Paucibranchia sinensis ( Monro, 1934 ) Molina-Acevedo, 2018

Molina-Acevedo, Isabel C., 2018, Morphological revision of the Subgroup 1 Fauchald, 1970 of Marphysa de Quatrefages, 1865 (Eunicidae: Polychaeta), Zootaxa 4480 (1), pp. 1-125 : 90-92

Paucibranchia sinensis ( Monro, 1934) n. comb.

Figures 63–66 , Tables 1, 3

Marphysa sinensis Monro, 1934:367 –369, Fig. 5A–F ; Liu et al. 2017:240 –241, 247, Figs. 1 , 6A–F , Table 3.

Material examined. Topotype material: USNM 22516 (1), Amoy, China, coll. T.Y. Chen.

Description. Specimen incomplete, with 56 chaetigers, L10= 6.6 mm, W10= 1.9 mm, the fragment with TL= 25mm. Anterior region of body with convex dorsum and flat ventrum, without groove; body depressed from chaetiger 6, widest at chaetiger 14, tapering after chaetiger 17.

Prostomium entire, 0.9 mm long, 0.9 mm wide, frontally rounded, without median sulcus ( Fig. 63A–B ), ventral sulcus deep ( Fig. 63B ). Prostomial appendages in a semicircle, median antenna isolated by a gap. Palps reaching second peristomial ring; lateral antennae reaching the middle of the second peristomial ring; median antenna reaching first chaetiger. Palpophores and ceratophores ring-shaped, short, slender; palpostyles and ceratostyles tapering, thick, without articulation. Eyes not observed, in Monro (1934) with orange eyes.

Peristomium wider than prostomium (1 mm long, 1.7 mm wide), first ring two times longer than second ring, separation between rings distinct on all sides ( Fig. 63A–B ). Inferior lip smooth ( Fig. 63B ).

Maxillary apparatus with MF= 1+1, 6+7, 7+0, 5+9, 1+1 ( Fig. 64A ). Maxillary carriers 2.6 times shorter than length of MI. MI forceps-like; closing system 6 times shorter than length of MI; ligament between MI and MII slightly sclerotized ( Fig. 64A ) . MII wide ; teeth recurved, sharped; cavity opening oval, 2 times shorter than length of MII ; ligament between MII and MIII, and right MIV, not sclerotized ( Fig. 64A ) . MIII short; with triangular teeth; with attachment lamella not sclerotized. Left MIV with a small basal tooth; attachment lamella semicircular, wide, situated 1/3 along length of posterior edge of maxilla. Right MIV with similar size teeth; attachment lamella wide, better developed in the middle, situated 1/4 along length of posterior edge of maxilla ( Fig. 64A ). MV rectangular, longer than wide, with a short rounded tooth ( Fig. 64A ). Mandibles slightly sclerotized; with whitish cutting plates, rectangular, with around 10 growth rings ( Fig. 64B ).

Branchiae pectinate with up to 15 filaments, in chaetigers 17–31 ( Figs. 63C ; 65D ). Number of branchial filaments per chaetiger in order anterior-posterior: 12, 13, 13, 12, 15, 14, 13, 13, 13, 14, 15, 13, 12, 12, 4?. Branchial filament longer than dorsal cirri.

First three parapodia smallest; most developed in chaetigers 4–24, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 4 (Ldc3: 0.52 mm, Ldc24: 0.75 mm), from chaetiger 18, gradually decreasing in width and increasing in length, in posterior region filiform, 1.8 times longer than prebranchial region ones (Ldc52: 0.95 mm); Hayashi & Yamane’s organ present ( Fig. 65A–E ). Prechaetal lobes as a transverse fold in all chaetigers ( Fig. 65A–E ). Chaetal lobes in chaetigers 1–21, rounded, shorter than postchaetal lobe, with aciculae emerging dorsal to midline; from chaetiger 22, triangular, longer than other lobes, with aciculae emerging in midline ( Fig. 65A–E ). Postchaetal lobes well developed in chaetigers 1–54; first three wide basally with digitiform end, from four chaetiger bluntly conical; thinner, elongated in branchial chaetigers; decreasing in size in chaetigers 16–54, following ones inconspicuous ( Fig. 65A–E ). Ventral cirri digitiform in chaetigers 1–5; in chaetigers 6–23 with oval swollen base and digitiform tip; from chaetiger 24, digitiform, gradually reducing in size posteriorly ( Fig. 65A–E ).

Aciculae blunt, amber ( Fig. 65A–E ). First four chaetigers with 3 aciculae; in chaetigers 5–18 with 3 or 4; in chaetigers 19–25 with 2; from chaetiger 26, with only one acicula.

Limbate chaetae of two sizes in same chaetiger, larger in anterior region, reduced in number around chaetiger 17. Two types of pectinate chaetae; in anterior chaetigers isodonts narrow with long and slender teeth, with 2–4 pectinate, with up to 7–8 teeth, with transverse distal edge ( Fig. 66A ); in median-posterior chaetigers isodonts narrow with short and slender teeth, with 4–5 pectinate, with up to 7–8 teeth, with transverse distal edge ( Fig. 66B ). Compound spinigers present in 1–30 chaetigers, with all blades of similar size ( Fig. 66C ). Compound falcigers present in all chaetigers, more abundant than spinigers; in anterior region with blades of two sizes (longer 80 µm, Fig. 66D ; smaller 65 µm, Fig. 66E ); all with triangular teeth distal, directed upward, proximal tooth directed laterally, distinctly shorter than distal, sometimes difficult to see; in media-posterior chaetigers with blades of similar size, shorter than blades of anterior chaetigers (45 µm, Fig. 66F ), all with triangular teeth, distal slightly shorter than proximal, distal tooth directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, amber, starting in chaetiger 36, with one hook per chaetiger; with triangular teeth, distal tooth smaller than proximal tooth, directed upward; proximal tooth directed laterally ( Fig. 66G ).

