Pareledone Robson 1932

Introduction

Pareledone is the most abundant and diverse cephalopod genus in Antarctica. It is restricted to the continental shelf and slope margins (in depths of less than 1000 m) of Antarctica and the surrounding islands of the Southern Ocean. Members of the genus tend to be small; total length reaches 95 mm (mantle length 30 mm) in the smallest species, and 350 mm (mantle length 100 mm) in the largest. The first specimens of this genus were caught in 1905, but because of the inaccessibility of their habitat there is still only limited information available on their behaviour and life history. They have no commercial value.

Characteristics

1. Hectocotylus clearly differentiated into ligula and calamus.
2. Ligula groove long, well marked and shallow without transverse ridges.
3. Funnel organ VV-shaped.
4. Cartilaginous stylets absent.
5. Ink sac present.
6. Anal flaps present.
7. Gills well developed, with 6-11 lamellae per demibranch.
8. Web well developed.
9. Crop well developed.
10. Spermatophores long and slender.
11. Beak medium sized, rostral tip of lower beak rounded.

Discussion of Phylogenetic Relationships

The status of this genus has been questioned as rather than being a group of species that share a unique evolutionary history, it is a group that simply shares primitive character states (Voight, 1993).  Certain characteristics, however, such as the absence of cartilaginous stylets, are almost certainly derived.  Furthermore, recent biochemical genetic analyses confirm that the species are closely related (Allcock, 1997).

Life History

Life history data on the Pareledone is limited.  Although live specimens have been successfully transported from Antarctica and kept in captivity, there are no reported cases of successful breeding.  Studies into the maturation of the gonads by Kuehl (1988) suggest that the spawning season extends over a considerable period of time. The eggs of Pareledone are large (reaching 20 mm in length), hence they are likely to be incubated for a considerable time. The incubation period probably extends over the winter months.  The large size of the eggs also means that the hatchlings are probably benthic in habitat.  The lack of a planktonic larval stage restricts gene flow between isolated populations (Allcock et al., 1997) and may have consequences for speciation.

Distribution

• Pareledone harrissoni (type locality: 65°06'S, 96°13'E), P. framensis (type locality: 67°29'S, 68°50'E) and Pareledone prydzensis (type locality: 66°48'S, 72°33'E) are restricted in their distribution to Eastern Antarctica.
• Pareledone turqueti (type locality: 65°05'S 63°55'W) is restricted in its distribution to Western Antarctica.
• Pareledone charcoti (type locality: 65°05'S 63°55'W) is the only circum-Antarctic species.

References

Allcock A L (1997). The genetics and taxonomy of Southern Ocean Octopodidae with special referance to the genus Pareledone. PhD Thesis, Liverpool University.

Allcock A L, Brierley A S, Thorpe J P and Rodhouse P G K (1997). Restricted gene flow and evolutionary divergence between geographically separated populations of the Antarctic octopus Pareledone turqueti. Mar. Biol., 129(1):97-102.

Kuelh S (1988). A contribution to the reproductive biology and geographical distribution of Antarctic Octopodidae (Cephalopoda).; Malacologia 29(1):89-100.

Lu C C and Stranks T N (1994). Synopsis of Pareledone and Megaleledone species, with descriptions of two new species from East Antarctica (Cephalopoda: Octopodidae). Mem. natn. Mus. Vict. 54:221-242.

Voight J R (1993). A cladistic reassessment of octopodid classification. Malacologia 35(2):343-349.