Sigambra sirilukae, 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 : 14-20

Sigambra sirilukae sp. nov.

Figs 8–11

Material examined. Thailand, Gulf of Thailand, Songkhla Sea. Fifty-three specimens, coll. Marine Ecosearch Management Company and Tetra Tech Inc., mud mixed with sand and shell fragments. Holotype: PSUZC-POL-0236, Sta. S 10–3 (7°28’32”N, 100°36’22”E), 5 Jun. 2010, 18.5 m. 52 paratypes: PSUZC-POL-0237–0239 (5), Sta. S 01 (7°46’29”N, 100°24’42”E), 9.5 m: 16 Oct. 2013 (1 on SEM stub), 8 Oct. 2014 (3, 1 on SEM stub), 16 Mar. 2016 (1); PSUZC-POL-0240 (1), Sta. S 02 (7°31’44”N, 100°28’15”E), 12 Sep. 2016, 10 m; PSUZC-POL-0241–0243 (3), Sta. S 03 (7°21’02”N, 100°31’45”E), 9 m: 30 Jan. 2012 (1), 11 Oct. 2012 (1), 2 Jun. 2013 (1); PSUZC-POL-0244–0248 (5, 4 on SEM stubs), Sta. S 04 (7°49’22”N, 100°29’11”E), 17.5 m: 11 Oct. 2012 (1 on SEM stub), 12 Mar. 2013 (1 on SEM stub), 1 Jun. 2013 (1 on SEM stub), 3 Mar. 2015 (1), 14 Oct. 2015 (1 on SEM stub); PSUZC-POL-0249–0252 (7, 2 on SEM stubs), Sta. S 06 (7°20’10”N, 100°36’59”E), 15.5 m: 3 Mar. 2011 (1 on SEM stub), 10 Oct 2012 (3, 1 on SEM stub), 2 Jun. 2013 (2), 6 Feb. 2014 (1); PSUZC-POL-0253 (1), Sta. S 31 (7°29’27”N, 100°31’22”E), 11 Sep. 2011, 13 m; PSUZC-POL-0254 (1), Sta. S 69 (7°30’17”N, 100°40’50”E), 16 Sep. 2014, 21.6 m; PSUZC-POL-0255 (1), Sta. S 46 (7°40’58”N, 100°29’39”E), 22 Feb. 2015, 14.5; PSUZC-POL-0256 (1), Sta. S 53 (7°27’59”N, 100°31’47”E), 23 Feb. 2015, 14.3 m; PSUZC-POL-0257 (1), Sta. S 28 (7°25’55”N, 100°33’35”E), 23 Feb. 2015, 14.2 m; PSUZC-POL-0258 (2), Sta. S 29 (7°23’18”N, 100°34’20”E), 24 Feb 2015, 13.4 m; PSUZC-POL-0259 (1), Sta. S 63 (7°30’40”N, 100°35’01”E), 8 Oct. 2015, 16.5 m; PSUZC-POL-0260 (1), Sta. S 45 (7°47’46”N, 100°28’10”E), 23 Feb 2015, 14.3 m; AM W.52917 (1), Sta. S 29 (7°23’18”N, 100°34’20”E), 27 Jan. 2015, 13.4 m; AM W.52918 (1), Sta. S 09-1 (7°32’13”N, 100°42’42”E), 8 Mar. 2014, 24 m.

