Neanthes glandicincta (Southern, 1921)

Azmi, Siti Syazwani, Ibrahim, Yusof Shuaib, Angsupanich, Saowapa, Sumpuntarat, Pornsan & Sato, Masanori, 2021, Epitokous metamorphosis, reproductive swimming, and early development of the estuarine polychaete, Neanthes glandicincta Southern, 1921 (Annelida, Nereididae) on the east coast of the Malay Peninsula, ZooKeys 1011, pp. 1-24 : 1

publication ID	https://dx.doi.org/10.3897/zookeys.1011.59780
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scientific name	Neanthes glandicincta (Southern, 1921)
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Neanthes glandicincta (Southern, 1921) Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7

Nereis (Nereis) glandicincta Southern, 1921: 589-593, text fig. 5a-e, pl. 23, fig. 9A-L.

Nereis glandicincta : Fauvel 1932: 92-93; Fauvel 1939: 314-315, Fauvel 1953: 181-182, fig. 91f-h.

Neanthes glandicincta : Lee and Glasby 2015: 80-85, figs 7-9; Misra 1999: 161-162; Ibrahim et al. 2019: 86-89, figs 3, 4.

Ceratonereis burmensis Monro, 1937: 532-536, fig. 1a-f; Misra 1999: 149; Ng et al. 2011: 426.

Nereis (Ceratonereis) burmensis : Fauvel 1953: 196-197, fig. 97d-f.

Ceratonereis (Composetia) burmensis : Hartmann-Schröder 1985: 49 (list); Chan 2009: 165-167, fig. 5a-r, in part.

Ceratonereis burmensis Not Neanthes glandicincta : Wu et al. 1985: 150-151, fig. 84; Wu et al. 1985: 174-177, figs 98, 99 (described as Ceratonereis burmensis ).

Type locality.

Brackish lakes or pools at four localities in Barantolla, Dhappa, and Garia near Calcutta in India ( Southern 1921).

Material examined.

Sexually fully mature specimens (epitokes). Epitokes collected during reproductive swimming in the mangrove area of Kuala Ibai (5°17'7.6"N, 103°10'10.3"E), Terengganu, Malaysia: 2 males (BW, 1.6-1.9 mm; UMTAnn 445-446), coll. YS Ibrahim, 31 January 2018; 2 males and one female (2.1-2.4 mm; UMTAnn 447-449), coll. YS Ibrahim, 28 February 2018; 3 males (2.2-3.2 mm; UMTAnn 450-452), coll. SS Azmi, 6 January 2019, 2 males (2.1-2.6 mm; UMTAnn 453-454), coll. SS Azmi, 21 January 2019.

Epitokes obtained by rearing immature atokes collected from Aowsai in the lower reaches of Songkhla Lagoon (7°10'37.4"N, 100°32'26.2"E), Thailand (PMBC 20732): 3 males (BW, 1.2-2.1 mm) and 3 females (BW, 1.5-1.7 mm), coll. P Sumpuntarat, 2 March 2006.

Atokous specimens collected from the same locality as the epitokes. Immature atokes collected from Aowsai in the lower reaches of Songkhla Lagoon, Thailand (as above): 5 specimens (BW, 1.6-2.5 mm; PMBC 21209), coll. P. Sumpuntarat, during the period from September to December 2005; 4 specimens (BW, 1.2-1.3 mm; PMBC 21211), coll. S Angsupanich et al., 1 March 2008; 1 specimen (BW, 1.5 mm; PMBC 21212), coll. S Angsupanich, 19 November 2008.

Description of atokes.

Ten atokes, including six complete specimens, 27-85 mm BL (Mean ± SD: 60.8 ± 19.7, n = 6), 1. 2-2.5 mm BW (1.7 ± 0.5, n = 10), with 86-122 chaetigers (108.3 ± 15.8, n = 4) (Table 1 View Table 1 ). Colour in preserved specimens whitish cream (Fig. 2A View Figure 2 ).

Two pairs of eyes arranged trapezoidally (anterior pair with space wider than that of posterior pair); anterior pair reniform; posterior pair round; two pairs of eyes almost same in size (Figs 2A View Figure 2 , 3E View Figure 3 ). Approximately ten transverse grooves conspicuous in each of massive palpophores. Apodous segment (peristomium) with four pairs of tentacular cirri of unequal length; posterodorsal tentacular cirri longest, reaching back to chaetigers V-VII.

Proboscis with pair of semi-transparent amber jaws, each with ca. ten teeth. Typical conical paragnaths present on maxillary ring (Fig. 2C-F View Figure 2 ); number of paragnaths and their arrangement on each area of everted proboscis as follows (Table 1 View Table 1 ): area I: 4-11, scattered and unequal (Fig. 2C View Figure 2 ); area II: 12-17, in two arched rows, markedly large paragnaths with sharply tapering and curved tip present in anterior and middle positions (Fig. 2D View Figure 2 ); area III: 38-55, in three or four rows of transversely elongated bands, each paragnath with papilla-like base (Fig. 2E View Figure 2 ); area IV: 10-14, in triangular patch with markedly large paragnaths present in middle and posterior positions (Fig. 2F View Figure 2 ). Oral ring with no or few minute paragnaths; number of paragnaths on each area are as follows (Table 1 View Table 1 ): area V: none; area VI: none or single minute paragnath present, seated on tip of each papilla (usually pair of small nipple-like round papillae visible in right and left of area VI; Fig. 2B View Figure 2 ); area VII-VIII: none or single minute paragnath present. Total number of paragnaths 94-119.

