Histotrophy

Histotrophy is a form of matrotrophy (extraembryonic nutrition) in which a developing embryo receives additional nutrition from its mother in the form of uterine secretions called histotrophs (or “intrauterine milk”). It is characteristic of some viviparous sharks and stingrays . This is one of the main ways of reproducing in the subclass of plate - gill along with oviparous birth , in which the embryo feeds exclusively at the expense of the yolk , and oophagy (the embryo feeds on underdeveloped eggs ).

There are two types of histotrophy:

• Mucus or limited histotrophy - a developing embryo swallows uterine mucus or histotroph, but the yolk sac is the main source of energy. This form of histotrophy occurs in katraobraznyh ( Squaliformes ) and electric rays ( Torpediniformes ).

• Fatty histotrophy - the embryo develops due to the histotroph enriched with proteins and lipids , which receives through specialized filamentous structures called trophonems , penetrating the embryo into the digestive tract through the sprinkler . Such nutrition provided by the enriched histotroph allows one to increase the mass of the embryo by several orders of magnitude by the time of its birth, much more than with mucus histotrophy. This form of histotrophy is found in caudate-like ( Myliobatiformes ).