Claxtonia goni, Degma & Meyer & Hinton, 2021

Degma, Peter, Meyer, Harry A. & Hinton, Juliana G., 2021, Claxtonia goni, a new species of Tardigrada (Heterotardigrada, Echiniscidae) from the island of Maui (Hawaiian Islands, U. S. A., North Pacific Ocean), with notes to the genus Claxtonia Gąsiorek & Michalczyk, 2019, Zootaxa 4933 (4), pp. 527-542 : 529-535

Claxtonia goni sp. nov.

( Figs 1–21 , Tables 1–3)

Type locality. U.S.A., Hawaiian Islands , SE Maui island, Central Crater District of Haleakalā National Park, ‘a‘ā lava flow adjacent to trail near ‘Ō‘ilipu‘u cinder cone, estimated coordinates 20°43’00”N 156°09’30”W, estimated altitude 2096 m asl .

Type material. Holotype: adult female, type locality, substrate not specified, collected 10.11.1985 by S. M. Gon, R. B. Kimsey, and M. A. Willis (slide S-0001814).

Paratypes (all from Central Crater District of Haleakalā National Park ): two adult females, pāhoehoe lava flow, E of ‘Ō‘ilipu‘u cinder cone, substrate not specified, estimated coordinates 20°43’00”N 156°09’20”W (linear distance from type locality nearly 300 m), 2018 m asl, collected 07.1985 by S. M. Gon, R. B. Kimsey and M. A. Willis (slides S-0001816 and S-0001819); one adult, sex unidentified, summit Kūiki, substrate not specified, estimated coordinates 20°42’30”N 156°08’10”W (linear distance from type locality about 2500 m), 2286 m asl, collected 13.08.1985 by S. M. Gon (slide S-0001818) .

Type depositories. Type material is deposited in the collection of Robert O. Schuster, the R. M. Bohart Museum of Entomology, University of California, Davis , California, USA. Photographs of examined slides with all their labels are available in http://mywaterbears.org/imglib/tardigrade/ Bohart _ Tardigrada /201412/S-0001814_1418153310.jpg, http://...S-0001816_1418153368.jpg, http://...S-0001818_1418153406.jpg and http://...S-0001819_1418153434.jpg ).

Etymology. The specific name goni is a genitive noun given in honour of Samuel M. ʻOhukaniʻōhiʻa Gon III, Senior Scientist and Cultural Advisor at the Nature Conservancy of Hawaiʻi, in recognition of his contributions to the study of Hawaiian tardigrades.

Description of the holotype (most measurements in Table 1, others as follow). Adult female, placed ventrolaterally with body colour imperceptible and without visible eye spots (neither body colour nor presence/absence of eyes were mentioned on slide labels) ( Figs 1–3 ).

Internal cephalic cirrus much shorter than external (both cirrophores 2.0 μm long) ( Figs 4–5 ). Broad oval cephalic papilla with apex broadly rounded from the midpoint; basal diameter 3.7 μm and maximal width, at the midpoint, 5.2 μm (82.2% of the length) ( Figs 4–5 ). Lateral cirrus A in the shape of filament; the cirrophorus 3.3 μm long (only the basal portion of the left cirrus A preserved) ( Figs 3 , 5 ). Thin clava with rounded apex from the apical third (more tapering in the distal side from cirrus A while adjoining side is straighter); the basal diameter 2.7 μm and maximal width, in the basal third, 2.9 μm (52.9% of its length) ( Figs 4–5 ). Ratio of maximal widths of clava and cephalic papilla is 55.8%. Cirrus A is the only trunk appendage present ( Figs 1–3 ).

