Magelona cf. agoensis Kitamori, 1967

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 : 11-15

Magelona cf. agoensis Kitamori, 1967

Figures 3 , 4,13G

Magelona agoensis Kitamori, 1967: 52 –53, fig. 5? (see remarks below)

Material examined. Persian Gulf, IRAN—Stn. B1–10 (MB29–000188, grab B, 2 af; MNCN.16.01/13228, grab C, 1 af), 2005; Stn. B1–15A ( NMW.Z.2010.037.0002; 4 af), 2005; Stn. B2–10C ( MNCN.16.01/13229; 1 af) 2005; Stn. B3–10 ( MNCN.16.01/13230, grab B, 1 af; MB29–000187, grab C, 1 af), 2005; Stn. B4–15 ( NMW.Z.2010.037.0003, grab A, 1 af; NMW.Z.2010.037.0004, grab B, 1 af), 2005; Stn. B4–20C ( NMW.Z.2010.037.0005; 1 af; dissected and slide mounted), 2005; Stn. E20(1) ( NMW.Z.2010.037.0006; 1 af), 2006.

Diagnosis. Prostomium width similar to length, subhexagonal without prostomial horns. Notopodia of chaetigers 1–8 with lanceolate postchaetal lamellae, prechaetal lamellae indistinct; without dorsal superior processes. Chaetiger 9 with broader postchaetal lamellae. All thoracic chaetae capillary. Abdominal chaetigers with lanceolate lateral lamellae. Abdominal hooded hooks predominately quadridentate, with the occasional pentadentate hook present. Hooks in 2 groups, vis-à-vis. Posterior unknown, no pouches observed.

Description. A small slender species; thorax marginally wider than, or of similar size to abdomen ( Figure 3 A). Dimensions of largest specimen (NMW.Z.2010.037.0004): prostomium 0.3 mm long, 0.3 mm wide; thorax (including prostomium) 1.4 mm long, 0.3 mm wide; abdomen 0.25 mm wide; total length 5.2 mm for 25 chaetigers (Note: last chaetiger now dissected and slide mounted). Other specimens 1.5–5.8 mm for 11–25 chaetigers. All material posteriorly incomplete.

Prostomium length similar to width (L:W ratio 1), subhexagonal, anterior margin smooth and straight ( Figures 3 C, 13G), without prostomial horns. Two pairs of longitudinal dorsal muscular(?) ridges; outer pair shorter and very indistinct (difficult to discern in several specimens), abutting inners for entire length. Inner pair adjoined for majority of length, diverging only at distal prostomial margin. No other obvious prostomial ornamentation. Proboscis everted in two specimens, heart-shaped when fully everted, oval when partially everted; very lightly ridged. One specimen (NMW.Z.2010.037.0006) possessing an everted ‘buccal organ/tube’ between the everted proboscis and prostomium (see Discussion). This elongate structure having a dorsal opening (mouth?), and a triangular grooved region on the ventral-most surface ( Figures 4 A–D). Both palps retained on one specimen (MNCN.16.01/ 13230), long, slender; reaching approximately chaetiger 19. Right - hand palp retained on another specimen (NMW.Z.2010.037.0002) reaching chaetiger 23. Non-papillated region long, reaching approximately chaetigers 5– 6. Papillae of similar lengths; one row of papillae either side of an inconspicuous groove for length of palp.

Achaetous region behind prostomium, of similar size to chaetiger 1. Chaetigers 1–8 similar; parapodia biramous ( Figures 3 D–K); notopodia with low indistinct prechaetal lamellae. Superior dorsal prechaetal processes (DML) and ventral neuropodial lobes (VNL) absent. Postchaetal lamellae lanceolate to triangular, and of about equal size along thorax; neuropodial lamellae slightly larger than notopodial lamellae in posterior thorax.

Chaetiger 9: Prechaetal lamellae low, confluent with postchaetal lamellae which are marginally longer and broader than on preceding chaetigers. Postchaetal lamellae lanceolate, of similar size in both rami ( Figure 3 L). All thoracic chaetae simple capillaries.

Abdominal chaetigers with lanceolate to triangular lateral lamellae of about equal size in both rami, with slight basal constrictions ( Figure 3 M). No processes (DML and VML) observed at inner margins of chaetal rows, however, this may be a consequence of the small size of specimens.

Abdominal hooded hooks predominately quadridentate ( Figures 3 N −P, 4E −H) with three secondary teeth surmounting main fang; two lower, and one on the back of, and in between the other two. However several pentadentate hooks observed ( Figure 3 Q) with two small teeth directly above the two lower teeth. Hooks in two groups, with main fangs vis-à-vis ( Figure 3 M). Around 8–10 hooks per rami, hooks split more or less equally between the two groups (4/4 or 5/3). An occasional smaller hook present next to lateral lamellae. No pouches observed; posterior unknown.

