Nereis denhamensis Augener, 1913

Figs 8A–G, 19G–H

Nereis denhamensis Augener, 1913: 156–159, fig. 16.a–b, pl. 3, fig. 51u; Fauvel 1917: 204–206, pl. 6, figs 45–46; Kott 1951: 99–101, figs 3.s–y, 4.l–q; Hartman 1954: 30–31; Hutchings & Turvey 1982: 124–125, fig. 11.a–k; Wilson 1985: 133–134; Glasby et al. 2013: 253–255, fig. 5A–B.

Nereis (Nereis) denhamensis .— Hartmann-Schröder 1980: 58, figs 47–55; Hartmann-Schröder 1984: 27.

Type locality. Shark Bay, Western Australia .

Material examined. Western Australia: Cape Bosut, Bidyadanga, 18°42′04.99″S 121°37′34.11″E, 3 November 2020, 2 specimens (WAM V11642) . Cape Keraudren, 19°57′51.30″S 119°47′16.94″E, 5 November 2020, male epitoke, 1 specimen (WAM V11643) . North West Cape, Ningaloo, 21°47′35.17″S 114°10′22.77″E, 27 September 2020, 3 specimens (WAM V11644) . Lighthouse Bay, Ningaloo, 21°48′19.86″S 114°07′48.61″E, 26 September 2020, 1 specimen (WAM V11645) . Jurabi, Ningaloo, 21°50′44.05″S 114°02′09.22″E, 25 September 2020, 6 specimens (WAM V11646) . Yardie Creek, Ningaloo, 22°19′35.90″S 113°48′33.70″E, 24 September 2020, 5 specimens (WAM V11647) . Bateman Bay, 23°02′32.68″S 113°49′39.59″E, 20 September 2020, 1 specimen (WAM V11648) . Gnaraloo, 23°46′21.83″S 113°32′09.24″E, 22 September 2020, 3 specimens (WAM V11649) . Shag Rock Beach, Nambung, 30°35′40.00″S 115°06′11.00″E, 31 December 2020, 4 specimens (WAM V11650) .

Comparative material. Nereis denhamensis, det. C. Glasby, East Point, Northern Territory, 12°25′S 130°49′E, coll. C. Glasby, 28 October 2003, 2 (NTM W19015) .

Description. Complete specimens with 57–62 chaetigers, body 16.1–25.4 mm long and 1.0– 1.8 mm wide; cream yellow to reddish brown in alcohol. Incomplete specimens with 31–55 chaetigers, posterior end missing, remaining body 10.4–32.5 mm long and 0.9–2.0 mm wide; cream yellow to reddish brown in alcohol.

Prostomium longer than wide. Eyes black, two pairs, equal sizes, in trapezoidal arrangement. Palps one pair, palpophores globose, palpostyles conical. Antennae one pair, shorter than palps. Tentacular cirri four pairs with basal articulation, longest one extending to chaetiger 1–3 (Fig. 8A). Pharyngeal jaws translucent reddish black, curved at tips, with eight teeth on each jaw. Paragnaths translucent reddish black, conical, present on maxillary and oral rings, arranged as follows: Area I= 1–3, Area II= 14–16 in two rows, Area III= 13–18 in 3–4 irregular rows, Area IV= 19–21 in four curved rows, Area V= 0, Area VI= 5–11 very small paragnaths in two rows, Areas VII–VIII= 10–13 in one row (Fig. 8B).

Apodous segment about twice longer than first chaetiger. First two chaetigers uniramous. Notopodia present with digitiform dorsal and ventral ligules in anterior chaetigers, basal dorsal ligules enlarged in posterior chaetigers. Dorsal cirri cirriform, attached on middle of dorsal parapodia, about three times longer than dorsal ligules. Neuropodia with subconical ventral ligules, acicular ligules, and rounded postchaetal lobes extending slightly below acicular ligule tips; ventral ligules become digitiform in posterior chaetigers. Ventral cirri cirriform, attached basally on ventral parapodia, slightly shorter than ventral ligules (Fig. 8C).

Notochaetae present with homogomph spinigers in anterior chaetigers, homogomph falcigers (Fig. 8D) from chaetiger 15–21. Notopodial falcigerous blades short, with terminal and one lateral tooth, and two smaller teeth basally. Neurochaetae present with homogomph spinigers (Fig. 8E) and heterogomph falcigers in dorsal fascicles, heterogomph spinigers (Fig. 9F) and falcigers (Fig. 8G) in ventral fascicles. All spinigerous blades long, with fine serrations. Neuropodial falcigerous blades short, with fine serrations. Acicula black. Pygidium with anus on dorsal side, anal cirri cirriform, as long as last three to five chaetigers.

A complete, male epitokous specimen with 56 chaetigers, body 21.1 mm long and 1.0 mm wide; cream yellow in alcohol. Specimen present black, enlarged, overlapping paired eyes, in rectangular arrangement. Body divided into 16 pre-natatory chaetigers, 23 natatory chaetigers, and 17 post-natatory chaetigers. Neuropodial postchaetal lobes modified into large, flat lamella in natatory chaetigers. In natatory chaetigers, dorsal cirri crenulated basally along outer margin of about two-third part and developing a small basal lamella. Ventral cirri unmodified but developing a small basal lamella in natatory chaetigers. Paddle-shaped notochaetae present in natatory chaetigers.

Remarks. Nereis denhamensis has been synonymised with N. jacksoni Kinberg, 1865 by Augener (1922b), Fauvel (1932, 1953), and Hartmann-Schröder (1979, 1980, 1984), but others have kept them as distinct species due to differences in parapodia and notopodial homogomph falcigers (Kott 1951; Hartman 1954; Hutchings & Turvey 1982; Wilson 1985). Paragnaths on Areas I and III can be fewer (0–1 cone) but it is rare (Hartmann-Schröder 1980; Hutchings & Turvey 1982; Hartmann-Schröder 1984) and only occur in small specimens (Wilson 1985). In specimens from Victoria, paragnaths on Areas VII–VIII can be arranged in 1–2 rows (Wilson 1985). Anal cirri can extend to last 5–10 chaetigers (Hutchings & Turvey 1982), longer than those of our specimens. Pre-natatory chaetigers of our male epitoke are same as those of a male epitoke examined by Glasby et al. (2013) but two more chaetigers than those of male epitokes examined by Kott (1951) and Hartman (1954).

A comparative specimen from Northern Territory agreed in all aspects with the description above except in Areas VII–VIII, where there were 15 paragnaths in one row (Fig. 19G–H).

Distribution. Australia: Northern Territory, Western Australia, and South Australia (Table 2).

Habitat. Intertidal, subtidal, rocky shores, inshore reefs, artificial hard substrates (Table 2).