Paucibranchia patriciae n. sp.

Figures 57–59, Tables 1–2

Marphysa cf. conferta Gathof 1884:40 –19, Figs. 40–15, 40–16a–i (partim)

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

Material examined. Type material: Holotype USNM 90030, sta. HR1, Hospital Rock, Texas, Gulf of Mexico, 27°32'05''N 096°28'19''W, Nov 1976, 75 m. Paratypes USNM 90026 (1), USNM 1458025 (1), sta. 19C, Alabama, Gulf of Mexico, 29°36'00'' N 087°23'00'' W, May 1974, 75 m. USNM 90029 (1), sta. SB3, Southern Bank, Texas, Gulf of Mexico, 27°26'06''N 096°31'47''W, Spring 1976, 82 m.

Description. Holotype complete, broken into two, with 84 chaetigers (anterior fragment with 39), L10= 2 mm, W10= 0.5 mm, TL= 12 mm. Anterior region of body with convex dorsum and flat ventrum, without groove; body depressed from chaetiger 5, widest at chaetiger 8, tapering after chaetiger 18.

Prostomium entire, 0.4 mm long, 0.4 mm wide, frontally rounded, without median sulcus (Fig. 57A–C), ventral sulcus deep. Prostomial appendages in semicircle, median antenna isolated by a gap. Palps reaching first peristomial ring; lateral antennae reaching first chaetiger; median antenna reaching second chaetiger. Palpophores and ceratophores ring-shaped, short, thick; palpostyles and ceratostyles tapering, slender, without articulation. Eyes rounded, dark, between palps and lateral antennae.

Peristomium slightly the same size as the prostomium (0.5 mm long, 0.4 mm wide), first ring two times longer than second ring; separation between rings distinct on all sides (Fig. 57 A–C). Inferior lip in specimen with a central depression.

Maxillary apparatus with MF= 1+1, 9+7, 5+0, 2+5, 1+1 (Fig. 57D). Maxillary carriers 2 times shorter than length of MI. MI forceps-like; closing system 5 times shorter than length of MI; ligament between MI and MII slightly sclerotized. MII wide; teeth recurved; cavity opening oval, 3 times shorter than length of MII (Fig. 57D); ligament between MII and MIII, and right MIV, not sclerotized. MIII short; with triangular teeth; attachment lamella not sclerotized (Fig. 57D). Left MIV with attachment lamella semicircular, wide, sclerotized, better developed in central portion, situated along length of posterior end of maxilla (Fig. 57D). Right MIV with attachment lamella wide, better developed in the middle, situated along length of posterior edge (Fig. 57D). MV square, with a short rounded tooth (Fig. 57D). Mandibles not examined.

Branchiae pectinate with up to 5 filaments, in chaetigers 8–11 (Figs. 57A, C; 58B). Number of branchial filaments per chaetiger in order anterior-posterior: 4, 5, 5, 5. Branchial filaments longer than dorsal cirri.

First two parapodia smallest; most developed in chaetigers 3–14, following ones becoming gradually smaller. Notopodial conical, increasing in size from chaetiger 3 (Ldc3: 0.28 mm; Ldc10: 0.36 mm), from chaetiger 14, gradually decreasing in size, in posterior region almost the same length as in the pre-branchial region ones (Ldc89: 0.25 mm) (Fig. 58A–E). Prechaetal lobes short, as a transverse fold in all chaetigers (Fig. 58A–E). Chaetal lobes in chaetigers 1–11, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 12, triangular, longer than other lobes, with acicula emerging in dorsally to midline (Fig. 58A–E). Postchaetal lobes well developed in chaetigers 1–18, oval basally with digitiform end, inclined dorsally in pre-branchial chaetigers and in branchial region; decreasing in size in chaetigers 6–18, following ones inconspicuous (Fig. 58A–E). Ventral cirri digitiform in chaetigers 1–5; in chaetigers 6–26 with oval swollen base and digitiform tip; following ones digitiform (Fig. 58A–E).

Aciculae blunt, translucent (Fig. 58A–E). Only one acicula per chaetiger.

Limbate chaetae of two sizes in the same chaetiger, larger in anterior region, reduced in number around chaetiger 11. Two types of pectinate chaetae in anterior region isodonts narrow with long and slender teeth, with 1– 2 pectinate with up to 10 teeth, oblique distal edge (Fig. 59A); in median-posterior chaetigers isodonts narrow with short and slender teeth, 5–6 pectinate with up to 12 teeth, with transverse distal edge (Fig. 59B). Compound falcigers present in all chaetigers; in anterior region with blades of similar size (38.5–42 µm, Fig. 59C), all with triangular teeth, of similar size, distal tooth directed upward, proximal tooth directed laterally; in median-posterior chaetigers with blades of similar size, slightly shorter than blades of anterior chaetigers (31.5 µm, Fig. 59D), all with triangular teeth, distal shorter than proximal, directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, translucent, starting in chaetiger 18, with one hook per chaetiger; with triangular teeth, distal tooth smaller than proximal, directed upward; proximal tooth directed laterally (Fig. 59E).

Pygidium with two pairs of anal cirri, without articulation; dorsal pair as long as last six chaetigers; ventral pair short, as long as last chaetiger.

Variation. Material examined varied in the following features: L10= 2–2.3 mm, W10= 0.5–0.7 mm. Maxillary formula varies as follows: MII 7–9+6–7, MIV 2–3+5–7. Branchiae start in chaetigers 7–8 to 11–12. Maximum number of branchial filament varied from 4 to 5. Ventral cirri with swollen base from chaetigers 3–4 to chaetigers 13–20. Start of subacicular hooks in chaetigers 17–18.

Distribution. Texas and Alabama, Gulf of Mexico.

Etymology. The species is named after my mother, María Patricia Acevedo Tabares, in recognition of her unconditional love and support.

Remarks. The specimen USNM 90028 identified by Gathof (1984) as M. cf. conferta is small and in poor condition (incomplete with 30 chaetigers; L10: 2.1 mm; W10: 0.8 mm). It likely belongs to Marphysa but it was not possible to assign to any of the species from the region due to its damaged state. The specimen is different from P. patriciae because it has very short antennae (barely reaching above the second peristomial ring), branchiae from chaetiger 15 as a single filament, and dark aciculae.

Paucibranchia patriciae n. sp. is close to P. adenensis n. comb., P. conferta n. comb., P. gemmata n. comb. and Paucibranchia sp. 2 by having translucent, bidentate subacicular hooks and only compound falcigers. However, P. patriciae n. sp. differs from P. adenensis n. comb., P. conferta n. comb. and P. gemmata n. comb. by having postchaetal lobes oval basally and digitiform distal end in pre-branchial chaetigers; whereas in the other species the postchaetal lobes are always conical. Likewise, in the new species all falcigers have blades of similar size; whereas P. gemmata n. comb., P. adenensis n. comb. and Paucibranchia sp. 2 have falcigers with blades of different sizes in anterior chaetigers. Furthermore, in P. patriciae n. sp. the aciculae are translucent; whereas P. conferta n. comb. has aciculae basally reddish end and distally translucent. The comparison with the other Paucibranchia n. gen. species having only compound falcigers present is provided in Table 2.