Re: Phyllodesmium briareum eggs

Thanks Mary Jane,
It certainly looks as though there could be a couple of eggs in some of the capsules. Usually there is only one egg per capsule in nudibranch egg masses but it is not unusual to find 2, 3 or 4 in some capsules. In some species with small eggs, multiple eggs per capsule is sometimes the norm.

Now to size. As a general rule each species has its own 'typical' egg diameter, though of course there is some intraspecific variation. The egg diameter can also give us an indication of the development type of the larvae - very small eggs almost certainly leading to planktotrophic veliger larvae which spend a long time feeding and growing in the plankton. At the other extreme very large eggs usually indicate that the larva is going to develop in the egg capsule, forgoing a free-swimming veliger larva stage, hatching out as a miniature crawling slug. Between these two extremes are eggs which develop into lecithotrophic larvae (free-swimming non-feeding larvae) which spend a very short time, sometimes only a few minutes, before settling to the bottom and metamorphosing into a crawling slug. There are exceptions to this rule as with any biological 'rule' but it gives us an indication which we can then set about proving or disproving for any species we are ineterested in.

As to egg size ranges, Tom Thompson produced a range of egg diameters based on nudibranchs of known development types.
• Planktotrophic: 40-170 microns
• Lecithotrophic: 110-250 microns
• Direct development: 205-400 microns
[1mm = 1000 microns]

There is considerable overlap between development types but your estimated diameter of 0.12mm (120 microns) suggests a veliger larval stage, and possibly one that is non-feeding. Certainly something worth following up.
Best wishes,
Bill Rudman