According to De Ridder & Segers (1997), T. clypeata is a widespread species occurring in the marine littoral and brackish waters all over the Palaearctic region.
Marine habitat: Balearic Archipelago (De Manuel et al. 1992); Albufera de Minorca (De Manuel 1995; Pretus et al. 1992); Camargue – France (De Ridder 1960, 1961); Spain (De Ridder 1962); Rovigno (Wulfert 1942a); Marismas, Spain (De Ridder, 1963b); Salt marsh near Puerta da Pollense, Mallorca, Sp. (De Ridder, 1967c); Spain: Barcelona & Huelva; Baleares: Mallorca (Velasco, 1990); Ionic and North Adriatic Sea (Fontaneto at al. 2008): Roscoff (d’Hondt 1970); Belgium (De Ridder (1957a, b); Nieuport – Belgium (Gillard 1959); Southern Finland (Godske Bjorklund 1972b); Sea & brackish water pools, S Finland (Björklund, 1972a); Norway (Godske Eriksen 1968); Baltic Sea (Remane 1929); Germany (Rentz 1940); Black Sea (Rudescu 1961); UK (Saunders-Davies 1995); North Germany (Schwarz 1955/1956; 1962); Baltic Sea (Sick 1933); Romania (Rudescu, 1960); Brackish water pools in Norway (Eriksen, 1968); Coast of S Finland (Eriksen, 1969); Gulf of Riga, Baltic Sea, Belt Sea, Kattegat, Skagerak, N & S North Sea, E & W English Channel, Bristol Channel & Irish Sea, S & W Ireland, Norwegian Sea (Berzinš, 1960); Oostduinkerke & Oostende, Belgium (De Ridder, 1986); Channel Nieuwpoort-Duinkerke in Oostduinkerke, Belgium (De Maeseneer, 1979); Zuiderzee; r. Tjunmer near Tjun; channel Harlingervaart; near Midlum, NL (Dresscher, 1976); Scandinavian coastal waters (Thane-Fenchel, 1968).
Continental water: Hortobagy Nat. Park, Hungary (Forro & Ronkay, 1983); Caspian area (Berzinš, 1978); Rügener, Hiddenseer & Darszer Boddengewässer, Germany (Schwarz, 1963); Lake Balaton, Hungary (Zankai, 1968); W Iceland (De Ridder, 1969b, 1970 & 1972); Obretin embanked basin, Danube delta, Romania (Godeanu et al., 1973); Ponds in Oltina, Dobrogea, Romania (Popescu-Gorj & Costea, 1961); One brackish & 2 freshwater localities in Poland (Radwan, 1967); River Volga, R.F. (Mordukhai-Boltovskoi, 1979); Waters near river Bodrog, NE Hungary (Dévai et al., 1972/1973); Cap Breton Island, Nova Scotia, Canada (Chengalath & Koste, 1987).
The reports from freshwater habitats are probably misidentifications concerning T. elliptica. De Ridder & Segers (1997) also report the species from the Nearctic region (Cap Breton Island, Nova Scotia, Canada), incorrectly referring to Chengalath & Koste (1988). However, the specimens mentioned sub T. elliptica by Jersabek et al. (2003; ANSP Catalog Number 1828) and originating from a brackish pool near Atlantic City, New Jersey, USA are distinctly T. clypeata, illustrating the species’ presence in the Nearctic.
Marine species, usually in the littoral zone.
The species has apparently often been confused with T. elliptica.
This species is easily recognized by the elliptical lorica (length/width ratio 1.30–1.55, average 1.45), which is often slightly angular postero-laterally apparently depending on the state of contraction or fixation. The dorsal anterior margin is convex, and the ventral anterior margin shows a broad Vshaped sinus; a dorsal transversal fold is often present at the end of the lorica. In cross-sectional view the dorsal margin appears convex, the lateral edges are broadly rounded and separated by a shallow sulcus from a convex median part ventrally. The characteristic foot-opening is a wide inverted U-shaped slit, situated ventral and sub-terminal. The foot is composed of a long and wrinkled proximal part, a clearly offset slender distal pseudosegment and a less defined short penultimate pseudosegment. The dorsal and lateral antennae are situated somewhat posterior to the anterior third of the lorica: ratio lorica length/position of antenna(e) relative to antero-dorsal margin varying from 2.70–2.85 (average 2.75) and 2.35–2.75 (average 2.58) respectively. Two red eyespots.
The trophi are characterized by 14–16/14–16 (left/right) unci teeth. The three major teeth show a slender and distinctly offset head. The manubria are composed of three large superimposed chambers, the dorsal, median and ventral, and a strongly reduced sub-ventral chamber. About 28–30/25–26 arched rami scleropili are apparent in caudal view. The fulcrum shows a distinct proximal opening frontally.
Measurements. Lorica length 150–170 μm, lorica width 100–130 μm, distal foot pseudosegment 18–22 μm.
