Paucibranchia andresi, 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 : 15-20

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.5953859
persistent identifier	https://treatment.plazi.org/id/CE78C444-FFC6-2169-FF5B-A203FC19FABB
treatment provided by	Plazi
scientific name	Paucibranchia andresi
status	sp. nov.

Treatment

Paucibranchia andresi View in CoL n. sp.

Figures 7–10 View FIGURE 7 View FIGURE 8 View FIGURE 9 View FIGURE 10 , Tables 1, 3

Marphysa belli Lu & Fauchald 1998:829 View in CoL –834, Figs. 1a–j View FIGURE 1 , 2–6 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 (partim) non Audouin & Milne-Edwards 1833.

Material examined. Type material: Holotype USNM 28955 About USNM , Woods Hole region , Massachusetts, USA, 1943, coll. M. Pettibone. Paratypes USNM 145278 About USNM (1), sta. 0 8, Georges Bank, Massachusetts, USA, 40°27’06’’N 067°37’24’’W GoogleMaps , 21 Jul 1982, 152 m. USNM 109825 About USNM (4), sta. 24, Southern Slope , Georges Bank, Massachusetts, USA, 40°35’06N 067°11’30’’W , 20 Feb 1977, 119 m. Additional material: USNM 1099831 About USNM (1), sta. 25, Southern Slope , Georges Bank, Massachusetts, USA, 40°26’35’’N 067°35’32’’W GoogleMaps , 17 Feb 1977, 159 m. USNM 145281 About USNM (1), sta. 16, Georges Bank , Massachusetts, USA, 40°34’12’’N 067°12’18’’W GoogleMaps , 10 Feb 1982, 142 m. USNM 56988 About USNM (1), off Maryland, Chesapeake Bay , USA, 31 May 1977 , 66 m. USMN 9166 (1), sta. 799, Pt. Judith, Narragansett Bay , Rhode Island, USA, 14 Aug 1880.

Description. Holotype complete, dissected laterally, with 248 chaetigers, L10= 4.5 mm, W10= 1.6 mm, TL= 77 mm. Anterior region with convex dorsum, flat ventrum, without groove; body depressed from chaetiger 5, widest at chaetiger 7, tapering after chaetiger 18.

Prostomium entire, 1 mm long, 1 mm wide, frontally rounded, without median sulcus ( Fig. 7A View FIGURE 7 ), ventral sulcus deep ( Fig. 7C View FIGURE 7 ). Prostomial appendages in a semicircle, equidistant. Palps reaching the middle of first peristomial ring; lateral antennae reaching second peristomial ring; median antenna reaching first chaetiger. Palpophores and ceratophores ring-shaped, short, slender; palpostyles and ceratostyles tapering, slender, without articulation. Eyes not observed, in paratypes rounded, brown, between palps and lateral antennae.

Peristomium wider than prostomium (1 mm long, 1.6 mm wide), first ring two times longer than second ring, separation between rings distinct on all sides ( Fig. 7A, C View FIGURE 7 ). Inferior lip in poor condition, not observed ( Fig. 7C View FIGURE 7 ).

Maxillary apparatus with MF= 1+1, 5+7, 7+0, 3+7, 1+1 ( Fig. 8A–B View FIGURE 8 ). Maxillary carriers 1.5 times shorter than length of MI. MI forceps-like; closing system 5.7 times shorter than length of MI; ligament between MI and MII not sclerotized ( Fig. 8A–B View FIGURE 8 ). MII wide; teeth recurved; cavity opening oval, 3.1 times shorter than length of MII; ligament between MII and MIII, and right MIV, slightly sclerotized ( Fig. 8A View FIGURE 8 ). MIII short; with triangular teeth; with attachment lamella slightly sclerotized ( Fig. 8A–B View FIGURE 8 ). Left MIV with a smaller basal tooth; attachment lamella semicircular, wide, situated along length of posterior edge of maxilla. Right MIV with three distal smaller teeth; attachment lamella wide, better developed in the middle, situated 1/2 along length of posterior edge of maxilla ( Fig. 8A View FIGURE 8 ). MV square, with a short rounded tooth. Mandibles amber, cutting plates whitish, with 13 growth rings ( Fig. 8C View FIGURE 8 ).

Branchiae pectinate with up to 13 filaments, in chaetigers 12–29 ( Figs. 7A View FIGURE 7 , 9C View FIGURE 9 ). Number of branchial filaments per chaetiger in order anterior-posterior: 6, 7, 10, 10, 11, 11, 11, 12, 13,?, 10, 10, 10, 10, 10, 6, 2, 1. Basal branchial filament, as long as dorsal cirri.

First two parapodia smallest; most developed in chaetigers 5–20, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 5 (Ldc3: 0.33 mm; Ldc14: 0.8 mm), from chaetiger 16, gradually decreasing in size, in posterior region 1.4 times longer than pre-branchial region ones (Ldc213: 0.45 mm); Hayashi & Yamane’s organ present ( Fig. 9A–E View FIGURE 9 ). Prechaetal lobes as a transverse fold in all chaetigers ( Fig. 9A–E View FIGURE 9 ). Chaetal lobes in chaetigers 1–20, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 21, triangular, longer than other lobes, with acicula emerging in midline ( Fig. 9A–E View FIGURE 9 ). Postchaetal lobes well developed in chaetigers 1–58; digitiform in first three chaetigers, bluntly conical from fourth chaetiger; thinner, elongated in branchial region; decreasing in size in chaetigers 12–58, following ones inconspicuous ( Fig. 9A–E View FIGURE 9 ). Ventral cirri digitiform in chaetigers 1–3; in chaetigers 4–36 with oval swollen base and digitiform tip; from chaetiger 37, conical, gradually reducing in size posteriorly ( Fig. 9A–E View FIGURE 9 ).

