Psychronaetes sp. CCZ_101

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

Psychronaetes sp. CCZ_101

Fig. 48

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 7; 4.8877°N, 141.757°W; 3132 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400690 (COI), ON406630 (18S); NHMUK 2022.62; Voucher code: CCZ_063. • 1 specimen; APEI 4; 7.2647°N, 149.7741°W; 3562 m deep; 03 Jun. 2018; Smith & Durden leg.; GenBank: ON400707 (COI), ON406631 (18S); NHMUK 2022.65; Voucher code: CCZ_101. • 1 specimen; APEI 4; 7.2647°N, 149.7741°W; 3562 m deep; 03 Jun. 2018; Smith & Durden leg.; GenBank: ON400709 (COI), ON406639 (18S); NHMUK 2022.67; Voucher code: CCZ_103. • 1 specimen; APEI 4; 7.2647°N, 149.7741°W; 3562 m deep; 03 Jun. 2018; Smith & Durden leg.; GenBank: ON400710 (COI), ON406632 (18S); NHMUK 2022.68; Voucher code: CCZ_104 .

Description.

Four specimens (Fig. 48A-D ). Body dorso-ventrally flattened (L = 15.9 cm, W = 3.4 cm), tapering at both ends; pronounced “neck” anteriorly; mouth anteroventral, anus posterodorsal. Tentacles 18, with long stems and large elongate oval discs (Fig. 48G ). Body wall firm and leathery, dark violet in preserved specimen, with evident, numerous calcareous wheel-like ossicles that make the skin sparkle under light. Mid-ventral ambulacrum is naked; one irregular row of ≥ 40 tube feet running along each ventrolateral ambulacra (Fig. 48G ), very conspicuous on live specimens (Fig. 48A-D ), but fully retracted on preserved specimens. Paired dorsal ambulacra with ~ 20 papillae each; ~ 7 long thick papillae distributed along each ambulacrum, interspersed with smaller ones (Fig. 48A-E ). There are ~ 18 large conical papillae surrounding the anterior margin dorsally, fully fused forming a fringe (Fig. 48B, D ). Dorsal ossicles numerous, wheel-like, of different sizes (ranging from 77-340 μm in diameter) but mostly large; strongly concave; central primary cross with 4-6 struts, mostly four; smooth rim; with 10-16, mostly 12, short spokes (Fig. 48F, H ).

Remarks.

Based on ossicle morphology, the four specimens were considered to belong to the same species. Sequence of the 18S were found to be identical between specimens CCZ_063, CCZ_101, and CCZ_104 (0.0% K2P distance) but 1.3% divergent from CCZ_103. The COI gene was amplified for the four specimens and genetic divergence ranges between 0.8% to 7.4%. The two specimens collected in APEI 4 are less genetically divergent (CCZ_101-CCZ_104 = 0.8% K2P). The specimen collected in APEI 7 (CCZ_063) is 2.3-2.9% divergent from the other three. The specimen CCZ_103 is 7.4% divergent to CCZ_101 and CCZ_104, but only 2.9% divergent from CCZ_063. While the former values are within the range of interspecific genetic divergence, we considered the specimen to belong to the same species as both the ossicle and external morphological characters are similar to the other three specimens. In addition, the trace files for both 18S and COI for this specimen are messy and the high genetic divergence could be an artifact of miss-called nucleotides. Unfortunately, there are no sequences available for Psychronaetes , but we included sequences of other genera within the family ( Pannychia , Laetmogone , and Benthogone ) for which COI genetic divergence ranged from 23-31%. In the phylogenetic tree, the four specimens were recovered in a well-supported clade (Fig. 34 ), close to other Laetmogonidae (poorly supported). This species has an anterior brim, which is characteristic of the monotypic genus Psychronaetes . Psychronaetes hanseni Pawson, 1983 differs from the four specimens in having smaller dorsal wheel ossicles (d = 50-80 µm) with 9-12 spokes, only 15 tube feet on each of paired ventral ambulacrum, 15 mouth tentacles instead of 18, and in the number of papillae on the dorsal paired ambulacra. The species and genus were described from two specimens collected in the CCZ ( Pawson 1983).

Ecology.

The four specimens were found on the sedimented seafloor of seamounts in APEIs 4 and 7 between 3132-3562 m depth.

Comparison with image-based catalogue.

No exactly similar Psychronaetes sp. morphotypes have been encountered in seabed image surveys conducted in the eastern CCZ or in abyssal areas of the Kiribati EEZ. Consequently, the in situ images of these specimens were catalogued as a new morphotype (i.e., Psychronaetes sp. indet., HOL_110). However, HOL_110 can resemble at least two other Laetmogonidae morphotypes catalogued from seabed imagery; Laetmogonidae gen. indet., HOL_030 (e.g., dark violet, but with 8+ long papillae) which is commonly found in the eastern CCZ (but not in the Kiribati EEZ); and Psychronaetes sp. indet., HOL_122 (e.g., violet, but only with six or seven long papillae and with fewer (<20) and larger, thick tube feet) which was also only found in the western CCZ.

Figures

Figure 34. Phylogenetic tree of the class Holothuroidea. Concatenated (12 S, 16 S, 18 S, 28 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 48. Psychronaetes sp. CCZ _ 101. Specimen CCZ _ 063 A in situ image. Specimen CCZ _ 101 B in situ image F dorsal ossicles. Specimen CCZ _ 103 C in situ image H dorsal ossicles. Specimen CCZ _ 104 D in situ image E dorsal view of specimen before preservation G ventral view. Scale bars: 5 cm (A, D); 2 cm (B); 1 cm (E, G); 75 μm (F); 100 μm (H). Image attribution: Durden and Smith (A-D); Wiklund, Durden, Drennan, and McQuaid (E, G); Bribiesca-Contreras (F, H).