Marphysa ibaiensis sp. nov.

Figs 1, 2, 14, 15, 16

Material examined.

Holotype. UMTAnn 2179, complete, antero-ventrally dissected, some parapodia mounted for SEM . Paratypes. AM W. 54052, complete, some parapodia mounted for SEM. LACM-AHF 13500 to 13502, complete, some parapodia removed; ZRC. ANN. 1610 to 1612, complete, some parapodia removed; SAM-MB-A 096022, complete, some parapodia removed . All material was collected from the east coast of Peninsular Malaysia, Terengganu, Kuala Ibai lagoon (05 ° 17.198 ' N, 103 ° 10.194 ' E) and estuary (05 ° 16.780 ' N, 103 ° 10.137 ' E), October 2021.

Diagnosis.

Prostomium completely bilobed, five prostomial appendages without articulations; eyes absent. Peristomium without Peristomial cirri. Maxillary apparatus with four pairs of maxillae, an unpaired on the left side, MI with falcal arch extended at sub-right angle, basal outer edge arched, basal inner edge lacking curvature. MII with triangular teeth and without attachment lamella. MIII slightly curved, with equal-sized triangular teeth, without attachment lamella. MIV with curved attachment lamella. Branchiae distributed along entire body. Dorsal cirri without articulations; postchaetal lobe well developed in anterior regions. Ventral cirri with swollen, inflated base. Sub-aciculae black, blunt, and translucent at distal end, pale brown in posterior-most parapodia. Supra-acicular chaetae include limbate, pectinate, thin, narrow isodont with short and slender inner teeth, pectinate thin, narrow heterodont with short and slender inner teeth, pectinate thick, wide isodont with long or short and slender inner teeth, and pectinate thick, wide anodont with long and slender inner teeth. Subacicular chaetae include limbate and compound spinigers. Subacicular hook bidentate. Pygidium with two pairs of anal cirri, without articulation.

Description

(based on holotype, with variation in parentheses for paratypes). Preserved specimens beige (Fig. 14 A), ~ 195 (66–401) chaetigers and 52 mm (20–91 mm) long, L 10: 4.5 mm (2.25–6.3 mm), W 10: 2.85 mm (1.2–3.75 mm), excluding parapodia. Anterior region of body cylindrical, with shallow groove until median chaetigers (Fig. 14 A); body depressed from chaetiger 30, elongated, and tapering at distal end. Live specimens red (Fig. 16 C).

Prostomium conically bilobed, with two dorsoventrally lobes separated by an anterior notch (Fig. 14 A, B). Prostomial appendages in a semicircle, median antennae separated by a gap. Palps, lateral and median antennae reaching first peristomium. Palpophores and ceratophores ring-shaped, short, and thin; palpostyles and ceratostyles tapering and slender. Prostomial appendage peduncles absent. Peristomium wider than prostomium; first ring 3 × longer than second ring, separation between rings distinct on all sides.

Maxillae pale brown (Fig. 14 C) and maxillary formula as follows: MF = 1 + 1, 6 (5–6) + 7 (6–7), 7 (7–8) + 0, 4 + 10 (9–10), 1 + 1. Maxillary carrier ~ 2.2 × shorter than MI, rectangular anteriorly, triangular posteriorly. MI forceps-like, without attachment lamellae, falcal arch extended at sub-right angle, basal outer edge arched, basal inner edge lacking a curvature. Closing system is ~ 5.5 × shorter than MI. Ligament between MI and MII pale brown. MII without attachment lamella, teeth triangular, present on <1 / 2 of plate length. Ligament between MII and MIII pale brown. MIII single, longer than left MIV, slightly curved, with equal-sized triangular teeth, without attachment lamella. Left MIV short (<1 / 2 the size of right MIV) with curved attachment lamellae. Right MIV long, with teeth triangular and curved attachment lamellae, decreasing in size and teeth curved posteriorly. MV paired. Mandibles whitish with pale brown core, longer than MI; cutting longer than MI; cutting plates whitish (Fig. 14 D).

First few parapodia inserted ventrolaterally, but then becoming lateral in anterior region and dorsolaterally in subsequent segments. Chaetal lobes rounded on all chaetigers (Fig. 14 F – H). Prechaetal lobe shorter than chaetal lobe along the entire body. Postchaetal lobe rounded and longer than chaetal lobe in anterior chaetigers and mid-body onwards (Fig. 14 F – H), becoming shorter and absent in the posterior-most chaetigers. Dorsal cirri digitiform and slender, longer than ventral cirri anteriorly, as long as or shorter from mid-body and shorter in posterior chaetigers (Fig. 14 F – H). Ventral cirri digitiform in first chaetigers, basally inflated with digitiform tip from chaetiger six onwards (Fig. 14 F – H). Branchiae pectinate, starting from chaetiger 20 (11–65) and continuing to near end (~ 13 last chaetigers without branchiae), branchial filament 3 × longer than dorsal cirri where best developed; number of filaments increasing from one anteriorly to eight in mid-body, decreasing to six in last several chaetigers. Pygidial cirri attached to ventral side of pygidium, dorsal pair ~ 4 × longer than ventral (Fig. 14 I).

