Megerlia truncata ( Linnaeus, 1767 )

Hansen, Jesper, 2024, Brachiopods of the Norwegian fauna northern North Atlantic and Arctic, with a focus on, Fauna norvegica 43, pp. 12-68 : 51-52

Megerlia truncata ( Linnaeus, 1767)

Figures 48 , 49

Anomia scobinata Linnaeus, 1758, p. 701 .

Anomia disculus Pallas, 1766, p. 184 , pl. 14, figs. 1a–g.

Anomia truncata Linnaeus, 1767, p. 1152 .

Terebratula scobinata – Retzius (1788), p. 14.

Terebratula truncata – Retzius (1788), p. 14.

Criopoderma truncatum – Poli (1795), p. 191 –192, 261, pl. 30, figs. 15, 15b.

Terebratula decustata Blainville, 1828, p. 142 .

Terebratula disculus – Blainville (1828), p. 140.

Terebratula irregularis Blainville, 1828, p. 140 .

Terebratula oblita Michelotti, 1839, p. 22 .

Delthyris ( Orthis) truncata – Anton (1839), p. 22.

Orthis oblita – Sismonda (1842), p. 11.

Orthis truncata – Philippi (1844), p. 69.

Terebratella truncata – d’Orbigny (1847b), p. 248, pl. 7, figs. 11, 12, 16.

Megerlia truncata – King (1850), p. 145.

Megathiris oblita – d‘Orbigny (1852), p. 94.

Terebratula ( Megerlia) truncata – Lovell (1861), p. 180.

Megerlea truncata – Brusina (1866), p. 47.

Muhlfeldtia truncata – Bayle (1880), p. 240.

Mühlfeldtia truncata – OEhlert (1887), p. 1322.

Mühlfeldtia disculus – Dall (1920), p. 333 –334.

Description: Shell resembling Megerlia echinata but differs in the following features. Shell low and biconvex with rather sharp dorsal sulcus and corresponding fold in ventral valve. Adult shells with sharply sulcate anterior commissure. Ornamentation of dense, subequal and fine costellate ribs on both valves, typically with low tubercles along rib crests and with growth lines and stops. Higher tubercles can develop posterolaterally on ventral valve. The radiating ornamentation and tubercles are strongest on ventral valve. Tubercles always situated on rib crests. Shell less often markedly deformed from attachment to substrate. Longest filaments in lophophore shorter than half shell length. Maximum shell length 20 mm.

Depth range: 8–1086 m depth (Logan 2007), but since Megerlia echinata is broadly synonymised with the species, the range is somewhat uncertain. When restricting to confirmed specimens from the Mediterranean and NE Atlantic region, the range is 16–586 m depth ( Fischer & OEhlert 1891; Anadón et al. 2022).

Temperature range: 11.5–19˚C ( Jeffreys 1878; Brand et al. 2003).

Salinity range: 37–39 ( Brand et al. 2003).

Substrate: Attached to corals ( Dendrophyllia corniger ), shells, artificial substrates or rocky substrates ( Gray 1853; Atkins 1961c; Koskeridou 2007; Toma et al. 2022).

Geography: Coast of Brittany in W France, Bay of Biscay, Portugal, Azores, the Mediterranean, the Canary Islands, and Cap Blanc in Mauritania ( Jeffreys 1878; Fischer & OEhlert 1891). The specimen collected by Turton and identified as Megerlia truncata from off Torquay/ Torbay in S England was, according to Jeffreys (1878), needing verification. However, Dall (1920) maintained the identification. No other specimens appear to have been collected since. Zezina (2014) listed it from the mid-Atlantic ridge Reykjanes Ridge at 58˚23’N south of Iceland, which requires verification.

Remarks: When synonymising the two species Anomia truncata Linnaeus, 1767 and Anomia scobinata Linnaeus, 1758 , the name Anomia scobinata was mistakenly attributed to Gmelin (1791) (e.g., Dall 1870, 1873). Thus, Anomia truncata was given seniority. According to the International Code of Zoological Nomenclature (Article 23) the senior name should normally be given precedence. However, Article 29.3 states that prevailing usage must be followed when the senior synonym has not been used as a valid name after 1899, and the junior synonym has been used for a particular taxon, as its presumed valid name, in at least 25 works, published by at least 10 authors in the immediately preceding 50 years and encompassing a span of not less than 10 years. In the present case, the demands for the exception are fulfilled, while the name A. truncata Linnaeus, 1767 is given precedence over A. scobinata Linnaeus, 1767 .

In their study on Kraussinid brachiopods, Simon et al. (2016) questioned the worldwide distribution previously attributed to the species and argued that true M. truncata are restricted to the Mediterranean and the Lusitanian Province of the Eastern Atlantic.

Figures

Figure 48. Megerlia truncata. a–e: dorsal, ventral, lateral, anterior and posterior views of shell, Arenys de Mar, Barcelona, Spain, 30–60 m (JH); f–j: dorsal, ventral, lateral, anterior, and posterior views of specimen, Samothraki Island, Greece, 240 m (JH); k–l: dorsal and ventral interior views of specimen ZMBN 42048, Penmarch, Brittany, France. Scalebar 1mm. Photos: Jesper Hansen.

Figure 49.Distribution of Megerlia truncata.