In theMysidae the branchiae are wanting, and some would form this family into a separate order, Mysidacea.
The genital papilla of the female acquires a great development during the breeding season and becomes produced into a tube nearly as long as the fish itself; this acts as an ovipositor by means of which the comparatively few and large eggs (3 millimetres in diameter) are introduced through the gaping valves between the branchiae of pond mussels (Unio and Anodonta), where, after being inseminated, they undergo their development, the fry leaving their host about a month later.
Patella, pallial branchiae forming a complete circle, no epipodial tentacles, British.
Some of the special modifications of branchiae are referred to below.
Mantle open; foot rather small; branchiae folded; shell inequivalve.
Ill-developed; branchiae generally retractile.
Veil; branchiae non-retractile.
Helcion, circlet of branchiae interrupted anteriorly, British.
When present, the branchiae are generally differentiations of parts of the appendages, most often the epipodites, as in the Phyllopoda.
Edwards (1879), which is unique in having supplementary ramified branchiae developed at the bases of the pleopods.