Namalycastis undetermined
Creators: name: Ibrahim, Nur Fazne
name: Ibrahim, Yusof Shuaib
name: Kan, Kotaro
name: Sato, Masanori
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Polychaeta
Phyllodocida
Nereididae
Namalycastis
Namalycastis undetermined

description: Namalycastis sp.
(Figures 3–8)
Namalycastis sp.: Ibrahim et al. 2017: 115–116, fig. 1b.
Material examined
Six stations in the estuarine lagoon of Setiu Wetlands, Terengganu, in the eastern coast of Peninsular Malaysia, September 2015 to September 2016 (Table 1; Figure 2), coll. N.F. Ibrahim et al., 507 specimens (UMT-Ann 1701–2146, NSMT-Pol 113582, 113583). The following description is mainly based on one of them (UMT-Ann 1741 collected from Sta. 2 on 27 November 2015).
Description
Complete female 4.1 mm BW, 180 mm BL, with 339 chaetigers (Figure 4 (a)). Body stout with dorsum convex and venter flat, tapering gradually posteriorly. Dorsum brown anteriorly, whitish posteriorly under preservation; venter pale.
Prostomium trapezoidal, with shallow cleft in anterior margin, with narrow longitudinal groove (Figures 4 (b) and 5(e,h,i)). Pair of antennae short, sub-conical, aligned at inner edge of palps, extending to one-quarter of palpophore (Figures 4 (b) and 5(e,h,i)). Two pairs of eyes, black or purple, arranged obliquely or transversely, with posterior pair slightly smaller (Figures 4 (b) and 5(i)). Jaws with single robust terminal tooth and around seven subterminal teeth, with gap separating terminal and subterminal teeth (Figures 4 (b,d) and 5(h)).
Four pairs of tentacular cirri with cirrophores distinct. Anterodorsal and posterodorsal tentacular cirri sub-equal. Posterodorsal tentacular cirri reaching chaetiger 2 or 3 (Figures 4 (b) and 5(e,h,i)).
Parapodia consist of triangular dorsal cirrus, neuroacicular ligule and ventral cirrus. Neuroacicular ligule distally bilobed in anterior chaetigers (Figure 4 (e)); superior lobe papilliform; inferior lobe globular. Dorsal cirri becoming slender and flattened posteriorly (Figures 4 (f–j) and 5(f,g)). Ventral cirri short, becoming slender posteriorly (Figure 4 (f–j).
Notochaetae all sesquigomph spinigers (Figure 6 (a)); more than 20 spinigers and 8 spinigers present in right parapodia of chaetigers 50 and 100, respectively.
Neurochaetae type A according to Glasby (1999). Upper neurochaetae (supra-acicular) consisting of sesquigomph spinigers posteriorly and heterogomph falcigers anteriorly. Sesquigomph spinigers with finely serrated blade (Figures 6 (b) and 7(a) for NSMT-Pol 113582) present throughout (more than 20, and more than 10 spinigers present in right parapodium of chaetigers 50, and 100, respectively). Heterogomph falcigers with finely serrated blade (Figure 6 (e,g)) present throughout; single nose-like projection sometimes presents at base of serrated edge (Figure 6 (e)).
Lower neurochaetae (sub-acicular) consisting of heterogomph spinigers posteriorly and heterogomph falcigers anteriorly. Heterogomph spinigers with minutely serrated blade (Figures 6 (c) and 7(b) for NSMT-Pol 113583) present throughout; additionally, a few heterogomph spinigers having blades with coarse serrations proximally (Figures 6 (d) and 7(c) for NSMT-Pol 113583) present in posterior parapodia, first appearing at around chaetiger 60; heterogomph spinigers absent in posterior-most parapodia. Heterogomph falcigers with finely serrated blade (Figure 6 (f,h,i)) present throughout. A few (usually 1 or 2) heterogomph falcigers having blades with coarse serrations proximally present at uppermost of sub-acicular position in posterior parapodia, first appearing at around chaetiger 140 (Figures 6 (j), 7(f)). A few additional thin sesquigomph spinigers (epitokal chaetae sensu Glasby 1999) present in lower neurochaetae, first appearing at around chaetiger 40 (Figure 7 (g) for NSMTPol 113582).
Pygidium with multi-incised rim, and anus dorsoterminal (Figures 4 (c)) and 5(g)). Pair of anal cirri arising ventrolaterally, as long as pygidium length.
Mature eggs about 140µm in diameter, containing many yolk granules (lipid droplets) (Figure 3 (a)).
Variation
Body size ranged from 1.0– 5.2 mm BW, with the largest complete specimen of 340 mm BL with about 400 chaetigers, and the smallest complete specimen of 20 mm BL with 30 chaetigers.
Colour of dorsum in live specimens was highly variable: pale red, dark red, or brown (Figure 5 (a,b)). Colour of dorsum of preserved specimens also variable from whitish cream to dark brown throughout, or dark or light brown anteriorly and pale posteriorly, with consistently brown epidermal pigment on pygidium (Figure 5 (c,d)).
