Sigambra pakbaraensis, Plathong & Plathong & Klangnurak & Dean, 2024

Plathong, Jintana, Plathong, Sakanan, Klangnurak, Wanlada & Dean, Harlan K., 2024, Two new species of Sigambra (Annelida, Pilargidae) from the Andaman coast and the Gulf of Thailand, Zootaxa 5555 (1), pp. 1-23 : 7-13

Sigambra pakbaraensis sp. nov.

Figs 2–5

Material examined. Andaman Coast, southern Thailand. Intertidal zone at Pak Bara , Mu Ko Phetra National Park ; muddy sediments mixed with sand; coll. Marine National Park Operation Center; Libong Island, seagrass beds, coll. Marine Ecosearch Management Company. 58 specimens. Holotype: PSUZC-POL-0423, Sta. PAKC2 (B2) (6°51’8”N, 99°43’38”E), 16 Nov. 2019. 57 paratypes: Pak Bara, mudflat; PSUZC-POL-0424 (3), Sta. PAK-1B (B3) (6°51’25”, 99°43’11”), 20 Jan. 2018; PSUZC-POL-0425 (7, 4 on SEM stubs), Sta. PAK-2A (B1) (6°51’22.19”N, 99°43’14”E); PSUZC-POL-0426 (3), Sta. PAK-2B (B2) (6°51’20”N, 99°43’12”E); Sta. PAK-2C (6°51’18”N, 99°43’10”E): PSUZC-POL-0427 (4, 1 on SEM stub), Sta. PAK-2C (B1); PSUZC-POL-0428 (3); Sta. PAK-2C (B2); PSUZC-POL-0429 (3), Sta. PAK-3C (B3); Sta. PAK-C2 (6°51’08”N, 99°43’38”E), 16 Nov. 2019: PSUZC-POL-0430 (3), Sta. PAK-C2 (B1); PSUZC-POL-0431 (5), Sta. PAK-C2 (B3); Libong Island, 19 Jan. 2022: PSUZC-POL-0432 (2), Sta. PC 2 (7°15’55”N, 99°25’54”E); PSUZC-POL-0433 (3), Sta. PC 3 (7°15’52”N, 99°25’53”E); 20 Jan. 2022; PSUZC-POL-0434 (1), Sta. PC 4 (7°15’54”N, 99°25’58”E); PSUZC-POL-0435 (1), Sta. HT 2 (7°15’19”, 99°27’37”); 18 specimens fixed for DNA analyses, Pak Bara, mudflat, 1–2 Dec. 2020: PSUZC- POL-0700 (5 fixed for DNA analyses, 2 used), Sta. PAK-C2 (6°51’08”N, 99°43’38”E); PSUZC-POL-0701 (2 fixed for DNA analyses, used), Sta. PAK-B2 (6°51’08”N, 99°43’38”E), 2 Dec. 2020; PSUZC-POL-0702 (3 fixed for DNA analyses, 1 used), Sta. PAK-A2 (6°51’09”N, 99°43’33”E); PSUZC-POL-0703 (2 fixed for DNA analyses used), Sta. PAK-L2S3 (6°51’14”N, 99°43’17”E); PSUZC-POL-0704 (6 fixed for DNA analyses), Sta. PAK-L3S2 (6°51’16”N, 99°43’12”E); AM W.52916 (2), Sta. PAK-S2 (6°51’09”N, 99°43’34”E), 4 Jul. 2019, mudflat.

Additional material. 596 specimens. Pak Bara intertidal zone (412 specs.): 21 Oct. 2017, 323 specs.: 4 specs., Sta. PAK-1A (6°51’25”N, 99°43’11”E); 10 specs., Sta. PAK-2C (6°51’18”N, 99°43’10”E); 6 specs., Sta. PAK-3B (6°51’16”N, 99°43’16”E); 20 Jan. 2018, 5 specs., Sta. PAK-1A (6°51’25”N, 99°43’11”E); 13 specs., Sta. PAK-1B

