Subfamily
Syllinae
Syllinae is one of the most diverse subfamilies of Syllidae (16 genera and more than 200 species), so it is not surprising that it presents a wide variety of morphologies.
DIAGNOSIS
Syllis prolifera is a species that varies in size from 10 to 15 mm (48 to 60 segments). His head has 2 prominent palps, longer than the prostomium, and 4 eyes arranged in the shape of a trapezoid. Its 3 antennae are, like the rest of its appendages (cirri), thin and elongated, with a large number of segments (15 or more). Its tentacle segment (the first one found right after the protomium) is narrower than the rest. Its followed by a pharynx and a proventricle of similar size. At the end, it presents a pygidium with two long anal cirri (Fig. 1A). Its compound chaetae are bidentate, with teeth of similar length and medium-sized spines, never exceeding the length of the teeth and directed slightly upwards (Figs. 1B, 1C, 1D). It also presents simple chaetae, also bidentate and with spines (Fig. 1E). Its aciculae are small and with a rounded tip. They are usually located on the anterior parapods (Fig. 1F).
Figure 1. Syllis prolifera: A) Dorsal anterior view; B) Anterior compound chaetae; C) Medium compound chaetae; D) posterior compound chaetae; E) Simple chaetae; F) Aciculae;. Scale: A, 0.8mm; B–G, 44.5 µm. Original work
VARIABILITY
The bodies vary from smooth to tuberculous (Fig. 2A), with variable lengths and widths. The coloration can be either uniform or banded, or even in the shape of a horizontal 8 figure (Fig. 2B). They may not present compound chaetae, and if they do, they can be hook-shaped (Fig. 2C), unidentate (Fig. 2D), or bidentate, with short or medium spines, although in some species they exceed the size of the teeth. These usually have the same length or exceed the distal to the proximal length, although there are also exceptions. The chaetae vary from short to long. Simple chaetae can be smooth and pointed or low-cut (Fig. 2E), uni or bidentate, and with or without spines (Fig. 2F). There are also chaetae with basal spurs (Fig. 2G). The needles have curved (Fig. 2H), rounded, pointed (Fig. 2I) or widened (Fig. 2J) tips.
Figure 2. Detail of the variabilities of the Syllinae family: A) Tubercular body; B) Coloration in horizontal 8 pattern; C) Hook-shaped compound chaetae; D) Unidentate compund chaetae; E) Simple low-cut chaetae; F) Simple unidentate chaetae; G) Simple bidentate chaetae, with a basal spur; H) Aciculae with curved tip; I) Aciculae with rounded and pointed tips; J) Widened and pointed aciculae. (1)
Syllinae colour image © Hans Hillewaert, Institute for Agricultural and Fisheries Research, 2015.
(1) San Martín, G. (2003). Museo Nacional de Ciencias Naturales, CSIC, 21.