ZooKeys 408: 61–70, doi: 10.3897/zookeys.408.7030
A peculiar cave species of Tomocerus (Collembola, Tomoceridae, Tomocerinae) from Vietnam, with a discussion of the postantennal organ and prelabral chaetae in Tomocerinae
Daoyuan Yu 1,†, Feng Zhang 2,‡, Louis Deharveng 3,§
1 School of Life Sciences, Nanjing University, Nanjing 210093, China
2 Department of Entomology, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China
3 Muséum National d’Histoire Naturelle, UMR7205 CNRS/MNHN, CP50, 45 rue Buffon, 75005 Paris, France

Corresponding author: Louis Deharveng (deharven@mnhn.fr)

Academic editor: L. Penev

received 13 January 2014 | accepted 20 April 2014 | Published 12 May 2014
(C) 2014 Daoyuan Yu. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
For reference, use of the paginated PDF or printed version of this article is recommended.

Citation: Yu D, Zhang F, Deharveng L (2014) A peculiar cave species of Tomocerus (Collembola, Tomoceridae, Tomocerinae) from Vietnam, with a discussion of the postantennal organ and prelabral chaetae in Tomocerinae. ZooKeys 408: 61–70. doi: 10.3897/zookeys.408.7030


The first Tomocerus species with a postantennal organ (PAO) in the adult stage is described from Vietnam. Tomocerus postantennalis sp. n. differs from the other PAO-possessing tomocerid, Tomolonus reductus Mills, 1948, mainly in the morphology of PAO, the number of ocelli, the number of chaetae in trochantero-femoral organ and several features of the furca. The new species is placed in Tomocerus because of the presence of a toothlet on the outer basal mucronal tooth and the absence of the diagnostic character states of Plutomurus Yosii, 1956 and Aphaenomurus Yosii, 1956. Besides the presence of PAO, the new species is peculiar in having six prelabral chaetae, instead of four as in other Tomocerus species. The new species is similar to Tomocerus folsomi Denis, 1929 and Tomocerus ocreatus Denis, 1948 in the type of dental spines but different from them in the body colour, the relative length of antennae to body, the number of unguis inner teeth and the number of mucronal intermediate teeth.


New species, Southeast Asia, taxonomy, Tomocerus folsomi, Tomocerus ocreatus, Tomolonus


In Collembola, PAO is a paired organ located dorsally on the head, behind the antennae. It is probably a sensory organ of smell, humidity or temperature (Altner and Thies 1976). In some group, e.g. Onychiuridae and Neanuridae, PAO is morphologically diversified and highly important for taxonomy (Hopkins 1997). In contrast, most Entomobryomorpha have this organ poorly developed (e.g. Isotomidae) or absent (e.g. most Entomobryidae, Tomoceridae, Paronellidae and Cyphoderidae).

PAO in Tomocerinae was firstly recorded by Mills (1948) in a new genus and species, Tomolonus reductus Mills, 1948. Goto (1956) showed that PAO is present in the first instar of Pogonognathellus longicornis (Müller 1776) but disappears in subsequent instars. Christiansen (1964) claimed this organ did not always appear in all specimens of Tomolonus reductus and accordingly rejected the generic state of Tomolonus, but later studies (Yosii 1967, Rusek 1977) supported Mills’ original position.

Until now, the only known species of Tomocerinae with PAO in the mature stage was Tomolonus reductus, from North America. The purpose of this paper is to describe a second species of this subfamily with well developed PAO, based on material from Vietnam.

Materials and methods

All type specimens were collected in caves with aspirators. After being photographed with a Jenoptik ProgRes C10+ camera mounted on a Leica MZ 16 stereomicroscope, specimens were cleared in lactic acid and mounted in Marc André II solution. The head, furca and legs were cut off from the trunk and mounted separately for detailed observation. The slide-mounted specimens were studied using a Leica DMLB microscope.

The pattern of dorsal cephalic chaetotaxy used here is modified from that Wang et al. (2013): the two posterior macrochaetae placed in the postocular area by these authors (Figure 2F in Wang et al. 2013) are here considered to belong instead to the posterior area. We follow Fjellberg (2007) for maxilla lamellae numbering and Christiansen (1964) for macrochaetotaxy. The dental spine formula follows that of Folsom (1913), in which the dental spines are arranged from basal to distal, with a slash indicating the separation between basal and medial subsegments and the Roman numerals referring to spines that are noticeably larger.


