Polydora hoplura Claparede 1868

Polydora hoplura Claparède, 1868 Figures 2 & 3 Polydora hoplura Claparède, 1868: 318–319, pl. XXII, figure 2; 1869: 58–59, pl. XXII, fig. 2; 1870: 58–59, pl. XXII, fig. 2. Radashevsky et al. 2017: 545–551, figs 2–4 (references); 2023a: 7–9, fig. 4 (references). Adult diagnostic features. The adult morphology of P. hoplura from different countries, including the neotype and other individuals from the type locality in the Gulf of Naples, Italy, was described by various authors (e.g., Read 1975; Sato-Okoshi 1998; Radashevsky & Olivares 2005; Radashevsky et al. 2017, 2023a; Radashevsky & Migotto 2017; Sato-Okoshi et al. 2017; Almón et al. 2022). The diagnostic features of the adults include palps with black bands, prostomium weakly incised anteriorly, caruncle extending to the end of chaetiger 3, short occipital antenna, and two kinds of spines (heavy sickle-shaped and slender awl-like) in addition to slender capillary chaetae in the posterior postbranchiate notopodia (Fig. 2A, B). However, some characters are variable (see Radashevsky et al. 2023a). None of these characters is unique; all of them are shared by some other spionids. Nevertheless, the combination of these characters defines the species unambiguously, and the heavy sickle-shaped spines in the postbranchiate chaetigers are the most diagnostic (Radashevsky et al. 2023a). Gamete morphology. Of more than 1000 individuals studied (from newly settled 17-chaetiger to the largest 180-chaetiger) from Europe, Asia and North and South America, those whose length did not exceed 10 mm for 80 chaetigers were immature and had no gametes. Of the more than 800 mature individuals, only two were males, and all the others were females. In males, spermatogonia were about 10 µm in diameter. Spermatids, each about 5 µm in diameter, were interconnected in octads. Spermatozoa were introsperm less than 1 µm in diameter, with pointed acrosome about 1 µm, nucleus 7 µm, midpiece 10 µm, and flagellum 85 µm long. Females laid oocytes into transparent capsules which attached to the inner wall of the burrow. Recently laid capsules each contained up to five fertile eggs or early embryos 140−153 µm in diameter, and up to 55 oval nurse eggs 130–155x175–205 µm in diameter. Post-fixation pigmentation. The formalin-fixed specimens had paired patches or narrow transverse bands of dark ochre pigment on the dorsal side of 10–50 posterior branchiate chaetigers (Fig. 2B). Ochre pigmentation was absent on the postbranchiate chaetigers with heavy spines in notopodia (Fig. 2C). Methyl green staining. In total, 58 formalin-fixed specimens were stained with MG, including 30 specimens from Italy (MIMB 28148, 33028, 33029), 21 specimens from South Korea (MIMB 28076), and 7 specimens from New Zealand (MIMB 28150). Most of the specimens showed the same pattern of staining, including dense staining on the anterior part of the prostomium in front of eyes, dorsal side of the peristomium, antero-lateral and ventral sides of chaetigers 1–4, paired blotches (gatherings of stained cells) on the dorsal side of chaetigers 1–4, and from chaetigers 9–10 onwards (Fig. 3A–F). Narrow transverse bands were stained on the anterior and posterior edges on the ventral side from chaetiger 7 to chaetigers 20–50. Ventral side of the peristomium did not absorb the dye. Five of the 19 specimens from Taranto (Ionian Sea, Italy) had dense staining on the dorsal side from chaetigers 9–10 onwards and moderate staining on the ventral side from chaetiger 7, very weak staining on the prostomium and ventral side of chaetigers 1–4, and complete absence of staining on the dorsal side of chaetigers 1–4.