Meristic variation in males of the hydrothermal vent octopus,Muusoctopus hydrothermalis(Cephalopoda: Octopodidae)

Abstract

Intraspecific variation in characters such as arm sucker and gill lamellae counts in octopodids is yet to be thoroughly investigated, potentially hampering our ability to recognize species. In this study, data from 13 specimens ofMuusoctopus hydrothermaliscollected at four hydrothermal vents on the East Pacific Rise between 8°38′N and 12°48′N are considered. Although the northern and southern octopuses differ minimally in size, mean sucker count by arm in the northern group is 11.7 to 22.8% higher than it is in the southern group; in addition these octopuses typically have an additional gill lamella and bulkier funnel organs. The arms of each individual carry a different number of suckers. The difference is significant on nonadjacent arms, a pattern that merits examination in a broader taxonomic context. Why these differences exist among conspecifics remains unknown, the incidence of parasitic copepods is not different between the groups and the between-group variation in arm suckers seen here compares well with a previous report of variation among 18 specimens from the type locality. Increases in meristic characters (counts) in fish are attributed to lower temperatures during embryonic development following Jordan's rule. Northern and southern vents offer the octopuses a wide temperature range, but vent fluid chemistry differs. Northern vent fluids may be more toxic; if so, developing octopus embryos may survive only minimal vent fluid exposure and therefore develop at low temperatures. At the less toxic southern vents, eggs may survive greater exposure to vent fluids and thus develop at higher temperatures.

A molecular sequence proxy for Muusoctopus januarii and calibration of recent divergence among a group of mesobenthic octopuses

“…The range of variation observed among the specimens identified here as conspecific is approximately the same as for other related octopus species (see for example Gleadall et al, 2010). Variation in characters such as sucker number has recently been highlighted for V. hydrothermalis by Voight (2012), although it does not appear to be much different from that seen in species of Muusoctopus (see Table 9). Note that octopus arm tips are commonly lost (a small price to pay for successful escapes from predation) and regenerate quickly.…”

“…Gleadall et al, 2010). In a recent paper, Voight (2012) applied it as the genus name for Vulcanoctopus hydrothermalis González and Guerra in González, Guerra, Pascal and Briand, 1998: a species highly specialized morphologically, apparently for its life near hydrothermal vents (Gleadall et al, 2010;González et al, 1998). However, that combination is invalid because Vulcanoctopus has priority as the senior genus name where V. hydrothermalis is included in the same genus with the Muusoctopus group of species: the type species of the genus and sole named member of the nominotypical subgenus would then be Vulcanoctopus (Vulcanoctopus) hydrothermalis.…”

Morphological assessment of the Octopus vulgaris species complex evaluated in light of molecular‐based phylogenetic inferences

“…Alternatively, as specimens from Mauritania display minimal overlap in this character compared with those from France and Spain, this may indicate the presence of further species‐level diversity within O. vulgaris s. s. Such a wide range in HASC values within O. vulgaris s. s. therefore suggests the need for caution in basing species within this group on discrimination between HASC values. Voight () questioned the validity of using HASC as a species delimiting trait, also citing wide variation in HASC as a potential problem for species‐level inferences, concluding that variation in sucker numbers of ≤15% between potential species should be interpreted with caution. Although variation in HASC values among Australasian members of the O. vulgaris species group showed western Australian O .…”

“…The utility of HASC has previously been demonstrated in species-level resolution of octopuses (Toll 1988 Voight (2012) questioned the validity of using HASC as a species delimiting trait, also citing wide variation in HASC as a potential problem for species-level inferences, concluding that variation in sucker numbers of ≤15% between potential species should be interpreted with caution. Although variation in HASC values among Australasian members of the O. vulgaris species group showed western Australian O. cf.…”

Phylogeny and biogeography of Muusoctopus (Cephalopoda: Enteroctopodidae)

“…Strugnell et al . () dismissed morphological characters that would warrant the distinction of Vulcanoctopus from Muusoctopus , and Voight () identified V. hydrothermalis as a species of Muusoctopus . Gene sequence analyses, including that of the present study, place V. hydrothermalis within the Muusoctopus clade.…”