Prionospio (Prionospio) depauperata Imajima 1990

Prionospio (Prionospio) depauperata Imajima, 1990

Figure 2

Prionospio (Prionospio) depauperata Imajima, 1990a:114 –118, figs. 6–7.

Material examined. ESFM –POL/05–273, 3 specimens, 9 September 2005, Iskenderun Bay, G2, 36º43΄19΄΄N, 36º09΄30΄΄E, 50 m, sandy mud; ESFM –POL/05–677, 8 specimens, 9 September 2005, Iskenderun Bay, D5, 36º43΄0 3΄΄N, 36º11΄28΄΄E, 11 m, gravel; ESFM –POL/05–3188, 2 specimens, 9 September 2005, Iskenderun Bay, G1, 36º35΄37΄΄N, 36º11΄0 9΄΄E, 8m, mud; ESFM –POL/05–3190, 7 specimens, 9 September 2005, Iskenderun Bay, G3, 36º51΄0 8΄΄N, 35º55΄42΄΄E, 25 m, mud; ESFM –POL/05–16, 29 specimens, 10 September 2005, Iskenderun Bay, D12, 36º43΄37΄΄N, 35º42΄44΄΄E, 9 m, muddy sand; ESFM –POL/05–302, 4 specimens, 10 September 2005, Iskenderun Bay, D14, 36º32΄51΄΄N, 35º34΄37΄΄E, 25 m, mud; ESFM –POL/05–380, 57 specimens, 10 September 2005, Iskenderun Bay, G5, 36º43΄44΄΄N, 35º43΄39΄΄E, 23 m, muddy sand; ESFM – POL/05–596, 16 specimens, 10 September 2005, Iskenderun Bay, D11, 36º46΄0 0΄΄E, 35º47΄45΄΄E, 10 m, mud; ESFM –POL/05–3191, 6 specimens, 10 September 2005, Iskenderun Bay, G4, 36º44΄0 9΄΄N, 35º44΄32΄΄E, 50 m, mud; ESFM –POL/05–3189, 4 specimens, 17 September 2005, Mersin Bay, G7, 36º46΄41΄΄N, 34º39΄39΄΄E, 10 m, mud; ESFM –POL/05–3208, 2 specimens, 17 September 2005, Mersin Bay, G8, 36º44΄22΄΄N, 34º39΄0 2΄΄E, 25 m, mud; ESFM –POL/05–861, 21 specimens, 23 September 2005, Mersin Bay, D28, 36º03΄37ʺN, 32º53΄11΄΄E, 25 m, muddy sand.

Description. All specimens incomplete, largest specimen 10.7 mm long, 0.39 mm wide, with 54 chaetigers. Body slender, enlarged anteriorly, gradually tapering to posterior end, pale yellow. Prostomium subrectangular, truncate on anterior margin, extending posteriorly as a narrow caruncle to anterior margin of chaetiger 2, with small median peak (Fig. 2 A). Two pairs of black eyes; anterior pair as single eyespots; posterior pair larger, crescent-shaped. Peristomium fused dorsally with chaetiger 1, forming low lateral wings (Fig. 2 A).

Four pairs of branchiae on chaetigers 2–5; first and fourth pairs with dense digitiform pinnules. First pair of branchiae extending back to chaetiger 5, with pinnules arranged on posterior face, extending nearly to tip of branchia (Fig. 2 A–B). Pinnules on fourth pair of branchiae present solely on basal part, distal tips naked. Second and third pairs apinnate, equal in length, subtriangular, shorter than pinnate pairs, slightly longer than notopodial lamellae; with densely ciliated sides and sharply pointed tip (Fig. 2 A–B).