(6°51’23”N, 99°43’09”E); 2 specs., Sta. PAK-1C (6°51’20”N, 99°43’08”E) ; 2 specs., Sta. PAK-2A (6°51’22”N, 99°43’14”E) , 81 specs., Sta. PAK-2B (6°51’20”N, 99°43’12”E) ; 64 specs., Sta. PAK-2C (6°51’18”N, 99°43’10”E) ; 19 specs., Sta. PAK-3A (6°51’18”N, 99°43’18”E) ; 73 specs., Sta. PAK-3B (6°51’16”N, 99°43’16”E) ; 44 specs., Sta. PAK-3C (6°51’14”N, 99°43’14”E) ; 2 Feb. 2024: 16 specs., Sta. PAK-A (6°51’13”N, 99°43’24”E) , 2 specs., Sta. PAK-B (6°51’13”N, 99°43’27”E) , 9 specs., Sta. PAK-C (6°51’12”N, 99°43’28”E) ; 3 Feb. 2024: 27 specs. Sta. PAK-D1 (6°51’11”N, 99°43’29”E) , 15 specs., Sta. PAK-D2 (6°51’10”N, 99°43’28”E) , 1 spec. Sta. PAK-D3 (6°51’08”N, 99°43’28”E); 4 Feb. 2024: 10 specs, Sta. PAK-E1 (6°51’10”N, 99°43’34”E) , 8 specs., Sta. PAK-E2 (6°51’08”N, 99°43’35”E) , 1 spec. Sta. PAK-E3 (6°51’07”N, 99°43’34”E). Ao Nun , intertidal zone (33 specs.): 3 Feb. 2024, 20 specs., Sta. Phetra 1 (6°50’06”N, 99°45’20”E) ; 7 Feb. 2024, 9 specs., Sta. Phetra 2 (6°50’08”N, 99°45’20”E) ; 4 specs., Sta. Phetra 3 (6°50’13”N, 99°45’22”E) . Pak Bara Bay (6 specs.): 17 Feb. 2018, 1 spec., Sta. PAK05 (6°50’33”N, 99°43’07”E), 2.7 m ; 4 specs., Sta. PAK06 (6°50’14”N, 99°43’59”E), 6.4 m ; 1 spec., Sta. PAK07 (6°49’12”N, 99°42’50”E), 3 m. Libong Island , seagrass bed (intertidal zone) (145 specs.): 17 specs., Sta. HT (7°15’20”N, 99°27’36”E) ; 6 specs., Sta. KN (7°16’09”N, 99°27’20”E) ; 51 specs., Sta. MT (7°17’46”N, 99°25’13”E) ; 5 specs., Sta. NK (7°13’08”N, 99°23’50”E) ; 56 specs., Sta. PC1 (7°15’57”N, 99°25’56”E) ; 7 specs., Sta. PL1 (7°13’58”N, 99°26’38”E) ; 3 specs., Sta. TG1 (7°13’49”N, 99°24’31”E) .

Diagnosis. Sigambra with median antenna reaching to chaetiger 4, 1.9–2.7 times as long as lateral antennae; dorsal cirri larger than ventral cirri; chaetiger 2 lacking ventral cirri; notopodia with dorsal hook from chaetiger 8; capillary chaetae in middle–posterior chaetigers; pharynx with 14 marginal papillae.

Description. Holotype complete, largest specimen 14.2 mm long and 1 mm wide, 102 chaetigers ( Fig. 2A ). Paratypes, complete specimens 5.3–8.2 mm long, 0.5–0.8 mm wide, 45–84 chaetigers; incomplete specimens, 3.2– 5.5 mm long, 0.5–0.7 mm wide, 31–56 chaetigers.

Eighteen paratypes were fixed for DNA analyses, seven complete specimens used for whole body extraction.All specimens with pharynx everted possessing 14 terminal papillae, first dorsal hooks from chaetiger 8 and notopodial capillary chaetae present. Others characters not observed.

Body elongate, annulated, tapering posteriorly; anterior region with deep transverse grooves, integument with small papillae on dorsal parapodia surface. Ventral groove present from chaetiger 4 ( Fig. 3B ). Noto-capillaries start from chaetiger 83 (19–67 in paratypes). Specimens white, or light tan–light brown in alcohol ( Fig. 2A–B ).

Prostomium short, wider than long, trilobed, median lobe blunt and lateral lobes with curved tips ( Fig. 3A, C–D ). Three long cirriform antennae with basal ceratophore located on posterior of prostomium. Median antenna located on median lobe at posterior edge of prostomium, extending to chaetiger 3 (chaetigers 2–5 in paratypes), twice longer than lateral antennae (499 μm: 245 μm) (2–2.7 times in paratypes) ( Figs 2A–B , 3A, C–D , 4A ). Eyespots absent. Prostomium separated from peristomium by shallow transverse groove ( Fig. 3A, C ).

Palps biarticulate, palpophores large, palpostyles small, terminating in small digitate ventrolateral papillae, palpophores with oblique ciliated band ( Figs 2B , 3B, D ).

Pharynx with 14 heteromorphic terminal papillae, five smaller along mid-dorsal area, four larger lateral, two per side, and 5 ventral alternating in size, two smaller, three larger ( Fig. 3B ; other specimens with less heteromorphic papillae, Fig. 3D ).

