Myriochele australiensis, Capa & Parapar & Hutchings, 2012

Capa, Maria, Parapar, Julio & Hutchings, Pat, 2012, Phylogeny of Oweniidae (Polychaeta) based on morphological data and taxonomic revision of Australian fauna, Zoological Journal of the Linnean Society 166 (2), pp. 236-278 : 257-261

MYRIOCHELE AUSTRALIENSIS SP. NOV.

( FIGURES 9E , 10 , 11 , 14 , TABLES 1, 5

Holotype: AM W20675, New South Wales, east of Long Reef , 33°44′43″S, 151°22′43″E, sand, 60 m, 13.iv.1989.

Paratypes: AM W37827, same sample (42 specs) .

Other material examined (Appendix 1): New South Wales (175 specs): Malabar, Cobblers, Cape Banks, Wattamolla, Basspoint, Murramarang National Park ; Victoria (1 spec.), Bass Strait .

Description of holotype: Specimen measuring 7.5 mm long and 0.5 mm wide, with 26 chaetigers. Body cylindrical in cross section ( Fig. 10A ) with tapering anterior and posterior ends ( Figs 10B–G ; 11A–C, L, M ). Epithelium wrinkled. Longitudinal ciliated grooves present along body in ventral, lateral, and dorsal sides, the dorsal being wider and more obvious ( Fig. 11C–E ). Head rounded, slightly wider than the rest of body, with anterior margin slightly pointed from ventral view and distinctly set off from segmented region by constriction ( Figs 10B–D ; 11A–C ). Eyespots not observed. First chaetiger uniramous ( Fig. 11A, B ); second and third biramous, increasing *The author described it as ‘rounded to quadrangular’.

B, biramous; nd, no data available; RLAS, relative length of anterior segments; U, uniramous. in length progressively, with RLAS = 1:2:3 ( Fig. 11A– C ). Following chaetigers similar in length to posterior end, where they are progressively shorter and thinner ( Fig. 10E–G ). Notopodia with capillary chaetae with proximal third smooth and distal end with scale covering ( Fig. 11G ), diminishing in length ventrally within each fascicle. Acicular chaetae present from segment 5 ( Fig. 11F ), about one third the length of capillaries with no ornamentation and abruptly tapered tips ( Fig. 11H ). Neuropodial tori narrow and nearly rectangular, with uncini arranged in two to three irregular rows in anterior segments ( Fig. 11I, J ) to three to four in middle segments ( Fig. 11K ). Uncini with two teeth arranged vertically, similar in size, curved and with tips slightly pointing upwards ( Fig. 11K ). Posterior end cylindrical, distally tapered, with compressed segments slightly directed dorsally ( Fig. 11L ). Pygidium consisting of two low lateral lobes ( Fig. 11M ). Tube with cylindrical middle section and long tapering ends, covered with sponge spicules ( Fig. 10H ).

Variation: Specimens found to be between 4–8 mm in length and 0.4–0.6 mm in width with 24–35 segments, with the exception of those exhibiting anterior or posterior regeneration. The shape of the head varies amongst the specimens, being in some wider than the rest of the body but in others not obviously wider. Anterior shape also diverges amongst specimens, being pointed to rounded. Brownish lateral eyespots have been observed on the head of some specimens, but are not always present (like in the holotype), so they probably fade after preservation. Several specimens showed posterior end regenerating at different stages ( Fig. 9E ).

Ecological notes: Myriochele australiensis sp. nov. has been found in several localities in New South Wales, in open water environments (not estuaries) ( Fig. 14 ) at around 60–80 m depth and mostly in sandy sediments. It is sympatric with Myrioc. heruensis and G. quelis sp. nov. (see Fig. 14 and Appendix 2).

Etymology: The name of this species follows the tradition of many species of the former genus Myrioglobula of naming the taxon after the country in which it was discovered, in this case Australia.

Remarks: Myriochele australiensis sp. nov. is characterized by the presence of only one anterior uniramous chaetiger, which using the traditional classification would have classified it as a species of Myrioglobula . This new species is unique amongst other species sharing this feature because it possesses peristomial eyes ( Table 5), although this feature should be used with caution as eyespots appear to fade in preserved material and could have been overlooked in the other taxa. Myriochele australiensis sp. nov. is distinguished from Myriochele antarctica ( Hartman, 1967) comb. nov. in the arrangement of the uncinal teeth, positioned in a vertical row in Myrioc. australiensis sp. nov. and other species of the genus but side by side in Myrioc. antarctica ( Table 5). Myriochele australiensis sp. nov. shares with Myriochele malmgreni ( Parapar, 2006) comb. nov., from Iceland, the shape of the pygidium with two blunt lobes; unlike Myriochele islandica ( Parapar, 2003a) comb. nov., which has a tetra-lobed pygidium and Myriochele japonica ( Imajima & Morita, 1987) comb. nov., with a pygidium consisting of two large lobes and five papillae. However, Myrioc. australiensis sp. nov. and Myrioc. malmgreni comb. nov. differ in the relative length of anterior segments (1:2: 3 in the former and 1:1.5: 5 in the latter) and in the appearance of the anterior-most acicular chaetae on notopodia, being in the fifth segment in Myrioc. australiensis sp. nov. and in the third in Myrioc. malmgreni comb. nov.

The uncini of Myrioc. australiensis sp. nov. ( Fig. 11K ) show a characteristic ‘S’ shape with a prominent subrostral process and the tip of the teeth pointing upwards slightly ( Fig. 15L ). These features were previously observed in three of the four species hitherto described in the genus Myrioglobula : Myrioglobula japonica ( Imajima & Morita, 1987; Figs 9F , 10F ), Myrioglobula islandica ( Parapar, 2003a; Fig. 8C ), and Myrioglobula malmgreni ( Parapar, 2006; Fig. 11G ) but not in the Myrioglobula type species: Myrioglobula antarctica .

