Paucibranchia gathofi, 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 : 53-56

Paucibranchia gathofi n. sp.

Figures 35–37 , Tables 1–2

Marphysa sp. A Gathof 1984:40 –17, Figs. 40–13 , 14a–j (partim).

Material examined. Type material: Holotype USNM 90025 (1), sta. 22C, off Florida, Gulf of Mexico, 25°17'11'' N 083°02'04'' W, Nov 1980, 53 m. Paratypes: USNM 90027 (1), sta. HR 1, Hospital Rock Texas, Gulf of Mexico, 27°32'05'' N 096°28'19'' W, Jul 1976, 75 m. USNM 1186791 (2), sta. HR4, Hospital Rock Texas, Gulf of Mexico, 27°33'02''N 96°29'03''W, 25 May–02 Jun 1977, 76 m. Additional material: USNM 1290844 (1), sta. 2423, off Apalachicola Bay, Florida, Gulf of Mexico, 29°20'00'' N 084°44'02'' W, 7 Jun 1975, 31 m.

Description. Holotype incomplete, with 73 chaetigers, L10= 3.4 mm, W10= 1.1 mm, the fragment with TL= 16 mm. Anterior region of body with convex dorsum, and flat ventrum, without groove; body depressed from chaetiger 5, widest at chaetiger 10, tapering after chaetiger 38.

Prostomium entire, 1 mm long, 1 mm wide, frontally rounded, without median sulcus ( Fig. 35A–B ), ventral sulcus deep ( Fig. 35B ). Prostomial appendages in a semicircle, median antenna slightly isolated by a gap. Palps reaching second peristomial ring; lateral antennae reaching second chaetiger; median antenna incomplete, in paratype median antenna reaching second chaetiger. Palpophores and ceratophores ring-shaped, short, slender; palpostyles and ceratostyles tapering, slender, without articulation. Eyes not observed; according to Gathof (1984), eyes rounded and dark.

Peristomium shorter than prostomium (0.6 mm long, 1 mm wide), first ring two times longer than second ring; separation between rings distinct on all sides ( Fig. 35A–B ). Inferior lip with a slight central depression with shallow wrinkles ( Fig. 35B ).

Maxillary apparatus lost. MF= 1+1, 5–6+7, 5–7+0, 2–4+5–12, 1+1 according to Gathof (1984: 40–17, Figs. 40–14j ).

Branchiae pectinate with up to 10 filaments, in chaetigers 15–27 ( Figs. 35C ; 36B ). Number of branchial filaments per chaetiger in order anterior-posterior: 8, 8, 10, 10, 10, 10, 9, 9, 9, 9, 9, 7, 6. Branchial filaments longer than dorsal cirri.

First two parapodia smallest; most developed in chaetigers 4–15, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 12 (Ldc5: 0.36 mm; Ldc22: 0.40 mm), from chaetiger 32, gradually decreasing in width; in posterior region almost the same length than pre-branchial region ones (Ldc69: 0.37 mm); Hayashi & Yamane’s organ present ( Fig. 36A–D ). Prechaetal lobes as a transverse fold in all chaetigers ( Fig. 36A–D ). Chaetal lobes in chaetiger 1–21, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 21, triangular, longer than other lobes, with acicula emerging dorsally to midline ( Fig. 36A–D ). Postchaetal lobes well developed in chaetigers 1–38, bluntly conical, thinner and elongated in branchial region; decreasing in size in chaetigers 15–38; following ones inconspicuous ( Fig. 36A–D ). Ventral cirri digitiform in chaetigers 1–5; in chaetigers 6–42 with oval swollen base and digitiform tip; from chaetiger 43, conical, gradually reducing in size posteriorly ( Fig. 36A–D ).

Aciculae blunt, with reddish basal end, distally amber; with only one per chaetiger present ( Figs. 36A–D ; 37G ).

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 isodont narrow with long and slender teeth, with 1–2 pectinate, with up to 5–6 teeth, with oblique distal edge ( Fig. 37A ); in median-posterior chaetigers isodont narrow with short and slender teeth, with 3–4 pectinate, with up to 8–9 teeth, with oblique distal edge ( Fig. 37B ). Compound falcigers in all chaetigers; in anterior chaetigers (first 11 chaetigers) with blade of two sizes (longer 125 µm, Fig. 37C , smaller 63 µm, Fig. 37D ); all with triangular teeth, of similar size, distal tooth directed upward, proximal directed laterally; in median-posterior chaetigers with blade of two sizes, shorter than blades of anterior chaetigers (longer 49 µm, Fig. 37E ; smaller 40 µm, Fig. 37F ), all with triangular teeth, distal tooth shorter than proximal, directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, reddish basal end, distally amber; starting in chaetiger 19, with one hook per chaetiger; with triangular teeth, distal tooth smaller than proximal, directed upward; proximal tooth directed laterally ( Fig. 37H ).

