Benthoctopus sp. B

Strugnell, Jan, Voight, Janet R., Collins, Patrick C. & Allcock, A. Louise, 2009, Molecular phylogenetic analysis of a known and a new hydrothermal vent octopod: their relationships with the genus Benthoctopus (Cephalopoda: Octopodidae), Zootaxa 2096 (1), pp. 442-459 : 447-448

Benthoctopus sp. B (embryo) FMNH 309724

Material examined: Benthoctopus sp. : * FMNH 309724 , RV Western Flyer ROV Tiburon, 42°45'N 126°43'W (near Sea Cliff Hydrothermal vent field Gorda Ridge), ROV Tiburon Lowering 884, 23 August 2005, 2752 m, embryo, leg. R. A. Zierenberg and D. Clague, det. JR Voight.

Remarks. A diagnosis of this species is not possible at this time; the only known specimen is an embryo with a mantle length of 7.5 mm. The hectocotylus carries a differentiated ligula and 47 suckers ( Voight, 2008). Outer gill with 11 lamellae. Funnel organ W-shaped. The skin has a few, scattered chromatophore organs. Whether the high gill lamellae count relates to the age of the specimen, or to its species membership is debatable. The embryo was collected from what appears to be an established area in which females brood eggs near the Sea Cliff, or GR-14 hydrothermal vent site. The aggregation has been seen twice since 2002; the high density of octopodids in this area was noted by Rona et al. (1990). Brooding by these octopodids has been suggested to occur within hydrothermal fluid flow which is unusually low in vent toxins ( R. Zierenberg, pers. comm.). Unfortunately, to our knowledge, no mature specimen has been collected. Measurements of the embryo are reported by Voight (2008).

Although this collection was made at a hydrothermal vent, the species cannot be held to be vent endemic for two reasons. First, the brooding females in situ appear to have normal skin with normal pigmentation; species we consider here to be more closely associated with vents, V. hydrothermalis and the Manus Vent specimen ( Figure 1 ), generally have translucent skin that lacks colour. Second, outside of a small area in which they brood eggs, octopodids are not often encountered at vents on Gorda Ridge. On the East Pacific Rise, individuals of V. hydrothermalis are encountered across broad areas of hydrothermally active mid-ocean ridge from at least 21°S to 13°N. Too few data are available from Manus Basin to allow comparisons. At Gorda Ridge, geologists speculate that brooding females congregate at this site as the warm hydrothermal fluid, or perhaps the warm rocks to which the eggs are attached, speed embryonic development.

Figures

FIGURE 1. The Manus Vent octopus specimen (FMNH 310455) in situ near a hydrothermal vent in the Manus Basin off Papua New Guinea, 1500 m depth.