Platynereis mahanga, Read, Geoffrey B., 2007

Read, Geoffrey B., 2007, Taxonomy of sympatric New Zealand species of Platynereis, with description of three new species additional to P. australis (Schmarda) (Annelida: Polychaeta: Nereididae), Zootaxa 1558, pp. 1-28 : 11-14

Platynereis mahanga sp. nov.

(Figs 2, 5B, 6D)

Nereis (Platynereis) australis .— Augener 1923:27 –39, Fig.16, Carnley Harbour, etc, Auckland I; Perseverance Harbour, Campbell I.

Diagnosis. Secondary-tooth-tipped homogomph falcigers in juveniles, with replacement ceasing when about 50 chaetigers developed; homogomph falcigers absent in adults. Male heteronereid 2-part, 18 (17–18) prenatatory segments, pygidial papillae structure a 2-part fan of 8 large papillae. Female heteronereid 3-part, 24 (22–25) pre-natatory segments, eggs blue, first 5 dorsal cirri enlarged. Benthic atoke dark green anteriorly, without or trace brown pigment on thickened lobes, prostomium or proboscis ring. Segment 11 notopodial superior ligule less bluntly rounded than preceding segment.

Heteronereid material examined. Holotype. Wellington, Karaka Bay, 41° 18.34' S, 174° 49.9' E, stn Y10207, 0 m, 27.vi.1970: het. male, 40 mm, coll G. Read, night light & dip net ( NIWA 3363, H-872). Paratypes. Banks Peninsula. Menzies Bay, 43° 38.4' S, 172° 57.6' E:- stn GAK19580501, 0 m, 1.v.1958: het. 1 male, 1 female. Lyttelton Harbour, 43° 36.6' S, 172° 42.6' E:- stn GAK19580000, 0 m, 1.vi.1958: het. 1 male, 1 female. Kaikoura Peninsula. Kaikoura, 42° 24' S, 173° 40.8' E, 0 m 19.viii.1961 (UCANTK K079A): het. 6 male, 6 female. Otago Harbour. Quarantine Island, 45° 49.8' S, 170° 37.2' E:- stn GAK19530606, 1 m, 6.vi.1953: het. 1 male, 1 female. Wellington Harbour. Greta Point (Evans Bay), 41° 18.6' S, 174° 48' E:- stn Y10152, 0 m, 24.viii.2003: het. 1 male, 1 female. Houghton Bay, 41° 20.4' S, 174° 46.8' E:- stn Z3875, 0 m, 2.viii.1964: het. 1 male, 1 female. Karaka Bay, 41° 18.34' S, 174° 49.9' E:- stn Y10203, 0 m, 28.v.1970: het. 32 male, 18 female; stn Y10204, 0 m, 30.v.1970: het. 15 male, 22 female; stn Y10206, 0 m, 24.vi.1970: het. 4 male; stn Y10207, 0 m, 27.vi.1970: het. 43 male, 19 female; stn Y10208, 0 m, 27.vii.1970: het. 6 male, 6 female; stn Y10209, 0 m, 25.viii.1970: het. 2 male, 5 female; stn Y10227, 0 m, 9.xi.1971: het. 1 female; stn Y10235, 0 m, 4.vi.1972: het. 1 female; stn Y10236, 0 m, 7.vi.1972: het. 2 male; stn Y10289, 0 m, 8.ix.1975: het. 1 male, 1 female. Kau Bay, 41° 16.8' S, 174° 49.2' E:- stn Y10216, 0 m, 1.v.1971: het. 1 male; stn Y10218, 0 m, 29.v.1971: het. 1 female; stn Y10219, 0 m, 16.vi.1971: het. 1 male, 1 female; stn Y10222, 0 m, 15.vii.1971: het. 1 male; stn Y10274, 0 m, 7.v.1975: het. 1 male. Mahanga Bay, 41° 17.4' S, 174° 49.8' E:- stn Y10241, 0 m, 3.viii.1972: het. 3 female; stn Y10242, 0 m, 10.viii.1972: het. 49 male, 46 female; stn Y10246, 0 m, 11.ix.1972: het. 1 female; stn Y10264, 0 m, 30.iv.1973: het. 4 male, 1 female; stn Y10267, 0 m, 29.vi.1973: het. 5 male, 4 female; stn Y10268, 0 m, 27.vii.1973: het. 13 male, 13 female; stn Y10269, 0 m, 24.viii.1973: het. 3 male, 1 female; stn Y10275, 0 m, 3.ix.1975: het. 2 female. Wellington, coast south. Island Bay, 41° 21.02' S, 174° 46.11' E:- stn Y10278, 0 m, 18.viii.1976: het. 5 male, 11 female; stn Y10281, 0 m, 9.ix.1977: het. 1 male; stn Y10284, 0 m, 6.x.1977: het. 1 male.

