Magelona conversa Mortimer & Mackie, 2003

Mortimer, Kate, Cassà, Susanna, Martin, Daniel & Gil, João, 2012, New records and new species of Magelonidae (Polychaeta) from the Arabian Peninsula, with a re-description of Magelona pacifica and a discussion on the magelonid buccal region, Zootaxa 3331, pp. 1-43 : 18-21

Magelona conversa Mortimer & Mackie, 2003

Figures 7 , 13 I

Magelona conversa Mortimer & Mackie, 2003: 164 –167, fig. 2

Material examined. Persian Gulf, IRAN—Stn. B4–10A ( NMW.Z.2010.037.0007; 1 af), 2005; Stn. B4–15A ( MNCN.16.01/13231; 2 af), 2005; Stn. 33FC (68–6806) ( BMNH.2010.234; 1 af), 2005.

Diagnosis. Prostomium longer than, or equal to width, subtriangular, without prostomial horns. Notopodia of chaetigers 1–8 with smooth-edged foliaceous postchaetal lamellae; superior prechaetal processes from chaetiger 5 (or 6) to 8. Neuropodial prechaetal lamellae longer than postchaetal lamellae on chaetigers 1–8. Chaetigers 1–8 with capillary chaetae; chaetiger 9 with mucronate chaetae. Abdominal lateral lamellae rounded subrectangular. Hooded hooks bidentate, main fangs unidirectional, pointing laterally. Anteriorly and posteriorly open lateral pouches present on abdominal chaetigers, posterior unknown.

Description. A moderately stout species; thorax marginally wider than, or equal to abdomen. However, thorax slightly dorso-ventrally flattened, thinner in comparison to the more rounded abdomen. Thoracic chaetigers with transverse furrows between parapodia, either side of the mid-body line ( Figure 7 A; shown as dotted lines). Dimensions of figured anterior: prostomium 1.3 mm long, 1.15 mm wide; thorax 5.3 mm long (including prostomium), 0.95 mm wide; abdomen 0.9 mm wide; total length 13.5 mm for 25 chaetigers (Note: 25th chaetiger now dissected, slide mounted). Other material 9.8–15.5 mm with 19–31 chaetigers. All material posteriorly incomplete.

Prostomium longer than, or equal to width (L:W ratio 1.0–1.13), subtriangular; anterior margin smooth and rounded; prostomial horns absent ( Figures 7 A–C, 13I, note: left-hand margin of prostomium in Figure 7 A folded underneath; slight tear in anterior margin, which is minutely curled. Prostomium in Figure 7 B curved upwards as shown in Figure 7 C, making prostomium look shorter and rounder. However shape and size much more akin to that figured for the holotype, Mortimer & Mackie 2003: figure 2A). Prostomial lateral edges occasionally undulating as shown for paratype ( Mortimer & Mackie 2003: figure 2B). Two pairs of prominent longitudinal dorsal muscular(?) ridges; inner pair joined for majority of length, diverging only at anterior margin of prostomium (lightly ridged transversely); outer pair abutting inners for entire length. Conspicuous patterns either side of ridges; irregular oblong regions proximal to ridges; smaller rounded areas towards lateral edges, initially in longitudinal lines at base of prostomium. Proboscis everted in 3 specimens (lightly squashed in figured anterior); a large heart-shaped sac when fully everted, oval when partially everted. Proboscis with conspicuous longitudinal ridges inferiorly, lightly ridged superiorly. One palp present in sample tube (MNCN.16.01/13231), very short with 2 rows of papillae either side of ventral groove; papillae extremely long making palp appear ‘frilly’ (similar to type material of a similar size).

Achaetous region behind prostomium, roughly equal size to, or approximately 1 and half times the size of chaetiger 1. Chaetigers 1–7 similar; parapodia biramous ( Figures 7 D–F) with small rounded notopodial prechaetal lamellae which, from chaetiger 5 (or 6) to 8, project dorsally as triangular superior processes (DML). Prechaetal lamellae confluent with large foliaceous postchaetal lamellae, which increase in size along thorax, distal tips pointing upwards. Neuropodia with long and slender, triangular prechaetal lamellae; postchaetal lobes short, rounded triangular. Ventral neuropodial lobes (VNL) absent. Neuropodial postchaetal lobes of chaetiger 7 more distinct, larger; triangular to oval.

Chaetiger 8: notopodial prechaetal lamellae similar to preceding chaetigers, but superior processes larger, distinctly triangular; postchaetal lamellae very large, foliaceous ( Figures 7 G, H). Neuropodial prechaetal lamellae broader and more triangular than previous chaetigers ( Figure 7 H); postchaetal lamellae well-developed, rounded oblong ( Figure 7 G). Chaetae of chaetigers 1–8 all simple capillaries.

Chaetiger 9: segment short ( Figure 7 A), notopodial and neuropodial prechaetal lamellae low and broadly rounded, encircling chaetae cuff-like to form higher postchaetal lamellae ( Figure 7 I). Neuropodial prechaetal lamellae inferiorly developed as large triangular processes (varying in length, as seen in the type material). Chaetae arranged in fan-like arcs; mucronate ( Figure 7 K).

