Imajimaea, Nygren, Arne, 2004

Nygren, Arne, 2004, Revision of Autolytinae (Syllidae: Polychaeta)., Zootaxa 680, pp. 1-314 : 105-110

Imajimaea gen. n.

Linnean name definition. Types species Autolytus japonensis Imajima & Hartman, 1964 .

PhyloCode definition. No name definition provided.

Apomorphies. Clade supported by 2 morphological apomorphies ( Fig. 4 ): 1) colour pattern as brown/black transverse intersegmental bands (character 1), character state change is a parallelism, unknown state in I. draculai ; 2) cirrostyles egg shaped (character 15), other most parsimonious reconstructions (MPRs) possible, character state change is a parallelism, character later reversed within clade.

Etymology. Named in honour of Prof. Minoru Imajima.

General description.

Atokous form. Length 11–21 mm for 67–160 chaetigers (excluding incomplete specimens); width, measured at level of proventricle and excluding parapodial lobes, 0.3–0.8 mm. Colour pattern as transverse brown/black intersegmental bands, unknown state in I. draculai . Body shape, excluding parapodial lobes, cylindrical in transection, venter flattened; body width fairly constant. Ciliation not assessed. Prostomium rounded rectangular, wider than long. Four eyes, with lenses, in trapezoid arrangement, anterior pair larger. Eyes confluent or separated, eye spots absent or present. Palps fused, in dorsal view not projecting in front of prostomium, or projecting 1/5–1/2 of prostomial length. Extension of nuchal epaulettes from end of tentacular segment to end of chaetiger 1 (unknown in I. draculai ).

Prostomium with 3 antennae; median antenna inserted medially on prostomium, lateral antennae on anterior margin. Tentacular cirri 2 pairs. Dorsal cirri from chaetiger 3, of equal length (reported cirri length compared to body width excluding parapodial lobes); cirrophores present on tentacular cirri and first dorsal cirri; cirrophores otherwise absent. Anterior appendages cylindrical or flaskshaped, dorsal cirri cylindrical or ovoid to egg shaped.

Parapodial lobes small to medium in size, rounded to rounded conical. Except for bayonet chaetae, simple chaetae present in chaetiger 1–4, in all chaetigers, or absent. Compound chaetae present from chaetiger 4, present in all chaetigers, or absent. Simple chaetae uni­ or bidentate with small distal tooth; compounds bidentate, with small distal tooth. Blade serration absent or present. Single thin bayonet chaetae, subdistally denticulated.

Pharynx with single to multiple sinuations anterior and lateral to proventricle. Trepan teeth arranged in 1 ring, with equal teeth, or with 2 large lateral teeth in combination with irregularly sized and arranged teeth. Basal ring present; infradental spines absent (unknown for some taxa). Proventricle with varying number of rows of square shaped muscle cells. Pygidium with 2 cirri (reported length compared to body width excluding parapodial lobes at level of proventricle if not otherwise stated), median papilla absent.

Reproduction. Schizogamy by anterior scissiparity recorded in Imajimaea zonata .

Epitokes. Unknown.

Imajimaea draculai ( San Martín & López, 2002) comb. n. (Fig. 48A–I)

Paraprocerastea draculai San Martín & López, 2002: 139 –141, fig. 3A–I; San Martín 2003: 460 – 462, fig. 252A–I.

Material examined. Spain: holotype MNCN 16.01/6095, NW Spain, off Foz, 43°58.46'N 7°11.8'W, 177 m, sand, 14 Jun 1991.

Diagnosis. Imajimaea with flaskshaped anterior appendages, dorsal cirri egg shaped; trepan with 2 lateral large teeth, smaller teeth in ventral and dorsal arc; simple chaetae in all chaetigers, first two chaetigers with distinctly different type of chaetae compared to following chaetigers.

Description. Holotype on slide, in two fragments, incomplete; length 2.4 mm for 4+7 chaetigers, width 0.4 mm. Absence/presence of ciliation not possible to assess.

Eyes separated (Fig. 48A); eye spots absent. Palps do not project in front of prostomium (Fig. 48A), fused. Absence/presence of nuchal epaulettes not possible to assess.

