Extended Pelagic Life in a Bathybenthic Octopus

Roger Villanueva,Jonathan D Ablett,Vladimir V Laptikhovsky,Stuart B Piertney,Fernando Ángel Fernández-Álvarez,Martin A Collins,Alejandro Escánez

doi:10.3389/fmars.2020.561125

Abstract

Planktonic stages of benthic octopuses can reach relatively large sizes in some species, usually in oceanic, epipelagic waters while living as part of the macroplankton. These young octopuses appear to delay settlement on the seabed for an undetermined period of time that is probably longer than for those octopus paralarvae living in coastal, neritic waters. The reason for this delay is unknown and existing information about their biology is very scarce. Here we report on the presence of juvenile and subadult forms of the bathybenthic octopusPteroctopus tetracirrhusin oceanic waters of the South and North Atlantic and its association with the pyrosomid speciesPyrosoma atlanticum, apparently used by the octopus as a refuge or shelter. The relatively large size of theP. tetracirrhusliving in oceanic waters as the individuals reported here, together with the morphological characteristics of this bathybenthic species including its gelatinous body, minute suckers embedded in swollen skin and the deep interbrachial web, indicates thatP. tetracirrhusmay be considered a model of a transitional octopus species that is colonizing the pelagic environment by avoiding descending to the bathyal benthos. This process seems to occur in the same way as in the supposed origin of the ctenoglossan holopelagic octopods of the families Amphitretidae, Bolitaenidae, and Vitreledonellidae, which have arisen via neoteny from the planktonic paralarval stages of benthic octopuses.

Highlights

Cephalopods are highly mobile molluscs, occupying diverse marine habitats and exhibiting different lifestyles
The specimen of P. tetracirrhus was defrosted, a fragment of the mantle was preserved in 96% ethanol for molecular studies and the remaining body was fixed in 4% formaldehyde and transferred to 70% ethanol before measurements were obtained (Supplementary Table S1)
From the specimen (ML 33 mm, total length 110 mm) a fragment of the arm was preserved in 96% ethanol for molecular studies and the remaining body was fixed in 4% formaldehyde and transferred to 70% ethanol before measurements were taken

Summary

Introduction

Cephalopods are highly mobile molluscs, occupying diverse marine habitats and exhibiting different lifestyles. There are merobenthic octopus species that are characterized by the production of numerous small eggs that hatch into planktonic, swimming hatchlings that have been termed paralarvae (Young and Harman, 1988) These planktonic octopuses have few suckers and a transparent musculature, live in the water column from a few weeks to half a year depending on the species and temperature, Pelagic Life in Bathybenthic Octopus and occupy ecological niches distinct from those of the adults before their definitive settlement on the seabed (Villanueva and Norman, 2008). In some species, individuals reach relatively larger sizes, usually in oceanic, epipelagic waters so form part of the macroplankton (2–20 cm) These young octopuses appear to delay settlement on the seabed for an undetermined period of time that is probably longer than for paralarvae living in coastal, neritic waters. The largest individuals attain 25 mm in mantle length (ML) in Octopus rubescens (Young, 1972, as Octopus sp.) and 127 mm total length (TL) in Macrotritopus sp. (Brower, 1981)

Methods

Results

Conclusion