Distribution. Amoy, China.

Remarks. This species was recently redescribed by Liu et al. (2017); however, some important characters used to separate the species within the genus, were herein included, such as the size of the dorsal cirri along the body, the shape of the postchaetal lobes, the distribution of the dorsal cirri with a swollen base, the size of falcigers blades, and the architecture of the maxillary apparatus.

Paucibranchia sinensis n. comb. shares with P. bellii n. comb. and P. oculata n. comb. the amber color of the bidentate subacicular hooks, and the presence of compound falcigers and spinigers. However, P. sinensis n. comb. differs from the P. oculata n. comb. because the former has falcigers with blades of two sizes and the proximal tooth is too small (difficult to observe); whereas in P. oculata n. comb. all falcigers have blades of the similar size and the proximal tooth is notorious. In addition, in P. sinensis n. comb. the compound falcigers are present from the first chaetiger, and they are more abundant than the spinigers; whereas in P. oculata n. comb. falcigers start from chaetigers 11–26, and the spinigers are more abundant than the falcigers. Moreover, in P. sinensis n. comb. aciculae are amber in the anterior region, the postchaetal lobes are wide basally with digitiform end, and the pectinate have teeth with transverse distal edge in anterior region; whereas P. bellii n. comb. has reddish aciculae in anterior region, the postchaetal lobes are tongue-form in pre-branchial chaetigers, and the pectinate have teeth with oblique distal edge in the same region. The comparison with other Paucibranchia n. gen. species having compound falcigers and spinigers is provided in Table 3.

Figures

FIGURE 1. Maxillary apparatus. A. Paucibranchia disjuncta n. comb. (Hartman, 1961), LACM-AHF POLY 6447, dorsal view; B. Marphysa viridis Treadwell, 1917, ECOSUR-P2678, dorsal view; C. Treadwellphysa yucatanensis Molina-Acevedo & Carrera-Parra, 2017, ECOSUR-P2811, dorsal view; D. Left MI-II-III-IV-V of P. disjuncta n. comb., dorsal view; E. Left MI- II-III-IV-V of M. viridis, dorsal view; F. Left MI-II-III-IV-V of T. yucatanensis, dorsal view. Scale bars: A, D, 0.4 mm; B, E, 0.45 mm; C, F, 0.25 mm. Dark and thin lines in D, E and F indicate the different forms in the MI of the apparatus of each species. fa= falcal arch, boe= basal outer edge, bie= basal inner edge, rp= rounded projection in base of MII.

FIGURE 5. Paucibranchia adenensis (Gravier, 1900) n. comb., non-type MNHN-A148. A. Parapodium 3; B. Parapodium 11; C. Parapodium 26; D. Parapodium 70; E. Parapodium 158; F. Parapodium 216. All in anterior view. Scale bars: A–F, 0.7 mm.

FIGURE 6. Paucibranchia adenensis (Gravier, 1900) n. comb., non-type MNHN-A148. A. Compound falciger, long blade, chaetiger, 11; B. Compound falciger, median blade, chaetiger, 11; C. Compound falciger, short blade, chaetiger, 216; D. Isodonts pectinate narrow with long and slender teeth, chaetiger 3; E. Isodonts pectinate narrow with short and slender teeth, chaetiger 216; F. Subacicular hook, distal end, chaetiger 158. Scale bars: A, 12.5 µm; B, 20 µm; C, F, 9.8 µm; D, 14 µm, E, 4.9 µm.

FIGURE 63. Paucibranchia sinensis (Monro, 1934) n. comb., topotype USNM 22516. A. Anterior end, dorsal view; B. Anterior end, ventral view; C. Anterior end with branchiae, dorsal view. Scale bars: A–C, 1.65 mm.

FIGURE 64. Paucibranchia sinensis (Monro, 1934) n. comb., topotype USNM 22516. A. Maxillary apparatus, dorsal view; B. Mandible. Scale bars: A. 0.2 mm; B. 0.3 mm.

FIGURE 65. Paucibranchia sinensis (Monro, 1934) n. comb., topotype USNM 22516. A. Parapodium 3; B. Parapodium 12, dorsal cirri broken; C. Parapodium 25; D. Parapodium 42; E. Parapodium 55. All in anterior view. Scale bars: A, B, 0.1 mm; C– E, 0.2 mm.

FIGURE 66. Paucibranchia sinensis (Monro, 1934) n. comb., topotype USNM 22516. A. Isodonts pectinate narrow with long and slender teeth, chaetiger 3; B. Isodonts pectinate narrow with short and slender teeth, chaetiger 55; C. Compound spiniger, chaetiger 3; D. Compound falciger, long blade, chaetiger 3; E. Compound falciger, median blade, chaetiger 3; F. Compound falciger, short blade, chaetiger 55; G. Subacicular hook, chaetiger 41. Scale bars: A, B, 5.5 µm; C, 12.4 µm; D, 20 µm; E, 16.3 µm; F, 9.5 µm; G, 25 µm.