Tjalfiellidae Komai, 1922

Bezio, Nicholas & Collins, Allen G., 2024, Redescription of the deep-sea benthic ctenophore genus Tjalfiella from the North Atlantic (Class Tentaculata, Order Platyctenida, Family Tjalfiellidae), Zootaxa 5486 (2), pp. 241-266 : 251

Family Tjalfiellidae Komai, 1922

Grammatical gender— feminine

Type genus— TJalfiella from Komai (1922): 92–93

Etymology— Formed as a stem from the genus TJalfiella .

Included genus (1)— TJalfiella Mortensen, 1910

Diagnosis— Platyctenida with tentacles that lack tentilla.

Description— Benthic and sessile, body laterally compressed, elongated in the transverse direction; two “chimney-like” cylindrical vertical projections originating at either end and distinctly perpendicular to the rest of the body, each housing a single tentacle without tentilla in its own sheath; pharyngeal cavity with an accessory opening on each transverse end of body at the distal end of the vertical projections; transverse canals reduced into short branching diverticula, showing no anastomoses; gonads arising on lateral walls of the above diverticula; viviparous, eggs developing into cydippid-like embryos in brood-cavities in the lateral parts of the body.

Remarks— Although Mortensen included the type genus ( TJalfiella ) in the family Ctenoplanidae due to his observation of “cydippid-like” larvae, in 1922, Komai argued that there was such a noticeable morphological difference between Ctenoplana and TJalfiella that the creation of Tjalfiellidae was justified. Presently, five families of Platyctenida are recognized: Coeloplanidae , Ctenoplanidae , Lyroctenidae , Savangiidae , and Tjalfiellidae . The latter is differentiated from Coeloplanidae , Ctenoplanidae , and Lyroctenidae by having tentacles that lack tentilla and branching diverticula that do not form anastomoses. The monotypic and only once observed Savangiidae lack an aboral sense organ and have tentacles that lack a primary filament, consisting solely of a tuft of tentilla. The two vertical projections that originate at either end of the laterally compressed body, and which are perpendicular to it, were called “chimneys” or “chimney-tops” by Mortensen (1912), in reference to their cylindrical shape and flat tops. Similarly positioned projections from the bodies of Lyrocteis imperatoris , L. flavopallidus , and Coeloplana meteoris were termed arms by Komai (1941), Robilliard & Dayton (1972), and Thiel (1968), respectively. In these taxa, the projections differ from those in Tjalfiellidae by not having flat tops and possessing oral groves that run down their lateral sides. We use the more general term “arm” to describe all of these raised structures, irrespective of the shapes of their distal ends.