Paucibranchia Molina-Acevedo 2018
Creators: name: Molina-Acevedo, Isabel C.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Polychaeta
Eunicida
Eunicidae
Paucibranchia

description: Paucibranchia sp. 1
Figures 67–69, Tables 1, 3
Marphysa cf. bellii Gathof 1984:40.10–40.12, Figs. 40–5, 6a–i.
Marphysa belli Lu & Fauchald 1998:829 –834, Figs. 1a–j, 2–6 (partim) non Audouin & Milne-Edwards 1833.
Material examined. Non-type material: ECOSUR-P2937 (1) sta. D20 R1, Campeche Bank, 0 3 Dic 2012, coll. Daniel Pech. USNM 90007 (2), sta. 11–221, off St. Petersburg, Florida, USA, 27°57' N 084°48'00 W, Aug 1977, 189 m.
Description. Specimen incomplete (ECOSUR-P2937) with 27 chaetigers, L10= 3.7 mm, W10= 0.9 mm, TL= 11.5 mm. Anterior region of the body with convex dorsum, and flat ventrum, without groove; body depressed from chaetiger 6, widest at chaetiger 6, tapering after chaetiger 12.
Prostomium entire, 0.6 mm long, 0.4 mm wide, frontally conical, without median sulcus (Fig. 67A–B), ventral sulcus deep (Fig. 67C). Prostomial appendages in semicircle, equidistant. Palps reaching second peristomial ring; lateral antennae reaching fourth chaetiger; median antennae reaching fifth chaetiger. Palpophores and ceratophores ring-shaped, short, slender; palpostyles and ceratostyles tapering, slender, without articulation. Eyes absent.
Peristomium wider than prostomium (0.6 mm long, 0.8 mm wide), first ring two times longer than second ring; separation between rings distinct on all sides (Fig. 67A–C). Inferior lip with a slight central depression, with a couple of shallow wrinkles (Fig. 67C).
Maxillary apparatus with MF= 1+1, 4+5, 5+0, 5+7, 1+1 (Fig. 68A). Maxillary carriers 2 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. 68A–B). MII wide; teeth recurved; cavity opening oval, 2.7 times shorter than length of MII; ligament between MII and MIII, and right MIV, slightly sclerotized (Fig. 68A–B). MIII short; with blunt teeth; with attachment lamella not sclerotized (Fig. 68A–B). Left MIV with smaller teeth; attachment lamella rectangular, situated in the basal portion of posterior edge of maxilla. Right MIV with blunt teeth; attachment lamella rectangular, in center of edge of maxilla (Fig. 68A–B). MV rectangular, slightly longer than wide, with a short rounded tooth. Mandibles translucent; with whitish cutting plates, with 10 growth rings (Fig. 68C).
Branchiae pectinate with up to 8 filaments, in chaetigers 8–17 (Figs. 67B; 69B). Number of branchial filaments per chaetiger in order anterior-posterior: 6, 8, 8, 8, 8, 7, 6, 6, 2. Branchial filaments longer than dorsal cirri.
First two parapodia smallest; most developed in chaetigers 4–12, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 4 (Ldc3: 0.30 mm; Ldc12:0.45), from chaetiger 23, decreasing in width and increasing in length, filiform (Ldc25: 0.53 mm); Hayashi & Yamane’s organ present (Fig. 69A–C). Prechaetal lobes as a transverse fold in all chaetigers (Fig. 69A–C). Chaetal lobes in chaetigers 1–15, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 16, triangular, longer than other lobes, with aciculae emerging slightly to midline (Fig. 69A–C). Postchaetal lobes well developed in chaetigers 1–23, bluntly conical; wide basally and digitiform end in branchial chaetigers; decreasing in size in chaetigers 13–23, following ones inconspicuous (Fig. 69A–C). Ventral cirri digitiform in chaetigers 1–6; from chaetigers 6 to end of the fragment with swollen base oval and digitiform tip (Fig. 69A–C).
Aciculae blunt, translucent (Fig. 69A–C). First three chaetigers with 3 aciculae; from chaetiger 4, with 2 aciculae.
