessory chaeta; g = guard chaeta; p = pretarsal chaeta, same as below). B. Hind claw (lateral view). C. Tenaculum (anterior view). D. Left side of manubrium (dorsal view). E. Disto-external corner of manubrium (dorsal view). F. Basal and middle subsegments of dens with dental spines (dorsal view). G. Mucro (dorso-inner view). Scale bars: B, C, E, G = 50 μm; D, F = 100 μm.