Bryodelphax instabilis, Gąsiorek & Degma, 2018

Gąsiorek, Piotr & Degma, Peter, 2018, Three Echiniscidae species (Tardigrada: Heterotardigrada) new to the Polish fauna, with the description of a new gonochoristic Bryodelphax Thulin, 1928, Zootaxa 4410 (1), pp. 77-96 : 79-85

Bryodelphax instabilis sp. nov.

( Figs 1–23 , Tables 3–5)

Locus typicus. Moss on carbonate bedrock from Homole Ravine in the Pieniny Mts. (49°24'17''N, 20°32'52''E; 595 m asl), Poland.

Type material. Holotype (mature female, slide no. PL.189.19), coll. Maciej Barczyk, 25th May 2016, allotype (mature male, slide no. PL.189.01), 30 paratypes (21 mature females, 7 males, one juvenile, and one larva; slides PL.189.02–32) and additional 15 paratypes (both juveniles and adults) on SEM stubs. Found together with numerous Bryodelphax parvulus Thulin, 1928 ( Fig. 24 ), Pseudechiniscus suillus ( Ehrenberg, 1853) , and single specimens of Testechiniscus spitsbergensis ( Scourfield, 1897) . All from the same moss sample. Holotype and most of paratypes deposited in the Institute of Zoology and Biomedical Research, Jagiellonian University, Kraków, Poland, two paratypes (slides PL.189.10–11) deposited in the Department of Zoology, Comenius University in Bratislava, Slovakia, and two paratypes (slides PL.189.22–23) deposited in the Zoological Museum, University of Copenhagen, Denmark.

Additional material examined. Two specimens in a moss sample from Chuda Alp in the Tatra Mts. (slide PL.258.06), coll. Piotr Gąsiorek, 24th September 2016, deposited together with type material. 128 specimens (44 males, 43 females, 3 juveniles, and 38 specimens of unidentified sex due to unsuitable orientation of a specimen on a slide; slides 390/7–10, 390/18, 390/20, 390/23, 390/25, 390/27–30, and 390/32; deposited in the Department of Zoology , Comenius University in Bratislava , except for 13 specimens deposited in the Institute of Zoology and Biomedical Research , Jagiellonian University , Kraków — slide 390/18) and 9 specimens used for SEM analyses (not deposited) in a moss sample on a rock from Rajtopíky hill, the Branisko Mts. (48°59'42''N, 20°51'59''E; ca. 1036 m asl — on the hill top area), Eastern Slovakia, coll. Peter Degma, 26th July 2003 .

Short description of holotype ( Figs 1 , 10 ; Table 3)

Adult female; colour greyish; eyes not visible (after preparation); body length 137 µm (685); cephalic cirri and papillae, and clava not enlarged; cirrus A 26.5 µm (132.5); claws I–III of similar size, claw IV longer; dentate collar present, with three teeth; small papilla on leg IV. Dorsal plates with sparse pseudopores/pores; ventral plates not obvious. Female gonopore rosette-shaped.

Short description of allotype ( Figs 2 , 12 ; Table 4)

Adult male; colour greyish; eyes not visible (after preparation); body length 123 µm (628); cephalic cirri and papillae, and clava enlarged; cirrus A 20.7 µm (103.0); claws I–III of similar size, claw IV longer; dentate collar present, with three teeth; small papilla on leg IV not visible. Dorsal plates with sparse pseudopores/pores; suggestion of deeper faceting on scapular and caudal plates; ventral plates present. Male gonopore simple, circular.

