Aphelochaeta longisetosa (Hartmann-Schroder, 1965)

Neal, Lenka, Paterson, Gordon L. J., Blockley, David, Scott, Ben, Sherlock, Emma, Huque, Cate & Glover, Adrian G., 2020, Biodiversity data and new species descriptions of polychaetes from offshore waters of the Falkland Islands, an area undergoing hydrocarbon exploration, ZooKeys 938, pp. 1-86 : 1

Aphelochaeta longisetosa (Hartmann-Schroder, 1965) Figure 20

Tharyx longisetosa Hartmann-Schröder, 1965: 222-223; Carrasco 1977a: 81-82, figs 32-33; Rozbaczylo 1985: 155.

Aphelochaeta longisetosa : Blake 2018: 29-30, fig. 13.

Material.

Holotype: Off central Chile; 84 m; 39°58'S, 73°44.8'W; coll. 15/03/1960; ZMH P-15068.

Description.

Holotype (ZMH P-15068) complete specimen, olive-brown colour. Body nearly cylindrical with a flattened ventral surface, widening gradually in thorax region, but then the same width to pygidial region; thoracic chaetigers crowded, narrow, wider than long, becoming longer in abdominal chaetigers and again becoming wider than long towards pygidium; no obvious junction between thorax and abdomen. Ventral groove present from mid thorax along body (Fig. 20b, c .)

Prostomium conical, bluntly pointed. Peristomium wider than long, with dorsal crest, three annulations seen laterally and horizontally. Dorsal tentacles separated, situated laterally on distal edge of peristomium at junction with first chaetiger, dorsal and proximal to first branchia. Following branchiae situated dorsal to notochaetae separated by at least one branchial diameter from dorsalmost notochaetae (Fig. 20a ).

Chaetae positioned laterally in thoracic segments but becoming more ventral in subsequent segments. Thoracic chaetae relatively long thin capillaries; notochaetae of two sizes, long capillaries of approximately up to ten chaetigers in length, giving specimens a ‘hairy’ appearance, long chaetae appear from anterior thoracic chaetigers and occur down body, only becoming shorter in distal part of abdomen, shorter capillaries less than six chaetigers long also present; thoracic neurochaetae slightly shorter. Pygidial segments widening before narrowing and tapering towards anus, distinct ventral groove observed, terminal anus with low lobes, ventral lobe large extending with an acute tip (Fig. 20c ).

Methyl Green stain pattern.

Holotype without any discernible pattern.

Remarks.

Aphelochaeta longisetosa has been only recently redescribed by Blake (2018) based on re- examination of holotype and additional material from offEcuador and Chile. However, as the holotype was never illustrated, we take the opportunity to further update the description of this species by providing images of the holotype (Fig. 20 ). Few minor differences have been detected between re-description provided here and that of Blake (2018) regarding the position of dorsal tentacles and first pair of branchiae. While Blake (2018) considered these structures to be associated with chaetiger 1, here we observed the dorsal tentacles on distal edge of peristomium and first chaetiger, dorsal and proximal to first branchia. Table 3 gives a comparison of Aphelochaeta species that might be found in the Falkland Islands region.

Figures

Figure 20. Aphelochaeta longisetosa (Hartmann-Schroeder, 1965) Holotype (ZMH- P 15068) a detail of anterior region, showing arrangement of dorsal tentacles (DT) and first branchiae (1 Br) b general view of complete specimen c view of pygidium, showing pointed anal lobe.