Linzhangia Karmakar, Ganguly & Mondal, 2022

Ganguly, Moumi, Mondal, Priyankar & Karmakar, Krishna, 2022, Complementary description of three species of Steneotarsonemus (Acari: Tarsonemidae) from rice agroecosystems of Eastern India with notes on their taxonomic status, spatial distribution, intraspecific variation and species composition, Zootaxa 5138 (5), pp. 501-532 : 514-515

Subgenus Linzhangia Karmakar, Ganguly & Mondal subgen. nov.

Type species: Steneotarsonemus subfurcatus Lin & Zhang, 1990 ; by original designation and monotypy.

Differential diagnosis. The subgenus Linzhangia is most concisely diagnosed by the presence of small tapering setae v2 posterolaterad setae v1 on the prodorsum of the female. In all other members of Tarsonemoidea this seta is a pair of alveolar vestiges. The subgenus also lacks trichobothrium (sc1), a state shared only by the members of Steneotarsonemus (Mahunkacarus) .

Remarks. Lindquist (1986) and Mitrofanov & Sharonov (1988) independently proposed a detailed subgeneric classification of Steneotarsonemus . Later, Seeman et al. (2016) summarised this classification system of six subgenera Carextarsonemus , Mahunkacarus , Neosteneotarsonemus , Parasteneotarsonemus , Steneotarsonemoides and Steneotarsonemus . Under this classification system, S. subfurcatus would be a species of Mahunkacarus . However, we consider the retention of seta v2 as a significant feature that deserves recognition as a new subgenus, here named Linzhangia . The absence of v2 on the female prodorsum is an ancestral character in superfamily Tarsonemidoidea while present in some related groups such as Tarsocheylidae , Heterocheylidae , Dolichocybidae , Trochometridiidae , Pyemotidae , Caraboacaridae , some Acarophenacidae and some Pygmephoridae ( Lindquist, 1986) . However, it is expressed in the adult male of most Tarsonemidae . Thus, the presence of v 2 in Linzhangia reflects the expression of the male condition in the female which might be considered as an autapomorphic feature for this subgenus within family Tarsonemidae .

Lin & Zhang (1990) stated that S. subfurcatus possess a vestigial trichobothrium (sc1) and classified this species under the nominate subgenus Steneotarsonemus . They showed the trichobothrium as lacking its shaft and illustrated sc1 with schematic circular markings. Similar markings were also illustrated to indicate the alveolar vestiges of sc 1 in three species of subgenus Mahunkacarus which is categorized by absence of sc1 viz. Steneotarsonemus (Mahunkacarus) gibber Suski, 1970 , S. abruptus Livshits et al. 1982 and S. badulini Wainstein, 1979 ( Sharonov et al. 1982). However, two other species of subgenus Mahunkacarus viz. Steneotarsonemus (Mahunkacarus) apartimerus Mahunka, 1971 and S. (Mahunkacarus) mayae Lin & Zhang, 2005 were originally illustrated without any such markings at the position of sc1 clearly indicating their absence on the prodorsum. The specimens of S. subfurcatus collected from India clearly do not have any trichobothrium and we believe the markings in the original description of S. subfurcatus also indicate absence of sc1 but shows the position of alveolar vestiges. Furthermore, we have confirmed the species identity of our specimens comparing the Holotype and allotype micrographs of S. subfurcatus (Acc. No. IOZ (E) 228033, 228034; Dated 1986-XI-20) sent by Dr. Chen Jun from Institute of Zoology, Chinese Academy of Sciences upon request to Dr. Jian-Zhen Lin. Unfortunately, we could not check the type specimens of S. furcatus despite requesting information from the colleagues in USA.

Absence of sc 1 in adult female is a homoplasious character for insect parasitic genera Asiocortarsonemus , Amcortarsonemus and few Coreitarsonemus in tribe Coreitarsonemini , Eotarsonemus in Hemitarsonemini, Tarsonemella in Tarsonemellini, and phytophagous Steneotarsonemus (subgen. Mahunkacarus and Linzhangia ) in Steneotarsonemini. Convergent evolution of these mites in confined spaces either as parasite on other insects or phytophagous inside tight plant parts like grass leaf sheaths may have caused the loss of sensory organs such as trichobothrium ( Lindquist, 1986). However, few tarsonemid species which might not experience similar selection pressure in the confined places, have retained well developed bothridial organs (Moraes et al. 2002; Mondal & Karmakar, 2021). We have updated the ‘provisional’ key to subgenera of Steneotarsonemus (females) by Seeman et al. (2016) with inclusion of Linzhangia as follows.

1. Female adult: prodorsal bothridia reduced, their setae vestigial…................... 2

- Female adult: prodorsal bothridia well developed, their setae capitate or narrowly lanceolate but not reduced in size...... 3

2. Female adult: Setae v2 present posterolaterad setae v1 .................................... Linzhangia subgen. nov.

- Female adult: Setae v2 present as alveolar vestiges only........................................... Mahunkacarus

3. Female adult: prodorsal bothridia slender or narrowly lanceolate. Larva and adult: where known, tarsi II and III with unguinal seta u ′′ modified, either split to its base or expanded or hyaline................................. Neosteneotarsonemus

– Female adult: prodorsal bothridia capitate. Larva and adult: where known, tarsi II and III with seta u ′′ unmodified (slender, smooth) or vestigial................................................................................... 4

4. Female adult: Prodorsum with tectum-like flange extending over mid-dorsal part of gnathosoma...... Steneotarsonemoides

– Female adult: Prodorsum without flange extending over gnathosoma............................................ 5

5. Female adult: Apodemes 3 with anterior projection near the medial extremity, in addition to their oblique proximal portion....................................................................................... .. Carextarsonemus

– Apodemes 3 without anterior projection, restricted to typical oblique proximal portion (which, distally, may curve posteromedially), or further reduced to remnant............................................................. 6

6. Male adult: Prodorsum with 3 pairs of setae; leg IV with anterolateral flange as well as large posterolateral flange on femorogenu, with small flange on tibia, and with reduced knob-like tarsal claw. Larva and adult: where known, femur II with 2 setae. Female adult: where known, legs I and II short and stubby, tarsus II no longer than its basal width; legs III no longer than legs IV (trochanters and ambulacra excluded)…........................................ Parasteneotarsonemus

– Male adult: Prodorsum with 4 pairs of setae; leg IV with or without large posterolateral flange on femorogenu, usually lacking supplementary flanges on this or other segments, and with normal, unguiform tarsal claw. Larva and adult: where known, femur II with 3 setae. Female adult: where known, legs I and II moderately short but not stubby, tarsus II usually longer than its basal width; legs III longer than legs IV (trochanters and ambulacra excluded)..................... Steneotarsonemus