Ant.: antennal segment; PAO: postantennal organ; Th.: thoracic segment; Abd.: abdominal segment. Institutional acronyms: NJAU, Nanjing Agricultural University, Nanjing, China; MNHN, Muséum national d’Histoire naturelle, Paris, France.

Type locality.

Vietnam, Tuyen Quang Province: Na Hang, Khuoi Sung, Hang Khuoi Sung, in cave, 22.5013°N, 105.3649°E, 24 Dec. 2003, Louis Deharveng and Anne Bedos leg.

Type specimens.

Holotype female and three paratype females on slides, labelled with collectors’ sample number Vn0312-56. Deposited in MNHN (holotype and two paratypes) and NJAU (one paratype).


Body length 3.4–4.3 mm. Body with diffuse dark pigment all over; Ant. II, base of Ant. III and ventral side of Ant. I darker than other parts of antenna; eye patches black and small; clypeus, antero-dorsal region and posterior margin of head darker than other parts of head; anterior half of trunk darker than posterior half; head and trunk with bilaterally symmetrical white pattern formed by numerous unpigmented patches (Fig. 1).

Figure 1.

Tomocerus postantennalis sp. n. Appearance in alcohol. Scale bar: 1000 μm.

Antenna longer than body, Ant. IV lost, Ant. I:II:III ≈ 1.0:1.8:21.0, Ant. I and II dorsally scaled, Ant. III unscaled. Antennal chaetae poorly preserved and not studied. PAO oval, with thickened inner margin, its long axis as long as the diameter of anterior ocelli (Fig. 2). Ocelli 6+6, anterior two larger than others (Figs 2, 3). Prelabral chaetae 3+3; labral chaetotaxy 5, 5, 4, distal four chaetae stronger, anterior margin of labrum with four papillae (Fig. 4). Mandibular head asymmetrical, left mandible with four teeth, right mandible with five teeth, molar plate of left mandible distally with a cone-like tooth (Fig. 5). Basal teeth of maxillary lamella 5 prolonged, distinct beard absent (Fig. 6). Mentum (baso-lateral area of labium) with 5 smooth chaetae, other parts of labium not clearly seen. Cephalic dorsal chaetotaxy: anterior area 2, 2; interocular area 2, 0, macrochaetae absent along transverse medial line; postocular area 2+2; posterior area 1+1; posterior margin with about 30+30 short chaetae (Fig. 3). Head scaled both dorsally and ventrally.

Figures 2–11.

Tomocerus postantennalis sp. n. 2 PAO and ocelli 3 cephalic dorsal chaetotaxy 4 labrum 5 mandible 6 maxillary lamella five 7 trochanteral-femoral organ 8 tibiotarsus 9 anterior view of distal tibiotarsal chaetae (t: tenent hair, a: accessory chaetae, g: guard chaetae) 10 claw 11 tenaculum. Scale bars: 2, 7, 9, 10, 11 = 50 μm; 3 = 500 μm; 4, 5, 8 = 100 μm; 6= 20 μm.

Trochanteral-femoral organ with 1, 1 chaetae (Fig. 7); fore, middle and hind tibiotarsi ventrally with 6–7, 5, 5 spine-like chaetae (Fig. 8). Distal whorl of tibiotarsus with 11 chaetae, tenent hair thin and probably pointed (judging from its small socket), two small accessory chaetae beside tenent hair larger than pretarsal chaetae, sockets of two outer guard chaetae larger than tenent hair (Fig. 9). Unguis slender, with baso-internal ridging, two lateral teeth pointed, of moderate size; inner edge of unguis with one basal and one distal tooth, the distal tooth at about one third of the length of unguis from base. Unguiculus length 0.50–0.67 that of unguis, with one inner tooth larger than ungual teeth (Fig. 10). Scales present on all segments except pretarsus of all legs.

Ventral tube scaled both anteriorly and posteriorly, lateral flap unscaled. Each side of anterior face with ca. 50 chaetae, posterior face with ca. 90 chaetae, each lateral flap with ca. 60 chaetae; all chaetae smooth.

