Paucibranchia carrerai, 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 : 26-31

Paucibranchia carrerai n. sp.

Figures 15–18 , Tables 1, 3

Marphysa belli Gallardo 1968:80 non Audouin & Milne-Edwards 1833.

Material examined. Type material: Holotype LACM-AHF POLY 6924 , sta. 142I, one nautical mile south of eastern end of Hòn Tằm, Bay of Nha Trang, South China Sea, SouthVietnam, 12°09'43'' N 109°14'10'' E, 16 Feb 1960, in mud, 13 m , coll. V.A. Gallardo. Paratypes: LACM-AHF POLY 6923 (1), sta. 142II/P3, one nautical mile south of eastern end of Hòn Tằm, Bay of Nha Trang , South China Sea, South Vietnam, 12°09'43'' N 109°14'10' E, 16 Feb 1960, in mud, 12 m , coll. V.A. Gallardo. LACM-AHF POLY 6922 (1), sta. 86I, east of Cau-da, Institut Oceanographique de Nha Trang, Bay of Nha Trang , South China Sea, South Vietnam, 12°12'12'' N 109°13'33'' E, 2 Feb 1960, in mud, 9 m , coll. V.A. Gallardo. Additional material: LACM-AHF POLY 6921 (1), sta. 139I, north of Mui Dong Ba (mainland), Bay of Nha Trang , South China Sea, South Vietnam, 12°09'41'' N 109°12'47'' E, 16 Feb 1960, in mud, 6 m , coll. V.A. Gallardo. LACM-AHF POLY 10192 (1), sta. 142II/P6, one nautical mile south of eastern end of Hòn Tằm, Bay of Nha Trang , South China Sea, South Vietnam, 12°09'43'' N 109°14'10'' E, 16 Feb 1960, in mud, 12 m , coll. V.A. Gallardo.

Description. Holotype complete, antero-laterally dissected, with 100 chaetigers, L10= 6.1 mm, W10= 1.8 mm, TL= 60 mm. Anterior region of body with convex dorsum, and flat ventrum, without groove; body depressed from chaetiger 5, widest at chaetiger 6, tapering after chaetiger 12.

Prostomium entire, 0.7 mm long, 0.5 mm wide, frontally rounded, median sulcus shallow ( Fig. 15A ), ventral sulcus deep ( Fig. 15B ). Prostomial appendages in a semicircle, equidistant. Palps reaching second peristomial ring; lateral and median antennae reaching first chaetiger. Palpophores and ceratophores ring-shaped, short, slender; palpostyles and ceratostyles tapering, slender, without articulation. Eyes absent.

Peristomium bigger than prostomium (1.8 mm long, 0.8 mm wide), first ring almost the same size than second ring; separation between rings distinct on all sides ( Fig. 15A–B ). Inferior lip without a central depression ( Fig. 15B ).

Maxillary apparatus lost, observed in paratype LACM-AHF POLY 6923. Maxillary apparatus with MF= 1+1, 6+7, 6+0, 4+9, 1+1. ( Fig. 15C ). Maxillary carriers 1.8 times shorter than length of MI. MI forceps-like; closing system 9 times shorter than length of MI; ligament between MI and MII not sclerotized ( Fig. 15C ). MII wide; teeth recurved, sharped; cavity opening oval, 6 times shorter than length of MII; ligament between MII and MIII, and right MIV, not sclerotized ( Fig. 15C ). MIII short; with triangular teeth; with attachment lamella slightly sclerotized ( Fig. 15C ). Left MIV with a smaller basal tooth; attachment not sclerotized. Right MIV with small teeth; attachment lamella not sclerotized ( Fig. 15C ). MV square, with a short triangular tooth ( Fig. 15C ). Mandibles translucent, cutting plates with 8 growth rings.

Branchiae pectinate with up to 15 filaments, in chaetigers 7–18 ( Figs. 15A ; 16B ). Number of branchial filaments per chaetiger in order anterior-posterior: 8, 10, 12, 14, 15, 15, 14, 14, 14, 10, 10, 4. Last branchia smaller; branchial filaments longer than dorsal cirri.

First two parapodia smallest; most developed in chaetigers 3–17, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 4 (Ldc4: 0.55 mm; Ldc19: 0.60 mm), from chaetiger 22, gradually decreasing in width and increasing in length; in posterior region filiform, twice longer than pre-branchial region ones (Ldc92: 1.1 mm); Hayashi & Yamane’s organ present ( Fig. 16A–D ). Prechaetal lobes as a transverse fold in all chaetigers ( Fig. 16A–D ). Chaetal lobes in chaetigers 1–21, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 22, triangular, longer than other lobes, with acicula emerging in midline ( Fig. 16A–D ). Postchaetal lobes well developed in chaetiger 1–29, conical, thinner and longer in branchial region; decreasing in size in chaetigers 18–29, following ones inconspicuous ( Fig. 16A–D ). Ventral cirri conical in chaetigers 1–5; in chaetigers 6–22 with oval swollen base and digitiform tip; from chaetiger 23, conical, short ( Fig. 16A–D ).

Aciculae blunt, translucent ( Fig. 16A–D ). First 17 chaetigers with 3 aciculae; in chaetigers 18–22 with 2 aciculae; from chaetiger 23, with only one acicula.

