Paucibranchia oculata (Treadwell, 1921) n. comb.

Figures 54–56, Tables 1, 3

Marphysa belli oculata Treadwell, 1921:61 –64, text-figs 201–211, Pl. 5, Figs. 13–14.

Marphysa belli Salazar-Vallejo & Carrera-Parra 1998:1486 –1487, Fig. 3f non Audouin & Milne-Edwards, 1833

Marphysa oculata Lu & Fauchald 1998:834 –839, Figs. 2–6, 7a–j, 8.

Material examined. Type material: Holotype AMNH VII –1915 –1292, Key West, Florida , Jun 1915. Additional material: USNM 129779 (2), sta. 52, off Florida, USA, 25°17'48.19'' N 81°39'47.88'' W, 10 Dic 1982, 14 m. USNM 130127 (1), USNM 130256 (1), USNM 130484 (1), sta. 52, off Florida, USA, 25°17'48.19'' N 81°39'47.88'' W, 4 Jun 1983, 14 m. USNM 90008 (1), sta . IV–6, off Port Isabel, Texas, USA, 26°10'11.95" N 96°31'11.98" W, Winter 1977, 65 m. USNM 90009 (1), sta . IV–3, off Port Isabel, Texas, USA, 26°10'11.95" N 96°31'11.98" W, Winter 1977, 91 m. USNM 90010 (1), sta . I–5, off Port O'Connor, Texas , USA, 27°44'00'' N 096°14'00'' W, Spring 1977, 82 m. USNM 90012 (1), off Port Isabel, Texas , USA, sta. IV–3, 26°10' N 096°24' W, Winter 1977, 91 m.

Description. Holotype incomplete, dissected ventrally, with 148 chaetigers, broken into two parts (anterior fragment with 50 chaetigers), L10= 5.1 mm, W10= 1.6 mm, TL= 55 mm. Anterior region of the body with convex dorsum and flat ventrum, without groove; body depressed from chaetiger 6 widest at chaetiger 9, tapering after chaetiger 15.

Prostomium entire, 0.8 mm long, 1 mm wide, frontally rounded, without median sulcus (Fig. 54A–C), ventral sulcus deep. Prostomial appendages in semicircle, median antenna equidistant. Palps, lateral and median antennae reaching the middle of the first peristomial ring. Palpophores and ceratophores ring-shaped, short, slender; palpostyles and ceratostyles tapering, thick, without articulation. Eyes rounded, dark, between palps and lateral antennae.

Peristomium bigger than prostomium (1 mm long, 1.7 mm wide), first ring two times longer than second ring; separation between rings distinct on all sides (Fig. 54A–C). Inferior lip dissected.

Maxillary apparatus lost. MF= 1+1, 5+7, 6+0, 6+8, 1+1 according to Treadwell (1921:201–211, Fig. 13, Pl. 5). Specimen USNM 130256 with MF= 1+1, 7+7, 7+0, 4+7, 1+1 (Fig. 54D). Maxillary carriers 1.8 times shorter than length of MI. MI forceps-like; closing system 5.4 times shorter than length of MI; ligament between MI and MII not sclerotized. MII wide; teeth recurved; cavity opening oval, 3.4 times shorter than length of MII (Fig. 54D); ligament between MII and MIII, and right MIV, slightly sclerotized. MIII short; with triangular teeth; with attachment lamella not sclerotized. Left MIV with a small basal tooth; attachment lamella semicircular, wide, situated along length of posterior edge of maxilla. Right MIV with similar size teeth; attachment lamella wide, better developed in the middle, situated 1/2 along length of posterior edge of maxilla. MV square, with a short rounded tooth (Fig. 54D). Mandibles not examined.

Branchiae pectinate with up to 16 filaments, in chaetigers 10–22 (Figs. 54C, 55B). Number of branchial filaments per chaetiger in order anterior-posterior: 9, 12, 13, 14, 14, 15, 15, 15, 16, 16, 12, 11. Branchial filaments as long as dorsal cirri.