Myriochele australiensis sp. nov. resembles Myriochele minor Caullery, 1944 , recorded from the Flores Island, Indonesia, in the shape of the head, elongated and with a rounded anterior end, and in the shape of the mouth. However, they differ in thoracic formula, U: B: B in Myrioc. australiensis sp. nov. and U: U: U in Myrioc. minor ; in the shape of the pygidium, bilobed in the new species and with three lobes (to dorsal and one ventral) in Myrioc. minor ; and in the relative length of the anterior segments, RLAS = 1:2:3:3:4: 3 in Myrioc. australiensis sp. nov. and RLAS = 1:1:1:1: 4 in Myrioc. minor .

Figures

Figure 8. Myriochele heruensis. A, anterior end, frontal view. B, anterior end, lateral view. C, anterior end, dorsal view. D, capillary notochaetae, segment 2. E, notopodia segment 2 and 3. F, notochaetae segment 3. G, detail of scales covering capillary chaetae. H, acicular chaetae, segment 3. I, neuropodial uncini field (part), segment 3. J, detail of uncini, top view. K, detail of uncini, side view. L, posterior end, dorsal view. M, posterior end, ventral view. Abbreviations: ac, acicular chaetae; b1, biramous segment 1; cc, capillary chaetae; cg, cephalic groove; u1-u3, uniramous segments 1 to 3. Registration numbers: A, J, AM W37178; B–E, M, AM W37181; F–I, K, AM W37179. Scale bars: A–C, L = 100 Mm; D, H = 10 Mm; E, M = 20 Mm; F = 3 Mm; G, K = 1 Mm; I, J = 2 Mm.

Figure 9. A–D, Myriochele heruensis in regeneration. A, anterior end regenerating, including uniramous and biramous segments. B, early stage of anterior end regeneration from a mid-body segment. C, regeneration of posterior end. D, detail of a torus with newly formed uncini at the point of piercing the cuticle (arrows). E, Myriochele australiensis sp. nov. Regeneration of posterior end. F–H, Myriowenia sp. in regeneration. F, anterior end, ventral view. G, head, ventral view. H, regeneration of anterior fragment with tubular projections (arrows). Abbreviations: b1-b4, biramous segment 1 to 4; u1-u3, uniramous segments 1 to 3. Registration numbers: A, D, AM W37182; B, AM W37179; C, AM W37181; E, AM W37201; F, G, AM W37185; H, AM W37186. Scale bars: A–C, E, G, H = 100 Mm; D = 10 Mm; F = 20 Mm.

Figure 10. Myriochele australiensis sp. nov. A, complete specimen, lateral view. B, anterior end, ventral view. C, anterior end, lateral view. D, anterior end, dorsal view. E, posterior end, ventral view. F, posterior end, lateral view. G, posterior end, dorsal view. H, tube. Abbreviations: b1-b4, biramous segments 1 to 4; u1, uniramous segment 1. Registration numbers: A–H, paratypes AM W20675. Scale bars: A–D = 200 Mm; E–H = 30 Mm.

Figure 11. Myriochele australiensis sp. nov. A, anterior end, ventral view. B, anterior end, lateral view. C, anterior end, dorsal view. D, detail of lateral ciliary band running between notopodia and neuropodia. E, segments 4–6 (b3-b5), lateral view. F, notopodial chaetae, segment 5. G, detail of distal end of capillary chaetae, scale covered, same segment. H, acicular chaetae, same segment. I, uncinal field, segment 2. J, detail of uncini, top view. K, detail of uncini, side view. L, posterior end, lateral view. M, posterior end, dorsal view. Abbreviations: ac, acicular chaetae; b1-b5, biramous segments 1 to 4; cc, capillary chaetae; u1, uniramous segment 1. Registration numbers: A, AM W37200; B–D, F–I, K, L, AM W37198; E, AM W37199; J, M, AM W37197. Scale bars: A, C, E = 100 Mm; B = 200 Mm; D, F, H, I = 10 Mm; G, J, K = 1 Mm; L, M = 30 Mm.

Figure 14. Distribution of Australian oweniids except for members of genus Owenia.

Figure 15. Stylized drawings of main morphological features in some representative species of Oweniidae genera (all redrawn from originals with permission). A, Galathowenia oculata. B, Myriochele heeri. C, Owenia fusiformis. D, Galathowenia oculata. E, Myriochele olgae. F, Myriochele danielsseni. G, Myriowenia gosnoldi. H, Myriowenia californiensis. I, Owenia fusiformis. J, Galathowenia oculata. K, Myriochele heeri. L, generalized drawings of disposition of the uncinal teeth in all genera. A, after Milligan (1984: 46–49, fig. 46.6a). B, after Nilsen & Holthe (1985: 20, fig. 3B). C, after Hartmann-Schröder (1996: 477). D, after Imajima & Morita (1987: 95, fig. 6). E, after Blake (2000: 112, fig. 5.5). F, after Imajima & Morita (1987: 93, fig. 5). G, after Hartman (1965: 347, fig. 44a). H, after Hartman (1960: 209, fig. 16.5). I, after Drasche (1885: plate 1, fig. 2). J, after a SEM picture in Purschke & Tzetlin (1996: 4, fig. 10B). K, after Parapar (2006: 530, fig. 7A). L, from diverse sources cited above. Abbreviations: al, anterior lobes; b1-b2, biramous segments 1 to 2; c, collar; dlf, dorsolateral folds; e, eyespots; m, mouth; ml, mouth lips; oec, oesophageal commissure; p, palps; tc, tentacular crown; u1-u3, uniramous chaetiger and position on body; vph, ventral pharyngeal organ; vs, ventral slit.