Prionospio steenstrupi Malmgren, 1867: 201 –202, pl. 10, fig. 55; Söderström 1920: 232 –233, figs. 136, 138, 140; Fauvel 1927: 60, fig. 21 f–i; Day 1967: 489, fig. 18.9 o–r; Hartman 1969: 165 –166, figs. 1–2; Foster 1971: 84 –87, figs. 175– 178; Blake & Kudenov 1978: 213, fig. 20 a; Sigvaldadóttir & Mackie 1993: 204 –207, figs. 1–2; Sigvaldadóttir 1996: 17, fig. 7.
Prionospio (Prionospio) steenstrupi: Light 1978: 88 –92, figs. 89–90; Johnson 1984: 47 –49, figs. 37, 38; Maciolek 1985: 332 –335, fig. 1; Blake 1996: 123 –125, fig. 9; Hartman-Schröder 1996: 327 –328, fig. 148.
Material examined. ESFM –POL/05– 3197, 6 specimens, 10 September 2005, Iskenderun Bay, G 5, 36 º 43 ΄ 44 ΄΄N, 35 º 43 ΄ 39 ΄΄E, 23 m, muddy sand; ESFM –POL/05– 3199, 1 specimen, 14 September 2005, Iskenderun Bay, K 9, 36 º 54 ΄ 22 ΄΄N, 35 º 58 ΄0 5 ΄΄E, 1 m, sand, rocky; ESFM –POL/05– 3198, 2 specimens, 17 September 2005, Mersin Bay, G 7, 36 º 46 ΄ 41 ΄΄N, 34 º 39 ΄ 39 ΄΄E, 10 m, mud; ESFM –POL/05– 3200, 1 specimen, 21 September 2005, Aydincik Bay, K 24, 36 º09΄ 11 ΄΄N, 33 º 20 ΄ 33 ΄΄E, 1 m, sand; ESFM –POL/05– 1875, 14 specimens, 0 6 October 2005, Fethiye Bay, G 32, 36 º 38 ΄ 42 ΄΄N, 29 º03΄ 18 ΄΄E, 100 m, mud; ESFM –POL/05– 1912, 42 specimens, 0 6 October 2005, Fethiye Bay, G 30, 36 º 39 ΄ 24 ΄΄N, 29 º04΄ 44 ΄΄E, 50 m, sandy mud; ESFM –POL/ 05– 1994, 41 specimens, 0 6 October 2005, Fethiye Bay, G 31, 36 º 38 ΄ 56 ΄΄N, 29 º03΄ 38 ΄΄E, 75 m, muddy sand.
Diagnosis. Largest specimen incomplete, 0.41 mm wide, 6.7 mm long, with 61 chaetigers. Color in alcohol opaque white to pale yellow. Prostomium subtriangular, truncated on anterior margin, extending posteriorly as a narrow caruncle to anterior margin of chaetiger 2. Two pairs of small indistinct subdermal eyes; anterior pair single eyespots, posterior pair larger than anterior. Four pairs of branchiae on chaetigers 2– 5; first and fourth pairs with dense digitiform pinnules, of equal size; second and third pairs apinnate, equal in length, subtriangular, shorter than pinnate pairs, with densely ciliated sides and sharply pointed tip. Notopodial lamellae foliaceous, largest in branchial region; following notopodial lamellae subtriangular, progressively decreasing in size and becoming more rounded in posterior region. Notopodial lamellae united across dorsum, forming low crests from chaetiger 7–18; dorsal crests initially conspicuous, slightly higher on chaetiger 7, gradually decreasing thereafter. Dorsal skin folds between chaetigers 5–12. Neuropodial lamellae on chaetiger 2 subtriangular and ventrally pointed; largest in branchial region; gradually decreasing in size on following chaetigers. Ventral sabre chaeta first present on chaetiger 10, numbering 1–2 per fascicle. Multidentate hooded hooks first appearing on neuropodia of chaetigers 14–16, on notopodia of chaetigers 38– 40.
Remarks. Prionospio (P.) steenstrupi has been reported from many areas in the world oceans (Foster 1971; Light 1978; Blake & Kudenov 1978; Hartman 1969; Johnson 1984; Maciolek 1985). According to Sigvaldadóttir & Mackie (1993), the distribution of P. (P.) steenstrupi is limited to the coast of Iceland and reports of this species from other regions are dubious. Blake (1996) reported that the distribution of this species includes the Arctic, Atlantic, and eastern Pacific Oceans. This species was also previously reported from the Mediterranean Sea (Fauvel 1927; Tebble 1959; Ben-Eliahu 1995; Simboura & Nicolaidou 2001; Çinar 2005). The comparion of the specimens collected during this study with the original and subsequent descriptions of this species indicated that P. (P.) steenstrupi occurs in the Mediterranean, at least in the eastern Mediterranean.
Ecology. The highest population density (420 individuals.m - 2) of this species was found on sandy mud substratum at 50 m depth at station G 30 (Fethiye Bay).
Distribution. Atlantic Ocean, Pacific Ocean, Arctic Ocean (Blake 1996); Indian Ocean (Johnson 1984); Iceland (Sigvaldadóttir & Mackie 1993); Mediterranean Sea (Tebble 1959; Ergen 1992); 0.3– 2700 m.