Phalacrophorus uniformis Reibisch 1895

Phalacrophorus uniformis Reibisch, 1895

(Figs 3–5)

Iospilopsis antillensis Augener, 1922:41.

Phalacrophorus attenuatus Treadwell, 1943:34.

Phalacrophorus uniformis Reibisch, 1895:15 –16; Ehlers 1913:460; Fauvel 1916:53; 1923:196; 1939: 277; Hartman 1956:276; Dales 1957 a:108; 1060: 483; Tebble 1962: 426 –428; Dales 1963: 502; Berkeley & Berkeley 1964:123; Day 1967:171; Dales & Peter 1972: 62; Orensanz & Ramírez 1973:33 –34; Fernández­Álamo 1983: 151 –154; Nuñez et al. 1992: 102 –103; Fernández­Álamo & Thuesen 1999: 615.

Material examined

Five specimens, CARIBE I, sta. A, 19° 13’ 05” N; 87° 23’ 04” W, February 11 1991, 22:05 h, 50 m, ECO­CH­Z­02885; 3 specimens, CARIBE I, sta. B, 19° 33´04”N; 87° 17’ 04” W, February 12 1991, 00:02 h, 50 m, ECO­CH­Z­02886; 4 specimens, CARIBE I, sta. 5, 21 ° 10’ 05” N; 86° 46’ 01” W, February 6 1991, 50 m, ECO­CH­Z­02887; 15 specimens, CARIBE I, sta. 10, 20 ° 33’ 00” N; 87° 00´00”W, February 12 1991, 06:30 h, 50 m, ECO­CH­Z­02888; 3 specimens, CARIBE I, sta.11, 20 ° 23’ 00” N; 87° 09’ 00” W, February 7 1991, 06:05 h, 50 m, ECO­CH­Z­02889; 1 specimen, CARIBE I, sta. 12, 20 ° 08’ 01”N; 86° 57’ 00”W, February 12 1991, 08:27 h, 50 m; 2 specimens, CARIBE I, sta. 15, 19 ° 34’ 03”N; 87° 20’ 04”W, February 11 1991, 05:50 h, 50 m; 13 specimens, CARIBE I, sta. 21, 18 ° 29’ 05”N; 87° 36’ 00”W, February 11 1991, 22:05 h, 50 m, ECO­ CH­Z­02890; 6 specimens, CARIBE II, sta. 7, 20 ° 41’ 00”N; 86° 16’ 00”W, March 6 1991, 00:24 h, 50 m, ECO­CH­Z­02891; 5 specimens, CARIBE II, sta. 13, 19 ° 52’ 00”N; 86° 45’ 07”W, March 6 1991, 17:19 h, 50 m, ECO­CH­Z­02892; 3 specimens, CARIBE II, sta. 14, 19 ° 44’ 01”N; 87° 02’ 07”W, March 6 1991, 20:04 h, 50 m; 1 specimen, CARIBE II, sta. 15, 19 ° 34’ 05”N; 87° 20’ 08”W, March 8 1991, 22:43 h, 50 m; 2 specimens, CARIBE II, sta 16, 19 ° 19’ 02”N; 87° 06’ 00”W, March 7 1991, 17:33 h, 50 m, ECO­CH­ Z­02893; 1 specimen, CARIBE II, sta. 18, 18 ° 54’ 08”N; 87° 11’ 06”W, March 7 1991, 11:31 h, 50 m, ECO­CH­Z­02894; 1 specimen, CARIBE III, sta. 1, 21 ° 33’ 07”N; 86° 46’ 30”W, May 7 1991, 06:29 h, 50 m, ECO­CH­Z­02895; 1 specimen, CARIBE III, sta. 2, 21 ° 31’ 02”N; 86° 29’ 01”W, May 7 1991, 08:43 h, 50 m; 1 specimen, CARIBE III, sta. 3, 21 ° 29’ 03”N; 86° 11’ 00”W, May 7 1991, 11:12 h, 50 m; 1 specimen, CARIBE III, sta. 5, 21 ° 10’ 05”N; 86° 46’ 01”W, May 7 1991, 19:42 h, 50 m; 1 specimen, CARIBE III, sta. 15, 19 ° 34’ 03” N; 87° 20’ 04”W, May 8 1991, 18:27 h, 50 m; 1 specimen, CARIBE III, sta. 16, 19 ° 19’ 01”N; 87° 16’ 00”W, May 8 1991, 22:33 h, 50 m; 1 specimen, CARIBE III, sta.18, 18 ° 54’ 04”N; 87° 11’ 03”W, May 9 1991, 20:25 h, 50 m; 3 specimens, CARIBE IV, sta. 5, 21 ° 10’ 09”N; 86° 46’ 02”W, August 6 1991, 07:45 h, 50 m, ECO­ CH­Z­02896; 3 specimens, CARIBE IV, sta. 6, 20 ° 57’ 08”N; 86° 26’ 05”W, August 6 1991, 23:40 h, 50 m, ECO­CH­Z­02897; 1 specimen, CARIBE IV, sta. 10, 20 ° 33’ 00”N; 87° 00’ 00”W, August 8 1991, 23:22 h, 50 m; 1 specimen, CARIBE IV, sta. 11, 20 ° 23’ 00”N; 87° 09’ 00”W, August 8 1991, 21:50 h, 50 m, ECO­CH­Z­02898; 1 specimen, CARIBE IV, sta. 16, 19 ° 19’ 02”N; 87° 06’ 00”W; August 7 1991, 20:32 h, 50 m, ECO­ CH­Z­02899; 1 specimen, CARIBE IV, sta. 17, 19 ° 04’ 00”N; 86° 51’ 00”W, August 7 1991, 23:40 h, 50 m.

