Angursa abyssalis Renaud-Mornant, 1981

Fujimoto, Shinta & Hansen, Jesper Guldberg, 2019, Revision of Angursa (Arthrotardigrada: Styraconyxidae) with the description of a new species from Japan, European Journal of Taxonomy 510, pp. 1-19 : 5-7

Angursa abyssalis Renaud-Mornant, 1981

Figs 2–3

Emended diagnosis

Angursa with club-shaped primary clavae longer than lateral cirri; pedestals of primary clavae and lateral cirri absent; flat, distorted-oval secondary clavae; flat, oval tertiary clavae slightly indented near external cirri; tapering cirri E with basal scapi; leg I sensory organs present; legs II and III sensory organs absent; leg IV sensory organs each as papilla enveloped in hemispherical cuticular sheath with short, apical spine; anal papillae absent.

Material examined

Holotype ATLANTIC OCEAN • adult ♀; Southeast Atlantic , collected from off Angola; 2063 m deep site; 12°03′ 3 S, 12°20′ 5 E; Dinet leg.; MNHN AF 05/77 Ma.

Additional specimens ATLANTIC OCEAN • 1 adult ♀; North Atlantic ; 2205 m deep; Dinet & Vivier leg.; MNHN AP 345/560Ma .

MEDITERRANEAN SEA • 1 adult; Cassidaigne Canyon; 460 m deep; Vitiello & Vivier leg.; MNHN AE120 /78Ma .

Remarks

There were two primary purposes for the re-examination of this taxon. One purpose was to identify the secondary and tertiary clavae, which were not reported in the original description ( Renaud-Mornant 1981). The second purpose was to accurately understand the morphology of the leg IV sensory organs, which was described as hemispherical papillae in the text, but drawn as elongate papillae in the figure of the original description ( Renaud-Mornant 1981).

Unfortunately, the secondary and tertiary clavae were not recognised in the holotype, MNHN AF05/77Ma. However, they were evident in the additional specimen, MNHN AP345/560Ma. In this specimen, the paired secondary clavae were positioned in the dorsal area between the median cirrus and the primary clavae and each was in the form of a flat, distorted-oval lobe (the complete contour was not recognisable) ( Figs 2 , 3A ). The paired tertiary clavae were position ventrally, immediately posterior to the external cirri and each was in the form of a flat, transversally-elongated lobe with a slight indentation where the external cirrus arises ( Figs 2 , 3B ). In the other additional specimen, MNHN AE120/78Ma, the secondary clavae were not recognised, but a paired structure indicative of clavae (tertiary clavae?) was observed in the latero-ventral position of the cephalic region ( Fig. 3C ). Further, a paired globular body fringing the mouth was recognised ( Fig. 3D ).

The leg IV sensory organs were recognised in all three specimens.The holotype and MNHN AP345/560Ma had leg IV sensory organs consisting of papillae enveloped in hemispherical cuticular sheaths with short, apical spines ( Fig. 3E ) similar to that described in the text of the original description ( Renaud-Mornant 1981). On the other hand, the leg IV sensory organs of MNHN AE120/78Ma lacked the enveloping cuticular sheaths and the papillae appeared slightly elongate and also constricted at the base ( Fig. 3F ) as in fig. 1A of Renaud-Mornant (1981). Further, it is clear that fig. 1C of Renaud-Mornant (1981) is based on MNHN AE120/78Ma ( Fig. 3F ).

Other morphological characters of the three specimens confirm the original description ( Renaud-Mornant 1981) except that a scapus was observed in one of the external cirri of the MNHN AP345/560Ma ( Fig. 2 ). Here we provide measurements of the holotype missing in the original description: internal cirrus, 3 μm; external cirrus, 6 μm; primary clava, 10 μm; leg IV sensory organ, 5 μm long and 3 μm in diameter.

Our re-examination reveals that the term “balloon-shaped” used by Bussau (1992) and Villora-Moreno (1998) (probably based on the figure in the original description of Renaud-Mornant 1981) to describe the sensory organs of leg IV of A. abyssalis is inadequate since those of the holotype and MNHN AP345/560Ma had a hemispherical appearance. Further, we consider MNHN AE120/78Ma with “balloon-shaped” leg IV sensory organs (in the sense of Bussau 1992 and Villora-Moreno 1998) as an undescribed species. The difference in the morphology of the tertiary clavae also supports this view. However, MNHN AE120/78Ma is not in an acceptable condition for species description.

Based on the observation of the holotype and MNHN AP345/560Ma, Angursa abyssalis resembles A. clavifera and A. capsula by the club-shaped primary clavae longer than the lateral cirri, the leg IV sensory organs in hemispherical shape, and the lack of the anal papillae ( Noda 1985; Bussau 1992). However, it differs from A. clavifera by the larger secondary clavae, the tertiary clavae slightly indented around the external cirri, and the absence of sensory organs on legs II and III ( Noda 1985). It differs from A. capsula by the larger and closer situated pair of secondary clavae (3 μm apart in MNHN AP345/560Ma and 9 μm apart in A. capsula measured from the drawing of a paratypic female in the original description see Bussau 1992), the tertiary clavae slightly indented around the external cirri ( Bussau 1992) and a much shorter cirrus E (10 μm (body length, 141 μm) in A. abyssalis versus 19 μm (170 μm) in A. capsula ).

Figures

Fig. 2. Drawing of Angursa abyssalis Renaud-Mornant, 1981, cephalic region (ventral view) (USNM W 50900).

Fig. 3. Micrographs of specimens observed by Renaud-Mornant (1981) to describe Angursa abyssalis Renaud-Mornant, 1981 (A–B, E) and of Angursa sp. (C–D, F) by the present authors. A. Cephalic region (dorsal view) (MNHN AP345/560Ma). B. Cephalic region (ventral view) (MNHN AP345/560Ma). C. Cephalic region (ventral view) (MNHN AE120/78Ma). D. Cephalic region with paired globular bodies (black arrowhead) (MNHN AE120/78Ma). E. Leg IV sensory organs (MNHN AF05/77Ma). F. Leg IV sensory organ (MNHN AE120/78Ma).