(Figs. 6, 7, 8; Table 3)
Material examined. MAURIT-0911, stn MUDR01, 16º08´24”N, 16º57´12”W, 488 m, 5-XII-2009: nine colonies, one colony with male gonotheca (SMF 12948), three colonies with female gonothecae (1 LZM-UV 15247, 2 MNCN 2.03 /684, 2.03/685), paratypes.
MAURIT-1011, stn MUDR20, 16º08´11”N, 16º56´08”W, 405 m, 7-XII-2010: one colony, with male gonothecae, paratype (LZM-UV 15261).
MSM 16 /3, stn GeoB 14796–1, ROV, 20°14.840’– 20°14.575’N, 17°40.193’– 17°40.071’W, 487–642m, 3-XI- 2010: two colonies 23 mm high, growing on Lophelia pertusa; one colony with female gonothecae is the holotype (SMF 12947) and the other a paratype(LZM-UV 02986).
MSM 16 /3, stn GeoB 14801–1, BG, 20°14.762’N, 17°40.173’W, 568 m, 3-XI-2010: eight colonies 13–22 mm high, no gonothecae.
MSM 16 /3, stn GeoB 14802–1, BG, 20°14.791’N, 17°40.188’W, 595 m, 3-XI-2010: one colony 17 mm high, on Lophelia pertusa with female gonothecae, paratype (RMNH.Coel.42585)
MSM 16 /3, stn GeoB 14871–2, ROV, 19°08.344’– 19°08.235’N, 16°45.849’– 16°45.664’W, 427–566 m, 9-XI- 2010: one colony, on Lophelia pertusa, without gonothecae.
Etymology. The specific name freiwaldi honours Prof. Dr. André Freiwald, Senkenberg am Meer, Wilhelmshaven, in appreciation and recognition of his wide contribution to the knowledge on cold-water coral habitats.
Biology. Some colonies were found growing on L. pertusa; the rest of the colonies were detached from the substrate, but some of them showed hydrorhizal adaptations for anchoring in muddy bottoms. The bathymetric range of the species extends from 405 to 642 m.
Distribution. This species was collected on the Mauritanian cold-water coral mounds and surrounding offmound muddy bottoms.
Description. Hydrorhiza formed by stolonal tubes growing attached to corals or composed of a compact mass of interwoven stolonal fibres to anchor the colony to the sediment in muddy bottoms. Hydrocauli monosiphonic, unbranched and divided into internodes by straight nodes visible along the stem. Each internode with 3–4 nematothecae and two apophyses in the distal part. Apophyses arranged in opposite pairs in one plane, each of them with one mamelon on its upper surface and three nematothecae: two in the axil and one in the distal part of apophyses, close to the node.
In basal half of colony, hydrocladia inserted on apophyses with first internode ahydrothecate and provided with a single nematothecae and two perisarc rings, one basal and the other distal; remaining hydrocladia composed of a succession of hydrothecate and ahydrothecate internodes.
Hydrothecate internodes with one hydrotheca located in the middle of the internode, and three nematothecae: two laterals and one mesial inferior. Hydrothecae cup-shaped, adcauline wall fully adnate, abcauline wall slightly smaller and straight; hydrothecal aperture perpendicular to longitudinal axis of hydrocladia or slightly tilted downwards; rim even and smooth. Ahydrothecate internodes only have two nematothecae, one basal and other distal.
In the distal part of colony, hydrocladia inserted on apophyses directly by a hydrothecate internode incorporating, in this case, the first ahydrothecate internode and its nematotheca, resulting in a longer internode with one hydrotheca in its distal third and four nematothecae, two mesial inferior and two laterals. Following internodes are hydrothecate internodes, provided with one hydrotheca in distal part and 4–5 nematothecae: two or three mesial inferior and two laterals. Only in the distal part of these hydrocladia, regular succession of hydrothecate and ahydrothecate internodes with the same disposition of hydrotheca and nematothecae described for the basal hydrocladia. All hydrothecate internodes have an oblique node basally and a straight node distally; reverse in ahydrothecate internodes. All nematothecae bithalamic and movable.
Female and male gonothecae borne on separate colonies, inserted on apophyses near mamelon by short pedicel; up to three gonothecae per apophysis may be present. Female gonotheca ovoid-shaped, with one convex wall and other straight; aperture lateral in its distal part, oval and closed by a lid. Male gonotheca narrower, long and slightly curved with a tilted latero-terminal opening.
Remarks.Nemertesia freiwaldin. sp. resembles N. belini and N. caboverdensisn. sp. because of the presence of several mesial inferior nematothecae in at least some hydrothecate internodes. Moreover, the morphology of the gonothecae described for both species resembles the female gonothecae of N. freiwaldin. sp. However, several traits separate all three species. Nemertesia freiwaldin. sp. differs from N. belini because the latter species has several endodermal canals on the hydrocaulus, a characteristic not observed in the former species. In addition, the segmentation pattern of the hydrocladia is quite irregular in N. belini but not in N. freiwaldin. sp., despite differences in the basal and apical parts of the colony; the position of the hydrotheca in the internodes is different: basal in N. belini versus distal in N. freiwaldin. sp.; the hydrothecal aperture is clearly tilted in the abcauline direction, and hydrocladial nematothecae are longer in N. belini. Finally, N. freiwaldin. sp. lacks distal unpaired nematothecae in the hydrothecate internodes. Moreover, N. belini has only one type of gonotheca, despite the presence of numerous gonothecae in the type material.
The inclination of hydrothecal aperture towards abcauline side, the length of nematothecae, clearly shorter, and the absence of unpaired distal nematothecae differentiate N. freiwaldin. sp. from N. caboverdensisn. sp. In addition, in the last species only one type of gonotheca, ovoid in shape and with latero-terminal aperture, was reported, whereas in N. freiwaldin. sp. the female gonothecae are strongly curved with lateral aperture and the male gonothecae are elongated.