Isotominella laterochaeta, Potapov & Janion-Scheepers & Deharveng, 2020

Potapov, Mikhail B., Janion-Scheepers, Charlene & Deharveng, Louis, 2020, Taxonomy of the Cryptopygus complex. III. The revision of South African species of Cryptopygus and Isotominella (Collembola, Isotomidae), ZooKeys 945, pp. 99-127 : 99

Isotominella laterochaeta sp. nov. Figures 47-53 , 54-59

Type material.

Holotype and eight paratypes: South Africa • Western Cape, Platboom, Cape Point National Park; 34.336017S, 18.447633E; 14 Nov. 2010; L. Deharveng and A. Bedos leg.; soil; SAF 318. Holotype and two paratypes on three slides deposited at SAMC, three paratypes on three slides at NMHN, and three paratypes on three slides at MSPU.

Diagnosis.

Blind. Labium with 7-9 basolateral chaetae. Chaetae on ventral side of Th. III present. Labial palp with 16 guard chaetae. Three sublobal hairs on maxillary outer lobe. Anterior side of manubrium with 9-10+9-10 chaetae. Dens with 12-14 anterior and four posterior chaetae. Mucro bidentate.

Description.

Body size 0.8-1.0 mm. White, without pigmentation, appearance as Mucrosomia caeca (Fig. 47 ). Mouth cone projected forward. Abd. V well separated from Abd. IV and fused with Abd. VI (Fig. 53 ). Cuticle “smooth”. Without ocelli. PAO small, not constricted, less than a half of width of Ant. I and 0.5-0.7 as long as inner unguis length. Maxillary head with slender lamellae and thin capitulum. Maxillary outer lobe with three sublobal hairs, maxillary palp simple (Fig. 52 ). Labral formula as 2/5,5,4, edge of labrum not reduced. Chaetae of labrum conspicuously projected forward (Fig. 50 ). Labral chaetae of middle and distal rows thicker than chaetae of proximal row. Inner chaetae of distal row shifted to more proximal position and integrated to middle row resulting the impression of 5,7,2 formula. Up to ten clypeal chaetae. Labium with five papillae (A-E), 16 guard chaetae (guard chaetae e7 present), and three proximal chaetae (Fig. 49 ). Terminal ‘sensilla’ of papillae A and B rod-like. All inner guard chaetae (b3, b4, d3, d4, e2, e3, e5, e6) strongly curved. With two curved and small accessorial hypostomal chaetae (h1, h2), main hypostomal chaeta (H) absent (Fig. 49 ). Basal part of labium with four basomedian and 7-9 basolateral chaetae (Figs 48 , 52 ). Ventral side of head with numerous chaetae (up to 13 on one side along ventral line), with numerous chaetae at base of labium (Fig. 48 ). Normal s-chaetae and basal micro s-chaetae hardly differentiated on antennae, their number difficult to ascertain. Ant. I with many chaetae and at least two ventral s-chaetae (s) mixed with normal chaetae (or thinner s-chaetae). Ant. III with five distal s (including one lateral), without additional s-chaetae. S-chaetae on Ant. IV weakly differentiated. Organite small, rudimental, close to subapical micro s-chaeta, which is long and bent (Fig. 51 ).

Common chaetae long. S-formula as 3,3/2,2,2,2,3 (s), 1,0/1,0,0 (ms) (Fig. 54 ). Tergal s-chaetae longer than common chaetae, less distinguishable on Th. II and III. Medial s-chaetae on Th. II-Abd. III situated in p-row of chaetae. On Abd. V, two dorsal s-chaetae (accp1, accp2) long, one lateral s-chaeta short (Fig. 53 ). Macrochaetae smooth and long, 1,1/3,3,3,4 in number. Macrochaetae on Abd. V longer than on Abd. VI: 0.8-0.9 and 0.6-0.7 as long as the dens and 3.3-3.5 and 2.3-2.8 times longer than mucro on Abd. V and VI, respectively. One thin macrochaetae (possibly additional s-chaeta) present in latero-ventral position on Abd. V. Foil chaetae at the tip of abdomen absent. Axial chaetotaxy for Th. II-Abd. IV 14-16,7-8/5-6, 5-6, 5-6, ca. 6. Th. III with 2-4+2-4 ventral chaetae.

Unguis of normal shape, without inner tooth and with two lateral teeth. Lateral teeth often asymmetrical in size and position. Empodial appendage thin, without lamellae, 0.6-0.7 as long as unguis. All tibiotarsi with many additional chaetae: Tibiotarsal tenent hairs not clavate. Ventral tube with 5-8+5-8 laterodistal and 6-9 posterior chaetae (with two larger in distal position), anteriorly without chaetae. Tenaculum with 4+4 teeth and two chaetae (rarely more). Anterior furcal subcoxa with 19-23, posterior one with 11-15 chaetae. Anterior side of manubrium with 9-10+9-10 chaetae arranged in two symmetrical group (Fig. 58 ), with distal pair thickened. Posterior side of manubrium with 11-14+11-14 chaetae on main part, 4+4 laterodistal and 2(3)+2(3) lateral chaetae (Fig. 59 ). Dens of medium length, with weak crenulation at the middle, with 12-14 anterior and four posterior chaetae (Figs 55-57 ). One minute chaeta-like process often seen close to distal chaeta. Mucro bidentate. Ratio manubrium: dens: mucro = 3.0-3.9: 3.2-4.3: 1.

Etymology.

The name is derived from its many lateral chaetae on the basal part of labium.

Distribution and ecology.

Known only from type locality (Cape Point National Park).

Discussion.

Isotominella laterochaeta sp. nov. and I. geophila (type species of the genus) differ by the number of anterior chaetae on the manubrium (9-10+9-10 vs. 1-4+1-4), chaetae on ventral side of Th. III (present vs. absent), number of guard chaetae on labial palp (16 vs. 13-14), and number of sublobal hairs (three vs. two) on maxillary outer lobe. Minute chaeta placed at the middle of posterior side of dens, numerous postlabial chaetae, and absence of hypostomal chaeta H are unique to I. laterochaeta sp. nov. The two last characters are unknown for I. geophila .

Figures

Figures 47 - 53. Isotominella laterochaeta sp. nov. 47 appearance and macrochaetotaxy (some macrochaetae lost) 48 ventral side of head 49 labial palp (hypostomal chaetae shown separately) 50 labrum, lateral view (chaetae of distal row marked, three, three, and two chaetae shown for proximal, middle, and distal rows, respectively) 51 apical part of Ant. IV 52 basal parts of labium and maxillary outer lobe, lateral view 53 posterior edge of Abd. IV and fused Abd. V and VI. Abbreviations: A and B papillae of labial palp, blf basolateral field of labium, e 7 guard chaeta e 7, mp maxillary palp, h 1 and h 2 hypostomal chaetae, org organit, sms subapical ms-chaeta, ss s-chaeta, msms-chaeta.

Figures 54 - 59. I. laterochaeta sp. nov. 54 macrochaetotaxy and s-ms-pattern 55 - 57 dens, posterior (55), anterior (56), and lateral (57) views 58, 59 manubrium, anterior (58) and posterior (59) views. Abbreviations: ss s-chaeta, msms-chaeta.