Megerlia echinata (Fischer & Oehlert, 1890)

Megerlia echinata View in CoL ( Fischer & OEhlert, 1890)

Figures 46 View Figure 46 , 47 View Figure 47

? Terebratula monstruosa Scacchi, 1833, p. 17 .

? Megerlia truncata var. monstruosa – Davidson (1887), p. 108, pl. 9, figs.

21–22.

Mühlfeldtia echinata Fischer & OEhlert, 1890, p. 73 –74.

? Mühlfeldtia monstruosa – Fischer & OEhlert (1891), p. 87 –90, pl. 7, figs. 12a–c.

Pantellaria echinata View in CoL – Dall (1919), p. 251.

? Pantellaria monstruosa View in CoL – Dall (1919), p. 251.

Megerlia echinata View in CoL – Atkins (1961b), p. 89 –94.

? Megerlia monstruosa View in CoL – Brunton (1988).

Description: Shell low, ventribiconvex to concavoconvex and typically taking shape after the substrate that the dorsal valve is lying on. Adult specimens transverse oval to subrectangular. Umbo blunt and very broad. Narrow and slightly unisulcate anterior commissure in less deformed adults, but rectimarginate in juveniles. Hinge line straight. Narrow deltidial plates not joined. Very large and subcircular pedicle opening almost entirely located in dorsal valve. Ornamentation on ventral valve of generally widely spaced, unequal, uneven, fine and rather poorly defined costellae with scattered tubercles. Minute alveolate thorns or spines usually on and between costellae, though often unevenly distributed and may be lacking entirely. Surface of dorsal valve usually just marked by coarse growth lines, but very weak and sporadic costellae may occur. Shell matrix endopunctate. Colour yellow or white. Dorsal interior with long brachial loop reaching 2/3 valve length and supported by median septum. Lophophoral filaments approximately as long as or longer than 1/2 shell length. Dorsal septum extending to approximately mid-valve length of shell. Inner surface of valves with radiating lines of tubercles, especially strongly developed in a broad submarginal rim. Maximum shell size 13.5 mm long and 18.5 mm wide.

Depth range: 10–2780 m depth ( Koskeridou 2007; Logan 2007). However, after excluding geographically isolated reports and certain misidentifications of the species, the depth range narrows to 128–2780 m, making it a moderately deep- to deep-water species ( Koskeridou 2007; Simon et al. 2016; Anadón et al. 2022).

Temperature range: 9.5–13.6˚C (this study).

Substrate: Attached to corals ( Dendrophyllia ramea and Desmophyllum pertusum ) or shells ( Costa 1838; Fischer & OEhlert 1891; Massy 1916; Atkins 1961c). This species usually seems to be associated with corals.

Geography: Along the shelf edge of the Celtic Sea and the Bay of Biscay, off Portugal and West Sahara, as well as in the Mediterranean Sea ( Jeffreys 1878; Fischer & OEhlert 1890; Massy 1916; Dall 1920; Atkins 1961c; Gaspard 2003). Observations were also reported from Florida, the Caribbean, the Cape of Good Hope, the Red Sea and SE Australia ( Dall 1920; Cooper 1981b; Logan et al. 2008); however, those from the Red Sea were later recognised as a new species within another genus by Simon et al. (2016), while the remainder are more likely representatives of other species.

Remarks: See the above remarks for the genus concerning synonymy for the species. The present study was based mostly on the collection housed at the Natural History Museum of London, including numerous specimens of M. truncata and many specimens and even populations assigned to both M. echinata and M. monstruosa .