Freyastera cf. tuberculata (Sladen, 1889)

Bribiesca-Contreras, Guadalupe, Dahlgren, Thomas G., Amon, Diva J., Cairns, Stephen, Drennan, Regan, Durden, Jennifer M., Eleaume, Marc P., Hosie, Andrew M., Kremenetskaia, Antonina, McQuaid, Kirsty, O'Hara, Timothy D., Rabone, Muriel, Simon-Lledo, Erik, Smith, Craig R., Watling, Les, Wiklund, Helena & Glover, Adrian G., 2022, Benthic megafauna of the western Clarion-Clipperton Zone, Pacific Ocean, ZooKeys 1113, pp. 1-110 : 1

Freyastera cf. tuberculata (Sladen, 1889)

Fig. 25

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 4; 6.9879°N, 149.9123°W; 5000 m deep; 02 Jun. 2018; Smith & Durden leg.; GenBank: ON400716 (COI); NHMUK 2022.80; Voucher code: CCZ_157 • 1 specimen; APEI 4; 6.9873°N, 149.9331°W; 5000 m deep; 06 Jun. 2018; Smith & Durden leg.; GenBank: ON400704 (COI); NHMUK 2022.79; Voucher code: CCZ_087 .

Comparative material.

Pacific Ocean • 1 specimen, holotype of Freyella benthophila Sladen, 1889; mid-South Pacific; 39.6833°S, 131.3833°W; 4663 m deep; Challenger Expedition, Stn. 289; NHMUK 1890.5.7.1078. Atlantic Ocean • 1 specimen, syntype of Freyella tuberculata Sladen, 1889; between west coast of Africa and Ascencion Islands ; 22.3°N, 22.0333°W; 4389 m deep; Challenger Expedition, Stn. 346; NHMUK 1890.5.7.1077. • 1 specimen, syntype of Freyella tuberculata ; between Canary Islands and Cape Verde Islands; 2.7° S, 14.6833°W; 4298 m deep; Challenger Expedition, Stn. 89; NHMUK 1890.5.7.1076 .

Description.

Two specimens (R = 106 mm, r = 3 mm; R = 164 mm, r = 6 mm); live specimens whitish on both actinal and abactinal surfaces, tube feet transparent with bright orange flattened discs (Fig. 25A, B ). Disc is small, somewhat rounded, slightly orange on actinal and abactinal surfaces (Fig. 25E, F ); with six long, slender arms (Fig. 25A-C ); lacking furrow spines (Fig. 25D ). Each abactinal plate on the genital area bears a single spinelet (Fig. 25E ), covered with a membrane with pedicellariae. Each mouth plate has two oral spines covered by a clear membrane bearing pedicellariae (Fig. 25F ); one located on the adoral margin of the mouth plate and the suboral spine located above the centre of the mouth plate.

Remarks.

The COI sequences were very similar to sequences of Freyastera cf. benthophila (Sladen, 1889) collected in the UK-1 contract area from the CCZ ( Glover et al. 2016a), and which were recovered in a single clade (Fig. 24 ). Only arm segments were recovered from the UK-1 specimens, and although they were found to resemble F. benthophila , the whole specimens collected in the western CCZ differ from the original description for the species. Only five species are known for having six rays: F. sexradiata (Perrier, 1885), F. benthophila , F. tuberculata (Sladen, 1889), F. basketa Zhang et al., 2019, and F. delicata Zhang et al., 2019. However, F. benthophila is easily distinguished from the other two species by its abactinal armament; each abactinal plate bearing two or three spinelets covered with a simple membrane with no pedicellariae ( Sladen 1889). The specimens from the CCZ have abactinal spinelets covered by a membrane that bears pedicellariae (Fig. 25E ). They also differ from F. benthophila in having the spines on the adoral margin of the mouth-plates covered by a clear membrane bearing pedicellariae instead of an opaque membrane with no pedicellariae ( Downey 1986). In addition, the suboral spines are located above the centre of the mouth plate (Fig. 25F ), as in F. tuberculata , and not below the centre of the mouth plate as described for F. benthophila ( Downey 1986). Syntypes from F. tuberculata are from the Atlantic Ocean ( Sladen 1889), but it has been reported for the Eastern Tropical Pacific (0.05°N, 117.25°W) at 4243 m depth ( Downey 1986). Unfortunately, there are no genetic sequences available for this species, but COI sequences from CCZ specimens are highly divergent from the sequence of F. benthophila collected in the Mariana Trench (K2P distance: 13-14%). In the phylogenetic tree they are also recovered in different clades, very close to another species reported herein, and to F. delicata and Freyastera sp. Yap (in Zhang et al. 2019) (Fig. 24 ). The specimen collected here represents the same species as found in the eastern CCZ, Freyastera cf. benthophila ( Glover et al. 2016b).

Ecology.

One specimen was observed on the sedimented seafloor (CCZ_157), while another was sitting on a nodule with the actinal surface against the muddy seafloor and lifting the tip of the arms like a basket (CCZ_087). Both seastars were collected on abyssal sediments of APEI 4 at 5000 m depth. During morphological examination of these samples, the exoskeleton of a large (> 6 mm long), digested copepod was found in the stomach of specimen CCZ_157.

Figures

Figure 24. Rooted Bayesian phylogeny of Asteroidea. Concatenated (12 S, 16 S, 18 S, COI, and H 3) median consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of PP> 0.70 and BS> 50 are shown, with values of PP> 0.95 and BS> 90 indicated with a circle. Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study are highlighted in violet.

Figure 25. Freyastera cf. tuberculata (Sladen, 1889). Specimen CCZ _ 175: A in situ image C whole specimen D ventral surface of the arms before preservation. Specimen CCZ _ 087: B in situ image E details of dorsal disc F ventral disc surface before preservation. Scale bars: 2 cm (A, B); 1 cm (C); 2 mm (D); 1 mm (E); 0.5 mm (F). Image attribution: Durden and Smith (A, B); Wiklund, Durden, Drennan, and McQuaid (C-F).