Cephalic plate with shallow median anterior depression in the shape of a letter ‘Y’ with long branches oriented antero-laterally ( Fig. 5 ). Scapular plate without any ridges ( Fig. 6 ). Paired plates I and II shortest along antero-caudal median body axis and transversally deepen in the anterior third ( Figs 7–10 ). Terminal plate with two posterolateral incisions and without faceting ( Figs 11–13 ). Cephalic, neck, scapular, median 1, median 2 and terminal plates undivided ( Figs 1–2 , 6–13 ). Both median plates 1 and 2 have laterally joined two lateral platelets (one on each side) equally wide as the lateral margins of adjacent median plates but subsequently tapering towards the lateral margins, which are approximately on the level of lateral margins of the adjoining plates (scapular plate, paired plates I and II) ( Figs 8, 10 ). Median plate 3 ( Figs 12–13 ) and ventral plates ( Fig. 3 ), absent. Anterior and posterior boundaries of dorso-lateral plates and platelets well marked with the exception of barely visible boundary between cephalic and neck plates ( Figs 2 , 5 ), anterior boundaries in the first pair of lateral platelets ( Figs 2 , 8 ), and first median plate ( Figs 2 , 7–8 ). Lateral margins of dorso-lateral plates and platelets and the edges of leg plates on I–III pair of legs marked less distinctly ( Figs 2 , 4–6, 9–10 ) than those in terminal plate ( Figs 2 , 12–13 ). Vague, elongated pulvinus on outer side of each leg just above the leg plate present ( Figs 1 , 17 ). Cuticular bars on inner leg sides just above bases of claws, distinct ( Figs 3 , 16, 18–19 ).

The surface sculpture of the plates (with some exceptions described below) consists of simple flat, irregularly polygonal (mostly penta- or hexagonal) tubercles of different sizes, up to 2.3 µm in diameter (in several of the largest tubercles), densely spaced as though tiled ( Fig. 2 ). This sculpture has the appearance of a system of dark patches when using 40x PhC lens ( Fig. 1 ). Under oil immersion 100x lens the space separating the epicuticular tubercles reveals a crown of round (slightly out of focus under PhC—apparently just weakly sloped), shallow dimples, i.e. pseudopores (0.2–0.3 µm, sometimes 0.4 µm in diameter), which form a more or less distinct hexagonal pattern around each tubercle ( Figs 12–13 ). Similar, but smaller and less developed sculpture (smaller tubercles, pseudopores around tubercles invisible), covers the anterior third of both paired plates I and II (before their transversal depression), lateral platelets, anterior parts of area between paired plates I and median plate 2, and the area corresponding to the median plate 3 ( Figs 1 , 8, 10, 12–13 ). Only granulation (most frequently 0.2–0.3 µm and alternatively 0.1 or 0.4 µm in diameter) covers a narrow transverse band on the neck plate just before a scapular plate, caudal corners of the cephalic plate, and leg plates on outer surface of legs ( Figs 1–2 , 4–5 , 8 , 17–19 ). In addition to the surface sculpture (of large tubercles, pseudopores, and granulation), irregularly and remotely distributed deep pores (under PhC having an appearance of round white spots), with most frequent diameter 0.3 µm (range: 0.2–0.4 µm), occur randomly on plates or parts with fully developed sculpture (i.e. with the exception of anterior third of both paired plates I and II, lateral platelets and leg plates; Figs 1–2 , 6 –15,17).

Focusing the 100x PhC oil immersion to under the surface of plates, the aforementioned pseudopores disappear and the subsurface structure of each tubercle appears in a form of a rosette of more or less round and in focus dark spots inside the perimeter of the tubercle and delimited by the peripheral spots (about 0.2–0.3 µm in diameter, 1–10 or a bit more spots per a tubercle depending on its size; Figs 6–11 , 14 ). Under DIC these spots appear as groups of granules ( Figs 5 , 13 , 15 , 17 ). These spots/granules are apparently intracuticular pillars that reinforce the tubercles internally.

The rest of the cuticle (unsculptured portions of neck plate and the cuticle out of plates including ventral body side) has an appearance of tiny, dense and regularly distributed dots/granules (depending PhC or DIC observation), not protruding above the cuticle surface and thus formed by intracuticular pillars (0.1–0.2 µm in diameter) (e.g. Figs 4–5 , 10, 12–13 , 19 ).