Additional materials. Gulf of Thailand, Songkhla Sea. 64 specimens : 8 specs., Sta. S 01 (same locality as paratypes): 21 Feb. 2013 (1), 1 Jun. 2013 (3), 8 Oct. 2014 (2), 26 Feb. 2015 (1), 14 Oct. 2015 (1); 15 specs., Sta. S 02 (same locality as paratypes): 29 Jan. 2012 (1), 11 Oct. 2012 (1), 21 Feb. 2013 (3), 2 Jun. 2013 (4), 17 Oct. 2013 (2), 6 Feb. 2014 (2), 5 Jun. 2014 (2); 15 specs., Sta. S03 (same locality as paratypes): 30 Jan. 2012 (3), 24 May 2012 (1), 20 Feb. 2013 (2); 6 Feb. 2014 (3), 21 May 2015 (1), 17 May 2016 (4), 18 Oct. 2016 (1); 10 specs., Sta. S04 (same locality as paratypes): 11 Oct. 2012 (1), 21 Feb. 2013 (2), 1 Jun. 2013 (1), 16 Oct. 2013 (2); 5 Feb. 2014 (3), 4 Jun. 2014 (1); 9 specs., Sta. S06 (same locality as paratypes): 30 Jan. 2012 (1), 6 Feb. 2014 (3), 12 Feb. 2015 (3), 19 May 2015 (2); 1 spec. , Sta. S 07 (same locality as paratypes), 16 Oct. 2013; 3 specs., Sta. S 09 (same locality as paratypes): 17 Mar. 2013 (1), 18 Mar. 2013 (2); 1 spec. , Sta. S12 (7°34’19”N, 100°36’34”E), 4 Mar. 2014, 20 m; 1 spec. , Sta. S14 (7°26’14”N, 100°36’13”E), 4 Mar. 2014, 15.5 m; 1 spec. , Sta. S68 (7°47’06”N, 100°41’37”E), 29 Feb. 2016, 22 m.

Diagnosis. Sigambra without ventral cirri at chaetiger 2, with an elongate median antenna with ceratophore as long as 2.8–5x of lateral antennae, dorsal hooks present from middle chaetigers, notopodial capillary chaetae present from chaetiger 4–5, up to five chaetae per parapodium, and pharynx with 12 marginal papillae. Body lacking pigmentation.

Description. All specimens incomplete. Holotype the longest specimen with coiled median and posterior regions; total length of the specimen 19.3 mm long and 0.6 mm wide, about 180 chaetigers ( Fig. 8A ). Paratypes, 14–85 chaetigers, 2.0– 15.4 mm long and 0.6–1.3 mm wide. Body long, annulated, with a wide ventral groove posteriorly ( Figs 8A , 9A–B ). Color in alcohol white to light tan ( Fig. 8A–B ).

Prostomium bilobed, wider than long, separated from peristomium by a deep transverse groove. Three tapering antennae, median antenna with large annulated, long ceratophore about 99 µm in length ( Fig. 9A, D ), 5 times longer than lateral antennae (1.84: 0.37 mm) (2.8–4.7 times as long in paratypes) extending to chaetiger 11 (10–12 in paratypes) ( Figs 8A–B , 9A ). Lateral antennae longer than palps ( Figs 8B , 9A, D ). Palpostyles long, ventrolateral palpal papillae thin, digitate ( Figs 8A–B , 9A–D ). Nuchal organs deep ciliated grooves, along lateral side of the posterior end of prostomium and above anterior end of peristomium ( Fig. 9A, D ). Paratype with pharynx everted; with 12 ciliated papillae, the four lateral papillae are slightly larger than dorsal and ventral papillae and bear subdistal papillae on the first ring of proboscis ( Fig. 9B–C ). Eyespot absent.

Peristomium with two pairs of slender tentacular cirri, shorter than lateral antennae; dorsal tentacular cirri longer than ventrals. A transverse row of small ciliated papillae (about 4–7 µm in diameter) located dorsally near the posterior margin of peristomium ( Figs 8A–B , 9A–D ).

Parapodia biramous, strongly annulated with dorsal and ventral cirri slender, tapered distally ( Figs 8A–C , 9A– B , 10A–B, D ); notopodia with strong curved acicular tips and dorsal cirrus; dorsal hooks from chaetiger 61 (50–62 in paratypes) continued to posterior chaetigers. Dorsal hooks small, transparent, first dorsal hooks small, subdermal ( Fig. 8C ).

