Paucibranchia gemmata (Mohammad, 1973) n. comb.

Figures 38–41, Tables 1–2

Marphysa gemmata Mohammad, 1973:32 –34, Figs. 4–5; Katsiaras et al. 2014:211 –213, Figs. 8a–d, 9a–d, Tab. 2.

Material examined. Type material: Holotype BNHM 1971.49, Al-Dbaiyyah, Kuwait, Arabian Gulf, 9 May 1969, 28°57’ N 48°11’ E, in sand, intertidal, coll. M. B. Mohammad.

Description. Holotype incomplete, dried, with 160 chaetigers, L10= 5.9 mm, W10= 1 mm, the fragment with TL= 51 mm. Anterior region of body with convex dorsum, and flat ventrum, without groove; body depressed from chaetiger 6, widest at chaetiger 92, tapering after chaetiger 136.

Prostomium in poor condition, entire, 0.8 mm long, 1.2 mm wide, frontally rounded, without median sulcus (Fig. 38A), ventral sulcus deep (Fig. 38B). Prostomial appendages in a semicircle, median antenna equidistant. Palps reaching first chaetiger; right lateral antennae broken, left lateral antennae reaching second chaetiger; median antennae reaching four chaetiger. Palpophores and ceratophores ring-shaped, short, thick; palpostyles and ceratostyles tapering, thick, without articulation. Eyes absent.

Peristomium wider than prostomium (1 mm long, 1.5 mm wide), first ring two times longer than second ring, separation between rings distinct on all sides (Fig. 38A–B). Inferior lip broken.

Maxillary apparatus with MF= 1+1, 8+8, 7+0, 7+9, 1+1 (Fig. 39A). Maxillary carriers 2.1 times shorter than length of MI. MI forceps-like; closing system 10.5 times shorter than length of MI; ligament between MI and MII slightly sclerotized (Fig. 39A–B) . MII wide; teeth curved, cavity opening oval 4 times shorter than length of MII; ligament between MII and MIII, and right MIV, slightly sclerotized (Fig. 39A–B) . MIII short; with triangular teeth; with attachment lamella slightly sclerotized (Fig. 39A–B). Left MIV with small basal teeth; attachment lamella triangular, wide, situated 1/2 along length of posterior edge of maxilla, slightly sclerotized. Right MIV with teeth of similar size; attachment lamella slender, semicircular, better developed in the middle, situated 1/3 along length of posterior edge of maxilla (Fig. 39A–C). MV square, with a short rounded tooth (Fig. 39A–B). Mandibles dark; cutting plates whitish, with 18 growth rings (Fig. 39D).

Branchiae pectinate with up to 16 filaments, in chaetigers 22–45 (Figs. 38C; 40C). Number of branchial filaments per chaetiger in order anterior-posterior: 10, 13, 14, 13, 15, 12, 13, 14, 16, 11, 16, 13, 13,?, 11, 15, 9,?, 8, 13, 12, 12, 16. Basal branchial filaments longer than dorsal cirri.

First parapodia smallest; most developed in chaetigers 3–17, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 3 (Ldc4: 0.60 mm; Ldc16: 0.86 mm) from chaetiger 46, gradually decreasing in width and increasing in length; in posterior region, filiform, two times longer than prebranchial region ones (Ldc105: 1.3 mm); Hayashi & Yamane’s organ present (Fig. 40A–E). Prechaetal lobes as a transverse fold in all chaetigers (Fig. 40A–E). Chaetal lobes in chaetigers 1–36, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 29, triangular, longer than other lobes, with aciculae emerging of midline (Fig. 40A–E). Postchaetal lobes well developed in chaetigers 1–94, conical; thinner, elongated in branchial region; decreasing in size in chaetigers 53–94, following ones inconspicuous (Fig. 40A–E). Ventral cirri digitiform in chaetigers 1–14; in chaetigers 15–66 with oval swollen base and digitiform tip; from chaetiger 67, conical, gradually reducing in size posteriorly (Fig. 40A–E).

Aciculae blunt; translucent (Fig. 40A–E). First 17 chaetigers with 3 aciculae; in chaetigers 18–29 with 2 aciculae; from chaetiger 30, with only one acicula.

Limbate chaetae of two sizes in same chaetiger, larger in anterior region, reduced in number around chaetiger 27. One types of pectinate chaetae; in anterior chaetigers isodonts narrow, with 1–2 pectinate, with up to 3–4 teeth, with transverse distal edge; in median-posterior pectinate not observed. Compound falcigers present in all chaetigers; in anterior region with blade of three sizes (longer 108.5 µm; Fig. 41A, median 90 µm, Fig. 41B; smaller 80 µm, Fig. 41C), the smaller more abundant; all with triangular teeth, of similar size, distal tooth directed upward, proximal tooth directed laterally; in media-posterior chaetigers with all blades of similar size, shorter than blades of anterior chaetigers (56 µm, Fig. 41D), with triangular teeth, distal tooth shorter than proximal, directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, translucent, starting in chaetiger 61L–62R; with one hook per chaetiger; with triangular teeth, distal tooth smaller than proximal, directed upward; proximal tooth directed laterally (Fig. 41E).

Distribution. Kuwait, Persian Gulf.

Remarks. The specimen studied here is the only record that has been found of this species. Katsiaras et al. (2014) commented that they did not observe pectinate chaetae in the posterior chaetigers, and this peculiar condition is confirmed here.

Paucibranchia gemmata n. comb. resembles P. adenensis n. comb., P. conferta n. comb., P. patriciae n. sp. and Paucibranchia sp. 2 in the translucent color of subacicular hooks and bidentate form, and the presence of only compound falcigers. However, P. gemmata n. comb. is different because it has dorsal cirri two times longer in the postbranchial region; whereas in all previous species dorsal cirri are of the same size in pre- and postbranchial regions. In addition, P. gemmata n. comb. has falcigers with blades of three sizes in anterior chaetigers; whereas P. adenensis n. comb. and Paucibranchia sp. 2 only have falcigers with blades of two size, and in P. patriciae n. sp. all blades are of similar size. Finally, the aciculae are translucent in P. gemmata n. comb.; whereas in P. conferta n. sp. are reddish on the basal end and translucent distally. The comparison with other Paucibranchia n. gen. species having only compound falcigers present is provided in Table 2.