Uniramous parapodia of first two chaetigers without notoacicula. In following biramous parapodia, notopodia consisting of dorsal cirrus and three ligules/lobe (dorsal ligule, prechaetal lobe and median ligule) throughout. Neuropodia consisting of four ligules/lobes (superior lobe, inferior lobe, postchaetal lobe, ventral ligule) and ventral cirrus in anterior and middle body; superior lobe absent in posterior body (from chaetiger L).

Notochaetae consisting of homogomph spinigers throughout. Upper neurochaetae including homogomph spinigers with long blades and heterogomph spinigers with short blades throughout; some or most of heterogomph spinigers replaced by heterogomph falcigers in middle body. Lower neurochaetae include heterogomph spinigers with long blade (at upper position) and heterogomph spinigers with short blade (at lower position) throughout; some or most of heterogomph spinigers with short blades replaced by heterogomph falcigers in anterior-mid body (from chaetigers XI-XIX usually). Heterogomph falcigers with finely serrated slender blades; few heterogomph falcigers rarely (two of ten specimens) present in lower neurochaetae of chaetiger 1. Conspicuous glandular patches present in dorsal ligules.

Coelom of three individuals filled with many oocytes with maximum diameter of ca. 100 µm.

Description of epitokes.

Twelve males, including eight complete specimens, 17-43 mm BL (Mean ± SD: 32.4 ± 8.3, n = 8), 1.2-3.2 mm BW (2.2 ± 0.5, n = 12), with 62-123 chaetigers (100.9 ± 19.4, n = 8). Four females, including three complete specimens, 25-34 mm BL (28.7 ± 4.7, n = 3), 1.5-2. 4 mm BW (1.8 ± 0.4, n = 4), with 84-116 chaetigers (102.0 ± 16.4, n = 3). There was no significant difference in BL, BW, and the number of chaetigers between males and females (Wilcoxon-Mann-Whitney test, P> 0.2). Live spent worms after spawning semi-transparent; live females with greenish eggs.

Two pairs of eyes enlarged in both males (Figs 3C View Figure 3 , 4A, B View Figure 4 ) and females (Figs 3B, D View Figure 3 , 5A-C View Figure 5 ) in comparison with those in atokes (Fig. 3E View Figure 3 ); enlargement of eyes more remarkable in males than females; two pairs of eyes almost same in size, shape (round or ovoid) and space between right and left eyes. Apodous segment with four pairs of tentacular cirri of unequal length; posterodorsal tentacular cirri longest, reaching back to chaetigers VII-X.

Proboscis with pair of semi-transparent amber jaws, each with ca. ten teeth (up to ca. 15 teeth in dissected jaw, Fig. 2G View Figure 2 ). Dark pigmentation present on surface of proboscis (in particular, ventral surface) of four males of Malaysian specimens (Fig. 4B, C View Figure 4 ). Conical paragnaths present on maxillary ring (Fig. 4B, C View Figure 4 ); number of paragnaths and their arrangement on each area of everted proboscis as follows (Table 1 View Table 1 ): area I: 3-10, scattered and unequal; area II: 8-19, in two arched rows, markedly large paragnaths with sharply tapering and curved tip present in anterior and middle positions; area III: 32-50, in three or four rows of transversely elongated bands; area IV: 6-16, in triangular patch with markedly large paragnaths present in middle and posterior positions. Oral ring with no or few minute paragnaths; number of paragnaths on each area are as follows (Table 1 View Table 1 ): area V: none; area VI: none; area VII-VIII: 0-2, in transverse row. Total number of paragnaths 58-124. Pair of small nipple-like round papillae usually visible in right and left of area VI, as those in atokes (Fig. 2B View Figure 2 ).

Male bodies divided into three regions (Fig. 3A View Figure 3 ): anterior (pre-natatory), middle (natatory), and posterior (post-natatory) regions; parapodia of pre-natatory and post-natatory regions similar to those of atokes (Fig. 6A, D View Figure 6 ).

Male pre-natatory region with 18-25 chaetigers, with dorsal cirri of first seven or eight chaetigers thickened mainly at base, and with ventral cirri of first 5-7 chaetigers thickened throughout (Fig. 7A View Figure 7 ). Neuropodial heterogomph falcigers (Fig. 6G View Figure 6 ) present in few chaetigers of pre-natatory region, appearing from chaetigers XV-XXI, or completely absent.

