Synallactida Miller, Kerr, Paulay, Reich, Wilson, Carvajal, and Rouse, 2017

Hausmann, Imelda M., Nützel, Alexander, Roden, Vanessa Julie & Reich, Mike, 2021, Palaeoecology of tropical marine invertebrate assemblages from the Late Triassic of Misurina, Dolomites, Italy, Acta Palaeontologica Polonica 66 (1), pp. 143-192 : 179-180

Order Synallactida Miller, Kerr, Paulay, Reich, Wilson, Carvajal, and Rouse, 2017

Family Synallactidae Ludwig, 1894 or “Stem group synallactids”

Genus Tetravirga Frizzell and Exline, 1956

Type species: Tetravirga imperforata Frizzell and Exline, 1956 ; USA, Pennsylvanian.

Tetravirga cf. perforata Mostler, 1968

Fig. 31G, H.

2005 Tetravirga sp. ; Bizzarini and Laghi 2005: pl. 2: 5.

Material.—Two body-wall ossicles (PZO 12790, 12791) from Misurina Landslide bulk sample, Italy, Carnian, Triassic.

Description and remarks.—Ossicles in form of a cross, arms placed at 70–110° angles; slender arms distally expanded and grooved. Grooved area is restricted to the distal third of each arm. These trenchlike impressions should be perforated, but are filled with sediment in our specimens. A solid spire (circular in shape) in the centre of the ossicle outer/upper side) is broken (e.g., Fig. 31H). After Reich 2010b), this type of ossicle resembles synallactid taxa with respect to general shape and morphology, spire, and especially the distally grooved and perforated arms.

Tetravirga sp.

Fig. 31D.

non 2014 Tetravirga sp. ; Nützel and Kaim 2014: fig. 11n, o. [= calcareous sponge spicules].

Material.—One body-wall ossicle (PZO 12792) from Misurina Landslide bulk sample, Italy, Carnian, Triassic.

Description.—Large ossicle in form of a cross, arms placed at 100° angles; wide arms distally decreasing and grooved. Grooved area is restricted to around 40% of each arm. These impressions should be perforated, but are filled with sediment in our specimen. A solid spire (oval in shape) in the centre of the ossicle (outer/upper side) is broken (e.g., Fig. 31D). This type of ossicle is closely related to T. cf. perforata and therefore resembles representatives of the Synallactidae .

Remarks.—Apodid sea cucumbers were mainly infaunal deposit feeders, whereas synallactids were epibenthic deposit feeders (e.g., rake-feeder or sweeper) and capable of active swimming. Representatives of both reported groups are therefore active and important bioturbators of the sediment floor.