Reproduction & Development

The cephalopods are gonochoric, i.e. there are two distinct sexes, and fertilisation of the eggs usually occurs in the mantle cavity. It involves the male transferring sperm to the female using one or more of his arms that has been modified to act as an intromittent (sperm delivery) organ, called a hectocotylus. Before this transfer occurs, the male makes courtship displays to the female which include changing body patterns and colours. During copulation, the male uses the hectocotylus to take club-shaped packages of sperm, called spermatophores, from his body and transfer them to the female’s body. The position in which they are placed varies in different species, typically into the mantle cavity but in some cases into specialised seminal receptacles or membranes on the head (Ruppert et al. 2004). In I. notoides, it seems the male deposits his spermatophores on to the arms and head of the female, who then uses the dorsal adhesive organ to attach to seagrass or other vegetation and lays fertilised eggs along the underside of the fronds (Norman and Reid 2000).

Cephalopod eggs are macrolecithal, i.e. have a large yolk that nourishes the growing embryo. Development is direct, there is no larval stage as in many other invertebrates, however the hatchlings typically stay in the plankton for some time (Ruppert et al. 2004). Idiosepius paradoxus, a species closely related to I.notoides, has been bred in captivity and observed to lay multiple batches of eggs over long periods of time, up to 42 batches in 70 days in one recorded case (Kasugai 2006). Another species in this genus, Idiosepius pygmaeus, was observed in captivity laying batches of 30 to 80 eggs every two to seven days (Nixon and Young 2003). Given these findings, it may not be unreasonable to expect that I. notoides may be able to lay large numbers of eggs over many days as well.

Side view of female I. paradoxus attached to seagrass by adhesive organ and laying eggs along the blade while another, possibly male, swims nearby. Photograph by Takashi Kasugai from Mangold and Young (2013).

Many species of cephalopods die after a single spawning and have short lifespans (Ruppert et al. 2004) which has lead to their lifestyle being described as “live fast, die young” (Mather and Kuba 2013). Although it seems I. notoides may be a multiple spawner, it does have a short life. From studies on the growth increments of the statolith (a sensory structure – see Anatomy & Physiology tab) of this species, the maximum ages of male and female I. notoides were estimated at 91 days and 115 days respectively (Tracey et al.2003). This study also found gender dimorphism in I. notoides. Although growth rates are similar between males and females, because females live approximately 25% longer than males, they are able to achieve greater body length and weight. Males, however, reach sexual maturity earlier and at a smaller length than females: 68 days, 6.5mm mantle length for males and 88 days, 14.0mm mantle length for females.

A positive correlation between the growth rate of I. notoides and the average sea surface temperature (SST) at the time of hatching was also found in the study by Tracey et al. (2003). If temperatures were higher during hatching, individuals grew faster on average than those hatched when temperatures were cooler. Because the geographic range of I. notoides extends over diverse climatic regions (see Biogeographic Distribution tab), there may be a great deal of variability between populations in their growth rates, final size and the age and size at which they reach sexual maturity.