ABSTRACT:A new small species of Siboglinum has been found in sediments of sub-tropical waters off southwest Florida, at 24 to 90 m depth, where bottom temperatures range from 17 to 26°C This is unexpectedly warm for a pogonophoran. The phylum in general is mostly deep sea except for a few species that reach shelf depths in cold boreal or arctic regions. The new find suggests Pogonophora may be more widely distributed than previously thought.Pogonophora are predominantly deep-sea animals. In the tropics they have not previously been reported from less than 300 m, seeming to be limited to subthermocline waters cooler than 10°C (Southward 1971b, 1972, Gureeva 1981. A few shallow water species have been found in Arctic shelf seas and in boreal stratified seas where bottom temperatures are low for most of the year (Southward 19?1a, 1971b(Southward 19?1a, , 1979. The recently discovered giant vestimentiferan worms (Riftia pachyptila Jones 1980) from the Pacific at 2500 m are related to pogonophores, and their occurrence close to hydrothermal vents at first sight seemed to contradict the idea that pogonophores are restricted to cold water. However, it appears that these vestimentiferan worms live in places where the hot vent waters mix with cold bottom waters, and although a recent measurement suggests an upper limit of 35 "C, most of the vestimentiferans experience temperatures from 2 to 14 "C (Desbruyeres & Laubier 1983, Hessler & Smithey 1983, Canadian American Seamount Expedition 1985. It is notable that related vestimentiferans occur in a brine seep at the foot of the Florida Escarpment (4.4"C) and in a n oil-rich seep area on the Louisiana Slope, also in the Gulf of Mexico, at only 600 m depth with no indication of elevated temperatures (Paul1 et al. 1984, Brooks et al. 1985.A clear exception to the 'cold-water rule' has now been discovered on the south-west Florida Shelf. A new small species of Siboglinum has been found quite (Fig. 1). At each of 15 soft-bottom stations 5 samples were taken with a modified Reineck box corer 19 X 30 cm, 30 cm deep. The top 15 cm of each core was washed through a 0.5 mm sieve and the residue preserved in formalin for later sorting in the laboratory (Woodward-Clyde Consultants 1983a, b).Pogonophores were found at 8 stations sampled during Cruises I, I1 and IV. They were most common at Station 8, where there were 45 m-2 in 1980. These pogonophores have a single tentacle, which shows that they probably belong to the genus Siboglinurn. They live in colourless, transparent tubes not wider than 0.2 mm and about 40 mm long. The presence of mature females, incubating embryos, shows that the population is adult and not merely a sporadic settlement of juveniles from some deep-water population. These pogonophores belong to a new species not closely related to other species known from nearby deepwater habitats (Ivanov 1971, Southward 1971b, 1972, Gureeva 1981.The stations at which pogonophores were found were fairly widely distributed in the mid-shelf region, with 6 stations at 38 to 58 m,...
