Trypanosyllis microdenticulata, Salcedo, Diana L., Martín, Guillermo San & Solís-Weiss, Vivianne, 2011

Salcedo, Diana L., Martín, Guillermo San & Solís-Weiss, Vivianne, 2011, Two new species of Syllidae (Annelida: Polychaeta) from the Southern Mexican Pacific, Zootaxa 2800, pp. 41-52 : 46-51

publication ID	https://doi.org/ 10.5281/zenodo.201624
DOI	https://doi.org/10.5281/zenodo.6183566
persistent identifier	https://treatment.plazi.org/id/BE47E558-FFDD-FFE9-5ED5-CCE1FB0BF3F4
treatment provided by	Plazi
scientific name	Trypanosyllis microdenticulata
status	sp. nov.

Treatment

Trypanosyllis microdenticulata View in CoL n. sp.

( Figs. 3 View FIGURE 3 A–B, 4A–G, 5A–F, 6A–D)

Material examined. Holotype: complete specimen (CPICML POH–37–003), El Jardín E3B1, 16°49.436’N and 99°54.981’W, 26 May 2006, 12 m, coarse sand. Paratypes: 9 specimens (CPICML POP-37-004) El Jardín E3B1, 16°49.436’N and 99°54.981’W, 26 May 2006, 12 m, coarse sand. 6 specimens ( MNCN 16.01/13263), Palmitas E2B2 16°49.420’N, 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. 6 specimens (LACM-AHF POLY 2640), El Jardín E3B2, 16°49.436’N and 99°54.981’W, 26 May 2006, 12 m, coarse sand. 6 specimens (AM: W.37087), Palmitas E2B1, 16°49.420’N and 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. Additional material. 2 specimens (CPICML PO–37–080), Palmitas E2B1, 16°49.420’N and 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. 7 specimens (CPICML PO–37–080), Palmitas E2B2 16°49.420’N, 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. 4 specimens (CPICML PO–37– 080), El Jardín E3B2, 16°49.436’N, 99°54.981’W, 26 May 2006, 12 m, coarse sand. 1 specimen (CPICML PO–37–080), Caleta E1B2, 16°49.797’N, 99°54.062’W, 25 May 2006, 12 m, coarse sand.

Comparative material examined. Trypanosyllis coeliaca : 4 specimens ( MNCN 16.01/6860). Spain: Mediterranean Sea, Columbrete Is., N of Columbrete Grande, 47 m. Trypanosyllis coeliaca : 3 specimens ( MNCN 16.01/ 6863). Spain: Cantabric Sea, “El Cachucho”, Asturias.

Description. Holotype complete specimen 6 mm long, 0.62 mm wide, with 66 chaetigers. Longest complete specimen 9.5 mm long, 0.72 mm wide, with 88 chaetigers. Body dorsoventrally flattened, colourless when preserved. Two dorsal transverse ciliated bands on each segment, visible under SEM: one with small tufts of cilia at midlength ( Fig. 5 View FIGURE 5 C, indicated by superior arrow), the other continuous, close to anterior margin ( Fig. 5 View FIGURE 5 C, indicated by inferior arrow). Additional small ciliated bands on parapodial lobes ( Fig. 5 View FIGURE 5 D, indicated by arrow) as well as on dorsal cirri and bases of lateral antennae ( Fig. 5 View FIGURE 5 A, indicated by inferior arrow). Prostomium oval to trapezoidal, wider than long, dorsally bilobed, with two pairs of eyes in trapezoidal arrangement, close to each other, anterior pair ventral and posterior pair dorsal; one pair of ventral eyespots (lacking in a few paratypes), close to anterior prostomial margin ( Figs. 3 View FIGURE 3 A, 3B).