Notochaetae (sesquigomph spinigers) were most abundant (up to 30) in chaetigers 10–50; sometimes few notochaetae occurring until around chaetiger 150. Notochaetae were absent throughout in 12 of 507 specimens examined.
Neuropodial supra-acicular sesquigomph spinigers (Figure 7 (a)) were most abundant (up to 40) in chaetigers 10–50; larger specimens tended to have more spinigers (Figure 8).
Neuropodial supra-acicular heterogomph falcigers were abundant (up to 10) in chaetigers 10–40, reducing in numbers in the posterior chaetigers (up to 2 at chaetiger 160).
Neuropodial sub-acicular heterogomph spinigers with finely serrated blade (Figure 7 (b)) were present up to around 20. A few heterogomph spinigers with coarsely serrated blade (Figure 7 (c)) were present in posterior parapodia, first appearing at various chaetigers from around chaetiger 20 to around chaetiger 100, depending on body size.
Neuropodial sub-acicular heterogomph falcigers present up to around 20, sometimes having a blade with only few small serrations proximally (Figure 7 (d,e)). A few heterogomph falcigers with coarsely serrated blade (Figures 6 (j) and 7(f)) were present at the uppermost of the sub-acicular position in posterior parapodia, first appearing at various chaetigers from around chaetiger 30 to around chaetiger 250, sometimes lacking throughout body.
A nose-like projection on the proximal edge of the blade of heterogomph falcigers with finely serrated blade was variable in size and shape (Figure 7 (d,e,g)).
In some specimens of both males and females (1.8–4.4 mm BW, probably during sexual maturity), thin semi-transparent sesquigomph spinigers (epitokal chaetae, up to 10) exist in sub-neuroacicular fascicle (Table 1; Figure 7 (g)).
Habitat
All specimens were found in the fibrous inside of the decaying fronds of the palm Nypa fruticans in estuarine mangroves, where the salinity of the ambient water seasonally fluctuates from 3.5 to 34 psu (Table 2). They have never been found in mudflats around the palm trees. It is unknown where this species spawn and where its larvae and smaller juveniles live.
Feeding habit
Plant fibres and plant cells were found in the gut contents of an individual (Figure 9 (a,b)), suggesting that this species may feed on the decaying tissue of the palm fronds. In another individual, however, nereidid parapodia with aciculae and chaetae were found in the gut contents (Figure 9 (c,d)), though it is unclear whether the prey worm belongs to Namalycastis sp. or not. This species may be a facultative carnivore.
Remarks
Our specimens showed high variability in such characteristics as the colour of dorsum, the presence or absence of notochaetae, the number of neuropodial sesquigomph spinigers, and the presence or absence of neuropodial heterogomph falcigers with coarsely serrated blade. According to Glasby (1999), some of our specimens with more than 10 neuropodial sesquigomph spinigers are keying out to N. multiseta Glasby, 1999, while the others with fewer than 10 neuropodial sesquigomph spinigers are keying out to the Namalycastis abiuma species group, which was established as an informal taxon including five nominal species or subspecies (Lycastis meraukensis Horst, 1918; N. meraukensis zeylanica Silva, 1961; Lycastis nipae Pflugfelder, 1933; N. rigida Pillai, 1965; and Lycastis vivax, 1933) by Glasby (1999). However, our results suggest that the number of neuropodial sesquigomph spinigers may increase continuously according to the growth of each individual (Figure 8). Therefore, we tentatively judged that our specimens belong to a single undetermined species (Namalycastis sp.) with high intraspecific variations.
a The sampling date shown is the first day of two successive dates in each sampling.
The exact identity of Namalycastis sp. should be clarified based on the future taxonomic revision of the related nominal species (N. multiseta and members of the Namalycastis abiuma species group). The present study revealed that a dense population of Namalycastis sp. is maintained within the decaying fronds of the Nypa trees, although this species has never been found in mudflats around the palm trees. The unique habitat preference of Namalycastis sp. may be a species-specific characteristic. Namalycastis nipae was described based on the specimens collected from the inside of the decaying leaf axes of Nypa fruticans in Medan-Belawan Strait, Indonesia (Pflugfelder 1933). No other species of the Namalycastis abiuma species group has been recorded from such a unique habitat, except for the following example: specimens collected from the inside of the fibrous husks of Nypa palm nuts immersed in brackish water (salinity, 5.6%) in a lagoon in the Solomon Islands, the eastern distributional limit of Nypa fruticans, were identified as Namalycastis indica (Southern, 1921) by Gibbs (1971); later, N. indica sensu Gibbs 1971 was also considered as a member of the Namalycastis abiuma species group by Glasby (1999).
description: Published as part of Ibrahim, Nur Fazne, Ibrahim, Yusof Shuaib, Kan, Kotaro & Sato, Masanori, 2024, Nereidid polychaetes (Annelida) inhabiting the inside of decaying fronds of the mangrove palm Nypa fruticans in a tropical estuary in Malaysia, with special reference to the life history of the dominant species, Namalycastis sp., pp. 2043-2074 in Journal of Natural History 58 (45 - 48) on pages 2049-2057, DOI: 10.1080/00222933.2024.2404472, http://zenodo.org/record/14243150