Laetmonice stet. CCZ_060

Fig. 3

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 7; 4.8897°N, 141.75°W; 3096 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400687 (COI); NHMUK 2022.76; Voucher code: CCZ_060 .

Description.

Single specimen (Fig. 3A). Body short, ovoid, flattened ventrally and somewhat arched dorsally. Specimen ~ 1 cm at widest point and 2 cm long, with 31 chaetigers. Dorsal felt not present. Specimen caked dorsally in dense layer of pale sediment (Fig. 3B, E), easily removed from dorsum but adhering to prostomium, parapodia, chaetae, and pygidium, obscuring respective features. Elytra 15 pairs, semi-translucent, smooth, and overlapping to cover dorsum (Fig. 3C). Dorsal cirri long, fine and tapering, extending beyond parapodia. Ventrum smooth. Ventral cirri, short, mostly broken off, not extending to base of neurochaetae. Parapodia biramous. Notochaetae include long, dark, brassy spines (Fig. 3E) with simple, tapered tips or with harpoon-shaped tips bearing four or five recurved fangs (Fig. 3D); both types of notochaetae with tuberculated shafts (Fig. 3G); neurochaetae include finer, shorter, paler chaetae with subdistal lateral spur and distal fringe of filamentous hairs (Fig. 3F), tips frequently broken off or covered in sediment.

Remarks.

The presence of harpoon-shaped notochaetae supports the placement of this specimen within the genus Laetmonice (Fauchald 1977). Forms a monophyletic clade with other species of the genus Laetmonice based on COI sequences. Genetically distinct from Laetmonice stet. CCZ_060, the closest match is with Laetmonice filicornis Kinberg, 1856 (90.8% similarity). Laetmonice filicornis is described from shelf depths near Sweden in the North Atlantic.

Ecology.

This specimen was observed crawling on the sedimented seafloor on the seamount of APEI 7 at 3096 m depth.

Comparison with image-based catalogue.

No exactly identical Aphroditiformia 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 Laetmonice stet. CCZ_060 was added as a new morphotype (i.e., Laetmonice sp. indet., ANN_019) in the megafauna imagery catalogue. Only one other Aphroditiformia morphotype (i.e., Aphroditidae gen. indet., ANN_022; with much larger spines and no sediment coating), was catalogued from seabed imagery in the eastern CCZ, also found on a seamount. In vertically-facing seabed images, Aphroditiformia morphotypes could potentially be confused with plate-shaped Xenophyophore tests (e.g., Psamminidae), particularly a dense layer of sediment is found coating specimens, as observed in Laetmonice stet. CCZ_060 (Fig. 3A).

Phylum Arthropoda von Siebold, 1848

Subphylum Crustacea Brünnich, 1772

Superclass Multicrustacea Regier, Shultz, Zwick, Hussey, Ball, Wetzer, Martin & Cunningham, 2010

Class Thecostraca Gruvel, 1905

Subclass Cirripedia Burmeister, 1834

Infraclass Thoracica Darwin, 1854

Superorder Thoracicalcarea Gale, 2015

Order Scalpellomorpha Buckeridge & Newman, 2006

Family Scalpellidae Pilsbry, 1907

To date, there is a single record at> 3,000 m depth for the order Scalpellomorpha in the CCZ (OBIS 2022), but no collected material. Three specimens were collected during the DeepCCZ expedition; these belong to three different species from which only one was confidently assigned to a previously described species. Sequences for the COI and 18S genes were generated for the three specimens and included in a phylogenetic tree estimated from 18S and COI sequences (Fig. 4).

Scalpellomorpha have been commonly found in image-based megafauna surveys across the north Pacific abyss, usually attached to sponge stalks or nodules. However, their classification beyond family level (e.g., Scalpellidae) from seabed imagery is constrained by their generally small size; only large specimens (> 3 cm) which are rarely encountered can sometimes be classified to genus level from in situ images. Consequently, scalpellid specimens usually are collated into a single, generic morphotype (i.e., Scalpellidae gen. indet., ART_010) in image-based quantitative analyses.