Notoaciculae absent. Neuroaciculae black, blunt, and translucent at distal end along most of body, pale brown in posterior-most parapodia; ~ 3 or 4 per parapodium in anterior, one or two per parapodium in median and one per parapodium in posterior chaetigers (Fig. 14 F – H). Supra-acicular chaetae with limbate capillaries and pectinates. Five types of pectinate chaetae were identified (types 1, 3, 4, 5, 7) (see Fig. 2): type 1: thin, narrow isodont with 12–15 short and slender inner teeth, present in anterior and median region (Fig. 15 A); type 3: thin, narrow heterodont with 12 short and slender inner teeth, outer teeth longer on one side, present in the anterior body region (Fig. 15 B); type 4: thick, wide isodont with 18–29 short and slender teeth, outer teeth different length to inner teeth, only present in median and posterior region (Fig. 15 C – F): type 5: thick, wide isodont with 15–18 long and slender inner teeth, present only posteriorly (Fig. 15 E, F); type 7: thick, wide anodont with ~ 15 long and slender inner teeth, only present in posterior parapodia (Fig. 15 F). Subacicular chaetae with compound spinigers and limbate capillaries in median and posterior chaetigers. Some limbate chaetae with inconspicuous serrations and numerous projections (Fig. 15 G). Subacicular hooks pale brown, translucent at distal end, from chaetiger 22 (22–46), 1–3 per parapodium; subacicular hooks bidentate present throughout (Fig. 14 E). Pygidium with crenulated margin, with two pairs of tapering pygidial cirri attached to ventral side of pygidium, dorsal pair ~ 4 × longer than ventral one (Fig. 14 I).

Etymology.

Name refers to the type locality Kuala Ibai River.

Type locality.

South China Sea, Malaysia, east coast of Peninsular, Terengganu, Kuala Ibai river estuary and lagoon (see Fig. 1).

Distribution.

Known only from the type locality.

Habitat.

Slightly gravelly sand sediment (Table 4) associated with oyster clumps within Rhizophora spp. (Fig. 16 A), burrowing in sediment deposited inside driftwood bark (Fig. 16 B) with salinity 26 ‰ (estuary) and 18 ‰ (lagoon) during spring low tide.

Remarks.

With the presence of subacicular limbate and compound spinigers in the median and posterior region, M. ibaiensis sp. nov. belongs to Group E (Gravelyi). There are four Marphysa species belonging to this group; M. borradailei Pillai, 1958 (type locality: Negombo Lagoon, Sri Lanka), M. fauchaldi Glasby & Hutchings, 2010 (type locality: Ardatek Barrumundi farm, Darwin, Australia), M. gravelyi Southern, 1921 (type locality: Chilka Lake, India) and M. madrasi Hutchings, Lavesque, Priscilla, Daffe, Malathi & Glasby, 2020 (type locality: Chennai, India). The morphological features of these species are given in Table 7.

Marphysa ibaiensis sp. nov. can be distinguished from M. borradailei by the number of branchial filaments, shape of the subacicular hooks, chaetiger where the branchiae and subacicular hook occur, and the shape of postchaetal lobe in the anterior region. Marphysa ibaiensis sp. nov. (TL: 52 (20–91) mm) has a maximum of eight branchial filaments whereas M. borradailei (TL: 1–8 mm) has up to 20 branchial filaments. The subacicular hook of M. ibaiensis sp. nov. is bidentate and occurs from chaetiger 22 (22–46) onwards while M. borradailei has a strongly hooded unidentate hook that occur from chaetiger 50 onwards. Marphysa ibaiensis sp. nov. has rounded postchaetal lobe in anterior region, while M. borradailei has sub-conical shaped postchaetal lobes in the anterior region. The original description of M. borradailei makes it challenging to undertake a detailed morphological comparison and additional material from the type locality (Sri Lanka) needs to be collected and redescribed.

The new species can also be differentiated from M. gravelyi and M. madrasi by the absence of eyes, number of types of pectinate chaetae, number of branchial filaments, chaetiger where subacicular hooks begin and the length of the pygidial cirri. Marphysa ibaiensis sp. nov. has no eyes, while both M. gravelyi and M. madrasi have a pair of eyes. Marphysa ibaiensis sp. nov. has five types of pectinate chaetae (types 1, 3, 4, 5, 7), whereas M. madrasi has only two (types 4, 5). While all these species have bidentate hooks, they begin on chaetiger 22 (22–46) in M. ibaiensis sp. nov. (L 10: 4.5 (2.25–6.3) mm), 26–35 in M. gravelyi and 33–72 in M. madrasi (L 10: 6 (4–9) mm). Marphysa ibaiensis sp. nov. has short and long pairs of pygidial cirri attached to the pygidium, whereas M. madrasi only has one pair of short pygidial cirri.

Marphysa ibaiensis sp. nov. differs from M. fauchaldi by the absence of peduncle in prostomial appendages, the chaetiger on which the branchiae and subacicular hook occur and the distribution of subacicular limbate chaetae. Subacicular hooks and branchiae of M. ibaiensis sp. nov. (TL: 52 (20–91) mm) have a wide range variation of chaetiger where they begin; from chaetiger 22 (22–46) and 20 (11–65), respectively compared to M. fauchaldi (TL: 190 (78–155) mm); they begin from chaetiger 40 (31–50) and 31 (22–32), respectively. The subacicular limbate chaetae in M. ibaiensis sp. nov. occur from mid-chaetigers onwards whereas in M. fauchaldi, they are restricted to posterior chaetigers.