Paucibranchia adenensis ( Gravier, 1900 ) 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 : 9-15

publication ID	https://doi.org/ 10.11646/zootaxa.4480.1.1
publication LSID	lsid:zoobank.org:pub:0D3D99EC-107A-4D6B-B19E-52147C6C141E
DOI	https://doi.org/10.5281/zenodo.5953857
persistent identifier	https://treatment.plazi.org/id/CE78C444-FFC0-2174-FF5B-A674FE27FE67
treatment provided by	Plazi
scientific name	Paucibranchia adenensis ( Gravier, 1900 )
status	comb. nov.

Treatment

Paucibranchia adenensis ( Gravier, 1900) View in CoL n. comb.

Figures 3–6 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 , Tables 1–2

Marphysa adenensis Gravier, 1900:270 View in CoL –272, Pl. XIV, Figs. 91–92, text-fig. 140–143; Day 1962:644 –645; Day 1967:399, Fig. 17.6 p–s; Katsiaras et al. 2014:203 –207, Figs. 1a–h View FIGURE 1 , 2a–d View FIGURE 2 , 3 View FIGURE 3 , 4a–d View FIGURE 4 , Tab. 2 (partim)

Material examined. Type material: Holotype MNHN-531, Yemen, Gulf of Aden, Red Sea. Additional material: MNHN-A148 (5), Djibouti, Gulf of Tadjoura, Red Sea , 10 Feb 1904, in the muddy sand to the east of the Residence, coll. C. Gravier.

Description. Holotype incomplete, with 115 chaetigers, L10= 4 mm, W10= 0.7 mm, the fragment with TL= 40 mm. Anterior region with convex dorsum, and flat ventrum, without groove; body depressed from chaetiger 9, widest at chaetiger 25, tapering after chaetiger 57. In non-type specimens (MNHN-A148) some areas of the anterior region with brown coloration.

Prostomium in poor condition, 0.5 mm long, 0.5 mm wide, frontally rounded, without median sulcus ( Fig. 3B– D View FIGURE 3 ), ventral sulcus deep ( Fig. 3F View FIGURE 3 ). Prostomial appendages in a semicircle, equidistant (MNHN-A148). Palps reaching second peristomial ring; lateral antennae and median antenna broken, in specimen MNHN-A148 reaching third and four chaetiger, respectively. Palpophores and ceratophores ring-shaped, short, slender; palpostyles and ceratostyles tapering, thick, without articulation. Eyes rounded, brown, between palps and lateral antennae.

Peristomium slightly wider than prostomium (0.4 mm long, 0.6 mm wide), first ring two times longer than second ring; separation between rings distinct on all sides ( Fig. 3A–F View FIGURE 3 ). Inferior lip broken, in specimen MNHN- A148 without central depression ( Fig. 3F View FIGURE 3 ).

Maxillary apparatus in poor condition, according to Gravier’s drawings with MF= 1+1, 7+?, 10+0,?+?,?+?, ( Gravier 1900, Pl. XIV, Fig. 92). Non-type specimen MNHN-A148 with MF= 1+1, 7+7, 7+0, 5+9, 1+1 ( Fig. 4A View FIGURE 4 ). Maxillary carriers 1.6 times shorter than length of MI. MI forceps-like; closing system 8 times shorter than length of MI; ligament between MI and MII, not sclerotized ( Fig. 4A, D View FIGURE 4 ) . 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. 4A, C View FIGURE 4 ) . MIII short; with triangular teeth; with attachment lamella slightly sclerotized ( Fig. 4A, C View FIGURE 4 ). Left MIV with basal tooth smaller; attachment lamella semicircular, wide, situated along length of posterior edge of maxilla. Right MIV with small teeth; attachment lamella wide, semicircular, better developed in the middle, situated along length of posterior edge of maxilla ( Fig. 4A, C View FIGURE 4 ). MV square, with a short rounded tooth ( Fig. 4C View FIGURE 4 ). Mandibles translucent; cutting plates whitish, with 12 growth rings ( Fig. 4B View FIGURE 4 ).

Branchiae pectinate with up to 11 filaments, in chaetigers 15–30 ( Figs. 3A, E View FIGURE 3 ; 5A View FIGURE 5 ). Number of branchial filaments per chaetiger in order anterior-posterior: 8, 8, 8, 9, 10, 10, 10, 11, 11, 10, 10, 10, 9, 9, 8, 6. Branchial filaments longer than dorsal cirri.

First two parapodia smallest; most developed in chaetigers 3–16, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 3 (Ldc3: 0.17 mm; Ldc26: 0.20 mm), from chaetiger 40, gradually decreasing in size (Ldc216: 0.13 mm), in posterior region almost the same length than pre-branchial region ones; Hayashi & Yamane’s organ present ( Fig. 5A–F View FIGURE 5 ). Prechaetal lobes as a transverse fold in all chaetigers ( Fig. 5A–F View FIGURE 5 ). Chaetal lobe in chaetigers 1–28, rounded, shorter than postchaetal lobe, with aciculae emerging dorsal to midline; from chaetiger 29, triangular, longer than other lobes, with acicula emerging in midline ( Fig. 5A–F View FIGURE 5 ). Postchaetal lobes well developed in chaetigers 1–48, bluntly conical in pre-branchial chaetigers, elongated and thinner in branchial region; decreasing in size in chaetigers 31–48, following ones inconspicuous ( Fig. 5C–F View FIGURE 5 ). Ventral cirri digitiform in chaetigers 1–7; in chaetigers 8–38 with oval swollen base and digitiform tip; from chaetiger 39, conical, gradually reducing in size posteriorly ( Fig. 5A–C View FIGURE 5 ).

