Trianguloscalpellum gigas (Hoek, 1883)

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

Trianguloscalpellum gigas (Hoek, 1883)

Fig. 5

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 7; 5.0442°N, 141.8165°W; 4874 m deep; 28 May. 2018; Smith & Durden leg.; GenBank: ON400698 (COI), ON406624 (18S); WAM C74110 ; Voucher code: CCZ_074 .

Description.

Single specimen, found attached to a glass sponge stalk (Fig. 5A ). Capitulum elongated, longer than wide (L = 8 mm, W = 5 mm), white, with short peduncle (2 mm) covered by large scales (Fig. 5B, C ). Capitulum is formed by 14 capitular plates, and growth lines are not visible. Carina is simply bowed, narrowing distally but being approx. the same breath proximally. The tergum is somewhat oval-shaped, long, ~ 2 × as long as wide, with pointed basal angle, carinal margin arched, and occludent margin straight. Scutum is somewhat quadrangular, broad, 1.5 × as long as wide, with occludent margin much longer than the lateral margin. Inframedian latus is triangular, reaching upper latus. Carinolatus triangular, umbo apical, higher than rostrolatus.

Remarks.

The specimen appears to be a juvenile of the species T. gigas based on the plate arrangement, although diagnostic characters are not fully developed. There are no sequences available on public databases for T. gigas , but the 18S gene sequence is very similar (> 99%) to other species within the family Scalpellidae , mostly within the subfamily Arcoscalpellinae . However, the COI sequence is highly divergent (> 15% nucleotide divergence and> 3% amino-acid divergence) from published sequences of other species within the subfamily. The phylogenetic tree from concatenated data for COI and 18S recovered a well-supported clade of species of Anguloscalpellum and Trianguloscalpellum , but did not recover the genera as monophyletic. The type material for T. gigas was collected during the H.M.S. Challenger expedition in the middle of the North Pacific (Station 246: 36.1667°N, 178.0°E) at 3749 m depth ( Hoek 1883). The species has been recorded from the Northwest and Southwest Pacific, and the Indian Ocean, from 3310 to 4820 m depth ( Shalaeva and Boxshall 2014).

Ecology.

The specimen was collected in the sedimented abyssal plain of APEI 7, at 4874 m depth. It was attached to a glass sponge stalk, along with another barnacle ( Catherinum cf. albatrossianum ; specimen CCZ_073), and an anemone ( Metridioidea stet. CCZ_072; specimen CCZ_072).

Comparison with image-based catalogue.

No exactly similar Scalpellidae morphotypes have been so far catalogued from seabed imagery collected in the eastern CCZ or in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of Trianguloscalpellum gigas was catalogued as a new morphotype (i.e., Trianguloscalpellum gigas sp. inc., ART_033). However, given the small size of specimen CCZ_074, this morphotype could have easily been i.e., undetected in seabed image surveys conducted in other areas of the CCZ.

Figures

Figure 5. Trianguloscalpellum gigas (Hoek, 1883). Specimen CCZ _ 074: A in situ photograph, attached to a glass sponge stalk B left C and right lateral views. Scale bars: 5 cm (A); 1 mm (B, C). Image attribution: Durden and Smith (A), Hosie (B, C). Arrows indicate position of T. gigas (specimen CCZ _ 074; lower, yellow) and Catherinum cf. albatrossianum (specimen CCZ _ 073; upper, green).