Magelona cincta Ehlers 1908

Magelona cf. cincta Ehlers, 1908

Figures 5−6, 13H

Magelona cincta Ehlers, 1908: 111 –112, figs 9–12?; Magelona cf. cincta- Mortimer & Mackie (2009: 194–196, fig. 6)

Material examined. Persian Gulf, IRAN—Stn. 15 (MNCN.16.01/13246; 1 af), 1998; Stn. B3–10A (MNCN.16.01/13247; 1 af), 2005; Stn. B3–15B (MB29–000203; 1 af), 2005; Stn. F10(3) (NMW.Z.2010.037.0037; 1 dissected specimen) 2006; Stn. F25(1) (MB29–000204; 1 af), 2006. QATAR—Stn. SB 1(1) (MNCN.16.01/13248; 1 af,), 2007; Stn. SBW 2(1) (MB29–000206; 1 af), 2007; Stn. SB 3(1) (NMW.Z.2010.037.0038; figured anterior & 1 af), 2007; Stn. SB 4(1) (MNCN.16.01/13249; 1 af), 2007; Stn. SBW 6(1) (NMW.Z.2010.037.0042; 1 c, 1 af), 2007; Stn. SB 7(1) (NMW.Z.2010.037.0039; 2 af,), 2007; Stn. SB 8(1) (MB29–000205; 1 af), 2007; Stn. SBW 9(1) (NMW.Z.2010.037.0043; 2 af), 2007; Stn. SB 14(1) (NMW.Z.2010.037.0040; 3 af), 2007; Stn. SB 15(1) (NMW.Z.2010.037.0041; 1 af), 2007.

Diagnosis. A stout species, prostomium wider than long, subtrapezoidal, with rudimentary horns. Chaetigers 1–8 with slender, smooth-edged, triangular notopodial postchaetal lamellae with pointed tips; no superior processes present. Ventral neuropodial lobes directly below chaetae in anterior thorax, postchaetal in posterior thorax. Neuropodial lamellae of first two or three chaetigers distally expanded. Chaetiger 9 similar in both rami, low ridges with short triangular lobes laterally. Thoracic chaetigers with simple capillary chaetae. Abdominal lateral lamellae sinuous leaf-shaped with pointed tips. Hooded hooks tridentate, in two groups facing vis-à-vis. Posteriorly open pouches on abdominal chaetigers.

Description. A stout species; thoracic width similar to, but wider than abdomen. Complete specimen dimensions: prostomium 0.4 mm long, 0.5 mm wide; thorax (including prostomium) 1.8 mm long, 0.6 mm at maximum width (around chaetiger 6); abdomen 0.55 mm wide; total length 13.5 mm for approximately 55 chaetigers. Other material 2.5–6.5 mm for 16–23 chaetigers. Median thoracic chaetigers characteristically rounded and bulbous laterally.

Prostomium wider than long (0.75–0.83 L:W ratio), subtrapezoidal; anterior margin smooth with rudimentary horns (Figures 5B, 13H). Two longitudinal dorsal muscular(?) ridges, anteriorly divergent and extending into the prostomial corners. Two inconspicuous outer ridges abutting inner ridges; no other obvious prostomial markings. Proboscis partially everted in one specimen (NMW.Z.2010.037.0039), oval, longitudinally ridged inferiorly. Palps retained in three specimens, arising ventrolaterally from base of prostomium; short, reaching approximately chaetiger 17. Palps papillated almost to base (non-papillated region reaching approximately chaetiger 2), 3 rows of papillae either side of an inconspicuous groove proximally, decreasing to one either side distally (papillae very long, length decreasing only at proximal end).

Achaetous region behind prostomium, roughly twice the size of chaetiger 1. Notopodia of chaetigers 1–8 similar (Figures 5C −M); low triangular notopodial prechaetal ridges confluent with slender triangular postchaetal lamellae, terminating in pointed tips. Postchaetal lamellae decreasing in size along thorax, appearing more lateral in position from chaetiger 5. Notopodial lamellae of chaetiger 8 marginally longer than on preceding chaetigers. No superior processes (DML) observed. Neuropodial ventral lobes (VNL) initially distally expanded, decreasing in size from chaetigers 1–5; but increasing again on chaetigers 6–8; becoming cirriform, and postchaetal in posterior thorax. Neuropodial lobes (VNL) of chaetigers 1 and 2 slightly distally expanded, almost scoop like, with small pointed tips (Figures 5D, F). Those of chaetiger 3 distally expanded to a varying degree (Figure 5H).

Chaetiger 9: lamellae similar in both rami, low pre- and postchaetal ridges. Postchaetal lamellae terminating in lateral subtriangular lobes (Figure 5N). All thoracic chaetae simple capillaries (Figure 5P), those of chaetigers 7 and 8 longer than on preceding chaetigers; bundles splayed distinctively (Figure 5A). Chaetae of chaetiger 9 shorter, but not otherwise modified.