Tenaculum unscaled, with 4+4 teeth, anterior face with 5 small smooth chaetae (Fig. 11). Ratio manubrium:dens:mucro 3.3–4.0:4.8–5.4:1.0. Manubrium laterally with large scales and 11 chaetae, the proximal one chaeta small and smooth, the distal 10 chaetae enlarged and serrated; dorsal scales absent; each dorsal chaetal stripe with 250–300 smooth chaetae of different sizes, including 2+2 pointed prominent chaetae larger and straighter than other chaetae (arrowed in Fig. 12); 22–27 pseudopores on each side (Fig. 12); external corner chaetae as large as mesochaetae in the chaetal stripe (Fig. 13). Ventral side of manubrium covered only with scales. Dental spines formula 4–5/5–7, I, 1–2, I. Distal most spine strongest, about 0.1 times length of dens, sizes of the proximal spines increasing gradually from basal to distal. All spines compound, with numerous denticles of moderate size at basal half and smaller at distal half (Fig. 14). Dens internally divided into three subsegments, basally without outer strong chaetae or inner pointed scales, dorsally with ordinary smooth chaetae and a longitudinal central stripe of feathered chaetae (Fig. 15) from base of middle subsegment to apex of distal subsegment between ordinary chaetae, ventrally covered with small oval scales. Mucro elongate and multi-setaceous; both basal teeth with proximal lamellae, outer basal tooth with a toothlet (Fig. 16); apical and subapical teeth subequal; two dorsal lamellae beginning from subapical tooth, outer lamella ending in inner basal tooth, inner lamella ending freely beside inner basal tooth. Outer dorsal lamella with 5–7 subequal intermediate teeth (Fig. 17).

Figures 12–18.

Tomocerus postantennalis sp. n. 12 dorsal face of manubrium (right side; prominent chaetae arrowed) 13 disto-dorsal chaetae on manubrium (left side) 14 dental spines (left side) 15 feathered chaeta on dens 16 basal teeth of left mucro 17 right mucro 18 body chaetotaxy. Scale bars: 12, 14 = 100μm; 13, 17 = 50 μm; 15, 16 = 21 μm; 18 = 400 μm. Large circles: macrochaetae; small circles: mesochaetae; wavy lines: bothriotricha; circles with a slash: pseudopores.

Macrochaetae distributed densely along anterior margin of Th. II (not drawn) and sparingly in posterior rows on terga. Th. II-Abd. V with 2, 1/0, 0, 1, 2, 0 bothriotricha and 3, 3/3, 3, 4, 2, 4 (3 central+1 lateral) posterior macrochaetae on each side; dorsal flap of Abd. VI with 13 macrochaetae (6+6 and 1 on middle line). Medial area of Th. II with two macrochaetae, the posterior one close to pseudopore; Abd. IV antero-laterally with one macrochaeta and one mesochaeta (Fig. 18). Most mesochaetae present at lateral margin of terga, especially from Abd. II to Abd. IV. Microchaetae uniformly distributed.


Named with reference to the presence of the postantennal organ.


Tomocerus postantennalis sp. n. is distinct from any other Tomocerus spp. in the presence of PAO and six prelabral chaetae. Besides, it is characterized by the unequal size of the ocelli, the lower number of cephalic macrochaetae and the reduction in the number of ungual inner teeth. Its compound dental spines are very similar to those of the Vietnamese species Tomocerus ocreatus Denis, 1948 and of the Chinese species Tomocerus folsomi Denis, 1929, which probably indicates a close phylogenetic relationship. The discrimination of these species is shown in Table 1.

Table 1.

Discrimination of Tomocerus postantennalis sp. n., Tomocerus ocreatus and Tomocerus folsomi on the basis of the original descriptions and notes (Denis 1929, 1948).

Species Body colour Length of antennae Unguis teeth Shape of dental spines Dental spines formula Number of mucronal intermediate teeth
Tomocerus folsomi yellowish with dark pigment along lateral margin of anterior terga shorter than body 4–5 compound with very fine denticles 5–8/3–6, I, 1–2, I 6–7
Tomocerus ocreatus pale as long as body 5 compound with denticles of moderate size 3/3–4, II 8–9
Tomocerus postantennalis sp. n. dark grey longer than body 2 compound with denticles of moderate size 4–5/5–7, I, 1–2, I 5–7

