Hyalonema stet. CCZ_020

Fig. 55

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 7; 5.1149°N, 141.8967°W; 4856 m deep; 25 May. 2018; Smith & Durden leg.; GenBank: ON400683 (COI), ON406634 (18S), ON406608 (16S), ON406597 (28S), ON411254 (ALG11); NHMUK; Voucher code: CCZ_020. • 1 specimen; APEI 1; 11.2954°N, 153.7422°W; 5245 m deep; 09 Jun. 2018; Smith & Durden leg.; GenBank: ON400721 (COI), ON406609 (16S); NHMUK 2022.8; Voucher code: CCZ_179 .

Description.

Two specimens. Lophophytous sponges (Fig. 55A-C). Body is white, ovoid, almost as wide as long (CCZ_020 W = 4.7 cm, L = 5 cm; CCZ_179 W = 8 cm, L = 8 cm); with an osculum (CCZ_020 d = 1 cm; CCZ_179 d = 4 cm) surrounded by a thin margin; separated atrial cavity. Attached to the sediment by a thin tuft of basalia that extends from the central lower body (CCZ_020 L> 7 cm; CCZ_179 L> 20 cm).

Remarks.

Genetic sequences between specimens CCZ_020 and CCZ_179 are 1% and 0.8% divergent (K2P distance) for COI and 16S, respectively. COI and 16S closest matches are sequences from Tabachnickia sp. within the Hyalonematidae . The sequence for the 18S is> 95% similar to other species of Hyalonema . In the phylogenetic tree, both specimens were recovered together, in a well-supported clade with other members from different subgenera within the genus Hyalonema and including Tabachnickia sp. (Fig. 54).

Ecology.

The specimens were collected attached to abyssal sediments of APEI 7 and APEI 1 at 4856 and 5245 m depth, respectively.

Comparison with image-based catalogue.

A very similar hyalonematid morphotype (i.e., Hyalonema sp. indet., HEX_002) has been commonly encountered in seabed image surveys conducted across the eastern CCZ and in abyssal areas of the Kiribati EEZ, mostly in nodule field areas. In situ images of HEX_002 (Fig. 55A, C) show that the aperture width of the central osculum is an unreliable character to distinguish different Hyalonema sp. morphotypes (nor these from other genera) in seabed imagery, as this contracts and expands episodically (e.g., Kahn et al. 2020).