Peristomium annulated, 5–6.2 times wider than long, slightly longer than following segment; anterior peristomium with two pairs of tentacular cirri, dorsal tentacular cirri slightly longer than ventral tentacular cirri. Transverse band of uniseriate papillae on mid-peristomium ( Figs 3A, C , 4A ), posterior margin of peristomium separated from anterior part and first chaetiger by a deep transverse groove.

Parapodial cirri triangular, longer than wide. Dorsal cirri long, cylindrical, longer than ventral cirri throughout. First dorsal cirrus reaching chaetiger 5 (chaetigers 3–6 in paratypes). Chaetiger 2 with tiny dorsal cirri, without ventral cirri. Dorsal and ventral cirri with rows of pores along dorsal and ventral sides ( Fig. 4A, C ).

Parapodia sub-biramous, notopodia reduced, neuropodia well-developed. First dorsal hooks from chaetiger 8 in all specimens ( Figs 3A , 4A ) continuing along body to last two pre-pygidial chaetigers; dorsal hooks longer in posterior chaetigers. Chaetigers 1–7 without hooks, notopodia with acicular and dorsal cirri; dorsal hooks accompanied by acicula from chaetiger 8 onwards to middle chaetigers; notopodia with single dorsal hook and one capillary chaeta from chaetiger 86 to posterior chaetigers, dorsal hooks longer in posterior chaetigers ( Figs 3A, C , 4A, D–E ). Parapodial glands present.

Neurochaetae present from chaetiger 1, neurochaetae with numerous limbate capillaries, up to 40 per fascicle, of various types and sizes, especially in middle chaetigers ( Fig. 5A–D ).

Holotype and paratypes mature females, with oocytes ( Fig. 2A, B ), hypertrophied gonopores occur ventral of parapodia located between dorsal cirrus and neuropodia in paratypes ( Fig. 4D ).

Pygidium with two slender, elongate lateral anal cirri (579 µm in length, left side), reaches to chaetiger 10 from posterior end (chaetigers 6 to 10 in paratypes) ( Figs 2A–B , 5F ).

Variations. Additional materials included large specimens and juveniles. All show first dorsal hooks fixed at chaetiger 8 and 14 pharynx marginal papillae. Notopodial capillary present. Other characters not observed.

Etymology. This species was named after Pak Bara, the locality where the specimens were collected for the first time.

Habitat. The intertidal zone at Pak Bara, Mu Ko Phetra National Park; seagrass bed in Andaman coast of Southern Thailand (fine muddy and fine sand sediments).

Distribution. Only known from the Andaman Coast, Southern Thailand ( Fig. 1 ).

Genetic data. GenBank OP437496-OP437498 for COI and OP445021-OP445024 for 16S—no identical matches on GenBank for COI or 16S.

Remarks. Sigambra pakbaraensis sp. nov. belongs to the group of Sigambra which lack ventral cirri at chaetiger 2, have 14 pharyngeal papillae, and notopodial capillary chaetae ( Table 1). It resembles the species in subgroup A ( Day 1963; Hartman 1945; Kitamori 1960; Licher & Westheide 1997; Salazar-Vallejo et al. 2019; Southern 1921; Treadwell 1941) by the presence of 14 pharyngeal papillae and notopodial capillary: S. bassi Hartman, 1945 , S. constricta Southern, 1921, S. diazi Salazar-Vallejo, Rizzo, León-González & Brauko, 2019 , S. hanaokai Kitamori, 1960 , S. parva Day, 1963 , S. phuketensis Licher & Westheide, 1997 , and S. tentaculata Treadwell, 1941 ( Table 1). However, it differs from all those species in the subgroup by having its first dorsal hook at chaetiger 8. Whereas other species have first dorsal hooks at chaetigers 3–5 and chaetigers 15–40 ( Hartman 1945; Licher & Westheide 1997; Moreira & Parapar 2002; Nishi et al. 2007; Salazar-Vallejo et al. 2019; Southern 1921) ( Table 1).

Pores on the dorsal and ventral cirri are herein described for the first time, these pores may or may not open and close.

Phylogenetic analysis. A phylogenetic tree was generated from each of 3 COI and 4 16S rDNA sequences of S. pakbaraensis sp. nov. and other related taxa ( Figs 6–7 ). DNA barcoding assessments in both COI and 16s rDNA clearly classified all S. pakbaraensis sp. nov. samples to the Sigambra clade. All S. pakbaraensis sp. nov. samples were designated to a monophyletic clade. The S. magnuncus clade was the sister group. The COI data revealed that the clade of Pilargidae does not cluster with the Microphthalmidae . S. pakbaraensis sp. nov. forms the sister clade with other Sigambra species, but with low bootstrap support. In contrast, the 16S rDNA phylogenetic tree shows that S. pakbaraensis sp. nov. is distinctly clustered from other Sigambra species, supported by high bootstrap values, with the Sigambra clade clearly separated from other families. These findings, based on both COI and 16S rDNA gene analyses, provide strong molecular evidence that S. pakbaraensis sp. nov. represents a genetically distinct species within the genus Sigambra . The genetic divergence observed across both markers highlights the evolutionary separation of S. pakbaraensis sp. nov. from other Sigambra in the available sequence databases, supporting its designation as a new species.