Median antenna lost. Lateral antennae reaching chaetiger 2, dorsal tentacular cirri as long as lateral antennae. Ventral tentacular cirri 1/2 as long as dorsal pair. First dorsal cirri broader and slightly longer than lateral antennae. Alternation in direction of cirri not assessed. Cirri from chaetiger 2, equal in length, c. 1/5 of body width. Cirrophores on tentacular cirri and first dorsal cirri present; cirrophores otherwise absent. Lateral antennae, tentacular cirri, and first dorsal cirri flaskshaped (Fig. 48A, B), dorsal cirri ovoid, egg shaped.

Parapodial lobes rounded conical, medium in size. Aciculae numbering 2–3 in all present chaetigers. Chaetal fascicle with 5–6 chaetae in chaetiger 1, and 2; 9–10 chaetae in chaetiger 3 and 4; remainder chaetiger with c. 15 chaetae. All chaetae simple. Chaetae in chaetiger 1–2 with minute distal tooth (Fig. 48F, G), difficult to see except in high magnification; from chaetiger 3 all chaetae clearly bidentate (Fig. 48H); distal tooth small, serration absent. Chaetae have small diffuse denticulation along fusion line (Fig. 48F–H). Single thin bayonet chaetae, subdistally denticulated, present in chaetiger 11 (Fig. 48I).

Pharynx and proventricle dissected. Pharynx with single sinuation. Position of trepan and pharynx not known. Trepan with 2 large teeth (Fig. 48D) and 29–30 small teeth, large teeth laterally positioned, alternating with 14–15 much smaller teeth in a dorsal (Fig. 48C) and ventral arc; small teeth irregularly sized, and arranged; teeth in 1 ring. Basal ring present; infradental spines present (Fig. 48C). Proventricle equal in length to 3 segments, unknown position, with c. 34–36 rows of muscle cells (Fig. 48E). Posterior part lost.

Reproduction. Unknown.

Habitat. Sand, 177 m. In the sample there were also specimens of Crinoidea, Decapoda and Pennatulacea, and it is possible that I. draculai may live associated with any of these as pointed out by San Martín & López (2002).

Distribution. North East Atlantic. North West Spain. Only known from type specimen.

Remarks. Imajimaea draculai is unique in many respects, including its shape of anterior appendages, type of trepan, and chaetal arrangement. Its phylogenetic position is somewhat uncertain. It was first placed in Paraprocerastea , based on the shape of the dorsal cirri. However, Paraprocerastea as outlined by San Martín and López (2002), is a nonmonophyletic heterogenous group as judged from present analysis, and I. draculai show little resemblance to the type species P. crocantinae . In this analysis, I. draculai groups together with. I. japonensis , I. tsugara , and I. zonata . Of the four Imajimaea taxa, I. draculai , I. japonensis , and I. tsugara , are the only one with simple chaetae, but in I. japonensi s, and I. tsugara these chaetae are restricted to the anterior 4 chaetigers. The detailed shape of the simple chaetae in I. draculai is very similar to the ones found in Virchowia spirifer .

Imajimaea japonensis ( Imajima & Hartman, 1964) comb. n. (Fig. 49A–H)

Autolytus japonensis Imajima & Hartman, 1964: 92 –93, fig. 17G– O. Autolytus (Autolytus) japonensis Imajima 1966: 37 –38.

Material examined. Japan: holotype LACM POLY­ 0152, off Shiriyasaki, c. 140 m, 13 Feb 1956.

Diagnosis. Imajimaea with nuchal epaulettes reaching end of tentacular segment; egg shaped dorsal cirri; simple chaetae in anterior 4 chaetigers; c. 45 spine shaped teeth in trepan.

Description. Holotype complete (Fig. 49A), length 11 mm for 66 chaetigers, width 0.4 mm at level of proventricle. Preserved material yellowish orange with faint pale brown transverse intersegmental colour markings (Fig. 49B). Eyes reddish. Ciliation not possible to assess.

Eyes separated; eye spots absent. Palps do not project in front of prostomium (Fig. 49B), fused. Nuchal epaulettes extending over tentacular segment (Fig. 49B).

