Reproduction in Heteroteuthis dispar (Rüppell, 1844) (Mollusca: Cephalopoda): a sepiolid reproductive adaptation to an oceanic lifestyle

Small cephalopods of the genus Heteroteuthis are the most pelagic members in the family Sepiolidae. This study examines the reproductive biology of Heteroteuthis dispar (Rüppell, 1844), the first such study on any member of the genus, based on 46 specimens (27 females and 19 males) collected during the Mar-Eco cruise in the North Atlantic in the region of the Mid-Atlantic Ridge in 2004, and compares it with reproductive features in the less pelagic members of the family. The unusually large spermatophores of the males have a very small ejaculatory apparatus and cement body, relative to the size of the sperm mass. Females first mate when they are still maturing: a large sperm mass (up to 3.4% of the female body mass), consisting of one to several spermatangia, was found in an internal seminal receptacle of the majority of the females examined regardless of their maturity state. The seminal receptacle has a unique form and position in this species. The receptacle is a thin-walled sac at the posterior end of the visceral mass that is an outpocketing of, and opens into, the visceropericardial coelom. Spermatangia and sperm from the spermatangia apparently enter into the visceropericardial coelom (which is mostly occupied by the ovary) from the seminal receptacle indicating that ova are fertilised internally, a strategy unknown for decapodiform cephalopods (squid and cuttlefish), but present in most octopods. Fecundity of Heteroteuthis dispar (1,100–1,300 oocytes) is much higher than in other sepiolids whereas the egg size (mean max. length ∼1.6 mm) is the smallest within the family. Spawning is continuous (sensu Rocha et al. in Biol Rev 76:291–304, 2001). These and other reproductive traits are discussed as being adaptations to an oceanic lifestyle

Sperm transfer or spermatangia removal: postcopulatory behaviour of picking up spermatangium by female Japanese pygmy squid

In the Japanese pygmy squid Idiosepius paradoxus, females often pick up the spermatangium using their mouth (buccal mass) after copulation. To examine whether the female I. paradoxus directly transfers sperm into the seminal receptacle via this picking behaviour, or removes the spermatangium, we conducted detailed observations of picking behaviour in both virgin and copulated females and compared the sperm storage conditions in the seminal receptacle between females with and without spermatangia picking after copulation in virgin females. In all observations, elongation of the buccal mass occurred within 5 min after copulation. However, sperm volume in the seminal receptacle was not related to spermatangia picking. Observations using slow-motion video revealed that females removed the spermatangia by blowing or eating after picking. These results suggest that picking behaviour is used for sperm removal but not for sperm transfer. Moreover, the frequency of buccal mass elongation was higher in copulated females than in virgin females, consistent with the sequential mate choice theory whereby virgin females secure sperm for fertilisation, while previously copulated females are more selective about their mate. Female I. paradoxus may choose its mate cryptically through postcopulatory picking behaviour

Biodiversity and systematics in cephalopods: Unresolved problems require an integrated approach

Some problems of cephalopod biodiversity are discussed. Many squid species are represented by 2–4 intraspecies groupings that may be wholly or partly sympatric, but differ in spawning season and size atmaturity. They may be genetically distinct stock units, but their taxonomic status remains unresolved. Discovery of a biochemical or molecular key to distinguish between intra- and interspecific differences may help to solvethe problem of subspecific taxa in cephalopods, as stated by G. L. Voss in 1977. Electrophoretic study of allozyme differentiation is a good method for clearing up relationships between taxa within a family, but thismethod cannot be used in situations when the concept of subgenus or subfamily is necessary. The problem of suprafamilial taxa needs urgent attention. However, restructuring only one family or group offamilies leaving others unrevised may lead to skewing the entire system. Examples are splitting the Enoploteuthidae into three families (as proposed by M. R. Clarke in 1988) and raising the rank of theSepiidae and the Sepiolidae to ordinal, a proposal by P. Fioroni in 1981. In such cases the method of common level should be applied: subdivisions in a large taxon shall be separated by approximately similar characters.Many attempts to select natural groups of families, for example in the Oegopsida, failed primarily because they were based on analysis of a single organ or system of organs when study of other organs/systems may lead to different natural groupings. The use of molecular techniques in cephalopod phylogeny may be profitable, but initial attempts have led to results that are not easily interpretable. The evolution of Recent Cephalopoda has probably proceeded with such large variations in rates among different clades that it is impossible to construct a non-contradictory system based on any single organ or system. No single organ/system-of-organs nor single methodology currently exists that will solve every problem in taxonomy. An integrated approach, based on analysis of as many organs and different taxa as possible, is necessary to construct an accurate picture and not a mosaic of dispersed random pieces