Terebellides Group C (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/B06F73F7-8E65-529D-8ACF-9EC4FB5A480F
treatment provided by	ZooKeys by Pensoft
scientific name	Terebellides Group C (sensu Nygren et al. 2018)
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Figs 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

Description.

The morphological features of the examined species in Group C in this paper (clade 24) are itemised below. Some of these are also shared by Groups A, B, and D as defined in Nygren et al. (2018) (see Remarks below). Clade 25 will be studied elsewhere; formal description of clade 22 will wait until more material is available.

Body appearance. Incomplete individuals ranging from 10.0-17.0 mm in length. Body tapering posteriorly with segments increasingly shorter and crowded towards pygidium. Prostomium compact; large tentacular membrane surrounding mouth (Fig. 3D View Figure 3 ), with typical buccal tentacles with expanded tips (Fig. 3D View Figure 3 ). SG 1 as an expanded structure below tentacular membrane in a lower lip (Fig. 3D View Figure 3 ).

Branchiae. Branchiae arising as single structure from SG 3, with a single stalked mid-dorsal stem, lobes not fused (Fig. 4C View Figure 4 ). Dorsal lobes ending posteriorly in short terminal papilla (Fig. 3D View Figure 3 ) and ventral lobes ones ending in long filaments. Anterior projection of dorsal lobes (fifth lobe) present. Posterior end of dorsal lobes reaching TC 4. Ciliary rows of cilia and ciliary tufts in inner face of branchial lamellae not observed. Ciliary papillae absent in branchial lamellae margin.

Thorax. Eighteen pairs of notopodia (SG 3-20) (Fig. 3D View Figure 3 ), those of TC 1 approximately as long as subsequent ones (Fig. 4C View Figure 4 ). 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. All notochaetae as simple capillaries. Size of notochaetae of TC 1 similar to subsequent ones. Neuropodia as sessile pinnules from TC 6 to body end, with uncini in single rows, from TC 7 throughout. Neuropodia on TC 6, provided with several sharply bent, acute-tipped, geniculate chaetae (Fig. 13B View Figure 13 ) with minute teeth forming a capitium only visible with SEM (Fig. 13B View Figure 13 ). From TC 7, neuropodia with one row of uncini per torus (Fig. 13C View Figure 13 ), 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 (Fig. 13D View Figure 13 ).

Abdomen and pygidium. Approximately half as long as thorax and progressively thinner (Fig. 3D View Figure 3 ). Neuropodia ranging from 18-20 chaetigers and forming erect pinnules 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 (Fig. 13E, F View Figure 13 ). Pygidium blunt, as funnel-like depression.

Colour pattern. Colour in preserved specimens whitish (Fig. 3D View Figure 3 ). MG staining pattern characterised by compact green colourant in SG 1-4, then turning into striped pattern in SG 5-14 and fading in following segments (Fig. 12 View Figure 12 ).

Remarks.

Among the above-mentioned characters, branchial features might serve to distinguish most of Group C species from those of Groups A, B and D. Those include branchial lobes size, presence of filaments in ventral ones and lobes which are not fused. Other taxa such as Terebellides mira Schüller & Hutchings, 2013 and T. rigel Schüller & Hutchings, 2013 also bear branchiae with similar shape ( Parapar et al. 2016a).