First three parapodia smallest; most developed in chaetigers 4–20, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 4 (Ldc3: 0.6 mm; Ldc18: 0.95 mm) from chaetiger 22, gradually decreasing in size, in posterior chaetigers 1.2 times longer than pre-branchial region ones (Ldc143: 0.7 mm); Hayashi & Yamane’s organ present (Fig. 55A–E). Prechaetal lobes as a transverse fold in all chaetigers (Fig. 55A–E). Chaetal lobes in chaetigers 1–22, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 23, triangular, longer than other lobes, with acicula emerging dorsally to midline (Fig. 55A–E). Postchaetal lobes well developed in chaetigers 1–31, bluntly conical; thinner and longer in branchial region; decreasing in size in chaetigers 10–31, following ones inconspicuous (Fig. 55A–E). Ventral cirri conical in chaetigers 1–5; in chaetigers 6–27 with oval swollen base and digitiform tip; from chaetiger 27, conical (Fig. 55A– E).

Aciculae blunt, amber (Fig. 55A–E). First 10 chaetigers with 2 or 3 aciculae; from chaetiger 11, with only one acicula.

Limbate chaetae of two sizes in the same chaetiger, larger in anterior region, reduced in number around chaetiger 22. Two types of pectinate chaetae, in anterior chaetigers isodonts narrow with short and slender teeth, with 2–3 pectinate, with up to 7 teeth, with tranverse distal edge (Fig. 56A); in posterior chaetigers isodonts narrow with long and slender teeth, with 5 pectinate with up to 9 teeth, with tranverse distal edge (Fig. 56B). Compound spinigers in chaetigers 1–35 (Fig. 56C), abundant in first 25 chaetigers, with all blades of similar size. Compound falcigers from chaetiger 26, less abundant than spinigers; in anterior region with blade of one size (50 µm, Fig. 56D), all with triangular teeth, of similar size, distal tooth directed upward, proximal directed laterally; in mediaposterior chaetigers with blade of similar size, shorter than blades of anterior chaetigers (28 µm, Fig. 56E), with all teeth of similar shape than in anterior chaetigers. Subacicular hooks bidentate, amber, starting in chaetiger 24, one or two hooks per chaetiger; with triangular teeth, distal tooth smaller than proximal tooth, directed upward; proximal tooth directed laterally (Fig. 56F).

Variation. Material examined varied in the following features: L10= 1.8–5.1, W10= 0.5–1.6 mm. Palps reaching middle of the first peristomial ring or first chaetiger. Lateral antennae reaching middle of the first presitomial ring or reaching second chaetiger. Median antenna reaching middle of the first peristomial ring or reaching third chaetiger. Maxillary formula varies as follows: MII 6+6–7, MIII 5–7, MIV 4–6+7–8. The proportion of maxillary apparatus varies as follows: maxillary carriers shorter with respect to the MI varies 2.3–2.6 times; closing system shorter with respect to the MI varies 5.6–7.2 times; cavity opening shorter with respect to MII varies 3.8–4 times. Branchiae start in chaetigers 7–10 to 14–22. Maximum number of branchial filaments in 6–16. Well developed postchaetal lobe in first 18–31 chaetigers. Ventral cirri with swollen base from chaetigers 5–8 to chaetigers 14–27. Compound spinigers present only in first 23–35 chaetigers. Start of the compound falciger in chaetigers 11–26. Start of subacicular hooks in chaetigers 15–24.

Distribution. Northern Gulf of Mexico.

Remarks. Treadwell (1921) described a variety of M. bellii (actually P. bellii n. comb.) as M. belli oculata based mainly on the presence of eyes in a single specimen. However, Lu & Fauchald (1998) compared materials from the Gulf of Mexico and the French coasts, and found differences in the distribution of the compound chaetae, and their abundance per chaetiger. Therefore, they raised it to species level. After examining the type and non-type materials of the species, I also recognize it as valid but in Paucibranchia n. gen., and provide further comparisons with P. bellii n. comb. and other related species.

Paucibranchia oculata n. comb. resembles P. bellii n. comb. and P. sinensis n. comb., by having amber, bidentate subacicular hooks, and compound falcigers and spinigers. However, in P. oculata n. comb., the falcigers start around chaetiger 11–26 being less abundant than spinigers; whereas in P. bellii n. comb. and P. sinensis n. comb., the falcigers start from the first chaetiger being more abundant than spinigers. In addition, in P. bellii n. comb. the postchaetal lobes are tongue-shaped in the pre-branchial chaetigers; whereas, in P. oculata n. comb. they are bluntly conical in the same region. Moreover, P. oculata n. comb. has falcigers with blades of similar size in anterior region; whereas P. sinensis n. comb. has falcigers with blades of two sizes in the same region. The comparison with other Paucibranchia n. gen. species having compound falcigers and spinigers is provided in Table 3.