Limbate chaetae of two sizes in same chaetiger, larger in anterior region, reduced in number around chaetiger 20. Two types of pectinate chaetae; in anterior chaetigers, isodonts narrow with long and slender teeth, with 2–3 pectinate, with up to 6–9 teeth, with transverse distal edge ( Fig. 17E ); in median-posterior chaetigers, isodonts narrow with short and slender teeth, with 5–6 pectinate, with up to 15–16 teeth, with oblique distal edge ( Fig. 17F ). Compound spinigers in chaetigers 1–22, 10–12 per chaetiger, with all blades of similar size ( Fig. 17D ). Compound falcigers in all chaetigers, more abundant than spinigers; first 18 chaetigers with blades of two sizes (longer 73.5 µm, Fig. 17A ; smaller 66.5 µm, Fig. 17B ); all with triangular teeth, of similar size, distal tooth directed upward, proximal tooth directed laterally; in media-posterior chaetigers with all blades of similar size, shorter than blades of anterior chaetigers (39.2 µm, Fig. 17C ), with triangular teeth, distal tooth shorter than proximal, directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, translucent, starting from chaetiger 21, with triangular teeth, distal tooth smaller than proximal, directed upward; proximal tooth directed laterally; several hooks per chaetiger: with 3 hooks in chaetiger 21, with 5 hooks in chaetigers 22–24, with 8 hooks in chaetigers 25– 30, with 10 hooks in chaetigers 31–42, with 10–14 hooks in chaetigers 43–73, with 10–7 hooks in chaetigers 74– 95; last five chaetigers with 5 hooks per chaetiger ( Fig. 18A–C ).

Pygidium with two pairs of anal cirri, without articulation; dorsal pair as long as last five chaetigers; ventral pair short, as long as last chaetiger.

Variation. Two of the five examined specimens without prostomium, a third specimen in poor condition. Material examined varied in the following features: L10= 4.2–6.1 mm, W10= 0.8–1.8 mm. Palps reaching first or second peristomial ring. Maximum number of branchial filaments varied from 14 to 15. Well developed postchaetal lobe in first 26–29 chaetigers. Start of subacicular hooks in chaetigers 20–21.

Type locality. Nha Trang, South Vietnam.

Distribution. South Vietnam.

Etymology. This species is named in honor of Dr. Luis Fernando Carrera-Parra in recognition of his valuable contributions to the taxonomic study of polychaetes, in particular with Eunicida .

Remarks. These specimens were identified as Marphysa bellii (Currently, Paucibranchia bellii n. comb.) by Gallardo (1968); however, some significant differences were found, and a new species was described. Paucibranchia carrrerai n. sp. differs from P. bellii n. comb. in the branchial distribution, since in the former branchiae start from chaetiger 7 and end on chaetiger 18 (holotype, L10: 6.1 mm), whereas in P. bellii n. comb. (ZMB 3996, L10: 4 mm) branchiae start on chaetiger 12 end on chaetiger 30. Also, the postchaetal lobe is tongueshaped in pre-branchial chaetigers and conical in the branchial region in P. bellii n. comb., whereas it is conical in both regions for P. carrerai n. sp. In addition, the new species presents a large number of subacicular hooks per chaetiger, reaching up to 14 per chaetiger; whereas in P. bellii n. comb. only has one or two hooks per chaetiger. Based on these significant differences, it was possible to conclude that the specimens from Vietnam belong to a different species and that P. bellii n. comb. is not distributed in Vietnam.

Paucibranchia carrerai n. sp. resembles P. stragula n. comb. by having several translucent bidentate subacicular hooks per chaetiger; however, the former has up to 14 hooks per chaetiger, whereas the latter has no more than 6 per chaetiger. Also, in P. stragula n. comb. the shape of postchaetal lobe is digitiform in pre-branchial chaetigers and conical in branchial region, whereas in P. carrerai n. sp. it is always conical. Furthermore, there are differences in the branchial distribution and start of subacicular hooks. The new species (holotype, L10: 6.1 mm) has branchiae in chaetigers 7–18, and subacicular hooks from chaetiger 20, whereas P. stragula n. comb. (holotype, L10: 3.7 mm) has branchiae in chaetigers 11–22, and subacicular hooks from chaetiger 25. The comparison with other Paucibranchia n. gen. species with compound falcigers and spinigers present is provided in Table 3.

Figures

FIGURE 15. Paucibranchia carrerai n. sp., holotype LACM-AHF POLY 6924. A. Anterior end with branchiae, dorsal view; B. Anterior end, ventral view; C. Maxillary apparatus, dorsal view. Scale bars: A, 1.25 mm; B, 0.63 mm; C, 0.5 mm.

FIGURE 16. Paucibranchia carrerai n. sp., holotype LACM-AHF POLY 6924. A. Parapodium 4; B. Parapodium 12; C. Parapodium 54, dorsal cirri broken; D. Parapodium 92. All in anterior view. Scale bars: A, D, 0.28 mm; B, C, 0.22.

FIGURE 17. Paucibranchia carrerai n. sp., holotype LACM-AHF POLY 6924. A. Compound falciger, long blade, chaetiger 4; B. Compound falciger, median blade, chaetiger 4; C. Compound falciger, short blade, chaetiger 92; D. Compound spiniger, chaetiger 4; E. Isodonts pectinate narrow with long and slender teeth, chaetiger 4; F. Isodonts pectinate narrow with short and slender teeth, chaetiger 92. Scale bars: A, B, C, 18 µm; D, F, 7 µm; E, 14 µm.

FIGURE 18. Paucibranchia carrerai n. sp., holotype LACM-AHF POLY 6924. A, B. Parapodium 54 with multiplex subacicular hooks; C. Subacicular hook, chaetiger 54. Parapodia in anterior view. Scale bars: A. 35.5 µm; B, 10 µm; C, 10.2 µm.