Aciculae blunt, translucent ( Fig. 5A–F View FIGURE 5 ). First 14 chaetigers with 2 aciculae; from chaetiger 15, with only one acicula.

Limbate chaetae of two sizes in same chaetiger, larger in anterior region, reduced in number around chaetiger 27. Two types of pectinate chaetae, in anterior chaetigers, isodonts narrow with long and slender teeth, with 1–2 pectinate, with 5 teeth, with transverse distal edge ( Fig. 6D View FIGURE 6 ); in median-posterior chaetigers, isodonts narrow with short and slender teeth, 2–4 pectinate, with 10–12 teeth, with transverse distal edge ( Fig. 6E View FIGURE 6 ). Compound falcigers present in all chaetigers; in anterior region with blades of two sizes (longer 105 µm, Fig. 6A View FIGURE 6 ; smaller 90 µm, Fig. 6B View FIGURE 6 ), smaller more abundant; all with triangular teeth, of similar size, distal tooth directed upward, proximal tooth directed laterally; in median-posterior chaetigers with all blades of similar size, slightly shorter than blades of anterior chaetigers (84 µm, Fig. 6C View FIGURE 6 ), with triangular teeth, distal tooth shorter than proximal, directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, translucent, starting from chaetigers 29L–30R, one per chaetiger; with triangular teeth, distal tooth smaller than proximal, directed upward; proximal tooth directed laterally ( Fig. 6E View FIGURE 6 ).

Pygidium with two pairs of anal cirri; dorsal pair as long as last four chaetigers; ventral pair short, as long as two last chaetigers.

Variation. Material examined varied in the following features: L10= 2.5– 4 mm, W10= 0.7–0.8 mm. Palps reaching second peristomial ring or first chaetiger. Lateral antennae reaching first or third chaetigers. Median antenna reaching third or fourth chaetiger. The maxillary formula varies as follows: MII 7–8+7–8, MIII 6–7, MIV 4–5+7–9. The proportion of maxillary apparatus varies as follows: maxillary carriers shorter with respect to MI varies 1.6–2 times; cavity opening shorter with respect to MII varies 5–6 times. Branchiae from chaetigers 14–17 to chaetigers 28–36. Maximum number of branchial filaments varied from 10 to 11. Well developed postchaetal lobe in the first 40–52 chaetigers. Ventral cirri with swollen base from chaetigers 6–7 to chaetigers 36–49. Start of subacicular hooks in chaetigers 29–35.

Distribution. Red Sea, Madagascar.

Remarks. Paucibranchia adenensis n. comb. was redescribed based on the holotype and specimens collected from Greece (Mediterranean Sea) by Katsiaras et al. (2014). They indicated that the Mediterranean specimens differ from the holotype in the length of the falcigers blade since in the former the longest blades are twice as long as the shorter ones; while in the holotype, the blades differ by only a few micrometers. They attributed this difference to the loss or breakage of falcigers in the holotype due to the time of preservation. Nevertheless, as in the holotype, the non-type specimens (MNHN-A148) do not have falcigers with such a marked difference in their blade's length. Katsiaras et al. (2014) also noted that the dorsal cirri are twice longer in the posterior region; while, in the holotype and additional material, the length of dorsal cirri is similar in pre- and postbranchial region. Based on the above, it is possible that the specimens from the Mediterranean may belong to an undescribed species, not to P. adenensis n. comb.

Day (1962, 1967) reported P. adenensis n. comb. from Nosy Be, Madagascar. According to his description, the two specimens agree with the holotype in the principal features, such as prostomium shape, branchial distribution and filaments number, the presence of only compound falcigers, and color and shape of aciculae and subacicular hook. Due to this similarity, it is possible that Day’s material belongs to the same species.

Paucibranchia adenensis n. comb. is similar to P. gemmata n. comb. P. patriciae n. sp. and Paucibranchia sp. 2 based on the presence of only compound falcigers and translucent color of aciculae; however, P. adenensis n. comb. differs from P. gemmata n. comb. in the presence of eyes, dorsal cirri of the same length in pre- and postbranchial region, and falcigers with blades of two sizes in anterior region; while P. gemmata n. comb. lacks eyes, posterior dorsal cirri are two times longer than anterior ones, and by having falcigers with blades of three sizes in the same region. The morphological differentiation of P. adenensis n. comb. with P. patriciae n. sp. and Paucibranchia sp. 2 is provided in the Remarks section of each species. The comparison with other Paucibranchia n. gen. species having only compound falcigers present is provided in Table 2.