Abdominal chaetigers with thick, ‘fleshy’ subrectangular lateral lamellae, directed towards each other, of about equal size in both rami ( Figure 7 J). Lamellae internally supported by several conspicuous, slender curved aciculae (3 or 4 at chaetiger 25), appearing continuous between rami; distal regions extending towards tips of lateral lamellae, conspicuous even under binocular microscope. Small triangular processes (DML and VML) evident throughout abdomen, at inner margins of chaetal rows. Abdominal chaetae bidentate hooded hooks ( Figure 7 L), of similar size. Hooks of unidirectional orientation, main fangs pointing laterally. Initially about 10 hooks per ramus in anterior abdomen, reducing to around 6 at chaetiger 25. Hooks arising from definite ridge. Paired anteriorly open lateral pouches present on anterior abdominal chaetigers ( Figure 7 A) (chaetigers 11, 14, 17 and 20); large, convoluted, bounded dorsally and ventrally by large cuticular flaps. Unpaired lateral pouches found posteriorly on two specimens, on chaetigers 24L (NMW.Z.2010.037.0007) and chaetigers 26L, 28R and 30L (MNCN.16.01/13231). Pouches posteriorly open, however, very large and convoluted, more akin to anteriorly open pouches (especially those on chaetiger 26L). Posterior unknown.

Colour. No live animals observed, cream-white in alcohol. One specimen stained with Rose Bengal (BMNH.2010.234). Staining with methyl green revealed dorsal and ventral transverse bands as white speckles between parapodia, in thorax ( Figure 7 A) and anterior abdomen (ventral and abdominal bands lighter). Strong interparapodial staining in the abdomen, and staining associated with the cuticular flaps of paired pouches. Staining with Rose Bengal of a similar pattern.

Habitat. Four specimens found at three stations off the coast of Iran in two surveys, in coarse sand, coarse shelly muddy sand, and shelly sand with low mud, 9– 15 m.

Distribution. Seychelles ( Mortimer & Mackie 2003), Iran (present study).

Remarks. The morphology of the Iranian material agrees well with the Seychellois type material in all respects. Although Rose Bengal staining has now dissipated in the type material, the staining pattern for the Iranian material agrees well with that described for the types. Prostomial shape of the figured specimen (BMNH.2010.234) agrees well with the holotype, despite appearing shorter and more rounded due to its curled nature. There is a slight variation in size and shape of prostomia in the Iranian material but this is mirrored by the variation seen within the type material. The form of the dorsal muscular(?) ridges and ornamentation either side in both sets of material agrees well.

The only variation seen was in the number of abdominal hooks, which were greater in number on the Seychellois material (between 15–18 in the anterior abdomen). The type material is generally larger than the Iranian material, however, when material of a similar size was compared, they were observed to have a similar number of hooks. A couple of adjustments to the original description of the type material should be made. Mortimer & Mackie (2003: 164) when describing M. conversa , stated that the thorax is narrower than abdomen. The thoracic width of type material is generally slightly wider, or equal to the width of the abdomen as seen here within the Iranian material. However, the original description should have stated that the thorax is thinner than the abdomen when viewed laterally. Secondarily, the neuropodial postchaetal lamellae of chaetiger 7 are more developed than previously described, being triangular or oval, and about a third of the length of the prechaetal lamellae.

The abdominal pouches of M. conversa as observed in both the Iranian and Seychellois material follow that as described by Mortimer (2010: 22) for species possessing both anteriorly and posteriorly open pouches.

Figures

FIGURE 7. Magelona conversa (A, D – L, NMW. Z. 2010.037.0007; B – C, BMNH. 2010.234): (A) anterior region, dorsal view; (B) prostomium, dorsal view (black marks indicate point at which prostomium is bent upwards, as shown in C); (C) prostomium, lateral view (arrow indicates the view point from which figure B was drawn); (D – F) chaetigers 1, 5, and 7 respectively (anterior views); (G – H) chaetiger 8, posterior and anterior views respectively; (I – J) chaetigers 9 – 10 (anterior views); (K) mucronate chaeta from chaetiger 9; (L) bidentate abdominal hooded hook lateral view.

FIGURE 13. Prostomia of Arabian Peninsula Magelona species, dorsal views: (A) M. obockensis, 39 chaetiger anterior fragment, proboscis not everted, both palps attached, syntype, MNHN Type 1357; (B) M. obockensis, BMNH: ZB. 1971.54; (C) M. pulchella, holotype, BMNH 1969.391; (D) M. cornuta, holotype, ZMUC-POL- 969; (E) M. montera sp. nov. MNHN A 895; (F) M. sinbadi sp. nov., NMW. Z. 2010.037.0001; (G) M. cf. agoensis, NMW. Z. 2010.037.0004; (H) M. cf. cincta, NMW. Z. 2010.037.0041; (I) M. conversa, BMNH. 2010.234; (J) M. crenulifrons, NMW. Z. 2010.037.0024; (K) M. cf. falcifera, NMW. Z. 2010.037.0010 b; (L) M. symmetrica, NMW. Z. 2010.037.0047 b.