New Zealand Journal of Zoology abstracts
Sexual dimorphism in the beaks of Moroteuthis ingens Smith,
1881 (Cephalopoda: Oegopsida: Onychoteuthidae)
K. S. Bolstad
Earth & Oceanic Sciences Research Institute
Auckland University of Technology
Private Bag 92006
Auckland 1020, New Zealand
kbolstad@aut.ac.nz
Abstract Sexual dimorphism in size and
morphology of the lower beak of the warty onychoteuthid squid Moroteuthis
ingens is analysed. Beaks of maturing males exhibit a band of
weak, clear cartilage across the shoulder region, while mature males
exhibit a pronounced excavation of this area; the hood remains intact.
Female beaks attain greater size, but relatively shorter lower rostral
lengths (LRL) than those of males; they display neither the shoulder
cartilage nor later erosion, but the hood is consistently eroded in
mature specimens. The angle ridge in females is considerably longer
than in males. Due to the difference in LRL relative to overall beak
size, M. ingens beaks from predator stomachs should be
sexed prior to calculating prey size using LRL; for both sexes, the
LRL-mantle length (ML) relationship is linear while the LRL-weight
relationship is exponential. Sex-specific equations are provided for
reconstructing ML and weight using LRL. Based on several incidences of
male-female pairs collected with beaks interlocked, M. ingens
is postulated to mate in a head-to-head position, with both individuals
incurring beak damage during the event.
Keywords Dimorphism; mating; behaviour; biomass
estimation; cephalopod beaks; Moroteuthis ingens;
Onychoteuthidae
Z06017; Online publication date 8 November 2006 Received 23
May 2006; accepted 1 November 2006
New Zealand Journal of Zoology, 2006, Vol. 33: 317–327
0301–4223/06/3304–0317 © The Royal Society of New Zealand
2006
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