Terebellides Group D (sensu Nygren et al. 2018)

Barroso, Maria, Moreira, Juan, Capa, Maria, Nygren, Arne & Parapar, Julio, 2022, A further step towards the characterisation of Terebellides (Annelida, Trichobranchidae) diversity in the Northeast Atlantic, with the description of a new species, ZooKeys 1132, pp. 85-126 : 85

publication ID	https://dx.doi.org/10.3897/zookeys.1132.91244
publication LSID	lsid:zoobank.org:pub:4168C32E-37A7-4912-A909-4912E69030AA
persistent identifier	https://treatment.plazi.org/id/9D7B9BB3-09D0-5C1A-B67A-DD154ED33036
treatment provided by	ZooKeys by Pensoft
scientific name	Terebellides Group D (sensu Nygren et al. 2018)
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Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 9 View Figure 9 , 10 View Figure 10 , 11 View Figure 11 , 12 View Figure 12 , 13 View Figure 13 , 14 View Figure 14 , 15 View Figure 15 , 16 View Figure 16 , 17 View Figure 17 , 18 View Figure 18

Description.

The morphological features shared by all examined species in Group D in this paper (clades 2 and 3) are itemized below. Some of these are also shared by Groups A, B, and C as defined in Nygren et al. (2018) (see Remarks below). Clade 15 will be studied elsewhere.

Body appearance. Complete individuals ranging from 5.0-34.0 mm in length. Body tapering posteriorly with segments increasingly shorter and crowded towards pygidium. Prostomium compact; large tentacular membrane surrounding mouth (Figs 2D-F View Figure 2 , 3E, F View Figure 3 ), with typical buccal tentacles with expanded tips (Figs 2E, F View Figure 2 , 3E, F View Figure 3 ). SG 1 as an expanded structure below tentacular membrane in a lower lip (Figs 2D, E View Figure 2 , 3E, F View Figure 3 ).

Branchiae. Branchiae arising as single structure from SG 3, with a single stalked mid-dorsal stem (Figs 2D, E View Figure 2 , 3E, F View Figure 3 ), one pair of dorsal (upper) partially fused lobes (Figs 2D, E View Figure 2 , 3E, F View Figure 3 ), and a pair of shorter ventral (lower) lobes (Fig. 3E, F View Figure 3 ) obscured or not by dorsal ones (Figs 2D-F View Figure 2 , 3E, F View Figure 3 ). Dorsal lobes ending posteriorly in short terminal papilla (Fig. 3E, F View Figure 3 ) and ventral lobes ending in long filaments. Anterior projection of dorsal lobes (fifth lobe) present (Fig. 2D-F View Figure 2 ). Posterior end of dorsal lobes reaching TC 4-5 (Figs 2D-F View Figure 2 , 3E, F View Figure 3 ). Branchial lamellae provided with several parallel rows of cilia and ciliary tufts present in inner face (Figs 14B, C View Figure 14 , 16B, C View Figure 16 , 17B View Figure 17 ). Ciliary papillae absent on the margin of branchial lamellae.

Thorax. Eighteen pairs of notopodia (SG 3-20) (Fig. 2D, E View Figure 2 ), those of TC 1 approximately as long as subsequent ones (Fig. 2D, E View Figure 2 ). Lateral lappets and dorsal projections of notopodia in anterior thoracic chaetigers with different degree of development depending on size and preservation conditions, but both more conspicuous on TC 1-5 (Figs 2D-F View Figure 2 , 3E, F View Figure 3 ). White ventral colouration present on TC 1-4 (Figs 2D View Figure 2 , 3E View Figure 3 ) or only on TC 4 (Figs 2E, F View Figure 2 , 3F View Figure 3 ). All notochaetae as simple capillaries (Fig. 15A View Figure 15 ). Size of notochaetae of TC 1 similar to subsequent ones. Neuropodia as sessile pinnules from TC 6 to body end, with uncini in single or double rows, from TC 7 throughout. Neuropodia on TC 6, provided with several sharply bent, acute-tipped, geniculate chaetae (Figs 15B View Figure 15 , 18A View Figure 18 ) with minute teeth forming a capitium only visible with SEM (Fig. 18A, B View Figure 18 ). From TC 7, neuropodia with one row of uncini per torus (Figs 15C View Figure 15 , 18C View Figure 18 ), with long shafted denticulate hooks, with large main fang (rostrum) longer than upper crest of teeth (capitium), rostrum/capitium length ratio of ~ 2:1, capitium composed by several teeth above main fang of decreasing length (Figs 15D View Figure 15 , 18D View Figure 18 ).

Abdomen and pygidium. Approximately half as long as thorax and progressively thinner (Fig. 2D, E View Figure 2 ). Neuropodia ranging from 18-44 chaetigers and forming erect pinnules (Figs 15E View Figure 15 , 18E View Figure 18 ) with several uncini per torus, number depending on specimen size. Uncini provided with several teeth above rostrum surmounted by a capitium composed of several teeth of decreasing length (Figs 15F View Figure 15 , 18F View Figure 18 ). Pygidium blunt, as funnel-like depression.

Colour pattern. Colour in preserved specimens whitish or pale brown (Fig. 3E, F View Figure 3 ). MG staining pattern characterised by compact green colourant in SG 1-5 and SG 7-13, SG 6 white and SG 14 striped (Fig. 12 View Figure 12 ).

Remarks.

Among the aforementioned characters, the white ventral colouration in anterior thoracic chaetigers may be a useful character to distinguish Group D species from those of Groups A-C. Other taxa described or reported worldwide showing this colouration pattern are Terebellides distincta Williams, 1984 and T. ceneresi Lavesque, Hutchings, Daffe, Nygren & Londoño-Mesa, 2019.