Hypechiniscus exarmatus (Murray, 1907) LCM

Gąsiorek, Piotr, Oczkowski, Artur, Blagden, Brian, Kristensen, Reinhardt M., Bartels, Paul J., Nelson, Diane R., Suzuki, Atsushi C. & Michalczyk, Łukasz, 2021, New Asian and Nearctic Hypechiniscus species (Heterotardigrada: Echiniscidae) signalize a pseudocryptic horn of plenty, Zoological Journal of the Linnean Society 192 : -

THE HYPECHINISCUS EXARMATUS MORPHOGROUP

SPECIES: HYPECHINISCUS CATARACTUS GĄSIOREK, OCZKOWSKI, KRISTENSEN & MICHALCZYK, SP. NOV.

Zoobank registration: 49CA86F7-0A6E-4909-AC49- 8F13A5DE2964.

( FIGS 16–19, 26F; TABLES 11–13)

Description

Females (i.e. from the third instar onwards; measurements and statistics in Table 11): Body translucent to white, cylindrical ( Figs 16A, C, 17A–C), with minute spheroid black eyes present after mounting. Elongated, dactyloid cephalic papillae (secondary clavae) and (primary) clavae ( Figs 16A, C, 17A, C, 18A); peribuccal cirri without cirrophores ( Fig. 18A). Cirrus A short, with cirrophore. Cirrus dorsalis absent.

Minute and densely arranged endocuticular pillars present (see the pillars exposed by a fragment of detached epicuticle in Fig. 17B, arrowhead), however their capituli (heads) are not visible either under LCM or SEM, thereby giving the cuticle an unsculptured appearance. Dorsal plates are thus uniformly grey in PCM ( Fig. 16A), and smooth in NCM and SEM ( Figs 16C, 17A, B, 26F). The cephalic plate is large and pentapartite, with two small anterior portions, a central keel-like portion, and two larger trapezoid posterior portions ( Figs 16A, 17A, B). The cervical (neck) plate is not visible in LCM and is reduced to an anterior thickening of the scapular plate ( Fig. 17A, B). The scapular plate divided into four parts by horizontal and longitudinal sutures ( Figs 16A, 19A). Three median plates, all weakly outlined and unipartite, with false secondary sutures dividing them into smaller subparts ( Figs 16A, 19A) and five pairs of lateral intersegmental platelets flanking their borders ( Fig. 19A). Two pairs of large segmental plates with very short incisions at their anterior and posterior margins, and folds of cuticle that subdivide them into smaller portions ( Figs 17A, 19A). Caudal (terminal)

824 P. GĄSIOREK ET AL .

plate large, with poorly marked incisions ( Figs 17A, 19A).

Ventral cuticle with a clear species-specific pattern of ornamentation that extends to the lateroventral margins of the body ( Fig. 19B). Ornamentation composed of endocuticular pillars of two sizes: large pillars forming a pseudoplate in the subcephalic zone, at the level of legs I, and a pair of genital pseudoplates; and smaller pillars forming thin stripes and an additional two pseudoplates at the level of legs II–III. Importantly, epicuticular thickenings are absent, thus the venter appears smooth under SEM ( Fig. 17C).

Pedal plates, belts of pillars, pulvini, and dentate collar IV absent ( Fig. 16A). A small spine or papilla on leg I absent and a papilla on leg IV present (LCM and SEM; Fig. 17A, C). Claws minute and resembling those of Pseudechiniscus . Claws IV higher than claws I–III. External claws on all legs smooth. Internal claws with small spurs positioned at c. one-quarter of the claw height and strongly bent downwards. Pseudoaccessory points absent ( Fig. 18B–D).

Males and sexually dimorphic traits (i.e. from the second instar onwards; measurements and statistics in Table 12): Almost identical to ♀♀, i.e. sexual dimorphism rudimentary, as even the clavae are of similar lengths and shapes in both sexes. The ♂♂ are significantly different from ♀♀ only in body size (see Figs 16B, 17D) estimated as mean body length ± SD: 153 ± 12 Μm vs. 179 ± 13 Μm (one-tailed Welch’s t -test with N ♀♀ = 15 and N ♂♂ = 10: t 21 = 5.31; P <0.001); and as average scapular plate length: 15.4 ± 1.5 Μm vs. 18.6 ± 1.9 Μm (t 22 = 4.58; P <0.001). The bs ratios for both sexes overlap (0.32– 0.37 in N = 10 ♂♂ vs. 0.33–0.43 in N = 15 ♀♀).

Juveniles (i.e. the second instar, sexually immature females; measurements and statistics in Table 13): Except for the lack of the gonopore, no qualitative differences with respect to adults were observed. Clearly smaller than adult females.