Details of the new species. Adults (i.e. from the third instar onwards; measurements and statistics for ♀♀ in Table 3, for ♂♂ in Table 4):

Body greyish; eyes absent or not visible after preparation. Mouth opening surrounded by a ring of 10 papulae (visible in SEM only). Cephalic papillae greatly enlarged in males (compare Figs 1 and 2, 4 ), and clavae are also more prominent ( Figs 13 , 17–18 ). Internal cirri much shorter than external ( Tables 3–4, Figs 1–4 , 7–9 ). Cirri A thinner at the tip (visible only under SEM; Fig. 17 ). Dorsal plates covered with sparsely distributed pseudopores or pores of large and intermediate size (visible in PCM as bright dots with margins either blurred (pseudopores) or obvious (pores); Figs 1–2 , 10, 12 ), true pores occur infrequently, being restricted to the posterior portion of the cephalic plate and the anterior portion of the scapular plate ( Fig. 13 ) in the proximal body part, to the posterior parts of segmental plates ( Fig. 14 ), and the anterior margin of the caudal plate in the distal body part. Pores rarely present on all plates ( Figs 11 , 15–16 ), but are often absent ( Figs 6–7 ). Pseudopores/pores density similar on all dorsal plates, approximate mean density 10–13 pseudopores/pores per 100 µm 2 in females and 8–10 pseudopores/ pores per 100 µm 2 in males ( Table 5). Intracuticular pillars visible as fine dark dots under PCM ( Figs 10–12 ). Scapular plate typically distinctly faceted with a median longitudinal fold and three smaller transverse folds ( Figs 2 , 12 ). In females, sometimes only pseudopore/pore rows mark borders of faint facets ( Figs 1 , 10–11 ). Paired plates divided into two unequal anterior and posterior parts by a transverse stripe ( Figs 10–12 , 14, 16 ). Caudal plate faceted with two evident longitudinal folds ( Figs 1–2 , 6 , 10–12 ), most often the central portion of this plate is subdivided into two parts by a transverse V-suture ( Figs 2 , 6 , 12 ). Median plates 1 and 2 with transverse division into two unequal parts (compare Figs 10–12 , 14, 16 ). Median plate 3 with faint transverse suture, triangular in shape, and with a roundish posterior edge ( Figs 14, 16 ). Poorly developed supplementary lateral platelets present at the levels of median plates (three pairs of platelets on each body side: a pair between scapular plate and first pair of the segmental plates, a pair between paired plates, and a pair between second pair of segmental plates and caudal plate; Figs 1 , 10–12 ), devoid of pores/pseudopores ( Fig. 7 ). Ventral cuticle typically with weakly developed plates. Ventral intracuticular pillars either absent or present and well-visible (compare Figs 4–5 ) at 100x oil immersion, and always less evident than dorsal (compare Figs 5 and 11 ). Ventral plate configuration: VII/IX:(2)-(1)-2/4-2-2/4- 2-2-2-1. Two small subcephalic longitudinal plates just below the mouth opening and one subpharyngeal plate weakly outlined and usually only visible under SEM (compare Figs 5 , 8–9 ). Typically, rows III–VIII/IX are discernible ( Figs 4–5 , 8–9 , 21 ). Rarely, ventral plates invisible under PCM (e.g. holotype). Ventral granules absent or restricted to the plate surface ( Fig. 5 ). Papilla on legs I absent, minute papilla on legs IV present ( Fig. 1 ). Dentate collar on legs IV with 3–6 teeth ( Figs 1–2 , 20 , arrowheads). External claws of all legs smooth, internal claws with tiny spurs pointing strongly downwards with very small gap between spur and claw base, making them almost invisible under PCM (however, always clear under SEM; Figs 19–20 ).

Remarks on the sexual dimorphism: Sex differences in the new species are well-marked and embrace: longer, tubbier primary and secondary ♂ clavae (compare Figs 1–2 and Tables 3–4); stronger faceting of the ♂ scapular plate (compare Figs 10–11 and 12 ); significantly lower pseudopore/pore density on unpaired plates in ♂ (compare ranges presented in Table 5).