Diagnosis

Body cylindrical (Fig. 3B), prostomium with anterior area provided with two heavily pigmented oval spots; eyes relatively small, dorsal; in some specimens with crystalline. Palps small, rudimentary, subtriangular on ventral surface over the mouth (sometimes not easily observable). Pharynx with large, falcate mandibles (Fig. 3A), inserted on thick muscle band, with set of dorsal and marginal papillae. First two segments apparently fused, with two pairs of digitiform tentacular cirri, dorsal cirri smaller than ventral ones, latter twice as long and bearing setae. Segments with thin ciliated bands near parapodia (Fig. 3C); rows of cilia present also on setal lobes (Fig. 3E). Third and fourth segments reduced, with single setal lobe bearing one or two short setae, cirri absent. Segments 5–10 with parapodia complete but reduced in size, bearing few setae. Suceeding segments carry globose dorsal cirri attached to conical setal lobe with acicula, a digitiform appendage, and long setae (Fig. 3D). Ventral cirri globose, smaller than dorsal cirri, also attached to setal lobe. Chromatophore distribution pattern is not consistent; pigmentation is faint in some specimens, other specimens with intense pigmentation. In general, chromatophores concentrate on dorsal bases of parapodia (Fig. 3F), but some have chromatophores on ventral surface as well. Pygidium lightly or intensely pigmented, rounded or plate­shaped, medial margin ciliated.

Remarks

The longest complete specimen measured 4 mm, with 43 setigers, although most of the individuals examined were incomplete. Specimens from South Africa (Day, 1967), the west Atlantic (Treadwell, 1943), and the southwest Atlantic (Orensanz & Ramírez, 1973) are noticeably larger, measuring 10–15 mm, with 40–60 setigers. The sizes recorded in the Caribbean specimens are more similar to those found by Tebble (1962), and Fernández­ Álamo (1983) in the Pacific Ocean (2–7 mm, 26–60 setigers).

The presence of a crystalline in the eyes was difficult to evaluate fully in the Caribbean specimens; it was clearly present in some specimens but in others these structures may be hidden by the peristomium. Tebble (1962) mentioned eye spots only, but no crystallines; Treadwell (1943) reported brown eyes and spots along the anterior margin. Orensanz and Ramírez (1973) mentioned the presence of a true crystalline in this species.

Palps were not observed in most Caribbean specimens, but these appendages are clearly visible in one specimen (vertical arrow in Fig. 3C); Fernández­Álamo (1983) reported these structures in a single individual of P. u n i f o r m i s, and Orensanz and Ramírez (1973) did not comment on them. This character was not included in the generic diagnosis. The size of the mandibles is variable in the Caribbean specimens; Orensanz and Ramírez (1973) observed this variability in P. pictus, but not in P. uniformis.

Some specimens of P. uniformis had gametes arranged in various patterns. In some females all the body is full of gametes, starting from setiger 13 backwards (Fig. 4B). The number of visible ova per segment is 20–30 by setiger 13, 42–45 by setiger 18, and up to 58–62 by setiger 24. Ova size varied too, since they were 10–18 µm in setigers 13–18, and 25–37 µm by setiger 24. Thus, the larger and more abundant ova posteriorly indicates that these setigers mature first. Other specimens showed a more uniform pattern concentrating the gametes along and in the coelom, but also starting from setiger 13.

Some specimens designated as females by having eggs, had large, lateral sac­like structures full of gametes from setiger 13 (Fig. 4B). These are presumed to be brooding pouches; each sac was placed between the parapodia and continued over more than a single segment. The remaining parts of the body bear smaller gametes. Female specimens have also enlarged segments in the middle part of the body, this was observed between segments 30 and 33 (Fig. 4C); these segments also contain ova. The histological sections of these segments in females show large nucleii, suggesting that these gametes are ova; swellings in ova­bearing segments at more advanced stages of development tend to be larger than processes with none or young ova. Another modification observed is the occurrence of ventral processes in segments 14–15 and 23–25 that appear as a thick, inwardly folded tissue in preserved specimens (Fig. 4A).

We observed a different morphological pattern in the specimens we designated as males. In these, the sac­like structures are noticeably smaller (Figs 5A, B), gametes, probably spermatic masses, are fewer and larger than in females (50–60 µm) and are located at segments 18–28; no female showed such pattern. Elongated segments and ventral infolds are absent in males (Figs 5A, B). A single male beared two paired processes on segments 18 and 19, probably nephridial structures functioning as seminal vesicles (Fig. 5B).

This was the commonest iospilid in the northwest Caribbean, it occurred in all cruises. It was most abundant during February, with a mean density of 43.5 org./ 1000 m 3, followed by March (11.7), August (10.6), and May (6.7). Its local distribution included both oceanic and coastal areas. The species was slightly more abundant in night samples, 54% of the specimens were caught at nighttime.

Type locality

North Atlantic. No types were designated by the species author.

Distribution

Atlantic Ocean, Pacific Ocean, Indian Ocean. This is the first record of this species in the Caribbean Sea. It was widely distributed in the surveyed area, mostly in oceanic zones, but some specimens were found quite near to the coast (Fig. 2).