Aciculae blunt, with reddish basal end, distally amber ( Fig. 9A–E View FIGURE 9 ). First 16 chaetigers with 2 or 3 aciculae; in chaetigers 17–21 with 2 aciculae; from chaetiger 22, with only one acicula.

Limbate chaetae of two sizes in same chaetiger, larger in anterior region, reduced in number around chaetiger 22. Two types of pectinate chaetae; in anterior chaetigers isodonts narrow with long and slender teeth, with 1–2 pectinate, with up to 5 teeth, oblique distal edge ( Fig. 10A View FIGURE 10 ); in median-posterior chaetigers, isodonts narrow with short and slender teeth, with 3–4 pectinate, with up to 8–9 teeth, with oblique distal edge ( Fig. 10B View FIGURE 10 ). Compound spinigers present only in first 45 chaetigers, 6 or 7 per chaetiger, with blade of two sizes ( Fig. 10C View FIGURE 10 ). Compound falcigers present in all chaetigers, more abundant than spinigers; in anterior region with all blades of similar size (65 µm, Fig. 10D View FIGURE 10 ); 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 (46 µm, Fig. 10E View FIGURE 10 ), all with teeth triangular, distal shorter than proximal, distal tooth directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, with reddish basal end, distally amber, starting from chaetigers 32L–33R, one-two hook per chaetiger; with rounded teeth, distal tooth smaller than proximal tooth, directed upward; proximal tooth directed laterally ( Fig. 10F View FIGURE 10 ).

Pygidium with two pairs of anal cirri; dorsal pair as long as last five chaetigers; ventral pair short, as long as last chaetiger ( Fig. 7D View FIGURE 7 ).

Variation. Material examined varied in the following features: L10= 2.1–4.1 mm, W10= 0.9–1.6 mm. Palps reaching middle of the first peristomial ring or first chaetiger. Lateral antennae reaching second peristomial ring or second chaetiger. Median antenna reaching second or third chaetiger. The maxillary formula varies as follows: MII 5–6+7, MIII 6–7, MIV 5–6+9–10. The proportion of maxillary apparatus varies as follows: maxillary carriers shorter with respect to the MI varies 1.7–2 times; closing system shorter with respect to the MI varies 7–10 times; cavity opening shorter with respect to MII varies 3–3.3 times. Branchiae from chaetigers 10–14 to chaetigers 17– 29. Maximum number of branchial filaments varied from 7 to 13. Well developed postchaetal lobe in first 30–63 chaetigers. Ventral cirri with swollen base from chaetigers 4–5 to chaetigers 28–42. Start of subacicular hooks in chaetigers 19–26. Compound spinigers present only in first 23–45 chaetigers.

Type Locality. Woods Hole , Massachusetts, USA.

Distribution. Massachusetts.

Etymology. The species is named after my brother, Andrés Molina Acevedo , in recognition of his unconditional love and support.

Remarks. Pettibone (1963) and Lu & Fauchald (1998) studied the material collected in Massachusetts, which was identified as Marphysa bellii . Although they found some slight differences, these were considered as part of the species. However, after examination of specimens collected from Massachusetts, some critical morphological differences were found. Paucibranchia andresi n. sp. has falcigers with the blade of similar sizes and 4 or 5 compound spinigers by chaetiger in the anterior region, pectinate chaetae with oblique distal edge in posterior chaetigers, and subaciacular hooks are reddish at the base and translucent distally; whereas P. bellii n. comb. has falcigers with blades of two sizes and 6 or 7 compound spinigers by chaetiger in the anterior region, pectinate chaetae with transversal distal edge in posterior region, and subacicular hook is amber. In addition, the specimens from Massachusetts were collected from 23 to 152 m depth, whereas the European specimens were from shallow waters. Thus, the distribution of P. bellii n. comb. in North America is questioned.

Paucibranchia andresi n. sp. is similar to P. totospinata n. comb. based on the presence of both compound falcigers and spinigers and the color pattern of the subacicular hooks, being reddish at basal end and distally amber; however, they differ by the chaetal distribution, since in the former compound spinigers are only present in the anterior-median region, while in the latter compound spinigers are present in all chaetigers. Also, P. andresi n. sp. has a lower number of branchial filaments (paratype USNM 145278, L10: 2.1 mm, 5 filaments), and compound spinigers and falcigers with blades of similar sizes in the anterior region; whereas P. totospinata n. sp. has a higher number of filaments (paratype NMWZ 1988,069,86, L10: 1.7 mm, 12 filaments), and compound spinigers and falcigers with blades of two sizes in the same region. The comparison with other Paucibranchia n. gen. species having compound falcigers and spinigers present is provided in Table 3.