Juveniles (i.e. the second instar, four-clawed without gonopore):

In appearance like adults, but clearly smaller (75 µm) and with indiscernible ventral plates ( Fig. 22 ). It is impossible to state firmly whether the species exhibits ontogenetic shifts in ventral armature or the lack of ventral plates in the first two life stages is inconstant. This issue certainly requires more studies, since changes in ventral armature occurring during development were recently detected by Gąsiorek et al. (2017).

Larvae (i.e. the first instar, two-clawed without gonopore; measurements in Table 4):

Median plates with poorly delineated margins, lacking pseudopores/pores; supplementary lateral platelets and pedal (leg) plates undeveloped. Pores/pseudopores present only on the anterior and posterior margins of the cephalic, scapular, segmental, and caudal plates ( Fig. 3 ). Claws with spurs formed as in adults. Legs IV without dentate collar. Ventral plates absent ( Fig. 23 ).

Eggs unknown.

Etymology: The name instabilis underlines the variability in the number of ventral plates (see Remarks), which is unusual for Bryodelphax . Moreover, often only some of the ventral plates rows are visible under the light microscope, thus an animal’s venter seems to be devoid of plates in its proximal part.

Remarks. Polish and Slovak populations have same ventral plates configuration but in three mature females from the Slovak population, row V has two additional, smaller ventral plates placed in a more marginal position, and two of the specimens also have such additional plates in row III ( Figs 5 and 21 ).

Differential diagnosis. Bryodelphax instabilis sp. nov. can easily be distinguished from the other members of the weglarskae group on the basis of the scapular plate faceting and being gonochorous. Nevertheless, the new species should be compared with four most similar taxa having last six ventral plates rows configuration same as the new species, i.e. 2-2-2-2-2-1 or 2-4-2-2-2-1 (due to the instability in ventral plate arrangement). It differs specifically from:

Bryodelphax iohannis Bertolani et al., 1996 , by a different ventral plate configuration (VII/IX:(2)-(1)-2/4-2-2/ 4-2-2-2- 1 in the new species vs X: 2-1-1-5-2-4-2-2-2- 1 in B. iohannis ), by the presence of lateral platelets (absent in B. iohannis ) and by longer teeth on the dentate collar (compare Figs 1–2 with Fig. 2A in Bertolani et al. 1996);

Bryodelphax parvuspolaris Kaczmarek et al., 2012 , by a different ventral plate configuration (VII/IX:(2)-(1)- 2/4-2-2/4-2-2-2- 1 in the new species vs VIII: 1-1-2-2-2-2-2- 1 in B. parvuspolaris ), and by well-developed dentate collar (dentate collar with poorly developed teeth in B. parvuspolaris );

Bryodelphax sinensis ( Pilato, 1974) , by a different ventral plate configuration (VII/IX:(2)-(1)-2/4-2-2/4-2-2-2- 1 in the new species vs VII:2-2-2-2-2-2- 1 in B. sinensis ), and by the presence of well-developed dentate collar on legs IV in adults (dentate collar absent in B. sinensis );

Bryodelphax weglarskae ( Pilato, 1972) , by a different ventral plate configuration (VII/IX:(2)-(1)-2/4-2-2/4-2- 2-2- 1 in the new species vs IX:2-1-5-2-4-2-2-2- 1 in B. weglarskae ), and by non-bifurcated cephalic appendages (bifurcated in B. weglarskae ).

Moreover, Bryodelphax instabilis sp. nov. must be primarily compared with the first described gonochoristic representative of the genus, namely Bryodelphax tatrensis (Węglarska, 1959) because it resembles the latter species when the ventral armature is faint. Bryodelphax instabilis sp. nov. is distinguished from B. tatrensis on the basis of: (1) the average pseudopore/pore size is larger in the new species in comparison with the minute pores in B. tatrensis (the difference is especially obvious between females of both species, compare Figs 10–11 and 26 ), (2) more pronounced faceting of the scapular plate (clearly visible median suture and typically well-developed facets in the new species vs only faint median suture, which can be absent in B. tatrensis ; compare Figs 11–12 and 26– 27 ), and (3) the caudal plate consisting of four facets in males of the new species instead of three in B. tatrensis males (compare Figs 2 , 12 and 25, 27 ). Additional discriminative criteria (e.g. morphometric) could be presented when measurements of a large population of B. tatrensis become available. Unfortunately, general rarity of B. tatrensis hinders the redescription of this taxon ( Dastych 1988, personal observations).