Variation. Material examined varied in the following features: L10= 2.1–3.4 mm, W10= 0.7–1.1 mm. Lateral and median antennae reaching first or reaching second chaetiger. The maxillary formula varies as follows: MII 5– 6+7, MIII 5–7, MIV 2–4+5–12. Branchiae from chaetigers 8–15 to 13–27. Maximum number of branchial filament varied from 6 to 10. Well developed postchaetal lobe in first 13–27 chaetigers. End of ventral cirri with swollen base in chaetigers 16–17. Start of subacicular hooks in chaetigers 17–30.

Type locality. Off Florida, USA.

Distribution. Texas and Florida, Gulf of Mexico.

Etymology. This species is named in honor of Dr. Jerry M. Gathof in recognition of his valuable contributions to the taxonomic study of the polychaetes from the Gulf of Mexico, particularly eunicids.

Remarks. Gathof (1984) described these specimens from the northern Gulf of Mexico as Marphysa sp. A and considered it to be close to P. conferta n. comb. (California). However, there are some morphological differences, in addition to the geographical distance that separates the two species. Paucibranchia gathofi n. sp. has compound falcigers with blades of two sizes in all chaetigers, and dark subacicular hooks; whereas P. conferta n. comb. has compound falcigers with all blades of similar size, and translucent subacicular hooks.

The material USNM 90026 identified by Gathof as Marphysa sp. An actually belongs to P. patriciae n. sp. (see below).

Paucibranchia gathofi n. sp. resembles P. miroi n. sp. and P. purcellana n. comb. by having subacicular hooks with reddish basal end and compound falcigers. However, P. gathofi n. sp. differs from P. miroi n. sp. because the former has eyes, postchaetal lobe bluntly conical in pre-branchial chaetigers, and falcigers with blades of two sizes along the body; whereas in the latter, eyes are absent, postchaetal lobe is digitiform in pre-branchial chaetigers, and all falcigers have blades of similar size along the body. Also, P. purcellana n. comb. differs because the dorsal cirri are 1.4 times longer in the postbranchial region and falcigers have blades of three sizes in the anterior chaetigers; whereas in P. gathofi n. sp. the dorsal cirri are of similar size in pre- and potsbranchial regions and the falcigers have blades of two sizes along the body. The comparison with other Paucibranchia n. gen. species having only compound falcigers present is provided in Table 2.

Figures

FIGURE 14. Paucibranchia bellii (Audouin & Milne-Edwards 1833) n. comb. A. Compound falciger, long blade, chaetiger 3; B. Compound falciger, median blade, chaetiger 3; C. Compound falciger, short blade, chaetiger 138; D. Compound spiniger, chaetiger 3; E. Isodonts pectinate narrow with long and slender teeth, chaetiger 9; F. Isodonts pectinate narrow with short and slender teeth, chaetiger 200; G. Subacicular hook, distal end, chaetiger 93. A from lectotype MNHN TYPE 568; B, C, D from non-type MNHN-A39; E, F, G, from ECOSUR–P2173. Scale bars: A, 14.5 µm; B, 24 µm; C, 21.64 µm; D, E, 7 µm; F, 9.8 µm; G, 6 µm.

FIGURE 35. Paucibranchia gathofi n. sp., holotype USNM 90025. A. Anterior end, dorsal view; B. Anterior end, ventral view; C. Anterior end with branchiae, dorsal view. Scale bars: A–C, 0.3 mm.

FIGURE 36. Paucibranchia gathofi n. sp., holotype USNM 90025. A. Parapodium 5; B. Parapodium 22; C. Parapodium 55; D. Parapodium 69. All in anterior view. Scale bars: A, B, 0.20 mm; C, 90 µm; D, 0.12 mm.

FIGURE 37. Paucibranchia gathofi n. sp., holotype USNM 90025. A. Isodonts pectinate narrow with long and slender teeth, chaetiger 22; B. Isodonts pectinate narrow with short and slender teeth, chaetiger 59; C. Compound falciger, long blade, chaetiger 22; D. Compound falciger, median blade, chaetiger 22; E. Compound falciger, median blade, chaetiger 55; F. Compound falciger, short blade, chaetiger 55; G. Aciculae, chaetiger 55; H. Subacicular hook, chaetiger 55. Scale bars: A, 14 µm; B, 7 µm; C, 45 µm; D, 22.5 µm; E, 19 µm; F, 15 µm; G, 5 µm; H, 10.5 µm.

FIGURE 40. Paucibranchia gemmata (Mohammad, 1973) n. comb., holotype BNHM 1971.49. A. Parapodium 4, dorsal cirri with bent tip, postchaetal lobe broken; B. Parapodium 16; C. Parapodium 31; D. Parapodium 50; E. Parapodium 105. All in anterior view. Scale bars: A, D, E, 0.15 mm; B, 0.22 mm; C, 0.48 mm.