Syllis imajimai, Martín & Lucas & Hutchings, 2023

Martín, Guillermo San, Lucas, Yolanda & Hutchings, Pat, 2023, The genus Syllis Savigny in Lamarck, 1881 (Annelida: Syllidae: Syllinae) from Australia (Part 3): new species and redescription of previously described species, Zootaxa 5230 (3), pp. 251-295 : 264-266

Syllis imajimai n. sp.

Figure 6

Typosyllis prolifera .— Imajima 1966: 292, text-fig. 65.— Hutchings & Murray 1984: 34. Non Krohn, 1852.

Material examined. AUSTRALIA. NEW SOUTH WALES. Hawkesbury River, just downstream from junction with Colo River , 33º 26’ 30”S, 150 º 53’E, small beach, 40 m off beach, 4 m, fine clean sand sediment, Jones et al. coll., 11 May 1979, id. as Typosyllis prolifera by Hutchings & Murray, Holotype, AM W.196660.

Diagnosis. Body robust, dark, reddish-brown, with numerous rounded hyaline dermal inclusions. Dorsal cirri slender and short. Compound chaetae with short, bidentate blades. Posterior aciculae slightly acuminate.

Description. Holotype 8 mm long, 0.61 mm wide, for 54 chaetigers. Body broad, robust, contracted, very dark and opaque, reddish-brown, especially on anterior segments, except peristomium, with numerous minute rounded hyaline inclusions on dorsum ( Fig. 6A ), extending also to ventral side although less numerous. Prostomium pentagonal to oval, with some pigment spots; four eyes in trapezoidal arrangement and two anterior eyespots. Palps robust, similar in length to prostomium. Median antenna inserted on posterior part of prostomium, between posterior eyes, with 20 articles, longer than combined length of prostomium and palps; lateral antennae shorter than median one, with 14–15 articles each, shorter than median antenna. Peristomium shorter than subsequent segments, covering posterior part of prostomium, less pigmented than subsequent segments ( Fig. 6A ). Dorsal tentacular cirri with about 15 articles each; ventral tentacular cirri with about 10 articles. Dorsal cirri shorter than body width, somewhat longer on anterior segments; dorsal cirri of chaetiger 1, distinctly longer, with 19 articles, with well defined cirrophores and articles; in midbody, with about 20–23 articles, usually coiled ( Fig. 6A ). Parapodia conical, distally bilobed ( Fig. 6B ). Ventral cirri digitiform. All compound chaetae heterogomph falcigers with relatively short, markedly bidentate blades and small dorsoventral gradation in length and shape ( Fig. 6C, D, E ). Anterior parapodia each with about 16– 18 chaetae, blades elongated, proximal tooth similar to distal one, and short spines on margin ( Fig. 6C ), blades about 24–21 μm long; midbody parapodia with 13–14 compound chaetae ( Fig. 6D ), with thick shafts and short bidentate blades, all similar, with short spines on margin, 20–17 μm long; posterior parapodia with eight compound chaetae ( Fig. 6E ), similar to those of anterior parapodia but with thicker shafts and more marked proximal teeth, about 17 μm long. Dorsal simple chaeta from midbody parapodia, markedly bidentate, apparently smooth ( Fig. 6F, G ); ventral simple chaetae smooth, bidentate ( Fig. 6H ), on far posterior segments. Anterior parapodia with three slender aciculae aciculae ( Fig. 6I ), two at midbody ( Fig. 6J ), and single, slightly acuminate acicula in posterior parapodia ( Fig. 6K ). Pharynx long, extending through about six segments; pharyngeal tooth not seen because of opacity of anterior segments ( Fig. 6A ). Proventricle, through about six segments, with 28 muscle cell rows. Pygidium triangular, with two articulated anal cirri and one stylus.

The holotype is developing a sexual dicerous stolon.

Remarks. This species is characterised by its colour pattern, reddish-brown with small hyaline, refringent dermal inclusions, especially marked on anterior segments, dorsal cirri similar in length or shorter than body width, and compound chaetae with relatively short falcigers, with strong, acute proximal and distal teeth, especially from midbody onwards. The Australian examined specimen agrees very well with the Imajima’ description of Typosyllis prolifera , but differs in many aspects with the descriptions of this species from European coasts, a non pigmented species, with aciculae ending in rounded, hollow tips, and pharyngeal tooth located just behind the anterior margin of pharynx (see Fauvel 1923; Campoy 1982, San Martín 2003). Imajima (1966) states that the pharyngeal tooth is located on the anterior margin. Also, the dorsal simple chaetae are very characteristic, markedly bidentate, with the proximal teeth prominent on his material which is why we have recognized his material as our new species Syllis imajimai n. sp.

Other species with hyaline, refringent dermal inclusion are Syllis pharobroomensis ( Hartmann-Schröder, 1979) , n. comb. (see this paper), Syllis deleoini Salcedo-Oropeza, San Martín & Solís-Weiss, 2012 , from southern Mexican Pacific, and Syllis ergeni Çinar, 2005 , from the Aegean Sea, Turkey. Syllis ergeni is also a strongly pigmented species, the compound chaetae and dorsal simple chaetae are not as markedly bidentate as in S. imajimai n. sp. Syllis deleoni lacks colour pattern, the compound chaetae are similar, with relatively short bidentate blades, but both teeth are short, somewhat broader and close to each other ( Salcedo-Oropeza et al. 2012).

Etymology. The species is named after Dr Minoru Imajima, a Japanese polychaetologist, who made important contributions to our knowledge of the family Syllidae .

Habitat. Fine clean sand sediment. Intertidal and shallow depths.

Distribution. Australia (NSW). Japan.

Figures

FIGURE 6. Syllis imajimai n. sp. Holotype.AM W.196660.A, anterior end, dorsal view. B, midbody parapodium. C, falcigers, anterior parapodium. D, falcigers, midbody parapodium. E, falcigers, posterior parapodium. F, dorsal simple chaeta, midbody parapodium. G, dorsal simple chaeta, posterior parapodium. H, ventral simple chaeta. I, aciculae, anterior parapodium. J, aciculae, midbody parapodium. K, acicula, posterior parapodium. Scale. A: 0.2 mm. B: 50 µm. C–K: 20 µm.