Dorsal cirrus bearing dorsal pores (seen only in SEM images), with 2–5 capillary chaetae from chaetiger 4 (chaetigers 4–5 in paratypes) ( Fig. 10A, C–E ). Dorsal cirrus of chaetiger 1 longer than lateral antennae and tentacular cirri, about twice longer than dorsal tentacular cirri and up to 6 times as long as dorsal cirrus of chaetiger 2; longer than all dorsal cirri. Chaetiger 2 with short dorsal cirrus, shorter than those of following segments ( Figs 8A–B , 9A, D , 10A, C , 11A, C ).

Each chaetiger with rows of small epidermal papillae along posterior dorsolateral margin of parapodia, at the base of parapodium, larger than papillae over prostomium ( Figs 8A , 10B, D , 11A ).

Neuropodia well developed with ventral cirrus smaller than dorsal cirrus, lacking at chaetiger 2. Each ventral cirrus bears pores similar in shape to those on dorsal cirrus. Ventral cirri slender, longer than neurochaetal lobes in posterior chaetigers. Neuropodia with straight acicula in a conical parapodial lobe and numerous simple neurochaetae in a bundle, variable in length and up to 60 chaetae per bundle ( Figs 9B , 10A, E ).

Neuropodia with four types of capillary chaetae, pectinate with long spinous chaeta, limbate chaetae with short, deep, upwardly oriented serrated teeth, limbate chaeta with 1–2 minute teeth between the main teeth, and long capillary chaeta. Supra-acicular chaetae pectinate, up to 9 chaetae per parapodium ( Fig. 11A ), limbate, and long limbate chaetae. Inferior subacicular chaetae shorter than superiors, with 1–2 minute teeth between main teeth ( Fig. 11B–C ). Superior subacicular chaetae long, limbate, lacking minute teeth between main teeth, limbate chaetae ventrally ( Fig. 11A–C ).

Pygidium unknown.

Reproduction. Oocytes were found in parapodial spaces in holotype and paratypes.

Variations. In additional materials, all specimens are anterior regions; median antenna very long and lateral antennae longer than palps. When median antenna broken, the ceratophore remains. Dorsal hooks absent and capillary chaeta also present from chaetiger 4–5 as holotype and paratypes. Pharynx with 12 marginal papillae.

Etymology. This species was named after Miss Siriluk Sutthinun, senior staff person at the Marine Ecosearch Management Company, for her initiation of taxonomy and establishment of database of benthic fauna from the Gulf Thailand.

Habitat. Found in 10–26.5 m depth, in muddy substrates mixed with sand and shell fragments.

Distribution. Gulf of Thailand, Western Pacific.

Remarks. Sigambra sirilukae sp. nov. belongs to the Sigambra group lacking ventral cirri on chaetiger 2 and with more than eight pharyngeal papillae ( Table 1). It is a very distinctive species having 12 pharynx papillae, a median antenna 2.8–5x longer than lateral antennae, and with a large ceratophore extending to chaetiger 11–12. It also has up to 5 notopodial capillary chaetae present per parapodia from anterior to posterior chaetigers, and dorsal hooks from mid chaetigers (chaetiger 50 or greater). Sigambra sirilukae sp. nov. differs from all Sigambra species by possessing 12 marginal papillae on the pharynx. Other species have marginal papillae either lower (8) or higher (13–16) than the new species. Moreover, the number of notopodial capillary chaetae in S. sirilukae sp. nov. is greater than other species (2–5: 1–2 chaetae per parapodium, respectively) ( Table 1).