Inter- and intraspecific genetic distances of Sigambra spp. were investigated from both COI and 16S rDNA sequences. For the COI gene, nucleotide substitutions occurred at eight positions within the 429-bp fragment, and all positions were singleton variables leading to 1.86% intraspecific genetic distances for S. pakbaraensis sp. nov. Intraspecific variation from the closest related species, S. magnuncus , was 4.2%. The average interspecific distance between the S. pakbaraensis sp. nov. clade and the S. magnuncus clade was 22.29%, while differences between the proposed new species and S. parva and S. cf. tentaculata were 20.59% and 17.87%, respectively.

For the 16S rDNA gene, nucleotide substitutions occurred at five positions within the 444-bp fragment, and all positions were singleton variables, leading to 1.13% intraspecific genetic distances for S. pakbaraensis sp. nov., whereas the distance for S. magnuncus was 1.78%. The average interspecific distance between the S. pakbaraensis sp. nov. clade and the S. magnuncus clade was 22.7%.

Since there is no recorded genetic data for S. sundarbanensis , a comparison with the new species cannot be made based on DNA analysis. We were able to separate S. pakbaraensis sp. nov. from S. sundarbanensis by the presence of notopodial capillary chaetae in the new species. This is a major morphological character that is absent in S. sundarbanensis ( Bhowmik et al., 2021) .

Figures

FIGURE 1. Stations in the Andaman Coast of Thailand and Gulf of Thailand, where specimens of Sigambra pakbaraensis sp. nov. (triangles) and S. sirilukae sp. nov. (squares) were collected.

FIGURE 2. Sigambra pakbaraensis sp. nov. light photographs (A, holotype: PSUZC-POL-0423; B, PSUZC-POL-0433). A. Whole specimen, anterior lateral view, posterior flips; B. Same, anterior dorsal view, posterior flips. Abbreviations: 1st dc, first dorsal cirrus; la, lateral antenna; ma, median antenna; py, pygidium; tc, tentacular cirri; tp, terminal papilla; vpp, ventrolateral palpal papilla.

FIGURE 3. Sigambra pakbaraensis sp. nov. (A–D, PSUZC-POL-0425). A. Anterior region, dorsal view; B. Same, ventral view; C. Prostomium, dorsal view; D. Same, frontal view. Abbreviations: 1st dc, first dorsal cirrus; 1st dh, first dorsal hook; dc, dorsal cirrus; la, lateral antenna; ldp, lateral distal papilla; ma, median antenna; pa, palp; pap, papilla; tc, tentacular cirri; tp, terminal papilla; vc, ventral cirrus; vg, ventral groove; vpp, ventrolateral palpal papilla.

FIGURE 4. Sigambra pakbaraensis sp. nov. (PSUZC-POL-0425) A.Anterior region, lateral view; B. Close up of body papillae, lateral view; C. Close up of pores on dorsal cirrus, dorsal view; D. Midbody notopodia, arrows point to gonopores, lateral view; E. Far posterior notopodium, dorsal view.Abbreviations: 1st dc, first dorsal cirrus; cc, capillary notochaeta; dc, dorsal cirrus; dh, dorsal hook; la, lateral antenna; ma, median antenna; pap, papilla; tc, tentacular cirri.

FIGURE 5. Sigambra pakbaraensis sp. nov. A. Anterior neurochaetae, ventral view; B. Close-up of pectinate chaetae, lateral view; C–E. Close up of various types of limbate capillary chaetae, lateral view; C. Short teeth chaeta; D. Inferior limbate chaeta with thin and long teeth, lateral view; E. Long limbate chaeta; F. Posterior end, dorsal view. Abbreviations: cc, capillary notochaeta; dh, dorsal hook; lc, limbate chaeta.

FIGURE 6. Phylogenetic tree from COI sequences was derived from maximum likelihood analyses. Bootstrap values show above branches and scale represents evolutionary distance in substitutions per position.

FIGURE 7. Phylogenetic tree from 16S rDNA sequences was derived from maximum likelihood analyses. Bootstrap values shown above branches and scale represents evolutionary distance in substitutions per position.