Raiarctus katrinae

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 : 427-429

Description of Raiarctus katrinae nov. sp.

Diagnosis. A characteristic cuticular ala-like structure supported by relatively long pillars surrounds the whole body. An additional row of pillars is embedded in the cuticle above the head, adding a second ala-like structure to the ovoid body. The dorsal epicuticle is supported by minor pillars arranged in parallel lines in six dorsal cuticular plate-like structures. The head has the Halechiniscus - type characteristic sense organs of club-shaped primary clavae with “van der Land’s organs” placed on the head appendage beside the lateral cirri. A small cuticular droplet is seen on the buccal tube between the three-lobed pharyngeal bulb and the bulbous mouth cone. The sense organ of the first leg arises from a minor basal cirrophorus on the coxa. The sense organ on leg IV comprises a cirrophorus and an ovoid-shaped scapus without a thread-like flagellum; “Van der Land’s organ” is not visible. The somatic cirrus E penetrates the dorsal epicuticle. Digits are of equal shape. A pad-like structure is visible dorsally, between the large folds of the internal digits. Each digit with a 3-pointed crescent claw. At the base of the digits of all four leg pairs is a prominent Styraconyx -like horizontal peduncle.

Type material. The holotypic female [ ZMUC TAR 1299] was collected on 11 January 1999 at Fish Rock Cave. Three additional paratypes were collected from Jim’s Cave. The material is deposited in The Natural History Museum of Denmark, University of Copenhagen, Denmark.

Etymology. The name honours Katrine Worsaae for her contribution to the knowledge of meiofauna in marine caves.

Description of the holotype. The holotypic female is 122 µm long and 70 µm wide between second and third legs pair (Figs 13–14). A characteristic cuticular ala-like structure supported by 112 relatively long pillars (10–15 µm long) surrounds the whole body. An additional row of pillars, embedded in the cuticula above the head, covers the prominent cirrophorus of the median cirrus, adding a second ala-like structure to the ovoid body. The dorsal epicuticle is supported by short 3 µm long pillars arranged in parallel lines within six dorsal cuticular plate-like structures (Figs 13 and 14A). The head has the 11 characteristic sense organs of the Halechiniscus - type; however, the secondary clavae are indistinct. The 23 µm long median cirrus consists of a prominent scapus and a large flagellum. The 23 µm internal cirrus has a prominent scapus and a composite flagellum with a thinner distal section. The 25 µm external cirrus comprises a prominent scapus and long, simple, undifferentiated flagellum. The 37 µm lateral cirrus extends from the large ventro-lateral head appendage and comprises a large cirrophorus, a thinner scapus and a long narrow flagellum with a thread-like proximal part. The 12 µm club-shaped primary clava has a “van der Land’s organ”, and is placed on the same head appendage as the lateral cirrus.

The 21 µm long buccal tube, with a characteristic small cuticular droplet, connects the three-lobed pharyngeal bulb with the mouth opening. The latter is situated in the centre of a bulbous mouth cone. The needle-shaped stylets, with characteristic well developed furcae distally, are 20 µm long. The straight stylet supports measure 7 µm and are attached to the buccal tube and the stylet furcae. Three hooked placoids are visible in the three-lobed pharyngeal bulb ( Fig. 14 B). A short esophagus connects the pharyngeal bulb to a large empty intestine, which ends at a posterior anus. The anus has a typical ovoid appearance and is covered with two large overlapping folds as well as a minor caudal fold with a wave-like pattern. The gonopore is located on an ovoid papilla surrounded by a rosette of six cells. The distance between gonopore and anus is 7 µm. The reproductive system consists of a single ovary with a single ovum and a very large oocyte. Nurse cells in the upper part of the ovary were not visible neither were seminal receptacles or spermatids.