Colour. No live animals observed; preserved colour uniformly white in alcohol. Staining with methyl green shows a distinct pattern ( Figures 3 A, B). Dorsally, small paired triangular areas present between chaetigers 1–4, comparable to indistinct white speckled areas seen in non-stained specimens; however, stain dissipates quickly from this region. Stain darkest between chaetigers 4–9; comprising of large speckles between chaetigers 4–6. Ventrally a light, transverse band of staining, level with the parapodia of chaetiger 2 present on some specimens, with a similar darker band on chaetiger 4. Ventral staining darkest between chaetigers 5–9, particularly on chaetigers 5 and 6. White patches which do not stain, present between chaetigers 6–9 either side of mid-ventral line. Abdominally, interparapodial staining present with additional pigmentation along the mid-ventral line adjacent to interparapodial patches ( Figure 3 B). Although this is a small species, it can be clearly identified from its methyl green staining pattern.

Habitat. Fourteen specimens found at 7 stations, from two surveys in various types of muddy sand, and in sandy mud, 10–20 m, Iran, Persian Gulf.

Remarks. There are three known species of Magelona that possess polydentate abdominal hooks: Magelona polydentata Jones, 1963 from the Bahamas, Magelona agoensis Kitamori, 1967 from Japan and an undescribed species (sp. I of Uebelacker & Jones 1984) from the northern Gulf of Mexico. All three of these species being somewhat larger than any of the material observed here.

Uebelacker & Jones (1984) stated that “ Magelona sp. I, is nearly identical to M. polydentata Jones, 1963 , from the Bahamas, apparently differing from the latter in possessing oblique dorsal slits on some thoracic setigers, in having abdominal dorsal and ventral medial lamellae, and in having predominately tridentate hooks on some specimens”. Both species differ from Magelona cf. agoensis in possessing rudimentary prostomial horns, ventral thoracic neuropodial lamellae, and somewhat rudimentary neuropodial lamellae on chaetiger 9. In addition, both are reported to have thoracic pigment bands, which on the holotype of M. polydentata is between chaetigers 5–9 but present between chaetigers 6–8 on Magelona sp. I. However, Jones (1963) when discussing this pigment band stated “it is believed that this does not constitute a valid taxonomic character. To be sure, such a band is faintly indicated on the other specimens from Bimini, but it is entirely lacking in the remaining specimens examined”. A pigment band was not observed on any of the Iranian material studied here. However, this area of the thorax does correspond with that which stained most strongly with methyl green.

Magelona polydentata is described as possessing only a single pair of prostomial ridges, which are well-separated. This appears also to be the case for Magelona sp. I (see Uebelacker & Jones 1984: figure 7–20a), in contrast to the two pairs of abutting ridges as described herein for Magelona cf. agoensis . However, it should be noted that the outer pair of ridges were often extremely difficult to discern.

The predominant abdominal hooded hooks reported for M. polydentata possess four accessory teeth above the hook’s main fang, some possessing five, and a small number with three. This is similar to the hooks seen in Magelona sp. I, however, the later species additionally possesses tridentate hooded hooks which predominate in some specimens. This is in contrast to the Iranian material observed here, which predominately has three accessory teeth above the main fang.

Small dorsal and ventral abdominal processes (DML and VML) were reported as being present on Magelona sp. I, but not on M. polydentata . These were not observed on any of the Iranian material, but this may be due to the small size of the specimens, especially in comparison with the other species.

Based on the original description of M. agoensis , the Iranian material observed here shares similarities with the type material, regarding the shape of the prostomium, the shape of the lamellae and the nature of the abdominal hooded hooks. However, the original description differs in possessing thoracic postchaetal lamellae that are longer in the notopodia than the neuropodia, and abdominal hooded hooks in a single unidirectional facing group. Unfortunately, the original description and drawings of M. agoensis are inadequate for direct comparison and the current location of the holotype is unknown (the holding institution was noted in the original description as the Tokai Regional Fisheries Research Laboratory, although accession numbers relating to the specimen were not given. Enquiries to the laboratory did not yield any further information on the holotype’s whereabouts). The holotype of M. agoensis is much larger than the Iranian material observed here, and it is possible that the variation observed between the specimens is caused by their difference in size. Nevertheless, it is believed that the Iranian specimens are likely to represent a new species. However, in the absence of the holotype of M. agoensis for re-description and comparison, and without more complete Iranian material we prefer not to describe it as so at the present time.

Figures

FIGURE 3. Magelona cf. agoensis (A – B, D – Q, NMW. Z. 2010.037.0005; C, NMW. Z. 2010.037.0004): (A) anterior region, dorsal view, showing methyl green staining pattern; (B) methyl green staining pattern of venter, anterior region; (C) prostomium, dorsal view; (D – M) chaetigers 1 – 10 respectively (anterior views); (N – P) quadridentate abdominal hooded hooks, lateral, lateral oblique and frontal views respectively (N, O hoods omitted for clarity); (Q) pentadentate abdominal hooded hook, frontal view.

FIGURE 4. Magelona cf. agoensis (A – D, NMW. Z. 2010.037.0006): (A) anterior, ventral view; (B) anterior, ventral view; (C) anterior, lateral view, showing view point from which figure A was drawn from; (D) anterior, ventral view; (E – H) polydentate abdominal hooded hooks. Pr = prostomium; Pb = proboscis; Pp = palp attachment site; BO = ‘ buccal organ / tube’, M = mouth.