General remarks on Bryodelphax in Polish Pieniny Mts. and Tatra Mts. There are four sympatric Bryodelphax spp. that inhabit Poland and occur in the Pieniny Mts. ( Dastych 1988); three (with the exception of B. weglarskae ) are also present in the Tatra Mts. Our new discovery confirms an eucalciphil and subalpine preference for these Central European members of the genus. In Poland, Bryodelphax spp. are frequently found in close proximity. For example, in the Pieniny Mts. B. parvulus was found in the same moss cushions as B. instabilis sp. nov. or B. weglarskae ; similarly, B. parvulus and B. tatrensis co-occur in mosses in the Tatra Mts.

Figures

FIGURES 1–5. Bryodelphax instabilis sp. nov., habitus (all but Fig. 3 in PCM): 1—female (holotype, dorsolateral view, incised arrowheads indicate supplementary lateral platelets); 2—male (allotype, dorsal view, an empty arrowhead points enlarged cephalic papillae; arrowheads indicate dentate collar on legs IV); 3—larva (paratype, dorsal view, slide PL.189.32, DIC); 4—male (paratype, ventral view, slide PL.189.05, Roman numerals indicate ventral plates rows); 5—female with aberrant additional ventral plates in rows III and V (Slovakian specimen, ventral view, slide 390/32, Roman numerals indicate ventral plates rows).Scale bars in µm.

FIGURES 6–9. Bryodelphax instabilis sp. nov., habitus (SEM):6—female (paratype, dorsal view); 7—male (paratype,lateral view); 8—female (paratype, ventral view); 9—male (paratype, ventral view).Scale bars in µm.

FIGURES10–12. Bryodelphax instabilis sp. nov., dorsal plates(PCM):10—female(holotype, dorsolateral view); 11—female (Slovakian specimen, dorsal view, slide no. 390/32); 12—male (allotype, dorsal view), note deep faceting of the scapular and caudal plates.Scale bars in µm.

FIGURES13–16.Bryodelphax instabilissp.nov., dorsalplates (SEM):13—the scapular plate (paratype, male);14—posterior part of the median 2—median 3 (paratype, male), note almost complete absence of true pores; 15—the scapular plate (Slovakian female); 16—posterior part of the median 1—median 3 (Slovakian female), note numerous large true pores. Scale bars in µm.

FIGURES 17–18. Bryodelphax instabilis sp. nov., male cephalic appendages (paratype, SEM): 17—cirrus A with clava, the arrowhead indicates the subterminal constriction; 18—enlarged clava. Scale bars inµm.

FIGURES 19–20. Bryodelphax instabilis sp. nov., claws (SEM): 19—claws III; 20—claws IV with dentate collar. Scale bars in µm.

FIGURES21–23. A semi-schematic illustration of the ontogenetic variability inthe ventral armature in Bryodelphax instabilis sp. nov.: 21—adult (mature female); 22—juvenile (second instar); 23—larva (first instar).

FIGURES 24–27. Other Polish members of the genus Bryodelphax Thulin, 1928, and the comparison of sculpture of dorsal plates (PCM): 24—B. parvulus Thulin, 1928 (female, dorsolateral view); 25—B. tatrensis (węglarska, 1959) (male, dorsal view), note lack of the scapular plate faceting, the arrowhead indicates dentate collar on legs IV, and empty arrowheads point enlarged cephalic papillae; B. tatrensis, sexual dimorphism in the pore size: 26—female; 27—male.Note numerous true pores distributedon all plates.Scale bars in µm.