Coronarctus dissimilis Gomes-Junior et al., 2020

Trokhymchuk, Roman & Kieneke, Alexander, 2025, Novel distribution records of marine Tardigrada from abyssal sediments of the Northwest Atlantic Ocean, Organisms Diversity & Evolution 25 (1), pp. 13-28 : 16

Coronarctus dissimilis Gomes-Junior et al., 2020

2 specimens (one female, SMF 72 , one male, SMF 73 ) Samples: SO286-42, core 19 (51° 58.255′ N, 038° 59.534′ W, 3685 m depth) ( Fig. 1 )

Tardigrades with robust cylindrical and elongated body with metameric cuticle structures. Coelomocytes and other spherical cells present (Fig. 5A). Buccal apparatus with pharyngeal bulb and stylets is visible. Primary clavae and cirri A are very short. Secondary clavae lobate, extending dorso-ventrally on the head. Ventral part of the secondary clava surrounds the external cirrus ( Fig. 1C ). Small median cirrus is present ( Fig. 1D ). Cirri B, C, E are present. Conical sensory organs IV and leg IV coxal processes are present. Claws show heteromorphy: on each leg, external claws are significantly smaller than internal claws. Claws on leg I are more robust than claws on legs II and III, especially the most internal claws on leg I ( Fig. 1C ). Claws on each leg with tiny accessory spines ( Fig. 1C, F ). Female has a well-observable anus, gonopore, and seminal receptacles ( Fig. 1E ). Some important morphometric values are compiled in Table 2.

Family Styraconyxidae Kristensen & Renaud-Mornant, 1983 Genus Angursa Pollock, 1979

Angursa capsula, Bussau, 1992

4 specimens (4 females), SMF 65 , 66 , 70 , 74

Samples: SO286-42, core 16 & 19 (51° 58.255′ N, 038° 59.534′ W, 3685 m depth); SO286-47, core 13 (51° 57.454′ N, 038° 59.325′ W, 3675 m depth) ( Fig. 2 )

Angursa representative with slender body and club-shaped primary clavae longer than lateral cirri (cirri A); secondary and tertiary clavae have a hardly visible outline ( Fig. 2A–C ). On the dorsal side of the head, secondary clavae placed in a distance between each other of more than 6 μm ( Figs. 2C , 5C). Cirri E with basal scapi. Leg I sensory organs present; legs II and III sensory organs absent; leg IV with “capsule-shaped” sensory organs with short apical spine; weak anal papilla present ( Fig. 2A, D ).

During the preparation of A. capsula for SEM, the rear end of the specimen was unfortunately damaged (Fig. 6D), because electrostatic charges made recovery from the sample cabinet difficult. Nevertheless, some structures are still visible and we were able to observe the gonopore surrounded by six plates (Fig. 6D).

First record of this species for the Atlantic Ocean Basin. Some important morphometric values are compiled in Table 2. Angursa abyssalis Renaud-Mornant, 1981

5 specimens (3 females, 2 with unknown sex), SMF 63 , 64 , 67 , 68 , 69

Samples: SO286-42, core 16 & 19 (51° 58.255′ N, 038° 59.534′ W, 3685 m depth) ( Fig. 3 )

Angursa representative with slender body ( Fig. 3A, B ) and club-shaped primary clavae longer than lateral cirri (cirri A; Fig. 3A ); secondary and tertiary clavae are placed close to each other ( Figs. 3A 2, B2 , 5B). Cirri E with basal scapus. Leg I with distinct, legs II–III with minute sensory organs; leg IV sensory organ with short apical spine; anal papilla inconspicuous, compared to the anal papilla of A. bicuspis .

SEM images of A. abyssalis clearly show minute sensory organs on legs II and III (Fig. 6A, B), which are sometimes difficult to observe even with the use of DIC. Boundary of secondary clavae is not clearly visible (Fig. 6A). Although tertiary clavae are better visible, their flat arrangement does not allow a definite delineation (Fig. 6B). However, details of the limbs, proximal pads, digits, and claws can be imaged with high resolution using SEM (Fig. 6A, B, F). Some important morphometric values are compiled in Table 2.

One peculiar specimen of sample SO286-42–16 possesses four primary clavae or, alternatively, a split primary clava on each side of the head ( Fig. 3C : arrowheads). We provisionally designate this specimen as Angursa cf. abyssalis (see “Discussion” for details).

Angursa lanceolata Renaud-Mornant, 1981

1 specimen (female), SMF 71

Samples: SO286-42, core 19 (51° 58.255′ N, 038° 59.534′ W, 3685 m depth) ( Fig. 4 )

Angursa species belonging to the “ A. lanceolata ” group ( Fujimoto & Hansen, 2019) with bulbous primary clavae and lateral cirri (cirri A) longer than primary clavae ( Fig. 4A ). Secondary clavae present; kidney-shaped tertiary clavae reported for the first time for this species ( Fig. 4B 2 ). Leg I sensory organ present; leg IV sensory organ elongated with short apical spine. Characteristic “lance-shaped” cirri E present ( Fig. 4C, C 2 ).

The single specimen of A. lanceolata was prepared for SEM after light microscopic investigation including CLSM. The condition of this specimen is unfortunately not optimal and this was probably caused by improper fixation during the expedition. However, several species-specific structures are visible quite well such as the primary clavae, head cirri, cirrus E, and the fine structure of the claws (Fig. 6C, E). Tertiary clavae are visible as well and are described for this species for the first time. They are kidney-shaped without lobes and are positioned halfway gonopore, seminal receptacles, and anus. F Female leg IV with claw accessory spines (arrowheads). Abbreviations: an—anus, ec—external cirrus, go—gonopore, mc—median cirrus, pc—primary clava, sc—secondary clava, s4—sensory organ on leg IV, rs—seminal receptacle between the anterior end and the level of the primary clavae (Fig. 6C). Claws with the characteristic pattern of the genus with primary and secondary hooks are clearly visible (Fig. 6E). Cirri E are “lance-shaped” and are clearly visible (Fig. 6C). The sensory organ on the IV leg also has a conspicuous elongate shape. Gonopore and anus are visible, too (Fig. 6C). Some important morphometric values are compiled in Table 2.

Figures

Fig.1 Coronarctus dissimilis, light microscopy with differential interference contrast (DIC). A Female specimen, habitus, ventral. B Male specimen, habitus, ventral. C Head of female, ventral view. Note the accessory spine on claws (arrowheads). D Head of female, dorsal view. E Female

Fig. 2 Angursa capsula, light microscopy with DIC. A Habitus, dorsal. B Habitus, ventral. C Head from dorsal, note the secondary clava (dashed line). D Leg IV (retracted). Abbreviations: ap—anal papilla,

Fig. 3 Angursa abyssalis, light microscopy with DIC. A Habitus, dorsal. A2 Head, dorsal, secondary clavae indicated (dashed line). B Habitus, ventral. B2 Head, ventral, tertiary clavae indicated (dashed

Fig. 4 Angursa lanceolata, light microscopy with DIC. A Habitus of slightly twisted specimen, ventral view. B Head and first pair of limbs. B2 Head, tertiary clava of left side indicated (dashed line). C Posterior part of animal with the fourth pair of limbs and sensory