Wingstrandarctus unsculptus

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 : 420-423

Description of Wingstrandarctus unsculptus nov. sp.

Diagnosis. Head with three cephalic vesicles, each filled with symbiotic bacteria, the lateral vesicles are not fused. The dorsal cuticle appears smooth without mammiliform sculpture. The caudal ala is broad with a large incision. The frontal ala is well-developed with a basal bacterial vesicle. Cephalic sense organs relatively long; the primary clavae are approximately double the length of the lateral cirri. All leg sense organs present; those on the fourth leg are slightly S-shaped. Six pairs of unicellular epidermal glands; two pairs in the cephalic region and one pair in each trunk segment.

Type material. The holotype is an adult female [ ZMUC TAR 1295] collected on 11 January 1999 from carbonate sand inside Fish Rock Cave (Fig. 8). Only three specimens of Wingstrandarctus unsculptus nov. sp. were collected from the samples ( Table 1 ). The paratypes are an allotypic male (Fig. 9) and a young adult mounted for SEM (Fig. 10). The type material is deposited at The Natural History Museum of Denmark, University of Copenhagen, Denmark.

Etymology. The name unsculptus refer to the unsculptured dorsal cuticle of this new species.

Description of the holotype. The holotypic female is 141 µm long and 86 µm wide between the second and third leg pair (Fig. 8). The head is well separated from the body with a small round swelling posterior to the common pedestal for the primary clava and the lateral cirrus. Three unfused cephalic vesicles filled with bacteria are present; one anterior and two lateral. The body is nearly ovoid and not dorso-ventrally flattened (Fig. 10A; SEM of paratype).

A halechiniscid complete set of 11 cephalic appendages are present. All the cephalic cirri consist of a large scapus and a well-developed flagellum. The median cirrus is 14 µm long; internal cirrus 27 µm and partly embedded in the frontal ala; external cirrus 21 µm long with a simple, undifferentiated flagellum and inserted ventrally; lateral cirrus 23 µm long and shares its cirrophorus with the primary clava. The primary clava is 60 µm long and slender. The 30 µm long secondary clavae are flat and unfused with a projection reaching the mouth cone from both sides (Figs 8 and 10B; SEM of paratype).

The buccal tube is 34 µm long. Three apodemes in front of the large straight placoids (14 µm long). The stylets are very long (39 µm) and stylet supports are lacking. The anus is covered with two overlapping folds and a caudal minor fold giving it a characteristic wave-like appearance. The distance is 13 µm between the gonopore and the three-lobed anus. Two seminal receptacles with an S-shaped duct and a well defined circular vesicle are filled with spermatozoa. The seminal receptacles open posterior to the rosette-shaped gonopore.

FIGURE 8. Drawing of the holotypic female of Wingstrandarctus unsculptus nov. sp. (ventral view). Abbreviations: al1–3—lateral ala 1–3; an—anus; bt—buccal tube; 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; mg—midgut; ov—ovary; pc—primary clava; pl—placoid; sc—secondary clava; se1–4—leg sense organs 1–4; sr—seminal receptacle; st—stylet; uc—unicellular epidermal glands; vo1—“van der Land’s organ” of primary clava.

FIGURE 9. Drawing of the allotypic male of Wingstrandarctus unsculptus nov. sp. (lateral view) on a carbonate sand grain. Note the long primary clava. Abbreviations: al1-3—lateral ala 1–3; bv—bacteria filled vesicle; ca—caudal ala; cE—cirrus E; ec—external cirrus; fa—frontal ala; ic—internal cirrus; lc—lateral cirrus; mc—median cirrus; pc—primary clava; pl—placoid; sc—secondary clava; se4—leg sense organ 4; sv—seminal vesicle; te—testis.

Each leg consists of a coxa, femur, tibia and tarsus. Unsegmented leg sense organs present on all legs. The leg sense organs on legs I–III have a wrinkled base (Fig. 10C). The first three sense organs are of identical length measuring 13 µm; that on leg IV is 15 µm long with a small but distinct “van der Land’s organ”, slightly S-shaped and without a flagellum (Fig. 8).

A dorsal spur is present only on the internal claws whereas the external claws each have an avicularia appearing as a small notch and a prominent dorsal calcar. 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. No spiral-like folds on the internal or external digits.

The long cirrus E (44 µm) is three-segmented with a large cirrophorus (6 µm), corrugated scapus (11 µm) and a long flagellum (27 µm). The dorsal cuticle is unsculptured. There are six pairs of unicellular epidermal glands; two pairs in the cephalic region and one pair in each trunk segment.

The body is surrounded by six well developed alae with fine punctuation without caestus. The frontal ala is well defined consisting of a thin membrane with a basal bacteria filled frontal vesicle. The anterior part of the anterio-lateral ala with two small incisions. The anterior and posterior part of the anterio-lateral ala is only separated by a cuticular fold. The posterior part of the anterio-lateral ala with a single small incision. The posteriorlateral ala is well separated from the anterio-lateral ala and "butterfly-wing" shaped with a distinct incision. The caudal ala is very broad with a single distinct circular incision and covers the legs from a dorsal view.

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

Remarks. The allotypic male [ZMUC TAR 1296] is 156 µm long but with 75 µm long primary clavae (Fig. 9). The primary clavae of the male is much longer than in the female, a sexual dimorphism already mentioned in Wingstrandarctus corallinus . The caudal ala is not as broad as in the female, suggesting that sexual dimorphism exists in Wingstrandarctus unsculptus . With its long tapering primary clavae, claw figuration and large incision of the caudal alae, W. unsculptus shows closest affinity to W. intermedius . However, Wingstrandarctus corallinus , W. crypticus , W. intermedius and the presently described W. stinae all have a very characteristic dorsal mammiliform cuticular structure, whereas Wingstrandarctus unsculptus has a smooth dorsal cuticle (Fig. 9) similar to some Florarctus (e.g. F. hulingsi ). The position of W. unsculptus in Wingstrandarctus is supported by the lack of procuticular caestus in the alae and distinct secondary clavae, which are not H-shaped and fused around the mouth cone as in Florarctus . The observed secondary sexual dimorphism in the primary clava and partly in the caudal ala is also seen in several Florarctus species, e.g. the type species F. h e i m i.

FIGURE 10. SEM of Wingstrandarctus unsculptus nov. sp. A. Ventrolateral view. B. Close-up of head. C. Close-up of claws and leg sense organ 1 on withdrawn first leg. Abbreviations: ed—external digit; go—gonopore; ic—internal cirrus; id—internal digit; lc—lateral cirrus; mc—median cirrus; mo—mouth cone; pc—primary clava; sc—secondary clava; se1—leg sense organ 1.