the endemic west african glycymerididae species
TRANSCRIPT
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The endemic West African GLYCYMERIDIDAE
species
summary and presentation of two new species
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The family GLYCYMERIDIDAE in West Africa
- limited to the genus Glycymeris;
- a very ‘difficult’ mind-breaking family;
- from 30 to 90 mm;
- equivalve, mostly symmetric (= equilateral);
- outline: circular, occasionally posteriorly angled = not a good identification tool;
- usually thick, solid shells;
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- opisthogyrate = the beaks are turned towards the posterior end of valves;
- ligament area: amphidetic or prosodetic;
- taxodont hinge: 2 rows of teeth = unusable as identification tool;
- anterior muscle scar: narrower than the posterior one, lower part truncated;
- posterior muscle scar: nearly circular but the lower part is narrowing below;
- no pallial sinus;
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- inner ventral margin strongly crenulated;
- microsculpture: very unique and constant characteristic for each species and a good identification tool; concentric growth lines or reticulated pattern;
- habitat: in sand, gravel or mud from the infralittoral zone to deeper waters.
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Glycymeris rafaelmesai Nolf & Swinnen, 2013
History:
- Gómez & Pérez (2011): report of an unknown species from the Canary Islands;
- coll. Mesa, Déniz, Guillén & Swinnen: several specimens from Lanzarote and Senegal;
- coll. F. Nolf: 2 spec. from Mauritania and 1 spec. from Angola (PEMARCO);
- no specimens from the Gulf of Guinea.
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Type material:
- holotype: RBINS
- paratypes: 1-13 (coll. Déniz, Guillén, Mesa, Swinnen & Nolf) – Lanzarote, Mauritania, Senegal, W Sahara and Angola;
- H. 35-67 mm L. 37-67 mm;
- derivation of the name: after Rafael Mesa (Canary Islands)
- habitat: in sand at a depth of 20-40 m;
- geographic range: Lanzarote (Canary Islds), Western Sahara (67-85 m), Mauritania (300-400 m), Angola (75 m)
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Glycymeris rafaelmesai paratype 1 - Lanzarote
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Glycymeris rafaelmesai paratype 1 - Lanzarote
inside
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Glycymeris rafaelmesai paratype 2 - Lanzarote
clear hump
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Glycymeris rafaelmesai paratype 2 - Lanzarote
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Glycymeris rafaelmesai holotype (KBIN) - Lanzarote
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Glycymeris rafaelmesai holotype (KBIN) – Lanzarote
inside
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Glycymeris rafaelmesai paratype 3 - Senegal
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Glycymeris rafaelmesai paratype 3 – Senegal
inside
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Glycymeris rafaelmesai paratype 4 – Senegal
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Glycymeris rafaelmesai paratype 4 – Senegal
inside
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Glycymeris rafaelmesai paratype 5 – Mauritania
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Glycymeris rafaelmesai paratype 6 – Mauritania
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Glycymeris rafaelmesai paratype 7 – Western Sahara
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Glycymeris rafaelmesai paratype 7 – Western Sahara
inside
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Glycymeris rafaelmesai paratype 8 – Western Sahara
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Glycymeris rafaelmesai paratype 8 – Western Sahara
inside
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Glycymeris rafaelmesai paratype 11 – Mauritania
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Glycymeris rafaelmesai paratype 11 – Mauritania
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Glycymeris rafaelmesai paratype 12 – Mauritania
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Glycymeris rafaelmesai paratype 13 – Angola
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Description
- shell: solid and heavy, equivalve and equilateral, globular;
- outline: subcircular, posterior shell margin is acute and slightly truncated, the anterior one is nearly perfectly rounded, sometimes a slight ridge runs from the umbo to the posterior ventral edge;
- umbo: opisthogyrate;
- ligament: amphidetic;
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- taxodont hinge plate: 2 series of 9-15 teeth;
- microsculpture: very fine concentric undulating ribs, no radial grooves, no reticulated pattern;
- periostracum: velvety, pale-olive coloured;
- colour: off-white to cream, sometimes with faint traces of fine brown zigzag lines in umbonal region; often completely or partly brown coloured (caused by a ferruginous bottom); inside: creamy white, partly or even almost completely brown coloured.