The junction between coxa and femur are not telescopic, whereas the junction between femur and tibia are strongly telescopic. The sense organ of the first leg arises from a minor basal ring or cirriphorus on the first leg coxa, comprising a short scapus and a tube-like flagellum with a combined length of 7 µm. The leg sense organs on the coxa of the next two pairs of legs are of equal length and shape consisting of a simple, 8 µm long cirrus. The sense organ on leg IV is 12 µm long and consists of a cirrophorus and an ovoid-shaped scapus without a thread-like flagellum. The “van der Land’s organ” is not visible. The 26 µm cirrus E projects through the dorsal epicuticle and consists of a tiny cirrophorus, a slender scapus with a long equally slender flagellum.

Each tarsus has four digits. On all four pairs of legs (I–IV) the digits have the same configuration. On the first three pair of legs there are two shorter (7 µm) external digits and two larger (8 µm) internal digits. A pad-like structure is visible dorsally between the large folds of the internal digits. On the fourth leg pair the external digits measures 8 µm and the internal digits 12 µm. Each digit has a 3-pointed crescent-shaped claw consisting of a thin accessory hook, the main claw and a secondary hook. Each claw may be covered by a membranous sheath. At the base of the external digits in all four leg pairs is a prominent Styraconyx -like horizontal peduncle. Claw glands are visible in the coxal part of each leg.

Morphometric data of the holotype of Raiarctus katrinae nov. sp. are presented in Table 2.

Remarks. The Australian Raiarctus katrinae nov. sp. is very similar to R. aureolatus , however, several differences can be recognised. Compared with the type description of R. aureolatus , the Australian animals are larger. The cap-like row of pillars embedded in the cuticula, which add a second ala-like structure to the dorsal epicuticle in R. katrinae , is not described in R. aureolatus . Nor is the arrangement of the short pillars in parallel lines embedded in the six dorsal cuticular plate-like structures.

The primary clava seems to be more cone-like in the R. aureolatus holotype, and thus differ from the clubshaped organs of the current species. This difference could, however, simply be a consequence of different degrees of compression in the mounted specimens. In R. katrinae nov. sp. (and R. jesperi nov. sp.) the internal cirri consist of a large scapus and a slender composite flagellum divided into proximal and distal sections whereas in R. aureolatus , R. colurus and R. variabilis the flagellum is simple. The composite flagellum of the lateral cirrus is a unique character for R. katrinae nov. sp. as other Raiarctus species have a simple flagellum.

The small cuticular droplet seen on the buccal tube was not described in R. aureolatus . The first leg sense organ arising from a small basal cirriphorus ring on the coxa and continuing in a small scapus and a tube-like flagellum has been seen in several Raiarctus species (pers. obs. R.M. Kristensen), but was not described in R. aureolatus . Furthermore the sense organ of the fourth leg does not have the short flagellum, which is present in the other species of Raiarctus . Cirrus E penetrates the dorsal epicuticle in the Australian type; though this is not clear in R. aureolatus . The pad-like structure in-between the large folds of the internal digits described in the Australian Raiarctus nov. sp. is not described in R. aureolatus , neither are the prominent Styraconyx -like horizontal peduncles. The pad-like structures and horizontal peduncles are present in R. colurus , R. jesperi nov. sp. and R. variabilis . Genital papillae, which are openings for the receptacula semini, are not clearly visible in the Australian material. The genital papillae have been shown for females in R. aureolatus ( Kristensen & Neuhaus 1999) and R. variabilis (D’Addabbo Gallo et al. 1986) .

FIGURE 13. Drawing of the holotypic female of Raiarctus katrinae nov. sp. (dorsal view). Abbreviations: an—anus; cE—cirrus E; cg—claw gland; ec—external cirrus; go—gonopore; ic—internal cirrus; lc—lateral cirrus; lp—lateral pillar; mc—median cirrus; ov—ovary; pb—pharyngeal bulb; pc—primary clava; pd—peduncle; pi—cuticular pillars; se1–4—leg sense organs 1–4.

Figures

FIGURE 14. LM of Raiarctus katrinae nov. sp. A. Dorsal rows of pillars. B. Buccal apparatus. Abbreviations: bt—buccal tube; cE—cirrus E; cp—caudal pillar; fp—frontal pillar; lp—lateral pillar; pc—primary clava; pl—placoids; ro—row of pillars; ss—stylet support; st—stylet.