Palps short, ovate, about half as long as prostomium, completely separated ( Figs. 3 View FIGURE 3 B, 5B). Antennae short, inserted on anterior prostomial margin; median antenna slightly longer than combined length of prostomium and palps, with 12 articles (13 in some paratypes); lateral ones shorter, with 10 articles ( Figs. 3 View FIGURE 3 A, 5A). Two nuchal organs as postero-lateral rows of cilia, one around each prostomial lobe ( Fig. 5 View FIGURE 5 A, indicated by superior arrow). Peristomium well defined, shorter than following segments, with two pairs of tentacular cirri; dorsal one similar to median antennae, with 14–15 articles; ventral one shorter, with 8 articles. Dorsal cirri short, thick, shorter than body width, slightly tapering distally, containing fibrillar material in each article, originating on short ceratophores ( Figs. 3 View FIGURE 3 A, 5A); longer on anterior segments, alternating long (14–18 articles) and short (10–11 articles) in midbody and posterior chaetigers, alternating long (13–14 articles) and short (9–10 articles). Ventral cirri short, digitiform to conical, similar in size or slightly shorter than parapodial lobes. Parapodial lobes conical ( Fig. 5 View FIGURE 5 D). About 13–15 heterogomph compound chaetae per parapodium, with thick shafts and bidentate blades, having short and coarse spines on margin; both teeth similar in size on anterior falcigers, subdistal tooth smaller than distal one on median and posterior chaetae ( Figs. 4 View FIGURE 4 A, 4C, 4E). Marked dorso-ventral and antero-posterior gradation in blade length; anterior chaetae elongated, with slender blades (10.7–16.8 μm) ( Figs. 4 View FIGURE 4 A, 5E), becoming shorter and thicker posteriorly (10–13.6 μm length) ( Figs. 4 View FIGURE 4 C, 4E, 5F). Dorsal and ventral simple chaetae only in most posterior chaetigers; dorsal one slender, smooth, bidentate, with subdistal tooth smaller ( Figs. 4 View FIGURE 4 G, 6A); ventral simple chaeta similar to dorsal one, but with short spines on subdistal margin (Fig. 6B). Two, sometimes three aciculae in anterior parapodia (one larger and thicker) ( Figs. 4 View FIGURE 4 B, 5D), and a single acicula in midbody and posterior parapodia ( Figs. 4 View FIGURE 4 D, 4F), all stout, straight, acute, protruding from parapodial lobes. Pharynx long, through nine segments ( Fig. 3 View FIGURE 3 A),(variation in type material is from 7 to 9), with a crown of ten soft papillae, surrounded by sinuous glands ( Fig. 3 View FIGURE 3 A, indicated by arrow) and dark ovate glands inserted between the folds of latter ( Fig. 3 View FIGURE 3 A, indicated by arrow). Pharyngeal tooth conical, small and thin, trepan with 10 small, short and transparent teeth, very difficult to distinguish in some specimens (Fig. 6C, indicated by arrow). Proventricle short, extending through 4 segments (variation among paratypes from 3 to 6), with 19 muscle cell rows ( Fig. 3 View FIGURE 3 A) (variation among paratypes from 17 to 21). Pygidium with two anal cirri, similar in length to dorsal ones at midbody, with 7 articles (or 8 in some paratypes).

Remarks. This species is characterized by having the anterior pair of eyes in ventral position and the posterior one dorsally, as well as by having bidentate compound chaetae and a small trepan with transparent teeth. The genus Trypanosyllis currently has more than 20 valid species ( Çinar 2007; Nogueira & Fukuda 2008). Of these, only T. parvidentata Perkins, 1981 and T. coeliaca Claparède, 1868 resemble T. microdenticulata n. sp. All three have small trepans, sinuous glands surrounding the pharynx, and antennae, dorsal cirri, pharynx and proventricle similar in size.

However, unlike T. microdenticulata n. sp., the other two species have two pairs of eyes in dorsal position. Additionally, T. parvidentata has a solitary acicula throughout the body. Unlike T. microdenticulata n. sp., the anterior falcigers of T. coeliaca have slender and longer blades and longer spines on distal margin, while T. parvidentata has longer falcigers with both teeth similar in size (in T. microdenticulata n. sp., the subdistal tooth is smaller in most falcigers). Trypanosyllis zebra ( Grube, 1860) is one of the most common littoral syllids, even in the Mexican Pacific, and is indeed similar to T. microdenticulata n. sp., but the former has a distinctive colour pattern, as well as much longer antennae and dorsal cirri. Furthermore, the pharynx in T. zebra is proportionally shorter and the proventricle is longer, and the species lacks the dorsal transverse ciliated bands.

Most specimens were dissected and their pharynx examined. All had a small and thin pharyngeal tooth, very difficult to distinguish, and a trepan with about 10 very small and transparent teeth. Even after dissection of the pharynx, the trepan is very difficult to observe in most of the specimens, since sometimes the teeth are shorter than the length of the papillae and also because of its colour and texture, it can be easily confused with pharyngeal tissues. This could be due to the fact that the teeth of the trepan are made up of soft and fibrous tissues when they begin to develop in young organisms (Fig. 6C, indicated by arrow), becoming larger and rigid structures in adults (Fig. 6D). Therefore, such a structure can be overlooked and assumed to be absent in some specimens depending on their stage of development and it could also be lost accidentally (San Martín 2003). However, after careful examination of a large number of specimens, it was concluded that all have a trepan, even small individuals although they may be minute and difficult to see.

In some species such as T. zebra , the presence of a pharyngeal tooth seems to be size-dependent, as mid-sized and large specimens lack one ( San Martín 1984, 2003; San Martín et al 2008). Nonetheless, in T. microdenticulata n. sp. the pharyngeal tooth is always present, while the only size-related differences is trepan teeth. The trepan is a diagnostic character of the genus (San Martín 2003), and it is considered homoplasic, so that it should be used with care to differentiate lower taxa ( Aguado & San Martín 2009).

6. SEM of Trypanosyllis microdenticulata n. sp. (A) Dorsal simple chaeta. (B) Ventral simple chaeta. (C) Everted pharynx, small specimen (Arrow: soft teeth). (D) Hard teeth, larger specimen. Scale: (A) 2 µm. (B) 1 µm. (C) 10 µm. (D) 20 µm.

Habitat. Subtidal coarse sand, 10.5 to 12 m depth.

Distribution. Western coast of Acapulco Bay, Southern Mexican Pacific. Etymology. The specific name refers to the small size of the teeth belonging to the trepan.