Claws on each leg well developed, basal portion straight, bent in the last third (broadest region), and continued with fluent arc to the apex ( Figs 16, 18–19 ). External claws slightly shorter than internal and claws on the hind legs are the longest. Internal claws in all legs with a well-developed rather protruding spur, oriented downwards (longer on hind legs), which is connected to the main claw at between the second fifth and a half the height (spur connection positions in the first and fourth pairs of legs 4.9 μm and 5.6 μm from the claw base respectively; thus 46% of the claw length). All external claws without spurs ( Figs 16, 18–19 ). Spine or papilla on the first three pairs of legs, absent. Drop-shaped papilla with rounded apex and dentate collar with mostly slender, triangular, sharp teeth having single tip and unequal base (0.4–1.5 μm) present on the fourth pair of legs. Tooth height (0.6–1.7 μm; the base of each tooth mostly shorter than the height with one exception) and very unequally spaced (some adjoining teeth in contact and others more remote—maximally 3.1 μm) ( Figs 17–19 ).

Eggs unknown.

Variability. Paratypes are similar to the holotype with slight differences when compared to the holotype—the delimitation of cephalic and neck plates is more visible in one paratype ( Fig. 20 ) and paired plates II apparently have a preterminal groove in another paratype ( Fig. 21 ). Measurements and morphometric indices of the holotype and the entire type series are given in Tables 1–3 .

Figures

FIGURES 1–3. Claxtonia goni sp. nov., habitus of the holotype: 1—dorso-lateral view, PhC; 2—dorso-lateral view, DIC; 3—ventro-lateral view, PhC. Scale bars: 50 μm; indented arrowheads—pulvini, flat arrowheads—cuticular bars.

FIGURES 4–5. Claxtonia goni sp. nov., cephalic structures of the holotype: 4—cephalic cirri, cephalic papilla, and clava (ventro-lateral view), PhC; 5—cephalic appendages and cephalic and neck plates (dorso-lateral view), DIC. Scale bars: 20 μm; arrows—some observable intracuticular pillars.

FIGURES 6–13. Claxtonia goni sp. nov., dorso-lateral cuticular plates of the holotype: 6—scapular plate, PhC; 7—median plate 1 and paired plates I (focused on posterior portion of paired plates), PhC; 8—first lateral platelet and paired plates I (focused on anterior portion of paired plates), PhC; 9—median plate 2 and paired plates II (focused on posterior portion of paired plates), PhC; 10—second lateral platelet, paired plates II (focused on anterior portion of paired plates), and area between paired plates II and caudal plate, PhC; 11–12—caudal plate, PhC; 13—caudal plate, DIC. Scale bars = 20 μm; 6–11 focused on the subsurface pattern, 12–13 focused on the surface of the plate; arrows—positions of lateral platelets.

FIGURES 14–15. Claxtonia goni sp.nov., details of the subsurface structure of the caudal plate of the holotype (NB: pores appear as white spots): 14—PhC; 15—DIC. Scale bars = 2 μm; arrows—pores; the same section in both figures.

FIGURES 16–19. Claxtonia goni sp. nov., legs of the holotype: 16—claws of first two legs, PhC; 17—pulvinus, leg plate, dentate collar and papilla on hind leg, DIC; 18–19—claws, dentate collar and inner cuticular bars on hind legs, PhC and DIC (inset with claw measurements: C—claw length, S—spur length, P—distance of spur position; not scaled). Scale bars = 20 μm; indented arrowhead—pulvinus, flat arrowheads—cuticular bars, arrows—several areas with well visible intracuticular pillars.

FIGURES 20–21. Claxtonia goni sp. nov., paratypes: 20—delimitation of cephalic and neck plates (paratype on slide S- 0001819), PhC; 21—dorso-lateral plates (paratype on slide S-0001816), PhC. Scale bars = 20 μm (Fig. 20) and 50 μm (Fig. 21); arrows—several areas with obvious intracuticular pillars.