Most tomocerids have four prelabral chaetae, which is also common number in other groups of Entomobryomorpha. The taxonomic significance of the prelabral chaetae in Tomocerinae was firstly discovered by Yosii (1966, 1967), who described several Plutomurus species with more than four such chaetae. As far as we know, tomocerids other than Tomocerus postantennalis sp. n. with six or eight prelabral chaetae belong to two genera: Plutomurus (Plutomurus grahami Christiansen, 1980, Plutomurus ehimensis Yosii, 1956, Plutomurus kawasawai Yosii, 1956, Plutomurus gul Yosii, 1966, Plutomurus iwatensis Yoshii, 1991, Plutomurus ortobalaganensis Jordana and Baquero, 2012, Plutomurus kelasuricus Martynova, 1969 and Plutomurus marmorarius Yosii, 1967) and Lethemurus Yosii, 1970 (Lethemurus finitimus Yosii, 1970). They all inhabit caves and most of them are eyeless, with the sole exception of Plutomurus kelasuricus, which has small ocelli. Although the function of prelabral chaetae is still unknown, the increased number of these chaetae appears to be a troglomorphic adaptation. The protruding prelabral chaetae probably provide a tactile sense in front of the mouthparts, and more prelabral chaetae may increase the sensitivity, which is important for living in darkness.

So far, only two species of Tomocerinae have the PAO developed in adults: Tomolonus reductus (Mills) and Tomocerus postantennalis sp. n. The former has the most reduced eyes of non-cave species (3+3) and lives in soil, while the latter has the maximum number of ocelli for the subfamily (6+6) and lives in a cave, where its eyes are useless because of darkness. PAO development in adult may therefore be assumed to compensate for deficient vision performance in both species. Under this assumption, we would expect PAO among other cave species of Tomocerinae, a presence difficult to detect given the inconspicuousness of the organ when present.

The PAO of Tomocerus postantennalis sp. n. is similar in shape to those of juvenile Pogonognathellus longicornis (Goto 1956) and some adult isotomids (Potapov 2001), but it differs from the compound PAO of Tomolonus, which is constituted of a small central vesicle and three larger tubercles (Mills 1948, Yosii 1967, Rusek 1977). Besides this structural difference, the PAO of Tomocerus postantennalis sp. n. is relatively larger than those of Tomolonus reductus and juvenile Pogonognathellus longicornis. The morphological differences in PAO between Tomocerus postantennalis sp. n. and Tomolonus reductus may reflect a functional difference or represent two evolutionary alternatives—enlargement of a simple organ or complication of a small organ, to enhance a similar function. In any case, the different PAOs in the two species are likely to be adaptive convergences rather than synapomorphies, since they are distantly related based on strong morphological differences.

Despite the presence of PAO, Tomolonus is more closely related to Plutomurus, since both have two posterior macrochaetae on the thoracic segments (Christiansen 1964, 1980, Jordana et al. 2012), a well developed trochanteral-femoral organ, strong outer basal chaetae on the dens and simple dental spines. The new species fits Tomocerus better than other genera because it has three posterior macrochaetae on the thoracic segments, poorly developed trochanteral-femoral organ, no strong dental chaetae and a toothlet on the outer basal tooth of the mucro.

The genus Tomocerus Nicolet, 1841 is so far poorly defined by a single character: the presence of a toothlet on the outer basal mucronal tooth, thus all species conforming to this criterion and lacking the diagnostic character of other genera have been assigned to this genus, resulting in a wider range of intrageneric diversity than in other genera. For instance, all types of dental spines from simple to strongly furcated can be found in Tomocerus, whereas in Pogonognathellus, Plutomurus and Monodontocerus the shape of dental spines are constant within genus. On the other hand, the single generic character is not exclusive for Tomocerus since Aphaenomurus interpositus denticulatus Yosii, 1956 and Plutomurus vigintiferispina Lee, 1974 also have a toothlet on the mucronal outer basal tooth. The situation of Tomocerus will remain problematic until a comprehensive and detail investigate is carried out.


We thank Dr Mark Judson (MNHN, Paris) for reviewing the English style. The China Scholarship Council provided a grant to the first author for studying at MNHN, Paris.

