It shows that one group of squid, whose life span is measured in a few months, has radically different growth rates and life spans (almost 2 to 1 difference) depending on the temperature. The summer lifespan was 3-4 months, winter squid of this species lived about 6 months.
Of particular interest was the discussion of how, and when, the squid grew compared to fish. They thought at first that the growth curve tapered off, but this was an artifact of measuring growth data independent of season. Once they corrected for that, it became obvious that the growth was continuous throughout their lives, and "it becomes apparent that growth is nonasymptotic; squids that hatched during warmer seasons had faster growth rates and shorter lives."
There was some discussion of growth at the cellular level:
Fish appear to grow initially by recruitment of new muscle fibers (hyperplasia) and with an increase in muscle fiber diameter (hypertrophy). Their final size may be influenced by the number of muscle fibers present once hyperplasia ceases, and individuals with more muscle fibers have the potential to reach a larger size (Moltschaniwskyj 1994). Squid also show both mechanisms of muscle fiber growth, but with the fundamental difference that hyperplasia does not cease; rather, recruitment of new muscle fibers is a continuous process throughout life. This phenomenon has also recently been documented for L. opalescens (Preuss et al. 1997).
But this quote is the closest to the kind of information being sought in this thread:
The deepwater squid M. ingens was shown to undergo a dramatic tissue breakdown process in association with maturation and spawning that results in the loss of virtually all mantle musculature, leaving only a collagen matrix. The loss of mantle thickness in L. opalescens (Fields 1965, cited in Hixon 1983) may be due to a similar process.
While there isn't a lot of info out there specific to octopus, there is a substantial (although not extensive) literature on cellular changes during end-stage reproduction (which is closely temporally-linked to senescence in some molluscs, including most cephs). If you are seeking a starting point, this might be good to explore. There is also a lot of work on aging in cuttlefish by Raymond Chichery's group - if you haven;t seen them you should take a look at these - they might give you some ideas of interesting things to look at on the cellular and sub-cellular level.
In vitro evidence and age-related changes for nicotinic but not muscarinic acetylcholine receptors in the central nervous system of Sepia officinalis: Cécile Bellanger, Marie-Pierre Halmb, François Dauphin, Raymond Chichery
Variations of the lipid constituents in the central nervous system of the cuttlefish (Sepia officinalis) during aging. E Dumont, M Chichery, A Nouvelot, R Chichery
Physiological aspects of post-reproductive senescence in Octopus vulgaris. RW Tait - 1986
Behavioural and neurohistological changes in aging Sepia. M P Chichery and R Chichery
Effect of aging on manipulative behavior in the cuttlefish, sepia. Halm MP, Agin V, Chichery MP, Chichery R.
Learning performances and aging in cuttlefish (Sepia officinalis). Chichery R, Chichery MP.