Abdominal chaetigers with sharply pointed, rather sinuous leaf-shaped lateral lamellae, of about equal size in both rami; not basally constricted (Figure 5O); no obvious postchaetal expansions. Occasional minute dorsal and ventral processes (DML and VML) observed on abdominal chaetigers, extremely difficult to see. Abdominal chaetae tridentate hooded hooks, of a similar size (Figures 5Q–S). Hooks in two groups, main fangs vis-à-vis (Figure 5O). Approximately eight to ten hooks per ramus in anterior abdomen, in roughly two equal groups; decreasing to six on median and posterior chaetigers. Hooks arising from definite ridge. Unpaired posteriorly open lateral pouches present, starting from approximately chaetiger 18 to posterior part of body. Pouches alternating on both sides of the body, occurring on alternate segments. Pouch location often difficult to discern due to presence of tube and condition of material. No pygidial cirri observed on complete specimen, presumed missing.

Colour. Preserved specimens cream-white in alcohol, majority of material initially stained with Rose Bengal. Distinct reddish/brown pigment band present between chaetigers 5–8, faded in some specimens, although always present (Figures 5A, 6C). Very light Rose Bengal staining interparapodially in the abdomen. Methyl green staining weak all over, light pigmentation between chaetigers 3–5 and 7–9. Small patches of darker pigment present on thorax (Figures 6 A, B), dorsally between chaetigers 1−5, and around segment margins in posterior thorax. Ventrally, light pigmentation is present as transverse bands between chaetigers 2 and 4. Light interparapodial patches of staining in abdomen. Patches of white speckles present (Figures 5A, 6C) dorsally and ventrally between chaetigers 1–5; closer to mid-line in venter and strongest around chaetigers 3–4. Speckles also present ventrally along the mid-ventral line from chaetigers 8 into abdomen. Methyl green pigment persisting around white speckled areas after much of the stain has dissipated.

Habitat. Found at five stations off Iran, from three different surveys, in fine sand, fine shelly sand, shelly muddy sand, and mud, 10–27 m, and at 10 stations off Qatar, from one survey, in muddy sand with shell debris, mud with shell debris, and mud, 58– 60 m. Several specimens in distinct sediment covered tubes (NMW.Z.2010.037.0040, NMW.Z.2010.037.0042, NMW.Z.2010.037.0043).

Distribution. Iran, Qatar (present study), Hong Kong (Mortimer & Mackie 2009)

Remarks. The Persian Magelona cf. cincta specimens observed here share many similarities with the Hong Kong Magelona cf. cincta specimens as described by Mortimer & Mackie (2009) in possessing a pigment band in the posterior thorax, lamellar and prostomial shape, methyl green staining patterns, characteristic bulbous chaetigers in the mid-thorax and the presence of white speckled regions in the thorax and abdomen. The only perceived differences are the slightly more expanded neuropodial thoracic lamellae of chaetiger 1 in Hong Kong material (which are more scoop-shaped, possessing higher edges) and the presence of occasional minute dorsal and ventral processes in the abdomen of the Persian material. The Hong Kong material has been re-examined and odd minute projections at the inner margins of chaetal rows have been observed on a couple of specimens. The fact that even in the Persian material these processes are sporadic (even on the same specimen) suggests that this is a variable character within this species. The degree of protrusion of these processes, and hence their conspicuousness may depend on the degree of contraction of the specimen. It is possible that these processes move in and out under coelomic pressure. We believe this to be the same species as those specimens observed from Hong Kong. Both the Iranian and Hong Kong material differed from the type material, in having less distally expanded neuropodial lobes of the first three chaetigers. However, the type specimen is much larger than either the Iranian or Hong Kong material examined. It is possible that the perceived differences seen here may be due to size. Therefore, more material in a better condition, and of a comparable size from the type locality needs to examined before any conclusions can be made.

FIGURE 5. Magelona cf. cincta (A, NMW.Z.2010.037.0038; B, NMW.Z.2010.037.0041; C −S, dissected specimen NMW.Z.2010.037.0037): (A) anterior, dorsal view, showing thoracic pigment band; (B) prostomium, dorsal view (note that right-hand side is slightly folded upwards); (C, E, G, I −O) chaetigers 1−9, 12 respectively (anterior views); (D, F, H) neuropodia of chaetigers 1−3 respectively (dorsal views); (P) thoracic capillary chaeta; (Q −S) tridentate abdominal hooded hooks from 13th chaetiger (oblique frontal, oblique lateral and lateral views respectively) (Q, hood omitted).