Order Terebratulida Waagen, 1883

Biconvex or rarer plane-convex shells, porous, with short usually curved and rarer with straight hinge-margin. Brachial skeleton looks like loop, which is more or less complicated.

The species of this order form the main part of recent brachiopod taxa and consist of 18 families. In the northern part of the Sea of Japan this order is represented by four families.

Key to families of the order Terebratulida

1(2). Brachial supports are short (less than 1/3 of brachial valve in length), join each other anteriorly by mean of transverse band and with crural processes which join each other in ontogenesis. There are star-shaped carbonate spicules in soft tissues of mantle and lophophore  Cancellothyrididae

2(1). Brachial supports are jointed to complicated brachial skeleton which appears on middle septum and fills up almost whole inner space of shell. Connection of brachial skeleton with hinge-margin (cardinal margin) or with middle septum can be secondary lost during ontogenesis. There are no spicules in soft tissues.

3(4). Ribbons of brachial skeletons keep connection to hinge-margin of brachial valve and to middle septum, and also connection of ascending branches of skeleton to descending branches during all life of specimen. Deltidial plates join each other to close pedicle foramen anteriorly (closed foramen)Laqueidae

4(3). Ribbons of brachial skeleton never have or loose connection of ascending branches to descending ones during ontogenesis. There are no deltidial plates or they are small and never join each other (open foramen)

5(6). Shells are not more than 20 mm in length, rounded in plan. Brachial middle septum is connected strongly to branches of brachial skeleton during all life of specimen Tythothyrididae

6(5). Shells up to 46 mm in length, frequently they are stretched transversely. Connection of brachial skeleton to middle septum becomes weak or disappears during ontogenesisTerebrataliidae