Median antenna reaching chaetiger 4–5. Lateral antennae and dorsal tentacular cirri, length 2/3 of median antenna. Ventral tentacular cirri 1/3 as long as dorsal pair. First dorsal cirri as long as median antenna, second dorsal cirri as long as ventral tentacular cirri. Alternation in direction of cirri not assessed. Dorsal cirri from chaetiger 3, of equal length, c. 1/8 of body width, shorter than parapodial lobes. Cirrophores on tentacular segment and first dorsal cirri present; cirrophores otherwise absent. Antennae, tentacular cirri and second dorsal cirri cylindrical, dorsal cirri from chaetiger 3 egg shaped.

Parapodial lobes rounded, small (Fig. 49B). Anterior chaetigers with 2–3 aciculae, 1–2 in median and posterior. Chaetal fascicle with 5–9 chaetae in all chaetigers. Chaetiger 1–2 with 8 simple chaetae, of which 5–6 are unidentate (Fig. 49C) and 2–3 slightly bidentate (Fig. 49D); chaetiger 3 with 8 simple chaetae, all bidentate; chaetiger 4 with 2 fused chaetae and 6 compounds (Fig. 49E), all bidentate; from chaetiger 5 all chaetae compound and bidentate (Fig. 49F, G). Denticulation present along fusion line in fused chaeta (Fig. 49C– D). Small distal tooth in both compound and simple chaetae; indistinct serration sometimes present on compounds. Single thin bayonet chaetae (Fig. 49H), subdistally denticulated, beginning at chaetiger 3.

Pharynx sinuation, trepan position, structure of trepan not possible to assess, dissected. Proventricle equal in length to 1 segment in chaetiger 7, with c. 33 rows of muscle cells. Anal cirri equal in length to 1/3 of body width (Fig. 49A).

Reproduction. Unknown.

Additional information. The trepan has 45 long, spine shaped teeth ( Imajima 1966).

Habitat. 140 m.

Distribution. North West Pacific. North Japan. Only known from type locality.

Remarks. Imajimaea japonensis is most closely related to I. tsugara . The chaetae, chaetal arrangement, and trepan structure are identical in the two taxa. Imajimaea japonensis differs from I. tsugara in 1) smaller palps not projecting in front of prostomium compared to projecting 1/2 of prostomial length, 2) shorter nuchal epaulettes reaching end of tentacular segment compared to end of first chaetiger, and 3) egg shaped dorsal cirri shorter than parapodial lobes, compared to cylindrical cirri longer than parapodial lobes.

Imajimaea tsugara ( Imajima, 1966) comb. n. (Fig. 50A–H)

Autolytus (Autolytus) tsugara Imajima, 1966: 38 –40, fig. 8A–H.

Material examined. Japan: holotype NSMT POL H­ 14, off Shirikishinai, Ohma, 140 m, 10 Jun 1958.

Diagnosis. Imajimaea with nuchal epaulettes reaching end of chaetiger 1; simple chaetae in anterior 4 chaetigers; c. 40 spine shaped teeth in trepan.

Description. Holotype complete, in two fragments; length 15 mm for 88 chaetigers, width 0.8 mm. Preserved material yellowish with brown transverse intersegmental bands (Fig. 50A, B); eyes brownish red. Ciliation not possible to assess.

Eyes confluent (Fig. 50A); eye spots absent. Palps in dorsal view projecting 1/3–1/2 of prostomial length (Fig. 50A), fused. Extension of nuchal epaulettes to end of chaetiger 1 (Fig. 50A).

Antennae lost, dorsal tentacular cirri reaching chaetiger 5. Ventral tentacular cirri, 1/2 as long as dorsal pair. First dorsal cirri lost, second dorsal cirri 2/3 as long as dorsal tentacular cirri. Alternation in direction of cirri not assessed. Dorsal cirri from chaetiger 3, of equal length, c. 1/5 of body width, longer than parapodial lobes. Cirrophores on tentacular segment and first dorsal cirri present; cirrophores otherwise absent. All appendages cylindrical.

Parapodial lobes rounded conical, small (Fig. 50B). Anterior chaetigers with 3 aciculae, 1–2 in median and posterior. Chaetal fascicle with c. 10 chaetae in anterior chaetigers, 5–8 in median and posterior. All chaetae simple in chaetiger 1–4; most chaetae unidentate in chaetiger 1 (Fig. 50C); chaetiger 2–4 with increasingly more bidentate chaetae (Fig. 50D, E); from chaetiger 5, all chaetae compound and bidentate (Fig. 50F, G). Denticulation present along fusion line in simple chaetae (Fig. 50C–E). Distal tooth smaller in both compound and simple chaetae (Fig. 50E–G); faint serration sometimes present on compounds. Single thin bayonet chaeta (Fig. 50H), subdistally denticulated, beginning at chaetiger 18.

