Tomocerus cthulhu, Yu, Daoyuan & Li, Youbang, 2016

Yu, Daoyuan & Li, Youbang, 2016, New troglomorphic species of Tomocerus with well-developed postantennal organs (Collembola: Tomoceridae), Zootaxa 4162 (2), pp. 361-372 : 368-371

Tomocerus cthulhu sp. nov.

Figs 1 D, E, 6, 7

Type material. Holotype female adult, on slide. Collected in Yanzhi Cave , Guijiao Village , Pingmeng Township , Napo County, Baise, Guangxi Province, China, 8.X.2015, by Youbang Li, Zhouquan Wei and Yueting Feng . Paratypes two female and three male adults on slides, 6 in 99% alcohol, same data as holotype. All types in NJAU .

Description. Body length 2.7–3.0mm for males, 3.9–4.5mm for females. Body with uniform light brownish to blackish grey pigment, with unpigmented patches. Clypeus, antero-dorsal area of head, Ant.I and Ant. II darker. Eye patches black ( Fig. 1 D).

Intact antenna not seen. Longest observed broken antenna more than two times as long as body. Length ratio of Ant I:II= 1.0:1.4–1.5. Both dorsal and ventral sides of Ant. I and Ant. II scaled, Ant. III dorso-basally with several scales. PAO with oval central pit and fusiform vesicle, long diameter of central pit subequal to or slightly longer than that of eye ( Fig. 6 A). Eyes 6+6, relatively small. Labral chaetae formula as 4/5, 5, 4. Distal edge of labrum with four curved spines. Mandibular head asymmetrical, the left one with 4 teeth and the right one with 5, left molar plate distally with a tapered tooth ( Fig. 6 B). Basal teeth of maxillary lamella 5 longer than apical ones, without beard-like appendage ( Fig. 6 C). Maxillary outer lobe with trifurcate palp, one basal chaeta and 4 sublobal hairs. Both dorsal and ventral sides of head scaled. Cephalic dorsal macrochaetotaxy: anterior area: 2; interocular area: 0; postocular area: 1+1; posterior area: 2+2. Posterior margin of head with 40–60 small chaetae ( Fig. 6 D). Mentum with 5 chaetae, submentum with numerous chaetae.

Pattern of body chaetotaxy as in Fig. 6 E. Number of bothriotricha as 2, 1/ 0, 0, 1, 2, 0, 0. Macrochaetae densely arranged along anterior margin of Th. II (not shown in figure). Th. II with file of macrochaetae behind anterior margin. Number of macrochaetae or large mesochaetae in posterior row as 3, 3/ 2, 2, 3–4, 1–2, 4 from Th. II to Abd.V. Th. II with one central macrochaeta near pseudopore; Abd.III with two anterior macrochaetae; Abd.IV with one lateral macrochaeta; Abd.VI with numerous chaetae of different sizes. Most mesochaetae laterally and posteriorly on terga. Pseudopores near the axis of terga, number of them as 1, 1/ 1, 1, 1, 1, 0, 0 from Th. II to Abd. VI.

Trochantero-femoral organ with 1, 1 small slender chaetae. Front, middle and hind tibiotarsus ventrally with 4– 5, 3–5, 4 pointed spine-like chaetae ( Fig. 6 F). Each tibiotarsus with distal whorl of 11 chaetae, ventral six as ordinary chaetae, dorsal five modified: tenent hair short, slender and pointed; one pair of accessory chaetae small, longer than pretarsal chaetae; one pair of guard chaetae slender, longer than tenent hair. Unguis slender, with basointernal ridges about 1/3 distance from base; lateral teeth pointed, of moderate size. Inner edge of unguis with an extremely minute basal tooth and 1–2 minute more distal teeth. Unguiculus slender, about 0.5–0.75 times as long as unguis, with sharply acuminate apex, its inner edge with one corner tooth. Pretarsus chaetae 1+1 ( Fig. 6 G).

