Swiftia phaeton, Sampaio & Beuck & Freiwald, 2022

Sampaio, I ́ ris, Beuck, Lydia & Freiwald, Andre ́, 2022, A new octocoral species of Swiftia (Holaxonia, Plexauridae) from the upper bathyal off Mauritania (NE Atlantic), ZooKeys 1106, pp. 121-140 : 121

Swiftia phaeton sp. nov.

Figs 2 , 3 , 4 , 5

Swiftia sp. Sampaio et al., 2019: 7, 14, 17, 20, 21, figs 2c, 3.

Material examined.

Holotype: Mauritania • Tanoudert Canyon ; 20°14'47"N, 17°40'11"W; depth 595 m; 3 Nov. 2010; RV Maria S. Merian exped.; stat. GeoB 14802-1; 1 colony; SMF 13112 . Paratypes: off Mauritania • 18°51'N, 16°53'W; depth 500 m; 10 Jun. 1988; RV Tyro exped.; stat. MAU 040; 1 colony; RMNH.COEL. 42327. off Mauritania • 18°51'N, 16°53'W; depth 500 m; 10 Jun. 1988; RV Tyro exped.; stat. MAU 040; 1 colony; RMNH.COEL. 42328. Mauritania • shallow Timiris Mound Complex ; 18°57'51"N, 16°51'90"W; depth 446 m; 10 Nov. 2010; RV Maria S. Merian exped.; stat. GeoB 14874-6; 1 colony; SMF 13113 . Mauritania • deep Timiris Mound Complex; 18°57'41"N, 16°52'17"W; depth 602 m; 10 Nov. 2010; RV Maria S. Merian exped.; stat. GeoB 14873-1; 3 colonies; SaM-ID 1352. Mauritania • deep Timiris Mound Complex; 18°57'45"N, 16°52'11"W; depth 498 m; 10 Nov. 2010; RV Maria S. Merian exped.; stat. GeoB 14873-4; 1 colony; SaM-ID 1469. Mauritania • deep Timiris Mound Complex; 18°57'54"N, 16°51'11"W; depth 493 m; 11 Nov. 2010; RV Maria S. Merian exped.; stat. GeoB 14878-1; 4 colonies; SaM-ID 1566. Mauritania • Tioulit Canyon (S); 18°39'00"N, 16°43'35"W; depth 618 m; 12 Nov. 2010; RV Maria S. Merian exped.; stat. GeoB 14886-4; 3 colonies and 1 fragment; SaM-ID 1596. Mauritania • Southern Tamxat Mound Complex; 17°28'55"N, 16°41'31"W; depth 450 m; 16 Nov. 2010; RV Maria S. Merian exped.; stat. GeoB 14911-1; 1 colony; SaM-ID 1629. Mauritania • Central Tamxat Mound Complex; 17°32'27"N, 16°39'60"W; depth 486 m; 15 Nov. 2010; RV Maria S. Merian exped.; stat. GeoB 14905-1; 1 colony; SaM-ID 1638 .

Type locality.

Tanoûdêrt Canyon and Timiris Mound Complex, Mauritania upper continental slope.

Etymology.

Species named after the German cruise MSM 16/3 ‘PHAETON’ and treated as a name in apposition. This cruise was the first to film this species alive underwater and forming coral gardens. These ecosystems are a contradiction to the African desert into which Phaeton, son of a Greek god, transformed the continent, burning it down while falling with his chariot from the sky.

Diagnosis.

Colonies unbranched or monopodial subdividing up to two times (Fig. 2A-C ). Dark red robust colonies. Dark brown axis. Branches sparsely distributed, rarely with anastomoses. Polyp colour red, darker than coenenchyme. Polyps form a conical prominent mound, numerous and densely crowded around the branches (Fig. 2D-F ). Anthocodiae red with yellowish white tentacles. Collaret absent. Coenenchyme formed by compact external layer with smaller capstans and an internal layer with long straight spindles, mostly not within a closed layer (Fig. 3 ). Polyp mounds with the same sclerite types, capstans and spindles, and a layer of compact dark red rods on top. Anthocodial sclerites thin warty spindles. Sclerite colours vary between dark red and transparent.

Description.

Holotype small dark red colony scantily ramified in one plane (Fig. 2B ). Colony extending up to 42.8 mm in length and up to 41.4 mm in width, attached to the substrate by an encrusting holdfast of ~ 6 mm wide in a main stem of 2 mm diameter (Fig. 2B ). Colony branches up to three, thick and robust, with numerous polyps that reach 1.8-2 mm in diameter and 1.5-40.8 mm long. Polyps red, darker than coenenchyme; abundant, well-spaced, either in biserial distribution or all over branches and mostly present on one side of colony. Approximately 5-8 polyps/cm, spaced between 1.8 and 3.4 mm, occurring on main stem and branches. Polyp mounds up to 2.5 mm high, 1.0-1.5 mm long, and 10.1-16.8 mm wide. Anthocodiae retractile within prominent polyp mounds and with yellowish white tentacles. Coenenchyme thin. Coenenchymal and polyp mound sclerites with outer layer of red or transparent small but packed capstans, 39-64 μm long and 22-51 μm wide (Fig. 4C ); and an inner layer of long, slender, pointed, warty, mostly straight spindles of several sizes (Fig. 4A ). Larger spindles 232-436 μm long and 29-73 μm wide, sometimes waisted (Figs 3 , 4A ). Smaller spindles 103-219 μm long and 25-45 μm wide (Figs 3 , 4A ). Irregularly branched spindles with expanded, warty tubercles or small immature sclerites (Fig. 4A, B ), occurring in lower numbers. Polyp mound top with armature formed by layer of flat rods showed by micro-CT, 108-321 μm long and 27-72 μm wide (Figs 4 , 5 ) on the distal end. Anthocodiae with spindles arranged in points, tiny capstans, and irregular flattened scales around peristome and tentacles (Fig. 5 ). No collaret.

