Brachiopodes Thecideida : genus Minutella

Minutella



Sous-embranchement (subphylum) des Rhynchonelliformea Classe des Rhynchonellata Ordre des Thecideida Sous-ordre des Thecideidina Super-famille des Thecideoidea Famille des Thecidellinidae Sous-famille des Minutellinae

Genus Minutella Hoffmann et Lüter, 2010

[Type-species = Minutella tristani Hoffmann et Lüter, 2010, p. 142]

Small endopunctate thecidellinine brachiopods, maximum length 2.5 mm. Ventral valve pseudodeltidium present; teeth small, covered with secondary shell material, single fibres well defined, rhombic or cubic, protruding. Dorsal valve with median septum; lophophore schizolophous; calcitic connection between intrabrachial ridge and brachial bridge always missing, in some cases secondarily filled with fine calcareous spicules; interbrachial lobes posteriorly highly raised, with reticulated canopying spicules, if present; tip of median septum often irregular, root-like; brachial bridge very broad; calcitic pole cone-like, never completely fused to floor of cardinal process, irregular appearance; two median adductor mus- cle scars on either side of visceral foramen; cardinal process massive, sub-quadrate, lateral lobes distally thickened, median lobe indistinct; lateral adductor muscle scars round to ovate, never extending beyond insertion of lateral lobes of cardinal process.

Holocene.

References:

Hoffmann J. & C. Lüter, 2010. Shell development in the thecidellinine brachiopods with description of a new recent genus. Special Papers in Palaeontology, 84, 137-160.

Extant species of Minutella

M. minuta (Cooper, 1981)

M. tristani Hoffmann et Lüter, 2010

M. bruntoni Hoffmann et Lüter, 2010

Diagnosis
Diagnosis
Diagnosis

Fossil species of Minutella

M. bulgarica Bitner et Motchurova-Dekova, 2016

Diagnosis

FIGURES : Minutella

Geographic distribution


Minutella minuta (Cooper, 1981) Type locality: MD.08 (St. 7, DC 57), Samper Bank, south-east of Madagascar (36°48'54"S 52°07'42"E, 380 m). Depth range: 30 - 380 m. Thecidellina minuta Cooper, 1981, p. 61 Minutella minuta : Hoffmann & Lüter, 2010 Minutella cf. minuta : Hoffmann & Lüter, 2010 Diagnosis from Hoffmann & Lüter (2010) and Simon et al. (2019) Very small endopunctate thecidellinine brachiopod. Ventral valve pseudodeltidium present. Dorsal valve median adductor muscle scar planar; canopying spicules reticulated, completely covering brachial cavity; median septum narrow, straight, almost reaching anterior margin of valve; interbrachial lobes posteriorly highly raised, brachial bridge very broad. Ventral valve floor granulose; hemispondylium of two thin plates with additional ventral projections, fused to posterior part of valve, ventral projection fused medially and connected to valve floor in adult specimens. Additional characters : schizolophous lophophore, until 80-85 tentacles, all at same length; brooding patterns.

Minutella tristani Hoffmann et Lüter, 2010 Type locality: North Andros Island, Bahamas (55 m) Depth range: 55 m. Diagnosis - Hoffmann & Lüter (2010) Small endopunctate thecidellinine brachiopods. Ventral valve pseudodeltidium present. Dorsal valve median adductor muscle scars bulging, not medially fused; canopying spicules, if present, reticulated, completely covering brachial cavity, creating a regular pattern of little holes; interbrachial lobes posteriorly highly raised; median septum wide, posteriorly heavily tapering; brachial bridge very broad, outer margin denticulate, inner margin with a row of characteristic branching calcareous spicules filling visceral gap, continuing around interbrachial lobes. Ventral vale floor heavily tuberculated forming regular longitudinal rows in posterior part of valve; hemispondylium with two plate-like prongs apically pointed, fused to posterior part of valve floor, ventrally not connected in adult specimens.

Minutella bruntoni Hoffmann et Lüter, 2010 Type locality: São Tiago, Tarrafal, Cape Verde (12 m) Depth range: 12 - 150 m Thecidellina barretti: Logan, 1977, p. 87-93. Thecidellina barretti: Logan, 1981, p. 735-744. Diagnosis - Hoffmann & Lüter (2010) Small endopunctate thecidellinine brachiopods. Ventral valve with pseudodeltidium. Dorsal valve median adductor muscles attached to single plate posterior of cal- citic pole, muscle plate medially fused or with minute median gap; calcitic pole flat, broad, very irregular, almost completely filling visceral foramen, leaving only two narrow slits; brachial cavities filled with spinose shell material, completely or incompletely covered by numer- ous branching canopying spicules, brachial cover irregular; median septum wide, posteriorly heavily tapering; interbrachial lobes posteriorly highly raised, brachial bridge very broad, inner margin with a row of characteristic branching spicules filling visceral gap and continuing around interbrachial lobes. Ventral valve floor heavily tuberculated and spinose with regular rows of spines in posterior part of valve; hemispondylium with two massive irregular plate-like prongs, apically only slightly pointed or blunt, fused to posterior part of ventral valve.

Minutella bulgarica Bitner et Motchurova-Dekova, 2016 Type locality: Yasen, Pleven District, Bulgaria (43°25'N, 24°31'E) Type horizon: Lower Badenian, Middle Miocene. Thecidellina sp.: Bitner, 1993, p. 151-152, pl. 6, fig. 6-7. Diagnosis - Bitner & Motchurova-Dekova (2016) Small-sized thecideide brachiopod, convex pseudodeltidium, hemispondylium with two plate-like prongs, straight and narrow median septum with a groove anteriorly, massive cardinal process, broad brachial bridge with denticulated inner margin.