In large specimens ventral tube covered with scales on both anterior and posterior faces, in small specimens both faces with only few scales or unscaled. Lateral flaps unscaled. Apical vesicles with 6–8 tentacle-like papillae on either side ( Figs 1 E, 7A). Anterior face with 35–65 chaetae on each side, posterior face with 80–170 chaetae, each lateral flap with 50–115 chaetae. Rami of tenaculum with 4+4 teeth, anterior face with 1–11 small chaetae, without scale ( Fig. 7 B, C). Furca length ratio as manubrium:dens:mucro=3.0–3.7:4.0–5.0:1.0. Manubrium ventrally scaled, without chaetae, laterally with large round scales and 12–16 large chaetae, in some specimens with several small chaetae among large ones; each dorsal chaetal stripe with 200–300 chaetae of different sizes and a few randomly distributed inner scales, prominent chaetae 2+2, pointed and relatively short; pseudopores 16–29 on each side ( Fig 7 D); external corner chaeta as large mesochaetae ( Fig. 7 E). Dens basally with one pointed prominent dorsal chaeta, without large modified inner scale or strong outer chaetae. Dental spines formula as 3–5/ 4–5, I, 0–1, I; all spines with numerous moderate sized denticles ( Fig. 7 F). Dens dorsally with ordinary chaetae and feather-like chaetae, ventrally covered by scales. Mucro elongated and multi-setaceous; both basal teeth with proximal lamellae, outer tooth with 1–3 toothlets; apical tooth longer than subapical one; structure of dorsal lamellae of Tomocerus type, outer lamella with 3–6 moderate sized intermediate teeth ( Fig. 7 G).

Etymology. Named after the fictional character Cthulhu from H. P. Lovecraft's novel The Call of Cthulhu , who has multiple tentacles on its face, similar to the appearance of ventral tube in the new species.

Remarks. Among Tomocerinae, Tomocerus cthulhu sp. nov. is so far unique for its multi-furcated vesicles of ventral tube, which appears in both subadults and adults (young juvenile specimen not available). The exact effect of this modification is unclear, but it can be inferred that the papillae can enlarge the surface of the vesicle and probably advance its function of water-ionic exchange ( Hopkin 1997). Tomocerus cthulhu sp. nov. is similar to T. postantennalis , T. dong sp. nov. and T. deharvengi sp. nov. in the habitus, the PAO, the claws and the shape of dental spines, but is different from the latters mainly in the lighter pigmentation, the cephalic and body chaetotaxy and the elongated apical tooth of mucro. Among all six specimens on slides, the females are distinctly larger than the males, tending to have more manubrial pseudopores and more chaetae on the ventral tube and dorsal side of manubrium. The number of chaetae on tenaculum has a large range of variation. In three observed males there are respectively 1, 1 and 2 such chaetae, while in three females the numbers are 3, 6 (or more) and 11, thus even within the same sex and similar body size the number is still variable. In three specimens the mucronal basal teeth are quite unusual on one or both sides, that the inner basal tooth could be doubled and the outer one could be trifurcated ( Fig. 7 H) or quadrifurcated ( Fig. 7 I). Most specimens have the dental spines arranged as 3–4/4–5, II, that no small spine appears between two large distal ones. But in one female the right dens bears 5/5, I, 1, I spines, and in this case the spines are arranged in approximately two rows ( Fig. 7 J), and this individual has doubled inner basal tooth and trifurcated outer basal tooth on the right mucro.

Figures

FIGURE 6. Tomocerus cthulhu sp. nov. (A) left PAO and eyes (dorsal view); (B) apices of mandibular heads (dorsal view); (C) lamella 5 of maxillary head (dorsal view); (D) cephalic dorsal chaetotaxy (dorsal view); (E) dorsal chaetotaxy of Th. II – Abd. V (dorsal view, circle with an asterisk: chaeta absent in some individuals); (F) tibiotarsi (lateral view); (G) middle claw (lateral view, arrows pointing to inner teeth of unguis, showing chaetae on only one side). Scale bars: A, B, G, 50 µm; C, 15 µm; F, 200 µm.

FIGURE 7. Tomocerus cthulhu sp. nov. (A) distal part of ventral tube (antero-lateral view); (B) tenaculum with two chaetae (anterior view); (C) tenaculum with 11 chaetae (anterior view); (D) right side of manubrium (dorsal view); (E) disto-external corner of manubrium (dorsal view); (F) spines and prominent dorso-basal chaeta on dens (common form, dorsal view); (G) mucro (inner view); (H) malformed basal teeth on left mucro (inner view); (I) malformed outer basal tooth on right mucro (outer view); (J) uncommon arrangement of dental spines (dorsal view). Scale bars: A, D, F, J, 200 µm; B, C, E, G, 50 µm; H, I, 15 µm.

FIGURE 1. A and B, Tomocerus dong sp. nov. (A) appearance in alcohol (lateral view); (B) left side of manubrium and base of dens (dorsal view, arrows pointing to prominent chaetae); C, Tomocerus deharvengi sp. nov. (C) appearance in alcohol (lateral view); D and E, Tomocerus cthulhu sp. nov. (D) appearance in alcohol (lateral view); (E) ventral tube (lateral view). Scale bars: A, C, D, 1 mm; B, 100 µm; E, 200 µm.