Broadening the definition of the genus Thalassaphorura Bagnall, 1949 (Collembola, Onychiuridae) with a new aberrant species from China
Author
Sun, Xin
Author
Deharveng, Louis
Author
Wu, Donghui
text
ZooKeys
2013
364
1
9
http://dx.doi.org/10.3897/zookeys.364.6332
journal article
http://dx.doi.org/10.3897/zookeys.364.6332
1313-2970-364-1
03592C54D17042FEB764A8B8383F74CF
03592C54D17042FEB764A8B8383F74CF
Thalassaphorura problematica
sp. n.
Type material.
Holotype female; paratypes 9 females and 3 males on slides-China, Heilongjiang: Wulindong town,
46°33'N
,
133°40'E
, 16 Aug 2010, forest soil and humus, Wu Donghui, Liu Dong, Yuan Xiaoqiang and Yuan Yabin leg.
Diagnosis.
Pso formula as 32/133/33343 dorsally, 11/000/00010 ventrally; psx formula as 0/000/112001+1m ventrally; Ant. III sensory organ with two granulated clubs (inner one bigger than outer); labium with 5 proximal chaetae; labial type AB; tibiotarsi of legs
I-III
with 14 (1, 7, 6) chaetae each; male ventral organ present on ventral tube as modified distal chaetae; anal spines 1.1-1.2 times as long as inner edge of hind unguis.
Description.
Body white in alcohol. Size 1000-1300
µm
in females, 800-1100
µm
in male; holotype: 1050
µm
. Body subcylindrical, body sides parallel.
Pseudocellar formula: 32/133/33343 dorsally, 11/000/00010 ventrally, subcoxa 1 of legs I-III with 2, 2 and 2 pso respectively (Fig. 1A, B). Parapseudocellar formula: 0/000/112001+1m (each of anal valve with one psx) ventrally, absent dorsally (Figs 1A, B, 2G). Pseudopore formula: 0/011/11110 dorsally, 00/111/0001m0 ventrally (Fig. 1A, B).
Figure 1.
Thalassaphorura problematica
sp. n. A dorsal side of body B ventral side of Abd.
I-VI
C PAO D clubs and papillae of AIIIO E Labium F Antenna. Scales: 0.1 mm (
A-B
, F), 0.01 mm (
C-E
).
Figure 2.
Thalassaphorura problematica
sp. n. A dorsal side of head B ventral side of head C Abd.
IV-VI
terga D ventral tube (showing male ventral organ) E distal part of leg III F furca G anal valves. Scales: 0.1 mm (
A-C
and
F-G
), 0.01 mm (
D-E
)
Head. Antennae short and distinctly segmented, as long as head. Length ratio of Ant. I: II: III: IV as about 1: 1.5: 1.5: 1.5. Subapical organite of Ant.IV with globular apex; basolateral ms at about 1/3 length from base, above the second proximal row of chaetae (Fig. 1F). Ant. III sensory organ composed of 5 papillae, 5 guard chaetae, 2 sensory rods and 2 granulated clubs, the inner bigger than the outer, and a lateral ms (Figs 1D, F). Ant. II with 13 chaetae. Ant. I with 8 chaetae. Antennal base well marked. PAO composed of 20-24 simple vesicles (Fig. 1C). Dorsal cephalic chaeta d0 absent (Figs 1A, 2A). 3+3 p-chaetae present between two inner posterior pso, p1 anterior to others. Mandible with strong molar plate and 4 apical teeth. Maxilla bearing 3 teeth and 6 lamellae. Maxillary palp simple with 1 basal chaeta and 2 sublobal hairs. Labral formula 4/1,4,2;. Labium with 5 proximal, 4 basomedian (E, F, G, f) and 5 basolateral (b, c, d, e,
e'
) chaetae (Fig. 2B); labial type AB, papillae
A-E
respectively with 1, 4, 0, 3 and 2 guard chaetae (Fig. 1E). Head ventrally with 4+4 postlabial chaetae along ventral groove (Fig. 2B).
Body chaetotaxy. S-chaetae subcylindrical, apically rounded, 11/011/222121 dorsally, 11/000/000110 ventrally (Figs 1A, B); subcoxae 2 of legs I, II and III with 0, 0, 1 S-chaeta respectively. Tiny and blunt ms, present on Th.
II-III
. Ordinary chaetae differentiated into meso- and macrochaetae, ratio Sp: m1: p1 on Abd. V tergum = 1: 2-2.3: 0.8. Th. I tergum with 7
-8+7-
8 dorsal chaetae. Th.
II-III
terga with 4+4 chae
tae
and Abd.
I-III
terga with 3+3 chaetae along axis respectively (Fig. 1A). Abd.
IV-V
terga with one axial chaeta (p0) each, sometimes with asymmetric chaetae along axis. Abd. VI tergum with two axial chaetae (a0 and p0) (Figs 1A, 2C). Sterna of Th. I, II, and III with 0+0, 1+1, 1+1 chaetae respectively.
