Polycirrus decipiens ( Gravier, 1905 )

Glasby, Christopher J. & Hutchings, Pat, 2014, Revision of the taxonomy of Polycirrus Grube, 1850 (Annelida: Terebellida: Polycirridae), Zootaxa 3877 (1), pp. 1-117 : 43-45

Polycirrus decipiens ( Gravier, 1905)

Figs 20a–c ; 21a–e

Anisocirrus decipiens Gravier, 1905: 437–441 .— 1906: 225–232, text figs 400–404, pl. V, figs 234–238.

Type locality. Gulf of Aden .

Material examined. SYNTYPES MNHN POLY TYPE 427 , 428 , several specimens collected from muddy sands west of the Residence at Djibouti, Gulf of Aden .

Description. Several specimens in good condition, two specimens illustrated (one with and one without buccal tentacles), both about 2 mm maximum width and 11 mm long without buccal tentacles. Body colouration when preserved yellowish brown, not transparent.

Dorsum anteriorly weakly tessellated ( Fig. 20b ). Venter anteriorly with mid-ventral groove and discrete ventro-lateral pads; pads deeply tessellated, extending from segment 3 to 12. Mid-ventral groove from segment 2 ( Fig. 20a,c ).

Buccal tentacles of three types, (1) leaf-shaped, deeply furrowed, (2) cylindrical, thickened distally and distinctly grooved and (3) cylindrical, uniformly thin and weakly grooved, all arising at junction between prostomium and upper lip ( Fig. 20a ). Prostomial ridge distinctly curved, extending laterally along anterodorsal base of upper lip. Upper lip trefoiled with lateral, blindly ending, enclosed diverticulae, margin of medial lobe thickened and overturned; oral surface glandular and ciliated. Inner lower lip oblong, smooth; outer region flat, shield-like, oblong, wider than long, tessellated, extending posteriorly to segment 2. Achaetous segments only visible ventrally, obscured by prostomial ridge dorsally.

Notochaetigerous segments 13, extending to segment 15. Notopodia more-or-less rectangular, distally flared, lobes triangular, postchaetal lobe longer ( Figs 20b, c , 21a ). Notochaetae within a chaetiger of two types, smooth, narrowly winged, uniformly tapered, posteriorly same form as those anteriorly; secondary notochaetae in all chaetigers pinnate ( Fig. 21b, c ). Neurochaetae beginning on segment 16, 28–30 uncini per row. Neuropodial tori ridge like, similar along body. Uncini have a short neck and straight to convex base (Type 1), teeth above main fang arranged in single vertical series (four teeth including main fang), subrostral process present as low protuberance ( Fig. 21d–e ).

Nephridial papillae present, cylindrical. Pre-gular membrane nephridial papillae absent. Post-gular membrane nephridial papillae present, extending from segment 5 to 10; situated at ventral base of notopodia. Pygidium smooth ring.

Comments. Gravier (1905) described this species from specimens collected at several localities in the Gulf of Aden including the Golfe de Tadjourah, from reefs off Pingouin and Météore, Iles Musha, and intertidally at La Résidence à Djibouti. Although Gravier (1905, 1906) provides an extensive description of the species, some key character information is missing. For example, he does not mention the presence of smooth chaetae in addition to the pinnate types and the first segment bearing neurochaetae is not stated. We have recorded this information from the syntypes. Other points of difference between the present description and that of the type description is that Gravier reports 14 chaetigerous segments (compared to 13 observed here) and nephridial papillae extending to chaetiger 12 (segment 14), but they were observed to extend only to segment 10 on the specimen we examined.

Hartman (1959) considered that P. decipiens Gravier, 1905 was a junior synonym of P. coccineus ; however, this view is incorrect because the two species have different uncini: P. decipiens has Type 1 uncini with teeth arranged in a single vertical series, whereas P. coccineus has Type 2 uncini arranged in a double transverse series.

Figures

FIGURE 20. Polycirrus decipiens (Gravier). Syntypes MNHN POLY TYPES 427, 428. A. Type 428, whole body, lateral view. B. Type 427, anterior end, dorsal view. C. Type 427, anterior end, ventral view.

FIGURE 21. Polycirrus decipiens (Gravier). Syntypes MNHN POLY TYPE 427. A, parapodium, chaetiger 4, x10 objective. B, parapodium, chaetiger 4, x40 objective. C. chaetae of chaetiger 10, x20 objective. D, uncini, posterior body, lateral view. E, uncini, posterior body, frontal view.