Altner H, Thies G (1976) The postantennal organ: a specialized unicellular sensory input to the protocerebrum in apterygoten insects (Collembola). Cell and Tissue Research 167: 97-110. doi: 10.1007/BF00220161
Christiansen K (1964) A revision of the Nearctic members of the genus Tomocerus (Collembola: Entomobryidae). Revue d’Ecologie et de Biologie du Sol 1: 668-675.
Christiansen K (1980) A new Nearctic species of the genus Tomocerus (Collembola: Entomobryidae). Proceedings of the Iowa Academy of Science 87: 121-123.
Denis J (1929) Notes sur les collemboles récoltés dans ses voyages par le Prof. F. Silvestri. Bollettino del Laboratorio di Zoologia generale e Agraria della R. Scuola Superiore d’Agricoltura in Portici 22: 166-180.
Denis J (1948) Collemboles d’Indochine. Notes d’Entomologie Chinoise 12: 183-311.
Fjellberg A (2007) The Collembola of Fennoscandia and Denmark. Part II: Entomobryomorpha and Symphypleona. Fauna Entomologica Scandinavica 42: 1-264.
Folsom JW (1913) North American springtails of the sub-family Tomocerinae. Proceedings of the United States National Museum 46: 451-472. doi: 10.5479/si.00963801.46-2037.451
Goto HE (1956) Architomocerura Denis, 1931 (Collemb., Isotomidae) an immature stage of Tomocerus Nicolet, 1841 (Collemb., Tomoceridae). Entomologist’s Monthly Magazine 42: 49-51.
Hopkin SP (1997) Biology of the springtails (Insecta: Collembola). Oxford University Press, Oxford, New York, 330 pp.
Jordana R, Baquero E, Reboleira S, Sendra A (2012) Reviews of the genera Schaefferia Absolon, 1900, Deuteraphorura Absolon, 1901, Plutomurus Yosii, 1956 and the Anurida Laboulbène, 1865 species group without eyes, with the description of four new species of cave springtails (Collembola) from Krubera-Voronya cave, Arabika Massif, Abkhazia. Terrestrial Arthropod Reviews 5: 35-85. doi: 10.1163/187498312X622430
Karuhize GR (1971) The structure of the postantennal organ in Onychiurus sp. (Insecta: Collembola) and its connections to the central nervous system. Zeischrift für Zellforschung und Mikroskopische Anatomie 118: 263-282. doi: 10.1007/BF00341570
Lee BH (1974) Etude de la faune coréenne des insectes Collemboles. V.-Inventaire des grottes de Corée et étude sur les Tomoceridae cavernicoles avec la description d’une nouvelle espèce. Annales de Spéléologie 29: 403-418.
Martynova EF (1969) Springtails of the family Tomoceridae (Collembola) from the fauna of the USSR. Revue d’Entomologie de l’URSS 48: 299-314.
Mills HB (1948) New North American Tomocerinae. Annals of the Entomological Society of America 41: 353-359.
Müller OF (1776) Zoologiae Danicae prodromus, seu Animalium Daniae et Norvegiae indigenarum; characteres, nomina, et synonyma imprimis popularium. Havniae, typis Hallageriis, 282 pp.
Nicolet H (1842) Recherches pour servir à l’histoire des Podurelles. Nouveaux Mémoires de la Société Helvétique des Sciences Naturelles 6: 1-88.
Potapov M (2001) Synopses on Palaearctic Collembola Vol. 3 Isotomidae. Staatliches Museum für Naturkunde Görlitz, Görlitz, 603 pp.
Rusek J (1977) The status of Tomolonus Mills, 1948 (Collembola: Tomoceridae). Revue d’Ecologie et de Biologie du sol 14: 225-230.
Wang TL, Yu DY, Zhang F (2013) Two new species of Pogonognathellus (Collembola: Tomoceridae) from China, with a discussion of East Asian species. Journal of Natural History 47: 1243-1255. doi: 10.1080/00222933.2012.752541
Yosii R (1956) Monographie zur Höhlencollembolen Japans. Contributions from the Biological Laboratory, Kyoto University 3: 1-109.
Yosii R (1966) Results of the speleological survey in South Korea 1966 IV. Cave Collembola of South Korea. Bulletin of the National Science Museum Tokyo 9: 541-561.
Yosii R (1967) Studies on the collembolan family Tomoceridae, with special reference to Japanese forms. Contributions from the Biological Laboratory, Kyoto University 20: 1-54.
Yosii R (1970) On some Collembola of Japan and adjacent countries II. Contributions from the Biological Laboratory, Kyoto University 23: 1-32.
Yoshii R (1991) A new species of tomocerid Collembola from the cave of Pref. Iwate. Annals of the Speleological Research Institute of Japan 9: 1-2.