Bobtail squids of the family Sepiolidae, which includes the genus Euprymna, are closely related to, but distinct from the true squids (Teuthoidea). Despite their ecological importance, there have been few studies on the age and growth of bobtail squids using hard parts. This study is the first to use statolith increments to estimate the age of Euprymna hyllebergi collected from the southeastern Arabian Sea. Statoliths were extracted from 80 individuals (24 males, 56 females) of dorsal mantle length (DML) 8–50 mm and total weight 0.45–37 g and assessed for their age. Statolith size ranged from 328 to 836 μm. Assuming a daily deposition of increments, growth was rapid and adult sizes were attained in around 2 months. The age of the individuals varied between 25 days (DML = 8 mm) and 91 days (DML = 37 mm) for males; 33 days (DML = 10 mm) and 92 days (DML = 44 mm) for females. The daily growth rate ranged from 0.20 to 0.49 mm DML day−1 for males and 0.23–0.59 mm DML day−1 for females. The lifespan of E. hyllebergi is short, based on the statolith increment analysis.

The first observation of the common bobtail squid Sepietta oweniana has been made in the Barents Sea (Tromsø Bank; 70°54′N 19°46.8′E). It is the northernmost area of this species distribution. No changes were found in the reproductive system structure. But the food spectrum was changed, particularly, juvenile fish of the Lotidae family was found. The bobtail squid of the Sepiolinae subfamily have never been recorded as fish eaters previously. The expansion of boreo-subtropical species of cephalopods into the Arctic during the last decade can be divided into two groups: (1) a foraging migration happening relatively regularly; and (2) a range expansion due to the ongoing Arctic warming. The case of S. oweniana obviously belongs to the second group.

A total of 208 Rondeletiola minor were sampled from the eastern Mediterranean with the depth contours of 150, 350 and 550 m. Body sizes of 32 mature females ranged from 11.8 to 19.5 mm dorsal mantle length (ML), that of mature males were 11.1–19.1 mm ML. Potential fecundity varied between 192 and 315 eggs in maturing females, and ripe egg sizes were 1.1–3.0 mm. Ripe egg amount did not exceed 15% of the fecundity. The average number of spermatophores was 176 with two extreme individuals that had 557 and 674 spermatophores, respectively. Spawning occurs continuously with an asynchronous ovulation pattern. Mature animals were found throughout the year with a peak in gonadosomatic index in spring. The life cycle of R. minor was estimated to be 10 months with different cohorts in reproduction depending on how temperature affects the hatching.

A total of 104 Semirossia patagonica were collected all over the Patagonian shelf between the depths of 47 and 295 m. Mature female size varied from 10 to 35 mm ML, mature male size was 16–32 mm. Potential fecundity ranged between 527–766 eggs in pre-spawning females, ripe egg size was 3.4–5.0 mm. The oviduct capacity probably was no more than 30 eggs. The maximum number of spermatophores in males was 229. Males transfer 2–19 spermatophores to females during copulation. The ovulation pattern is asynchronous, individual spawning is continuous. Reproduction occurs all year round. Semirossia patagonica is a south-west Atlantic ecological sibling of north-east Atlantic bobtail squids Sepiola spp. and Sepietta spp.