Limbate chaetae of two sizes in the same chaetiger, larger in anterior region, reduced in number around chaetiger 14. One type of pectinate chaetae; in anterior chaetigers isodont wide with short, fine teeth with 7–8 pectinate, with up to 9–10 teeth, with transverse distal edge (Fig. 69H): in median-posterior not examined. Compound spinigers in chaetiger 1–25, 6–7 per chaetiger, with all blades of similar size (Fig. 69D). Compound falcigers in all chaetigers, more abundant than spinigers; in anterior region with blade of one size (49 µm, Fig. 69E), all with triangular teeth, of similar size, distal tooth directed upward, proximal tooth directed laterally; in median chaetigers with all blades of similar size, shorter than blades of anterior chaetigers (28 µm, Fig. 69F), with triangular teeth, distal tooth shorter than proximal, distal tooth directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, translucent, starting in chaetiger 22, with triangular teeth, distal tooth smaller than proximal tooth, directed upward; proximal tooth directed laterally, one or two per chaetiger (Fig. 69G).
Variation. Material examined varied in the following features: L10= 2.8–3.7, W10= 0.5–0.9 mm. The maxillary formula varies as follows: MII 4–6+5–6, MIII 5–6, MIV 4–5+7. Branchiae from chaetigers 7–8 to 16– 17. Maximum number of branchial filament varied from 6 to 8. Well developed postchaetal lobe in first 13–23 chaetigers. Ventral cirri with swollen base from chaetigers 5–6 to chaetigers 17–27. Start of subacicular hooks in chaetigers 18–22. Compound spinigers present only in first 13–25 chaetigers.
Type locality. Campeche bank, Gulf of Mexico.
Distribution. Florida, USA and Campeche, Gulf of Mexico.
Remarks. The specimens examined from Florida (Gulf of Mexico) were previously regarded as Marphysa cf. bellii by Gahtof (1984). He did not find enough evidence to separate them from the nominal European species. Later, Lu & Fauchald (1998) reviewed Gathof’s specimens and others collected from Massachusetts and referred them as M. bellii.
After a detailed revision of the specimens from the Gulf of Mexico, some critical morphological differences were herein found to consider them in Paucibranchia n. gen. and as a different species from P. bellii n. comb.. Paucibranchia sp. 1 (ECOSUR-P2937, L10: 3.7 mm) lacks eyes, the postchaetal lobes are triangular with a wide base, and branchiae begin from chaetiger 8; whereas, P. bellii n. comb. (ZMB 3996, L10: 4 mm) has eyes, the postchaetal lobes are in tongue-shaped in pre-branchial chaetigers, and branchiae begin from chaetiger 12.
Paucibranchia sp. 1 is close to P. carrerai n. sp., P. fallax n. comb. and P. stragula n. comb. by having a translucent subacicular hook and both types of compound chaetae (spinigers and falcigers). However, Paucibranchia sp. 1 differ from P. carrerai n. sp. and P. stragula n. comb. by having only one or two hooks per chaetiger; whereas latter two species have a greater number of subacicular hooks per chaetiger (14 and 6, respectively). Furthermore, in Paucibranchia sp. 1 (ECOSUR-P2937, L10: 3.7 mm) branchiae start in chaetiger 8 and ending on chaetiger 17 with up to 8 filaments; whereas in P. fallax n. comb. (MNHN-A39, L10: 3.3 mm) the branchiae are distributed from chaetigers 16 to 48, with only 2 branchial filaments. The comparison with other Paucibranchia n. gen. species having compound spinigers and falcigers present is provided in Table 3.
All specimens reviewed are incomplete (up to 27–34 chaetigers) and not in good condition; formal description of the species requires additional material.
description: Published as part of Molina-Acevedo, Isabel C., 2018, Morphological revision of the Subgroup 1 Fauchald, 1970 of Marphysa de Quatrefages, 1865 (Eunicidae: Polychaeta), pp. 1-125 in Zootaxa 4480 (1) on pages 93-98, DOI: 10.11646/zootaxa.4480.1.1, http://zenodo.org/record/1453031