Variation.

The variation of body measurements of the paratypes is presented in Table 2 and a published dataset (https://doi.pangaea.de/10.1594/PANGAEA.910893). All colonies examined were homogeneous in colouration, in agreement with the holotype. Colonies extending up to 93 mm in length but smaller in width than holotype. Colonies unbranched or branching up to two times. Branches as in holotype with 1-5 mm diameter but longer than holotype, reaching up to 77 mm lenght. Anastomosis present uniquely in paratype SaM-ID 1469. Polyps similar to those described for holotype, yet in most cases more densely distributed on branches of paratypes (6-21/cm) and less spaced than on holotype, 0.3-2.26 mm. Polyp mounds as those of holotype, height <1.8 mm and 0.67-2.28 mm wide, with anthocodiae mostly retracted after preservation. Tentacles, coenenchyme, and sclerite colours and arrangements as in holotype. Sclerite sizes vary. Capstans of outer layer uniform in size along both coenenchyme and polyp mounds (22-97 μm length; 13-58 μm width), and with broader range of sizes than holotype. Larger spindles of inner layer of coenenchyme smaller (167-413 μm length; 23-63 μm width) than larger spindles of polyp mounds (198-436 μm length; 17-73 μm width), and with minimum sizes smaller than larger spindles of holotype. Smaller spindles of inner layer of coenenchyme slightly bigger (90-243 μm length; 18-56 μm width) than smaller spindles of polyp mounds (91-231 μm length; 16-59 μm width), and with minimum sizes smaller than small spindles of holotype. Rods form layer on top of polyp mounds as in holotype, 108-455 μm long, 25-77 μm wide.

Distribution.

This species is known to occur uniquely in the upper bathyal off Mauritania in deep-sea canyons and on deep-water coral mounds, where it lives in association with framework-forming species like Desmophyllum pertusum (Linnaeus, 1758) at the world largest known deep-water coral mound barrier ( Ramos et al. 2017c; Wienberg et al. 2018). With the exception of the first ROV dive, Swiftia phaeton sp. nov. was observed in all dives of the ‘PHAETON’ expedition from north to south of Mauritania (Fig. 1 , Table 3 ). It inhabits the canyons Tanoûdêrt, Nouamghar, Inchiri, and Tioulit and the coral mound complexes, both shallow and deep Timiris, Banda, Tamxat, and Tiguent between 20°N and 17°N at 396-639 m depth (Fig. 1 , Table 3 ). It is widespread at Nouamghar Canyon and at the deep Timiris Mound Complex, while its occurrence varies from isolated to highly dense populations, forming monospecific or multispecific coral gardens containing other Plexauridae species ( Sampaio et al. in press). Moreover, it was found attached to dead coral framework portions, coral rubble, and rocks.

Figures

Figure 1. Map showing MSM 16 / 3 ' PHAETON' ROV dive locations along the Mauritanian slope. Location names and GeoB 14 stations (sta.): grey = canyons; black = coral mounds; orange = scleractinian distributions. Basemap from ESRI (2019) (www. esri. com) and contours from GEBCO (2019) (www. gebco. net), scleractinian framework distribution, canyon positions, and names from Sanz et al. (2017).

Figure 2. Swiftia phaeton sp. nov. from Mauritania A in situ colony with expanded polyps on coral framework (copyright Tomas Lundaelv, Sven Loven Center for Marine Infrastructure at Tjarnoe, Sweden) B colony after ethanol preservation with expanded polyps (holotype SMF 13112) C in situ colony with retracted polyps on coral framework (copyright Tomas Lundaelv, Sven Loven Center for Marine Infrastructure at Tjarnoe, Sweden) D part of a branch (paratype SMF 13113), E fragment of specimen with anthocodiae slightly expanded (paratype SaM-ID 1566) F polyp and coenenchyme details (paratype SaM-ID 1352). Scale bars: 1 cm (A-C); 300 μm (D-F).

Figure 3. Layers of sclerites of Swiftia phaeton sp. nov. A coenenchyme under light microscope B polyp mound under electron microscope (paratype SaM-ID 1566). Outer layer (OL) with capstans and inner layer (IL) with spindles. Scale bars: 100 μm.

Figure 4. Sclerites from type specimens of Swiftia phaeton sp. nov. A overview of sclerites of the inner layer of the coenenchyme: spindles B polyp sclerites: spindles, rods, and scales from the tentacles C overview of sclerites of the outer layer of the coenenchyme: capstans (also occurring in polyp mounds). Scale bar: 100 μm.

Figure 5. 3 D reconstruction of polyp of Swiftia phaeton sp. nov. (paratype SaM-ID 1352). Coloured sclerites: in red, rod-forming layer on top of the polyp mound and in rose, spindle of the anthocodium. Scale bar: 1 mm.