Male natatory region constituting of 30-56 chaetigers, with parapodia markedly modified (Figs 6B View Figure 6 , 7B View Figure 7 ); round lobes newly present on upper and lower base of ventral cirri, appearing from chaetigers XIX-XXVI to chaetigers LII-LXXIII. Neuropodial postchaetal lobe developing into large round flat lamella with or without small triangular protrusion on lateral edge in almost same range of chaetigers; dorsal cirri frequently serrated on lower edge, slightly elongated; ovoid lobe newly present on upper base of dorsal cirri; all parapodial ligules and lobes enlarged as thin lamellae (Figs 6B View Figure 6 , 7B View Figure 7 ). Epitokous paddle-like natatory chaetae (Figs 6H View Figure 6 , 7E View Figure 7 ) appearing from chaetigers XXII-XXVIII to chaetigers LIV-LXXVIII, substituting atokous chaetae (Fig. 6E-G View Figure 6 ) completely in most of middle natatory region, and incompletely in few anteriormost and posteriormost chaetigers of this region (with atokous chaetae remaining there); blade of epitokous paddle chaetae semi-transparent, flat and wide, with minutely serrated edge on one side, and tapering tip.

Male post-natatory region constituting 13-64 chaetigers, with unmodified parapodia (Figs 3A View Figure 3 , 6D View Figure 6 ); neuropodial heterogomph falcigers absent. Pygidium with pygidial rosette.

Females with unmodified parapodia throughout, except for with dorsal cirri of first 4-8 chaetigers thickened mainly at base, and with ventral cirri of first 4-8 chaetigers slightly thickened throughout (Figs 3B View Figure 3 , 5A View Figure 5 , 6C View Figure 6 , 7C, D View Figure 7 ). Epitokous paddle chaetae present together with atokous chaetae in both notochaetae and neurochaetae in middle body from chaetigers XXVI-XXXV to chaetigers XLVI-LII. Neuropodial heterogomph falcigers usually appearing from chaetigers XV-XVIII to chaetigers LIV-LXXII. Pygidium without pygidial rosette. Few eggs (full-grown oocytes) remained in coelom of females; eggs spherical, 100-140 µm in diameter in fixed specimens.

In both sexes, body wall of epitokes thin. Small slits on body wall of ventral surface at base of parapodia present in middle and posterior chaetigers of females (Fig. 5D View Figure 5 ).

Variation.

Paragnath numbers in epitokes from Thailand and Malaysia and atokes from Thailand are summarised together with the atokes from the previous studies in Table 1 View Table 1 .

In three specimens, an epitokous female (PMBC 20732) and two atokes (PMBC 21211, 21212), a few heterogomph falcigers were present in the lower neurochaetae of chaetiger 1, whereas falcigers were usually absent in the anterior chaetigers (at least first 10 chaetigers) in the present study, as reported in the previous studies on N. glandicincta ( Southern 1921; Lee and Glasby 2015; Ibrahim et al. 2019).

The papilla-like base of paragnaths in area III was not conspicuous in the ethanol-fixed epitokous materials.

Habitat.

Intertidal and shallow subtidal bottoms of sandy or muddy sediment in the estuaries, where the salinity of ambient water widely ranges from 18 to 32 psu at Kuala Ibai in Malaysia (see below), and from 1 to 33 psu in the coast of the lower reaches of Songkhla Lagoon ( Angsupanich and Rakkheaw 1997; S Angsupanich, unpublished data).

Geographic distribution.

India, Myanmar, Singapore, the east coast of Malay Peninsula (Malaysia and Thailand). Based on Southern (1921), Fauvel (1932, 1939, 1953), Misra (1999), Lee and Glasby (2015), Ibrahim et al. (2019), and the present study.

Remarks.

The morphological characteristics of present Thailand and Malaysian specimens of swimming epitokes agreed well with the atokes collected from Thailand in the present study and also the atokes previously described from India ( Southern 1921; Lee and Glasby 2015), Myanmar ( Monro 1937; Lee and Glasby 2015), Singapore ( Lee and Glasby 2015), and Malaysia ( Ibrahim et al. 2019), except for their epitokous modification of parapodia and chaetae in the middle body, and enlarged eyes. However, we found that a few falcigers were exceptionally present in the lower neurochaetae of chaetiger 1 in three Thailand specimens, unlike the previous descriptions of this species and also the diagnosis of Neanthes glandicincta species complex ( Ibrahim et al. 2019). Therefore, the diagnosis of this species and the Neanthes glandicincta species complex should be amended here from Ibrahim et al. (2019) to allow for the occasional presence of falcigers in chaetiger 1.

The Indian specimens described as N. glandicincta by Misra (1999) seem to belong correctly to this species if Misra’s description "Notosetae homogomph spinigers and homogomph falcigers" is a mistake. The Chinese specimens described as N. glandicincta by Wu et al. (1985) seem to belong to an undescribed species of another member of the Neanthes glandicincta species complex because they differ from all other members of this species group in the absence of notopodial prechaetal lobe. Both atokous and epitokous specimens collected from southern China and identified as Ceratonereis burmensis by Wu et al. (1985) do not seem to belong to N. glandicincta ; atokes with a lesser number of paragnaths seem to belong to N. wilsonchani , according to Lee and Glasby (2015) and the key of Ibrahim et al. (2019), whereas an epitoke with an indented anterior margin of the prostomium seemed to belong to Ceratonereis .