Subfamily
Exogoninae
Exogoninae has a smaller number of genera but a notable number of species (9 genera, approximately 185 species).
DIAGNOSIS
Exogone dispar has a relatively thick, uncolored body, short (between 2 and 4 mm, 20 to 40 segments), with a rounded prostomium, four large eyes arranged in a trapezium, separated two by two by 3 antennae, and two prominent palps, fused, with a joining suture. Its appendages are short, oval, and smooth (Fig. 1A). It has two types of compound chaetae, with an elongated blade ending in a fine point, and a short blade with the distal tooth more prominent than the proximal one (Figs. 1C, 1D, 1E, 1F). The spines do not exceed the length of the distal tooth. Likewise, its simple chaetae end in a rounded point, followed by a flank of short spines (Figs. 1B, 1G).
Figure 1. Exogone dispar: A) Dorsal anterior view; B) Anterior simple chaetae; C) Anterior compund chaetae with short blades; D) Anterior compound chaetae with a long blade; E) Medium compound chaetae with a long blade; F) Medium compound chateae with short blade; G) Medium simple chaetae. Scales: A, 0.18 mm; B–G, 20 µm. Original work
VARIABILITY
The bodies are usually thick and robust, with uniform coloration or with spots on the sides or longitudinal bands. They can be smooth or have papillae or warts. Its palps may be totally or partially fused, and its appendages are smooth and often short and oval, more elongated in some species. Their compound chaetae are highly variable (Figs. 2A, 2B). They can be uni or bidentate, with teeth of similar length or the distal one longer, with varying opening (Fig. 2C). Its simple chaetae can be smooth or with spines, uni or bidentate, and crowned by spines (Fig. 2D). The aciculae can be rounded, topped by spines, pointed, or curved (Fig. 2E). To access more figures on these morphologies, review other subfamilies.
Figure 2. Detail of the variability of the Exogoninae family: A) Modified compound chaetae; B) Compound spinigerous chaetae; C) Compound chaetae with the proximal tooth more prominent than the distal; D) Simple chaetae ending in a rounded tip crowned by thorns; E) Aciculae with curved edge. (1)
Exogoninae colour image © Arne Nygren, Maritime Museum and Aquarium - Göteborg, 2017.
(1) San Martín, G. (2003). Museo Nacional de Ciencias Naturales, CSIC, 21.