Pharynx with sinuation anterior and lateral to anterior half of proventricle. Trepan dissected, lost. Proventricle equal in length to 2.5 segments in chaetiger 7–9 with 44 rows of muscle cells. Anal cirri lost.

Reproduction. Unknown.

Additional information. The trepan has about 40 long, spine shaped teeth ( Imajima 1966: Fig. 8b).

Habitat. 140 m.

Distribution. North West Pacific. North Japan. Only known from type locality.

Remarks. See remarks for I. japonensis .

Imajimaea zonata ( Mohammad, 1973) comb. n. (Fig. 51A–G)

Autolytus zonata Mohammad, 1973: 27 –28, fig. 2A–G.

Material examined. Kuwait: holotype BMNH 1969:387, Salimiyah, Kuwait Arabian Gulf, 29°20'W 48°06'E, near low tide mark on coral, 3 Feb 1969.

Diagnosis. Imajimaea with nuchal epaulettes reaching end of tentacular segment; egg shaped dorsal cirri; more than 80 spine shaped teeth in trepan.

Description. Holotype complete, in two fragments; length 21 mm for 160 chaetigers, width 0.3 mm. Preserved material with brown transverse intersegmental bands across each segment, except between tentacular segment and chaetiger 1 (Fig. 51A); eyes red­brown. Ciliation not observed.

Eyes rather large, almost confluent (Fig. 51B); eye spots present. Palps in dorsal view projecting 1/2 of prostomial length (Fig. 51B), fused. Extension of nuchal epaulettes to end of tentacular segment.

Median antenna reaching chaetiger 7–8. Lateral antennae and dorsal tentacular cirri, length 1/2 of median antenna. Ventral tentacular cirri 1/2 as long as dorsal pair. First dorsal cirri equal in length to 2/3 of median antenna. Second dorsal cirri equal in length to ventral tentacular cirri. Alternation in direction of cirri not assessed. Dorsal cirri from chaetiger 3, of equal length (Fig. 51A), 1/3 of body width. Cirrophores on tentacular segment and first dorsal cirri present; cirrophores otherwise absent. Antennae, tentacular cirri, and cirri in anterior 20–30 chaetigers more or less cylindrical, following cirri more ovoid to egg shaped.

Parapodial lobes rounded, small (Fig. 51A). Anterior chaetigers with 2–3 aciculae, 1– 2 in median and posterior. Anterior chaetigers with 12 compound chaetae, 5–8 in median and posterior. Compound chaetae with small distal tooth (Fig. 51F); serration present. Single thin bayonet chaetae (Fig. 51G), subdistally denticulated, beginning at chaetiger 9.

Pharynx with several sinuations anterior and lateral to proventricle (Fig. 51D). Trepan in chaetiger 3, with numerous equal teeth>80 (difficult to assess) (Fig. 51C). Absence/ presence of basal ring and infradental spines not possible to determine. Proventricle equal in length to 1.5 segments in chaetiger 9–10 with c. 13 rows of muscle cells (Fig. 51E). Anal cirri equal in length to body width.

Reproduction. Anterior scissiparity. The type specimen with developing head behind chaetiger 13 (Fig. 51A), eyes or antennae not yet developed.

Habitat. Intertidal, on corals.

Distribution. Indian Ocean, Arabian Gulf. Kuwait. Only known from type locality.

Remarks. Imajimaea zonata is the only Imajimaea that lack simple chaetae, in addition the pharynx is much more convoluted and the proventricle has fewer rows of muscle cells than in the other three taxa. It is unique among Autolytinae in having more than 80 spine shaped teeth in its trepan.

Figures

FIGURE 4. Character transformations. Symbols as follow: black box, only one most parsimonious reconstruction (MPR) exists; white box, more than one MPR exist; X reversal; = parallelism; character later reversed within clade; character further changed within clade;? unknown character state for one or several taxa within clade.