Appendages. Subcoxa 1 of legs
I-III
with 4, 5 and 5 chaetae, subcoxa 2 with 0, 4 and 4 chaetae respectively. Tibiotarsi of legs I, II and III with 14 (1, 7, 6) chaetae each (Fig. 2E). Unguis without teeth. Unguiculus short, about 0.3 times as long as inner edge of unguis, with inner basal lamella (Fig. 2E). Ventral tube with 1+1 basal and 8
-11+8-
11 distal chaetae (8
-10+8-
10 in female, 11+11 of which 9+9 modified in males) (Fig. 2D). Furca reduced to a field of fine granulation with 4 small dental chaetae arranged in 2 rows posteriorly; only one manubrial row of chaetae present posteriorly to dental chaetae (Fig. 2F).
Genital plate with 14-15 chaetae in females, 33-36 chaetae in male. Anal valves with numerous acuminate chaetae; each lateral valve with a0 and 2a1; upper valves with chaetae a0, 2b1, 2b2, c0, 2c1, 2c2 (Fig. 2G). Anal spines set on distinct papillae, 1.1-1.2 times as long as inner edge of hind unguis.
Derivatio nominis.
Named for its unusual characters among
Thalassaphorura
.
Discussion.
The new species is closest to the genus
Thalassaphorura
by its simple vesicles in PAO and the furcal rudiment. However, it does not match the definition of this genus proposed by
Sun et al. (2010)
, nor those given previously by
Weiner (1996)
,
Fjellberg (1999)
or
Pomorski (1998)
for three characters: absence of chaeta d0 on head, 6 chaetae in the distal whorl of tibiotarsi of all legs, and labium type AB. In order not to erect a new genus in a tribe in need of revision (
Sun et al. 2011
) and for a species otherwise very similar to existing
Thalassaphorura
, we placed our new species in the genus
Thalassaphorura
and broadened its diagnosis.
The new species belongs to the species-group of
Thalassaphorura
which has modified ventral chaetae in the adult male ("male ventral organ"), including the species
Thalassaphorura petiti
Sun & Wu, 2013,
Thalassaphorura bisetosa
Sun & Wu, 2013,
Thalassaphorura qinlingensis
Sun & Wu, 2013,
Thalassaphorura macrospinata
Sun & Wu, 2012 and
Thalassaphorura qixiaensis
Yan, Shi & Chen, 2006, all described from China. These species can be distinguished easily by the position or the number of modified chaetae of the male ventral organ, dorsal and ventral pso formula, and ventral psx formula.
Assigning the new species to this genus led us to re-examine three important taxonomic characters that separate the new species from most other
Thalassaphorura
.
The distal tibiotarsal chaetae have been recently checked in the genera
Allonychiurus
,
Onychiurus
and
Thalassaphorura
(
Sun et al. 2010
;
Sun et al. 2011
;
Sun and Zhang 2012
), showing that this character has a limited taxonomical value to discriminate these genera. In addition, paratypes of
Thalassaphorura petaloides
(Rusek, 1981) from Iraq and specimens of the same species from southern China were found to actually have 15 (1, 7, 7), 14 (1, 7, 6) and 14 (1, 7, 6)) chaetae on tibiotarsi I, II and III. Together with reduced tibiotarsal chaetotaxy of the new species described here, this leads us to extend the diagnosis of
Thalassaphorura
to species with 6, 7 or 9 chaetae in the distal row of tibiotarsus.
Chaeta
d0 on head is considered as a stable character at the generic level. It is present in all species of
Thalassaphorura
(
Sun et al. 2011
) except
Thalassaphorura jailolonis
(Yoshii & Suhardjono, 1992) from Malukku (Indonesia) and the new species
Thalassaphorura problematica
sp. n. The species
Thalassaphorura jailolonis
was described in
Jailolaphorura
Yoshii & Suhardjono, 1992 (a subgenus of
Onychiurus
, upgraded to genus level by Weiner in
1996
), but was subsequently transferred to
Thalassaphorura
by
Bellinger et al. (1996-2013)
according to a personal communication of Pomorski in 2002. This assignation is however uncertain because the chaetotaxy of the furcal rest is unknown in
Thalassaphorura jailolonis
. At this point, we consider that the diagnosis of the genus
Thalassaphorura
should provisionally state that d0 is present or absent on head, waiting for a re-examination of
Thalassaphorura jailolonis
on fresh material.
The third character, labium type, is not stable in several genera of
Thalassaphorurini
, being AC or ABC in
Allonychiurus
and
Sensillonychiurus
(
Babenko et al. 2011
), and even A, AC or ABC in
Thalassaphorura
(
Sun et al. 2010
). In our new species, labium is still of another type - AB. Moreover, labial type is undescribed in many species. This high intra-generic variability implies that this character should not be considered diagnostic at a generic level among
Thalassaphorurini
.
An amended diagnosis of the genus
Thalassaphorura
and an updated key of the genera of
Thalassaphorurini
integrating these changes are given below.