Parapodia of chaetiger 1 with lanceolate notopodial lamellae and smaller, squarish neuropodial lamellae (Fig. 2 B); noto- and neurochaetae present. Chaetiger 2 with erect, triangular notopodial postsetal lamellae, and neuropodial lamellae of chaetiger 2 small, subtriangular and ventrally pointed. Notopodial lamellae on chaetiger 4 large, triangular, with pointed tips, slightly folded anteriorly; neuropodial lamellae subrectangular. Following notopodial lamellae large; V–shaped on chaetigers 5 and 6. Notopodial lamellae united across dorsum, forming low crests from chaetiger 7 to 16. Dorsal crests initially conspicuous, slightly higher on chaetiger 7, gradually decreasing thereafter. Notopodial lamellae on median chaetigers low and broadly rounded, becoming elongate leaf-like lobes on posterior chaetigers. Neuropodial lamellae on chaetiger 3 earshaped, decreasing gradually in size, becoming more rounded on following chaetigers. Neuropodial lamellae on posterior chaetigers similar to notopodial lamellae.

Capillary notochaetae on anterior and middle chaetigers unilimbate, arranged in two rows; those of anterior row shorter, with wider sheaths than those of posterior row (Fig. 2 E). Both types of chaetae with granulations on distal half of shaft. Capillaries thinner in far posterior chaetigers. Ventral sabre chaetae usually from chaetiger 10, sometimes from chaetiger 11, numbering 1–2 per fascicle; each chaeta moderately granulated (Fig. 2 D). Neuropodial multidentate hooded hooks first present on chaetiger 16; numbering up to 8–9 per fascicle; 5–6 pairs of small teeth above main fang (Fig. 2 C). Notopodial multidentate hooded hooks first present from chaetiger 42, numbering up to 8 per fascicle. Hooks accompanied by capillaries throughout.

Pygidium missing on all specimens.

Remarks. Prionospio (P.) depauperata belongs to the Prionospio steenstrupi species group (Maciolek 1985), which is characterized by having pinnate branchiae on chaetigers 2 and 5 and apinnate branchiae on chaetigers 3 and 4. The Mediterranean specimens agree well with the original description of the species from the coast of Japan in the shape of the anterior margin of prostomium, eyes, branchiae, hooded hooks, and dorsal crests. However, some slight differences were observed. For example, notopodial hooded hooks first appeared on chaetigers 41 or 42 in the Mediterranean specimens, whereas they first occurred on chaetigers 45 or 47 in the Japanese specimens. The other differences between our specimens and Imajima’s specimens are: (1) the first branchiae extend back to chaetiger 5 in the Mediterranean specimens vs. chaetiger 7 in the Japanese specimens; (2) the prostomium has a small median peak in the Mediterranean specimens, whereas this structure was not noted in the Japanese specimens; and (3) dorsal crests are present from chaetigers 7 to 16 in our specimens vs. 7 to 13 in the Japanese specimens.

Prionospio (P.) depauperata is closely related to P. (P.) steenstrupi in morphological and chaetal appearances. Prionospio (P.) steenstrupi has two pairs of indistinct eyes, dorsal crests extending from chaetiger 6 to 15–20, and dorsolateral skin folds between chaetigers 4 and 9–13 (Sigvaldadóttir & Mackie 1993). Unlike P. (P.) steenstrupi, P. (P.) depauperata has large posterior eyes, dorsal crests extending from chaetigers 7 to 16 and no dorsolateral skin folds.

Maciolek (1985) regarded P. (P.) fallax Söderström 1920 as a synonym of P. (P.) steenstrupi. However, Sigvaldadóttir & Mackie (1993) re-established the validity of P. (P.) fallax. Prionospio (P.) fallax, originally described from Iceland, also appears to be closely related to P. (P.) depauperata. They are similar to each other in having an anteriorly truncated prostomium, distinct black eyes, and no dorsal skin folds. However, P. (P.) fallax differs from P. (P.) depauperata in having sparse digitiform pinnules on the first and fourth branchiae, a high dorsal crest only on chaetiger 7, and small, indistinct neuropodial prechaetal lamellae in the anterior region.

Ecology. The maximum population density (570 individuals.m -2) of this species was found on muddy sand substratum at 23 m depth at station G5 (Iskenderun Bay).

Distribution. This species was previously known only from the coast of Japan (Imajima 1990a); 8 to 920 m. It could have been introduced to the Mediterranean area by ballast waters of ships as the investigated area has large international harbors.