Wingstrandarctus stinae

Jørgensen, Aslak, Boesgaard, Tom M., Møbjerg, Nadja & Kristensen, Reinhardt M., 2014, The tardigrade fauna of Australian marine caves: With descriptions of nine new species of Arthrotardigrada, Zootaxa 3802 (4), pp. 401-443 : 417-420

Description of Wingstrandarctus stinae nov. sp.

Diagnosis. Head with three cephalic vesicles, each filled with symbiotic bacteria, the lateral vesicles are not fused. Dorsal mammilliform cuticular sculpture. The caudal ala has a small incision. The cephalic sense organs are relative short, especially the primary clavae, which are of equal size to the lateral cirri. The short primary clava have a medial incision. All leg sense organs are present, fourth leg sense organs are straight with a diminutive flagellum. Seven pairs of star-shaped unicellular epidermal glands with small cytoplasm rays; one pair belonging to the cephalic region, three pairs in the first trunk segment and one pair in the other trunk segments.

Type material. The holotype is an adult female [ ZMUC TAR 1293] in simplex stage with genital duct openings for seminal receptacles and fully developed gonopore. Newly synthesized claws appear from claw glands in each coxa. The specimen was collected on 11 January 1999 from carbonate sand inside Fish Rock Cave. One of the paratypes is a young adult female 118 µm long. The primary clavae are very short (22 µm). It is not in moult; therefore, the length of the stylets (37 µm) can be measured. Stylet supports are lacking. The third specimen is mounted for SEM. A total of eight specimens of Wingstrandarctus were retrieved of the sediment samples from Fish Rock Cave; three were W. stinae nov. sp., two W. corallinus and three W. unsculptus nov. sp. ( Table 1 ). The type material is deposited in The Natural History Museum of Denmark, University of Copenhagen, Denmark.

Etymology. The name honours the scientific illustrator Stine B. Elle who’s work is feaured in this study.

Description of the holotype. The holotypic female is in simplex stage, 120 µm long and 76 µm wide between leg pairs II and III (Fig. 6). Body ovoid with an anterior head which appears separated from the rest of the body by a furrow (Fig. 7A; SEM of paratype). Anteriorly the head is slightly curved with a complete halechiniscid set of 11 cephalic appendages and three cephalic vesicles, one frontal and two lateral, each filled with associated symbiotic bacteria. Two apparently unfused lateral vesicles surround the protruding mouth area, the buccal tube and the stylets. The frontal vesicle is also filled with symbiotic bacteria and is placed anteriorly around the median cirrus.

The 20 µm long median cirrus is placed close to the margin of the head and consists of a conical scapus and a thin composite flagellum divided into proximal and distal sections. The 19 µm internal cirrus consists of a strong scapus with a composite flagellum divided into proximal and distal sections, each of the three parts are of comparable length. The 13 µm external cirrus is comprises a minor scapus and a simple flagellum. The 24 µm lateral cirrus shares its cirrophorus with the primary clavae (Fig. 6). From the cirrophorus the lateral cirrus continues in a strong scapus and a long undivided thread-like flagellum. All cephalic cirri are free and not imbedded in the small frontal ala (Figs 6 and 7B). An incision is located in the middle of the robust and short (25 µm long) primary clava; it extends from the joint cirrophorus in which a “van der Land’s organ” is clearly visible. The secondary buccal clavae are lying ventrally between the three cephalic vesicles and the mouth cone. Each secondary clava is located separately on each side of the mouth cone.

From the short esophagus the pharyngeal bulb is connected to the large apparently empty intestine which ends at a posterior anus. The anus is covered with two overlapping folds and a caudal minor fold giving it a characteristic wave-like appearance. The gonopore is located on a large ovoid papilla surrounded by a rosette of six myoepithelial cells typical of arthrotardigrades. The distance between gonopore and anus is 12 µm. The reproductive system consists of an ovary with a large ovum and six smaller oocytes. The two lateral cuticular seminal receptacles are visible at the level between leg pair III and IV, each consists of a large spheroid vesicle located dorsolaterally and an S-shaped genital duct, which ends in a ventro-caudal opening. The spheroid vesicle is filled with mature spermatozoa.

