Terebellides bigeniculatus Parapar, Moreira & Helgason, 2011

Parapar, Julio, Capa, Maria, Nygren, Arne & Moreira, Juan, 2020, To name but a few: descriptions of five new species of Terebellides (Annelida, Trichobranchidae) from the North East Atlantic, ZooKeys 992, pp. 1-58 : 1

publication ID	https://dx.doi.org/10.3897/zookeys.992.55977
publication LSID	lsid:zoobank.org:pub:0F038B5B-120E-4583-8E85-4092C9798566
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treatment provided by	ZooKeys by Pensoft
scientific name	Terebellides bigeniculatus Parapar, Moreira & Helgason, 2011
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Treatment

Terebellides bigeniculatus Parapar, Moreira & Helgason, 2011 View in CoL Figs 1 View Figure 1 , 2 View Figure 2 , 3D View Figure 3 , 4D View Figure 4 , 8D View Figure 8 , 9 View Figure 9 , 10 View Figure 10 , 26 View Figure 26 , 28E View Figure 28 ; Table 1; Suppl. material 1: Table S1; Suppl. material 2: Table S2

Terebellides bigeniculatus Parapar, Moreira & Helgason, 2011: 6-10, figs 1b, 4-7.

Species 20 + 28 Nygren et al. 2018: 18-22, figs 6, 10.

Type locality.

Off North West Iceland; 333 m deep ( Parapar et al. 2011).

Material examined.

6 specimens: Barents Sea (ZMBN 116511); Norwegian coast and shelf (ZMBN 116417, ZMBN 116510, ZMBN 116512, ZMBN 116513, ZMBN 116514).

Additional material.

T. bigeniculatus : Holotype (IIH 24923) and 5 paratypes (IINH 24925) (Suppl. material 1: Table S1).

GenBank accession numbers of material examined (COI).

MG025318, MG025319, MG025351, MG025352, MG025353, MG025354, MG025355.

Diagnostic features of studied material.

Complete individuals ranging from 10.0-24.0 mm in length. Branchiae clearly fitting with type 1 only in some specimens, irregular in others; dorsal lobes lamellae not provided with papillary projections. Lateral lappets from TC1-TC5 and well-marked dorsal projection of notopodia in TC3 (Figs 3D View Figure 3 , 4D View Figure 4 ). Geniculate chaetae present in TC5 and TC6 (Fig. 26C View Figure 26 ), acutely bent and provided with hardly distinguishable capitium (Fig. 26D View Figure 26 ). Ciliated papilla dorsal to thoracic notopodia. Thoracic uncini of type 3, with rostrum/capitium length ratio of approximately 2: 1 (Fig. 26E View Figure 26 ), and capitium with a first row of four medium-sized teeth, followed by several progressively smaller teeth. Abdomen with 20-25 chaetigers provided with type 1 uncini (Figs 26F View Figure 26 , 28B View Figure 28 ).

Material examined herein corresponds to a few small and incomplete specimens. Therefore, the list of diagnostic characters given was developed with the aid of the type specimens re-examined and the original description.

Nucleotide diagnostic features.

All sequences of T. bigeniculatus share the unique apomorphic nucleotides in positions 67 (G) and 138 (G) of the alignement.

Distribution and bathymetry.

Around Iceland at both sides of the GIF Ridge; 179-968 m deep ( Parapar et al. 2011). Material examined here also confirms its presence in shallow and deep bottoms of Norway and Barents Sea (Fig. 8D View Figure 8 ).

Remarks.

In some of the species delimitation analyses performed, Nygren et al. (2018) were able to distinguish between two closely related lineages, clades 20 and 28, but some analyses of nuclear and mitochondrial datasets lump them together in a single entity. Given that all specimens examined share characteristic features that are distinct from other Terebellides species studied herein, clades 20 and 28 have been considered in the present study as a single species and identified as T. bigeniculatus .

As stated above, the sequenced specimens are small and not well preserved, hindering the examination of relevant morphological features with taxonomic value (i.e., branchial type). However, this species is characterised by having geniculate chaetae on TC5 and TC6 instead of only on one chaetiger ( Parapar et al. 2011: 7) as in congeners listed in the Key of the present study. Furthermore, T. bigeniculatus is characterised by the low fusion of the usually irregularly-shaped branchial lobes ( Parapar et al. 2011: 7-8, figs 4, 5a, b), ventral lobes are not obscured by dorsal ones, the lack of marginal papillae in the anterior region of the branchial dorsal lamellae, the presence of ciliated papilla dorsal to thoracic notopodia, and by having thoracic uncini of type 3 and abdominal uncini of type 1. However, it is likely that the irregular shape of the branchiae may correspond to an artefact related to fixation/preservation; other specimens show instead well-defined branchiae that agree with those of A1 and A2 species but less developed (Fig. 26A, B View Figure 26 ; Parapar et al. 2011: 8, fig. 5a). Regarding the four branchial types as defined by Parapar et al. (2016c), branchiae of T. bigeniculatus might correspond therefore to type 3 but with lobes showing a more variable shape.

The original description states that nephridial papillae are located on TC3-TC4 or TC4-TC5 (Suppl. material 1: Table S1; Parapar et al. 2011: 7-9, figs 5c, 6d). Examination of the holotype and several paratypes confirmed that pores are on TC4 and TC5, as in other Group A species. Nephridial pores, as found in most Terebellides species, are usually flat and can be easily overlooked when examined with STM and even SEM; those of T. bigeniculatus are larger and easier to distinguish comparatively with STM ( Parapar et al. 2011: 9, fig. 6d).

Members of species 21 (see below, as Terebellides sp. 2) also bear geniculate chaetae in two chaetigers; this feature had been considered as unique to T. bigeniculatus regarding other NEA species. However, species 21 is present in Arctic waters (cf. Nygren et al. 2018: fig. 6) while the distribution of members of species 20 + 28 and identified here as T. bigeniculatus agrees with that of the type specimens (see Fig. 8D View Figure 8 ).