Trichotriidae Harring, 1913

Luo, Yongting & Segers, Hendrik, 2013, On Pulchritia new genus, with a reappraisal of the genera of Trichotriidae (Rotifera, Monogononta), ZooKeys 342, pp. 1-12 : 2-3

Family Trichotriidae Harring, 1913

Diagnosis.

Trophi unspecialized, malleate; head, trunk and foot largely loricate, but head retractable. No discernible separate lorica plates or sulci on the trunk, but lorica stiffness not homogeneous. Lorica granulated and/or facetted. Distal part of trunk (anal segment) illoricate, separated from trunk proper. Foot with two pseudosegments and a pair of terminal toes.

Discussion.

The diagnostic autapomorphic feature for the family is the stiffening of the tegument of the head region, especially of the neck and lateral parts of the head, which in contracted specimens folds into a characteristic, more or less symmetrical shape protruding from the head aperture. The feature distinguishes family members from Brachionidae , Epiphanidae , Euchlanidae , and Mytilinidae who have an illoricate head; Lepadellidae has a characteristic sclerotized head shield overlaying the corona but the rest of the head is illoricate ( Colurella , Lepadella ), and not retractile ( Squatinella ). In contrast, Sørensen and Giribet’s (2006) detailed phylogenetic analysis could not confirm monophyly of Trichotriidae , neither on molecular nor morphological data.

The classic diagnoses of Trichotriidae genera are problematic. They refer to features that are not present in all species of the genus (e.g., the purported synapomorphic dorsal spines in Macrochaetus ), or features which appear to have been misinterpreted. This holds in particular for the structure of the foot which, in its basic form, consists of two foot pseudosegments bearing two toes, and is inserted on an illoricate terminal part of the trunk, termed the anal segment. This anal segment is a part of the trunk proper as it lies anterior to the (dorsal) anal opening. Its tegument is always relatively weakly sclerotized, which enables mobility of the rigid foot relative to the rigid trunk lorica, but which may also make it difficult to distinguish it from the trunk and/or from the two distal pseudosegments of the foot in contracted specimens. The structure is occasionally mistaken for a part of the foot and is then referred to as first of three foot pseudosegments. Note that in Koste and Shiel (1989) both terms (anal segment and first foot segment) appear to have been used for the same structure, and that the position of the anus as indicated in their fig. 16:1 is incorrect.

In view of these inconsistencies, and awaiting a full review, preferably integrating both molecular and morphological data of genera in this and the related Euchlanidae and Mytilinidae , we tentatively propose emended diagnoses of the trichotriid genera, and propose a new genus to accommodate Monostyla dorsicornuta Van Oye, 1926 and Macrochaetus kostei José de Paggi, Branco & Kozlowsky-Suzuki, 2000.