Each leg consists of a coxa, femur, tibia and tarsus. Leg sense organs are present on all legs. The first three sense organs are of equal length measuring 9 µm. The sense organ on leg IV is 10 µm long and consists of a straight slender cone-like scapus with a diminutive flagellum.

Each tarsus with four digits; on the leg pairs I–III two shorter external digits of equal length (6 µm) and two larger internal digits of equal length (8 µm) are present (Figs 6 and 7C; SEM of paratype). The external digits on leg pair IV are 6 µm long and the internal digits 9 µm. The internal digits in all leg pairs have spiral-like folds. A short dorsal spur is present only on the internal claws whereas calcars are present in all claws. Strong hook-shaped peduncles are seen at the bases of the external digits in all leg pairs. The hook of the peduncle is partly located in the tarsus. Claw glands in each coxa contain visible claws for the next cuticle stage.

The cirri E are 42 µm long, each comprising a 5 µm long robust cirrophorus and a 15 µm long scapus with a 22 µm long thread-like flagellum (Figs 6 and 7D; SEM of paratype). The dorsal cuticle is sculptured by fine mammaelike dots. The ventral cuticle has a fine punctuation formed by very small pillars. A total of seven pairs of unicellular epidermal glands are observed; one of the cephalic pairs is located anterio-dorsally close to the base of the median cirrus, the two other cephalic pairs form a row of four epidermal glands very close to or in the first trunk segment. The pairs in the three other trunk segments are located dorso-laterally. Usually the unicellular glands are highly refractive, but in moulting animals, as the holotype, they can be difficult to observe.

FIGURE 6. Drawing of the holotypic female of Wingstrandarctus stinae nov. sp. (dorsal view). Abbreviations: al1-3 lateral ala 1–3; an—anus; bv—bacteria filled vesicle; ca—caudal ala; cE—cirrus E; ec—external cirrus; fa—frontal ala; go—gonopore; ic—internal cirrus; lc—lateral cirrus; mc—median cirrus; ov—ovary; pc—primary clava; sb—symbiotic bacteria; se1–4—leg sense organs 1–4; sm—mouth opening on simplex stage; sr—seminal receptacle; uc—unicellular epidermal glands; vb1—“van der Land’s organ” of primary clava.

FIGURE 7. SEM of Wingstrandarctus stinae nov. sp. A. Dorsolateral view. B. Close-up of head. Note that the primary clava is broken. C. Close-up of tarsus on second leg. D. Close-up of cirrus E. Abbreviations: cE—cirrus E; ec—external cirrus; ed—external digit; ic—internal cirrus; id—internal digit; lc—lateral cirrus; mo—mouth cone; pc—primary clava; se3–4—leg sense organ 3–4.

Thin expansions of the dorsal cuticle appear as five large alae with a fine punctuation. The frontal ala is not well-developed and can only be observed dorsally as a thin membrane. The frontal vesicle with bacteria is not located in this ala. Anterio-lateral alae are split by a deep furrow, so they look like two separate parts. The posteriolateral alae are small about the same size as the caudal ala. The caudal ala has a weak distal incision.

In the periodically molting stage (simplex stage) the new body cuticle and the cuticle of the intestinal system including the buccal tube, stylets and placoids are resynthesized from large glands (so-called salivary or stylet glands) which are visible in the buccal area. During this period the animal does not feed and the mouth appears sealed (Fig. 6).

Morphometric data of the holotypic female of W. stinae nov. sp. are presented in Table 2.

Remarks. Wingstrandarctus stinae nov. sp. shares many characters with other Australian florarctids, especially W. corallinus and W. crypticus and fewer with W. intermedius and W. unsculptus nov. sp. Wingstrandarctus stinae nov. sp. and W. corallinus have small caudal alae wereas W. intermedius and W. unsculptus nov. sp. have larger divided caudal alae, which is comparatively larger in the females. However, instead of an S-shaped spine on leg IV as in all other Wingstrandarctus species, W. stinae nov. sp. has a straight and strongly developed spine. A large furrow in the anterio-lateral ala, a short but robust primary clava with a medial incision and different morphology of the leg IV spine, constitute the unique characters that define W. stinae nov. sp. as a new species.