Melinna elisabethae McIntosh, 1885

Gunton, Laetitia M., Zhang, William, Kupriyanova, Elena K. & Hutchings, Pat A., 2023, New Species of Melinna (Melinnidae, Annelida) from the Australian Abyss with Comments on M. albicincta, M. cristata and M. elisabethae, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 125-154 : 143

Melinna elisabethae McIntosh, 1885

Figs 13–15 ; Tables 4, 5

Melinna elisabethae McIntosh, 1885: 438 ; 1914 106–107 (in part).

For complete synonymy see Mackie & Pleijel, 1995.

Material examined. AM W.21793, 4 specimens, including prepared for SEM, Cleveland , Tees Bay, England (54°36'N 1°48'W), gravelly mud/rock, 44 m, coll. Analytical & Environmental Services, 7 September 1984 .

Remarks

The original description by Mackie & Pleijel (1995) only provided line drawings, we give additional information based on light and SEM images.

Prostomium well­developed and divided into anterior and posterior parts, anterior part trilobed ( Fig. 15B ), posterior part raised triangular glandular with anterior margin bearing longitudinal slits ( Fig. 15B ). Buccal tentacles numerous and equal in length to the branchiae ( Fig. 13B ). Four pairs of branchiae annulated with distal surface exhibiting cilia patches ( Fig. 14A,C ). Branchiae circular in cross­section, anterior pair showing 40% of basal fusion and outer pair 20% fusion ( Figs 13B,C , 14C ). One pair of dorsal hooks strongly curved and with pointed tips ( Figs 13B,D,E , 14B,C ), solid without internal canal. Dorsal membrane with about 12 triangular projections on anterior margin ( Figs 13E , 14A ). First segment achaetous ( Fig. 14A ) with crenulated ventral margin ( Fig. 15B ). Segments 2–5 with acicular neurochaetae arranged in elongated tori, progressively inserted more laterally ( Fig. 13B,C ). From segment 6 neuropodia with uncini continuing to pygidium. Notopodia present from segment 4, initially very small with short notochaetae, then progressively becoming larger, more laterally inserted and well­developed by segment 7 ( Figs 13D , 14A , 15C ) and on all subsequent ones. Notochaetae arranged in two tiers ( Fig. 14H ) with tips of longer ones curved ( Fig. 15A ) and with blades finely ornamented ( Figs 14F,H , 15A,E ). Notopodia globular with posterior lobe longer than anterior one ( Fig. 14D,E,F ) and well separated from neuropodia ( Figs 14E , 15C ). Thoracic neuropodia raised glandular tori slightly curved, bearing about 26 uncini ( Fig. 14E ). Thoracic uncini with a single row of four teeth with ornamentation on lateral face and becoming marked and behind anterior tooth strongly ornamented with small teeth ( Figs 14G , 15D,F ). Abdominal rudimentary notopodia not observed as in Mackie & Pleijel (1995), specimens very small and thin ( Fig. 15G ).Abdominal neuropodia well­developed but not elevated, anteriorly bearing four teeth arranged in a single row ( Fig. 15H,I ). Terminal anus bounded by pair of large lateral lobes and several smaller lateral ones ( Fig. 13a ) and lacking anal cirri. Methyl blue stain shows extensive ventral glandular areas ( Fig. 13F ). Tube with attached shell fragments on anterior end and rest of tube made of smaller sand grains and mud ( Fig. 13G ).

Figures

Figure 13. Light microscopy images of Melinna elisabethae (AM W.21793). (A) Whole specimen. (a) Pygidium. (B) Anterior end dorsal view, stained with methyl blue. (C) Lateral view of anterior end stained with methyl blue. (D) Lateral view of anterior end. (E) Dorsal hooks. (F) Anterior end ventral view, stained with methyl blue. (G) Tube. Scale bars:A, 2 mm; a, 250 µm; B, C, F, 500 µm; D, 250 μm; E, 100 µm; G, 3 mm.Abbreviations: l, lobes; br, branchiae; bt, buccal tentacles; seg, segment; neuro, neurochaetae; dh, dorsal hooks.

Figure 14. SEM of Melinna elisabethae (AM W.21793.002).(A) Dorsal view of anterior end with segments numbered.(B) Dorsal hook.(C) Surface of branchiae. (D) Lateral view of chaetigers 5–10.(E) Chaetigers 5 and 6. (F) Notochaetae chaetiger 6. (G)Anterior neurochaetae of chaetiger 6. (H) Mid­thoracic notopodium showing two types of chaetae. Scale bars: A, 500 μm; B, E, 100 μm; C, D, 200 μm; F, 20 μm; G, 10 μm; H, 50 μm.Abbreviations: dh, dorsal hooks; bf, branchial fusion; 2t, notochaetae of 2 tiers + neurochaetae; c, cilia patches.

Figure 15. SEM of Melinna elisabethae (AM W.21793.002). (A) Close­up view of notopodial chaetal surface of chaetiger 14. (B) Ventral view of anterior end. (C) Dorsal view of chaetigers 6, 7, 8, 9. (D) Neurochaetae chaetiger 7. (E) Chaetiger 11. (F) Posterior thoracic neurochaetae.(G)Abdominal chaetigers showing lack of notopodia.(H) Posterior neurochaetae.(I) Close­up view of posterior neurochaetae. Scale bars: A, 20 μm; B, 1 mm; C, 200 μm; D, 10 μm; E, 50 μm; G, 100 μm; H, I, 10 μm. Abbreviations: tri, trilobed prostomium; pr, triangular glandular prostomium with anterior margin bearing longitudinal slits; st, small teeth.