There are three previously described species: S. constricta Southern, 1921, S. olivai Salazar-Vallejo, Rizzo, León-González & Brauko, 2019 , and S. rugosa Fauchald, 1972 that have the dorsal hooks in middle chaetigers (starting from chaetiger 30–40, 30–39 and 43–46 respectively). In S. sirilukae sp. nov. the first dorsal hooks begin more posteriorly, up to chaetiger 60. Moreover both S. constricta and S. olivai having greater than 12 marginal papillae (14 and 13–16, respectively) ( Fauchald 1972; Salazar-Vallejo et al. 2019; Southern 1921). Additionally, S. constricta has capillary chaetae only in posterior chaetigers, while they are absent in both S. olivai and S. rugosa ( Bhowmik et al., 2021; Fauchald 1972; Salazar-Vallejo et al. 2019; Southern 1921). Sigambra sirilukae sp. nov. also differs from those three species in median antenna length being 3–5x longer than lateral antennae. In S. constricta and S. olivai the median antenna is about 2x longer than the lateral antennae and in S. rugosa the median antenna is subequal in length to the lateral antennae ( Bhowmik et al. 2021; Fauchald 1972; Salazar-Vallejo et al. 2019). Additionally, there are up to 60 chaetae per neuropodium in the new species with up to 9 chaetae per bundle in the other species. There are up to 5 notochaetae per parapodium which is greater than the other species.

Of the 26 known Sigambra species and the proposed two new species, the number described from the Indo-Pacific region is quite high, totalling 11 species including the proposed new species. All these species are from the larger group that lack ventral cirri on chaetiger 2. Three of the ten species bear eight pharyngeal papillae: S. bidentata Britaev & Saphronova, 1981 from Japan, S. papagayu Bamber in Muir & Bamber, 2008 from Hong Kong, and S. qingdaoensis Licher & Westheide, 1997 from China. One species, S. sirilukae sp. nov. from the Gulf of Thailand bears 12 pharyngeal papillae. The other seven species bear 14 pharyngeal papillae. They include S. elegans Britaev & Saphronova, 1981 and S. hanaokai Kitamori, 1960 , both from Japan; S. constricta Southern, 1921 and S. sundarbanensis Bhowmik, Ghoshal, Salazar-Vallejo & Mandal, 2021 , both from India; S. pettiboneae Hartmann-Schröder, 1979 from Western Australia; and S. phuketensis Licher & Westheide, 1997 and S. pakbaraensis sp. nov. both from the Andaman Sea, Thailand ( Table 1).

Figures

FIGURE 8. Sigambra sirilukae sp. nov. light photographs (A, C, holotype: PSUZC-POL-0236; B, PSUZC-POL-0252). A. Whole specimen, lateral view; B. Anterior region, dorsal view; C. Posterior region, lateral view. Abbreviations: 1st dc, first dorsal cirrus; dc, dorsal cirrus; dh, dorsal hook; la, lateral antenna; ma, median antenna; tc, tentacular cirri.

FIGURE 9. Sigambra sirilukae sp. nov. (A, PSUZC-POL-0238; B–C, PSUZC-POL-0244; D, PSUZC-POL-0245).A.Anterior region, dorsal view; B. Same, ventral view; C. Pharynx papillae, top view; D. Anterior end, lateral view. Abbreviations: 1st dc, first dorsal cirrus; cp, ceratophore; dc, dorsal cirri; ddp, dorsal distal papillae; la, lateral antenna; ldp, lateral distal papillae; ma, median antenna; mpp, mount papillae; no, nuchal organ; pe, peristomium; pr, prostomium; sp, subdistal papilla; tc, tentacular cirri; vc, ventral cirrus; vdp, ventral distal papillae; vg, ventral groov; vpp, ventrolateral palpal papilla.

FIGURE 10. Sigambra sirilukae sp. nov. (PSUZC-POL-0328).A. Anterior parapodia, chaetigers 7–9 (from left to right), in circles are pores, dorsal view; B. Close up papillae on cheatiger, dorsal; C. Close up notopodial capilary chaeta, lateral view; D. Close up parapodia, arrows point to gonopores, dorsal view; E. Neurochaetae, dorsal view. Abbreviations: cc, capillary notochaeta; dc, dorsal cirrus; ne, neurochaetae; pp, papillae; vc, ventral cirrus.

FIGURE 11. Sigambra sirilukae sp. nov. A. Long limbate and pectinated neurochaetae, lateral view; B. Inferior limbate neurochaetae, ventral-lateral view; C. Close up teeth of inferior limbate chaeta, lateral view. Abbreviations: llc, long limbate chaeta; pec, pectinated neurochaeta.