Non-type other material examined. Wairarapa, coast south, Windy Point, 41° 24' S, 174° 58.8' E:- stn Y10322, 0 m, 17.iv.1976: 22 atoke. Wellington Harbour, Kaiwharawhara, 41° 15.6' S, 174° 47.4' E:- stn Y10324, 2 m, 23.iii.1977: 5 atoke. Karaka Bay, 41° 18.34' S, 174° 49.9' E:- stn Y10315, 0 m, 30.iv.1975: 12 atoke; stn Y10318, 0 m, 8.ix.1975: 7 atoke. Scorching Bay, 41° 18' S, 174° 50' E:- stn Y10297, 0 m, 24.vi.1970: 36 atoke. Wellington, coast west, Plimmerton north, 41° 4.8' S, 174° 51' E:- stn Y10320, 0 m, 11.xi.1975: 3 atoke.

Size and shape. Atoke length up to 170 mm for 140 segments. Male heteronereid pre-natatory region almost uniform in width, but eighteenth parapodium often smaller than those anterior to it, posterior body narrow and tapered. Wellington region specimens mean length 33 mm, range 21–57 mm (std dev. 8 mm, n 45). Female heteronereid body uniform in width, Wellington region specimen mean length 29 mm, range 18–64 mm (std dev. 9 mm, n 36).

Atoke description. Head region, paragnaths and proboscis, and parapodia and chaetae as in P. australis except area III paragnaths better developed, maxillary ring not usually expanded in width anteriorly, segment 11 notopodial superior ligule transitional, slightly conical rather than bluntly rounded.

Atoke live colouration. Anterior dorsal body behind head green pigmented, dark pigment on head less developed than in P. australis , proboscis pigment absent, brown pigment on chaetiger 5 to 11 parapodial lobes slight or absent. Posterior pigment as in P. australis .

Male heteronereid description. A two-part heteronereid. Enlarged eyes dark red and head carried bent down when proboscis retracted. Pre-natatory region with 18 (17–18) segments. Variation in Wellington specimens rare with fewer than 10% with 17 segments ( Table 4 ). Anterior first 7 dorsal cirri, first 4 ventral cirri enlarged, without variation (Fig. 2A). Chaetiger 8–18 parapodia unmodified; anterior parapodia as in P. australis . Natatory parapodia beginning from chaetiger 19 (18) with morphology as in P. australis males, except posteriorly natatory region narrow, tapering, heteronereid lamellae absent or small, with parapodia correspondingly altered in shape (Fig. 2C). Only natatory chaetae present, identical to those of P. australis . Taper of posterior body accentuated as axes of posterior parapodia directed upwards, at up to 80 degrees from the horizontal, so that parapodial structures dorsal. Pygidial structure a horizontally orientated ‘fan’ with a total of eight papillae divided into two branches of four (Fig. 2B). Gravid male in-life colouration as in P. australis , except also scattered dots of reddish surface pigment on dorsal anterior body. Holotype male as above, 40 mm for 110 segments, with 18 pre-natatory segments, proboscis everted, paragnaths typical, except lines somewhat thickened, segments 5–10 with glandular blunt anterior superior notopodial ligules, segment 11 ligule transitional, slightly conical.

Female heteronereid description. Three-part heteronereid but development of posterior region variable. Head and eyes as in male. Pre-natatory region with 24 (22-25) segments with fewer than 5% with 22, 27% with 23, 55% with 24, and 3% with 25 ( Table 5 ). Anterior first 5 dorsal cirri enlarged ( Fig. 6 D, 50% of specimens) although 6 enlarged dorsal cirri common (38%) and one specimen with 7 ( Table 6 ). Always 4 enlarged ventral cirri. Parapodia of chaetigers 6–24 (mean values) unmodified. Natatory parapodia as in P. australis females. Posterior region of 20 to 30 segments with almost unmodified parapodia, usually lacking chaetae, although occasionally with a few natatory chaetae, notochaetal spinigers, and very rarely neurochaetal falcigers. Pygidium as in atoke except lacking anal cirri. Eggs 170–190 µm in diameter. Gravid females in life colouration blue except at extreme anterior due to colour of eggs masking all other body colour ( Fig. 6 D). Dorsal blood vessel as prominent as in males, spent females appearing similar in colouration to spent males.

