Myrianida prolifera O.F. Muller 1788

Myrianida prolifera (O.F. Müller, 1788) (Fig. 75A–E)

Nereis prolifera O.F. Müller, 1788: 15, pl. 52, fig. 5–9.

Autolytus prolifera Grube 1850: 310.

Myrianida prolifera Quatrefages 1866: 63 –64.

Autolytus ehbiensis in part Saint­Joseph, 1887: 228 –233. pl. 11, fig. 106–107, pl. 12, fig. 114–115; McIntosh 1910: 243 –245, pl. 86, fig. 16, plate 87, fig. 15; Fauvel 1923: 314 –315, fig. 121 I–L.

Autolytus prolifer Gidholm 1963; 1965; 1967: 182, 186–188, figs 2A, D, 7A, 8A, B, 14A, 15, 18; Mattisson 1969; Hamond 1969a; Hartmann­Schröder 1971: 179–180, fig. 57A–F; Schiedges 1979a; 1979b; Kirkegaard 1992: 231–233, fig. 133A–F; Hartmann­Schröder 1996: 184, fig. 79A–F; Nygren & Sundberg 2003: GenBank sequences, 16S rDNA partial sequence AF474249, and 18S rDNA partial sequence AF474295.

Material examined. France: 2 syntypes of Autolytus ehbiensis MNHN 1050, 1055, Dinard, Aug– Jul 1876 –1881. Faroes: 8 spms (7 spms on slides (6 rear ends in author's collection for DNA analyses), 1 spm in author's collection for DNA analyses), Kaldbak marine laboratory, 62°N 06°W, dive, 1–4 m, Laminaria with epifauna, 21 Jun 1997. Wales: 7 spms on slides (rear ends in author's collection for DNA analyses), Black Point, 53°18.8'N 04°2.4'W, intertidal, algae with epifauna, May 2000. Sweden: 6 spms in author's collection for DNA analyses, Gullmarsfjorden, Lökarna, 58°13.6'N 11°24.8'E, dredge, 32–36 m, shells and stone with hydroids, 19 Nov 1997; 30 spms in formalin, Tjärnö archipelago, Inre Vattenholmen, 58°52'N 11°06'E, intertidal, algae with epifauna, Apr, 2002. Norway: 4 spms on slides (rear ends in author's collection for DNA analyses), Trondheim, Zoologisk station, 63°26.5'N 10°20.9'E. intertidal on docks, mussels with epifauna, 20 Jan 2002.

Diagnosis. Myrianida with 24–33 equal teeth in trepan, and a well­developed basal ring with infradental spines; cirrophores and cirrostyles unequal, cirrophores always shorter than cirrostyles.

Description. Length 3.6–12.2 mm for 22–69 stock chaetigers, width 0.25–0.45 mm. Live specimens faintly reddish (Fig. 75A) or yellowish, intestine with scattered white specks from intestinal granular accumulations; tips of anterior appendages sometimes reddish; eyes red. Ciliation as 1 troch per segment.

Eyes separated (Fig. 75A); eye spots present. Palps in dorsal view projecting c. 1/3 of prostomial length (Fig. 75A), fused. Extension of nuchal epaulettes from beginning to end of chaetiger 2 (Fig. 75A).

Median antenna reaching chaetiger 8–13 (n=9) in live specimens. Lateral antennae and dorsal tentacular cirri, length 1/2–2/3 of median antenna. Ventral tentacular cirri 1/2 as long as dorsal pair. First dorsal cirri as long as median antenna, second dorsal cirri 1–1.5 times the ventral tentacular cirri. From chaetiger 1–27 cirri with usual alternation in direction, followed by 1–2 DDUU­groups, and a varying number of DMU­, DDU­, and DDUU­groups (n=9). Dorsal cirri from chaetiger 3, alternate in length (Fig. 75A, B); short cirri equals 1/2–2/3 of body width, long cirri equal or 3/4 as long as body width. Cirrophores present on tentacular cirri, and all dorsal cirri. Cirrophores and cirrostyles unequal (Fig. 75B); cirrophores and cirrostyles on short cirri 3/ 4 in length of its counterpart in long cirri; cirrophores on short cirri equal to or slightly shorter than parapodial lobes, cirrophores on long cirri longer than parapodial lobes; cirrophores shorter than cirrostyles. All appendages cylindrical (Fig. 75A, B).

Parapodial lobes rounded, of medium–large size. Anterior chaetigers with 2 or rarely 3 aciculae, 1–2 in median and posterior. Chaetal fascicle with 9–16 compounds in anterior chaetigers, 4–9 in median and posterior. Compound chaetae with small distal tooth (Fig. 75D); serration present. Single thin bayonet chaetae (Fig. 75E), beginning between chaetiger 1–25.

Pharynx with 1 sinuation anterior to proventricle. Trepan in chaetiger 1–3, with 24–33 equal teeth, arranged in 1 ring (Fig. 75C). Basal ring present; infradental spines present (Fig. 75C). Proventricle equal in length to 2–3 segments (Fig. 75A) in chaetiger 8–13 with 28–35 rows of muscle cells (n=16). Anal cirri equal in length to 1.5 times body width.

Reproduction and morphology of epitokous stages. Schizogamy by gemmiparity behind chaetiger 22–44. No mature stolons examined. Gidholm (1965; 1967) present detailed information on stolon morphology. Male c. 3 mm for 3+(17–20) chaetigers, 2 pairs of tentacular cirri; female c. 3 mm for 2+(15–18) chaetigers, 2 pairs of tentacular cirri. Single egg sac. Stolon­bearing specimens collected from June to October (Gidholm 1967).

Habitat. From shallow waters to 40 m, most common from 0– 5 m. Feeds on hydroids like Laomedea geniculata, L. longissima, and Lafoea sp. (Gidholm 1967).

Distribution. North East Atlantic.

Remarks. As already pointed out by Gidholm (1967), the name Myrianida prolifera (as Autolytus prolifer) has been used for many different, inadequately determined species, but also for stolons of various taxa. Preserved specimens may be confused with a number of taxa, perhaps mostly with M. edwarsi that occur in the same area. Synonymy of A. ehbiensis is concluded from type material and from the original description, but some of the syntypes belong to M. brachycephala. See also remarks for M. brachycephala, and M. edwarsi.