Phalacrophorus pictus Greeff 1879

Phalacrophorus pictus Greeff, 1879

(Fig. 2A–B)

Phalacrophorus borealis Reibisch 1895:15.

Phalacrophorus maculatus Treadwell 1943:34

Phalacrophorus pictus Greeff,1879:249; Viguier 1886:395; Reibisch 1895:10; Ehlers 1913:460; Fauvel 1916:52;1923:196; Augener 1929:290; Støp­Bowitz 1951:6; Hartman 1956:276; Dales 1957: 109; Uschakov 1957:274; Berkeley & Berkeley 1957:573, 1964:123;1960:789; Mileikovsky 1961: 1101; 1962: 1067; Tebble 1962:426 –427; Hartman 1964:65; Bhaud 1966:436; Guille & Laubier 1966:264; Day 1967:171; Dales & Peter 1972:62; Orensanz & Ramírez 1973:32 –33; Sun & Wu 1979:61; Fernández­Álamo 1983: 155 –157; Núñez et al. 1992:102; Fernández­Álamo & Thuesen 1999: 615.

Material examined

One specimen, CARIBE II, sta. 7, 20 ° 41’ 00” N; 86° 16’ 00”W, March 6 1991, 00:24 h, 50 m, ECO­CH­Z­02900; 1 specimen, CARIBE III, sta. 2, 21 ° 31’ 02”N; 86° 29’ 01” W, May 7 1991, 08:43 h, 64 m, ECO­CH­Z­02901; 1 specimen, CARIBE III, sta. 18, 18 ° 54’ 04” N; 87° 11’ 03” W, May 9 1991, 20:25 h, 50 m.

Diagnosis

Pharynx thick, strong, with thick muscle band in the base of the falcate chitinous mandibles. Dorsal margin of pharynx with five small digitiform papillae, ventral margin smooth. Two first segments fused, with two pairs of digitiform tentacular cirri, dorsal pair relatively small, ventral pair twice as long as dorsal. Dorsal pair usually armed with 2–3 setae, absent in some specimens. Segments 3–4 poorly developed, with one setal lobe and a few short compound setae (Fig. 2A). Segments 5–6 well­developed but reduced in size, following parapodia increasing in size posteriorly, with globose dorsal cirri attached to conical setal lobe, slightly larger than dorsal cirri, with single acicula and digitiform appendage. Setae slender compound spinigers. Ventral cirri smaller than dorsal ones, attached to setal lobe. Pygidium rounded, short (Fig. 2B). Chromatophores well developed, arranged in variable patterns; several specimens with heavily pigmented chromatophores on pygidium.

Remarks

The largest Caribbean specimen was 2 mm long and had 26 setigers. This figure is lower than that reported by Day (1967) for specimens from South Africa, but within the size range found by Treadwell (1943) in the west Atlantic, and by Fernández­Álamo (1983) in the east Pacific. Most specimens have sessile eyes, but in one of them eyes are inserted on a short peduncle, a character not previously described in this group. The ventral tentacular cirri of the two first segments usually bear a group of 2–3 setae (Treadwell, 1943; Orensanz & Ramírez, 1973; Fernández­Álamo, 1983); however, tentacular segments of all the Caribbean specimens lack setae. In the studied specimens, pigmentation was discontinuous along the body; chromatophores were arranged in a transverse pattern forming a dark belt involving some segments both on dorsal and ventral surfaces, thus dividing the body into regions. In some of the specimens examined, the concentration of chromatophores in the pygidium produced a strong pigmentation. Different chromatophore and pigmentation patterns related to distinct body parts, were described by Treadwell (1943), Day (1967), and Nuñez et al. (1992). The distribution and delineation of this species should be revised in the light of its overall morphological variability.

Some authors recognize two subspecies in Phalacrophorus pictus Greef, 1879: P. p. pictus Reibisch, 1895, and P. p. borealis Reibisch, 1895. The latter was originally described as P. borealis by Reibisch, but it was synonymized to P. pictus, as a junior synonym (Støp­Bowitz 1992; Fernández­Álamo & Thuesen 1999). It was redescribed recently retaining the subspecies status by Druzhkov et al. (2000) based on specimens collected in the Arctic Sea; they regarded it as restricted to the Arctic Ocean. Phalacrophorus pictus is a widely distributed species in tropical and temperate seas.

This species was the second most abundant iospilid in surface waters of the northwest Caribbean. Its densities ranges between 3.7 and 5 org./ 1000m 3 and occurred during March and May; in May it represented up to 22% of the iospilids in the area. It was found in oceanic stations only.

Type locality

Off the Canary Islands, east Atlantic.

Distribution

Mediterranean Sea, Indian Ocean, Atlantic Ocean, Pacific Ocean, polar seas. The finding of this species represents the first record of P. p i c t u s in the Caribbean Sea.