Planicirrata Nygren, 2004, gen. n.

Planicirrata gen. n.

Linnean name definition. Type species Myrianida proceraeae Hartmann­Schröder & Rosenfeldt, 1990.

PhyloCode definition. No name definition provided.

Apomorphies. Supported by 3 morphological apomorphies (Fig. 4): 1) cirrostyles flattened (character 15), character state change is a parallelism; 2) pharynx sinuation with several sinuations (character 39), character state change is a parallelism; 3) number of rows of muscle cells equals 41–50 (character 48), character state change is a parallelism.

Etymology. Plani is latin, meaning flat. Named for its flattened cirrostyles.

Planicirrata proceraeae (Hartmann­Schröder & Rosenfeldt, 1990) comb. n. (Fig. 46A–G) Myrianida proceraeae Hartmann­Schröder & Rosenfeldt, 1990: 100 –101, figs 1–3; 1992: 104.

Material examined. Antarctic: holotype, ZMH 19924, Elephant Island, 60°51.3'S, 55°45.6'W, 290 m, stones, 26 Feb 1985.

Diagnosis. Procerini with flattened lanceolate cirrostyles.

Description. Holotype complete, length 14 mm for 90 chaetigers, width 1.4 mm at level of proventricle. Preserved material yellowish, without colour markings; eyes reddish orange.

Body shape, excluding parapodial lobes, cylindrical in transection, stout (Fig. 46A), venter flattened. Body distinctly thicker in anterior 20 chaetigers. Ciliation not possible to assess. There is an indication of a stolon head behind chaetiger 13, with 3 minutely developing antennae (Fig. 46B).

Prostomium rounded rectangular, wider than long. Four eyes, with lenses, present in trapezoid arrangement, anterior pair larger. Eyes separated; eye spots absent. Palps small, in dorsal view projecting 1/5 of prostomial length (Fig. 46A), fused. Nuchal epaulettes reaching end of tentacular segment.

Antennae as well as ventral tentacular cirri and first dorsal cirri lost. Dorsal tentacular cirri reaching chaetiger 3. Alternation in direction of cirri not assessed. Dorsal cirri on anterior 10 chaetigers lost, all other cirri equal in length (Fig. 46C), c. 1/8 of body width. Indistinct cirrophores on tentacular segment and first dorsal cirri present; cirrophores otherwise absent. Dorsal tentacular cirri, as well as median antenna, and first dorsal cirri (Hartmann­Schröder & Rosenfeldt 1990), cylindrical, dorsal cirri lanceolat, flattened (Fig. 46C).

Parapodial lobes rounded conical, small. Number of aciculae not possible to assess. Chaetae in anterior 10 chaetigers broken, other chaetae compounds (Fig. 46E). Chaetal fascicle with 20–25 chaetae in anterior chaetigers, 5–20 in median and posterior. Compound chaetae with small distal tooth (Fig. 46E); serration absent. Single thick, distally dilated, bayonet chaetae, with distal denticulation (Fig. 46D), beginning at chaetiger 20.

Pharynx and proventricle dissected, placement unknown. Pharynx with at least 3 sinuations. Trepan with c. 30 small, more or less equal, teeth (Fig. 46F, G). Basal ring absent; infradental spines absent (Fig. 46F, G). Proventricle, unknown position, equal in size to 5– 6 segments with 45 rows of square shaped muscle cells. Anal cirri lost.

Reproduction. Anterior scissiparity, the holotype is developing a stolon behind chaetiger 13.

Habitat. Stones, 290 m.

Distribution. Antarctic. Only known from type specimen.

Remarks. Planicirrata proceraeae is unique among Procerini in having flattened dorsal cirri. Apart from the flattened cirri, P. proceraeae show few similarities with Myrianida, with which it was first associated. In general appearance P. proceraeae is possibly most similar to Pachyprocerastea hydrozoicola but the chaetal arrangement is quite different in P. hydrozoicola with simple chaetae in all chaetigers. Simple chaetae is lacking in P. proceraeae as far as is known, but presence of simple chaetae in anterior chaetigers can not be excluded as these chaetae are broken.