Juvenile chaetation and colour. Homogomph notopodial falcigers developing in laboratory-reared individuals at about 10-chaetiger stage, with morphology as in P. australis . No wild juveniles obtained. Falcigers present at chaetigers 7–11th at 13-chaetiger stage, at 10–15th at 17-chaetiger, 10–21st at 25-chaetiger, and intermittently remain from chaetiger 32 at 45-chaetigers and onwards.

Juvenile pigmentation pattern of dorsal white surface pigment on head, on pygidium, and along midline on either side of dorsal blood vessel, and large lateral dots of red pigment on anterior 8 to 9 segments ( Fig. 5 B). White midline pigment semi-continuous anteriorly, posteriorly usually in more or less rectangular blocks. Pattern apparent until white head pigment gradually lost and red pigment spots becoming smaller when about 50 chaetigers developed. White middorsal pigment then taking on linked-chain pattern, and diffuse green anterior colouration of adult present. Region of anterior thickened ligules present.

Reproduction. At Wellington P. mahanga sp. nov. swarming occurred over an extended autumn to spring period, late March to November inclusive, with the period of maximum abundance late autumn to late winter (May to late August). Spawning in the laboratory occurred as in P. australis , except that P. mahanga sp. nov. males did perform rapid swimming in tight circles before spawning, and pairs did not spawn as readily. Males normally spawned first, but on two occasions P. mahanga sp. nov. females in a bowl together spawned one after the other although the males in the bowl did not spawn at all.

Habitat. Intertidal and subtidal on rocky ground under stones and in crevices. A detritus and secretion tube is formed.

Distribution. New Zealand mainland islands, Auckland and Campbell Islands.

Etymology. The epithet mahanga is a noun in apposition.

Remarks. Platynereis mahanga sp. nov. differs markedly from P. australis in heteronereid morphology, particularly in the male pygidial structure, and as an atoke less definitively in colour pattern and minor morphological differences.

P. mahanga sp. nov. heteronereids were not significantly different in length between sexes or in relation to P. k a u sp. nov. They were larger than P. karaka sp. nov. and smaller than P. australis . Females usually had 6 more pre-natatory segments than males. Although P. mahanga males usually had 9 fewer pre-natatory segments than P. australis males, the ratio of total length to anterior region length was not significantly different. The pronounced taper of male bodies associated with more dorsally directed, less modified posterior parapodia is a feature shared with P. k a u sp. nov., along with the fan-like pygidial papillae.

Augener (1923) recorded male heteronereids of this species from Auckland and Campbell islands as Nereis (Platynereis) australis . One specimen was a completely metamorphosed heteronereid in which the 18th parapodium was the last of the pre-natatory region. Augener also figured the characteristic pygidial structure ‘mit handförmigen Fortsätzen’ ( Augener, 1923 pp.28–29, fig.16).

Figures

FIGURE 5. Platynereis juvenile dorsal pigmentation pattern, A – C, P. australis, P. mahanga sp. nov., P. k a u sp. nov. respectively. Scale bar 0.5 mm.

FIGURE 6. A, Platynereis australis female anterior dorsal; B, P. australis male anterior lateral; C, P. australis juvenile distal tip of homogomph falciger; D, P. mahanga sp. nov. female anterior dorsal; E, P. k a u sp. nov. female anterior dorso-lateral; F, P. k a u sp. nov. male dorsal pygidium; G, P. australis male pygidium in left lateral view; H, P. karaka sp. nov. male anterior lateral; I, P. karaka sp. nov. male dorsal midline papillae (anterior to top). Images A, B, D – I are photographs of live heteronereid specimens captured at night. Scale bar: 1 mm A, B, D, E, G; 0.5 mm F, H; 0.2 mm I; 5 μm C.

Tables

TABLE 4. Platynereis mahanga male heteronereids pre-natatory region segment totals.

Location	Number of pre-natatory segments		Mean	Std.dev.	n
	17 17+t 18	18+t
Cook Strait	9 1 75	1	17.9	0.32	86
Kaikoura	6 0 0	0	17.0	-	6

TABLE 5. Platynereis mahanga female heteronereids pre-natatory region segment totals.

Location	Number of pre-natatory segments			Mean	Std.dev.	n
	22 22t 23 23t 24	24t	25
Cook Strait	3 1 17 5 35	1	2	23.62	1.19	64
Kaikoura	0 0 0 2 3	0	1	-	-	6

TABLE 6. Platynereis mahanga female heteronereids anterior dorsal enlarged cirri totals.

Location	Number of dorsal enlarged cirri		Mean	Std.dev.	n
	5 5t 6	7
Cook Strait	20 4 15	1	5.4	0.53	40