Macellicephala mirabilis

Macellicephala mirabilis (McIntosh, 1885)

(Figure 2A, Figures 3, 4; Table 2.)

Polynoe (Macellicephala) mirabilis in Mclntosh (1885): 121, p.16: Fig. 1, p. 12A: Figs. 9–11 [original description]. Macellicephala mirabilis in Pettibone (1976): 10, p. 11: Fig. 1a–f [re-description].

Not Polynoe (Macellicephala) mirabilis in Mclntosh (1905): 59.

Not Macellicephala mirabilis in Pettibone (1976): 10, p. 12: Fig. 3a–e.

Not Macellicephala mirabilis in Monro (1936): 100.

Material examined. Holotype of McIntosh (1885), BMNH 1885: 12: 1: 100, New Zealand (off North Island, blue mud), Challenger station 169, collected on 10/07/1874, 37°34'S, 179°22'E, 1280 m depth.

Additional material examined. Two specimens of McIntosh (1905), BMNH 1924: 7: 21: 12, South Africa (Cape of Good Hope), 540–900 m depth. Two specimens of Monro (1936), BMNH 1936: 2: 8: 488, South Georgia (mouth of Stromness Harbour), Discovery station 144, 155– 178 m depth.

Re-description. Holotype in relatively poor state, but many characters observable; specimen complete but now in two fragments (Fig. 3A, B) as a result of previous examinations, chaetae mostly broken off, all elytra missing. Holotype 25 mm long, 6 mm wide including parapodia and 4 mm wide excluding parapodia; with 18 segments (segment 1 = tentacular segment); body dorsoventrally flattened, tapering anteriorly and posteriorly; yellow in alcohol.

Prostomium bilobed with deep anterior notch; prostomial lobes pronounced, greatly extended, with angular (truncated) anterior margins (Fig. 2A, Fig. 3C). Frontal filaments now missing, but once present according to McIntosh (1885) as slender, elongated filaments, inserted internally on the margin of truncated prostomial lobes. Eyes absent. Facial tubercle consisting of two disconnected inflated pads, each medial to bases of palps. Ceratophore of median antenna very long (approaching anterior margin of prostomial lobes), cylindrical, inserted posteromedially on prostomium (near base of anterior notch) (Fig. 2A, Fig. 3C); style of median antenna smooth, slender, tapering and long (extending to segment 5). Palps shortest and thickest of head appendages (extending to about segment 3), tapered, smooth.

Tentaculophores prominent, of equal size, cylindrical, inserted laterally to prostomium, achaetous; styles mostly missing, only style of a ventral cirrus present (on left side), smooth, very slender and long (longer than palps but shorter than style of median antenna) (Fig. 2A, Fig. 3C). Pharynx not observed. Second segment with elytrophores, biramous parapodia, chaetae and ventral cirri.

Nine pairs of prominent, bulbous elytrophores, on segments 2, 4, 5, 7, 9, 11, 13, 15 and 17; all elytra missing. Dorsal ridges absent.

Parapodia biramous. Notopodia reduced to elongate acicular lobe, tip of notoacicula not penetrating epidermis (Fig. 4A). neuropodial large (Fig. 4A), subtriangular and tapering to elongate acicular lobe, tip of neuroacicula not penetrating epidermis. Cirrigerous segments with prominent, bulbous dorsal cirrophores, inserted basally on notopodia; all dorsal styles now missing, but once present according to McIntosh (1885) as slender, smooth, cirriform appendages, far exceeding length of adjacent neuropodial; small, but distinct conical dorsal tubercles present. Ventral cirri smooth, tapering, present from segment 2; inserted basally on segment 2, where very long, about 1.5 times length of associated neuropodial lobe; inserted medially on subsequent segments, where short (not reaching the distal margin of neuropodial l lobe).

Notochaetae stouter than neurochaetae (Fig. 4B), short to very long, few (about 7 present per ramus) often broken off entirely, smooth, with blunt tips. Neurochaetae numerous, upper and lower neurochaetae shorter, others very long; two forms present: either flattened, with only faint denticulation of each side (Fig. 4C) or with distinct spines, spines moderately separated (Fig. 4D, E); both forms tapering into sharp tip.

Two distinct white lines running through ventral side of neuropodia and ventrum of each segment (except for tentacular segment) (Fig. 3D). Nephridial papillae of segments 10, 11 and 12 prominent (Fig. 3D), inconspicuous in other segments, present from segment 5. Reduced parapodia of segment 18 lateral to pygidium, consisting of notopodia only. Pygidium rounded. Anal cirri not observed (Fig. 3E).

Remarks. During the examination of Macellicephala specimens collected as part of this study, several inconsistencies emerged with regards to the revision of the genus carried out by Pettibone (1976). Given that Macellicephala mirabilis (McIntosh, 1885) is the type species of Macellicephala and this genus is in turn the type genus of Macellicephalinae, it is important to clarify the definition of Macellicephala mirabilis. Pettibone (1976) based her re-description of M. mirabilis on the following specimens found in the collections of the NHM London: holotype of McIntosh (1885), BMNH 1885: 12: 1: 100; two specimens of McIntosh (1905), BMNH 1924: 7: 21: 12 (see M. macintoshi sp. nov.) and two specimens of Monro (1936), BMNH 1936: 2: 8: 488.

The material above was re-examined as part of this study and the definition of Macellicephala mirabilis is here restricted to characters derived from the holotype BMNH 1885: 12: 1: 100, which was described in detail by McIntosh (1885). This form has very extended, anteriorly angular (truncated) prostomial lobes (Fig. 2A) rather than shorter, rounded or tapering form of prostomial lobes as seen in other species of Macellicephala (see Fig. 2 for comparison). The description and drawing provided by McIntosh (1885) clearly depicted slender elongated frontal filaments and dorsal cirri, which have since fallen off and were therefore not observed by Pettibone (1976) or in our examination. Papillation medial to bases of elytrophores and dorsal cirrophores reported by Pettibone (1976) was not observed.

For a full comparison of all valid Macellicephala species based on examination of material presented in this study and published literature for the others see Table 2.

Distribution. Known only from its type locality: New Zealand, off North Island, 37°34'S, 179°22'E, 1280 m depth.