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Comparison with other species
- West Atlantic Ocean:
* G. americana (Defrance, 1826): juvenile specimens
* G. decussata (Linnaeus, 1758)
* G. undata (Linnaeus, 1758)
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Glycymeris americana (juvenile) East Panama
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Glycymeris decussata Guadeloupe, Lesser Antilles, Caribbean Sea
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Glycymeris undata East Panama
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Comparison with other species
- East Atlantic Ocean: * Glycymeris concentrica (Dunker, 1853) * G. formosa (Reeve, 1843) * G. glycymeris (L., 1758) * G. vanhengstumi Goud & Gulden, 2009 * G. nummaria (L., 1758) * G. pilosa (L. 1767) * G. scripta (von Born, 1778) * G. stellata (Bruguière, 1789)
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Glycymeris concentrica (Dunker, 1843)
- where?: Mauritania, Canary Islands, Cape Verde Islands, Senegal, Guinea, Ivory Coast, Ghana, Principe Island, Gabon, Angola;
- outline: circular, posterior end slightly produced and obliquely truncated;
- ligament: amphidetic;
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- microsculpture: reticulated pattern of an enormous number of very regular concentric fine cords crossed by a smaller number of broad flattened radiating ribs;
- periostracum: dark brown velvety, rather resistant;
- colour: variable, completely brown or occasionally with white bands crossed with brown interrupted lines;
- measurements: 20-45 mm.
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Glycymeris concentrica Senegal
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Glycymeris concentrica Senegal
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Glycymeris concentrica Ivory Coast
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Glycymeris concentrica Angola
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Glycymeris concentrica Angola
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Glycymeris formosa (Reeve, 1843)
- where?: Cape Verde Islands, Gulf of Guinea;
- outline: nearly circular, posteriorly truncated;
- ligament: amphidetic;
- microsculpture: faint reticulated pattern of very weak radiating threads and irregular concentric flattened ribs;
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- periostracum: velvety, limited to the border of the valves, similar to G. rafaelmesai, G. concentrica and G. scripta;
- colour: a pattern of 10-15 of violet-brown flammules and stripes running over the whole surface of the valves;
- measurements: 30-80 mm;
- differs from G. stellata by a smaller number of internal crenulations.
- Remark: G. formosa var. tumida Dautzenberg & H. Fischer, 1906 is much more swollen with dark-red coloured flammules.
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Glycymeris formosa Cape Verde Islands
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Glycymeris formosa Cape Verde Islands
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Glycymeris formosa Cape Verde Islands
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Glycymeris formosa Cape Verde Islands
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Glycymeris formosa Cape Verde Islands
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Glycymeris formosa var. tumida
Cape Verde Islands
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Glycymeris formosa var. tumida
Principe Island, Gulf of Guinea
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Glycymeris formosa var. tumida
Principe Island, Gulf of Guinea
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Glycymeris scripta (von Born, 1778)
- where?: Canary Islands, Mauritania, Senegal, Sierra Leone;
- outline: almost completely circular;
- ligament: mostly prosodetic, slightly amphidetic in large adult specimens;
- microsculpture: homogenous cancellate pattern of very fine concentric threads and equal narrow radiating ribs;
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- periostracum: velvety, olive-brown;
- colour: 10-15 brown zigzag lines on a yellowish white background;
- measurements: 40-70 mm.
- Remark: this is Le Vovan of Adanson
Pectunculus vovan ´Adanson’ Lamy, 1942 (Fischer-Piette,1972)
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Glycymeris scripta Mauritania
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Glycymeris scripta Mauritania
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Glycymeris scripta Senegal
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Glycymeris scripta Senegal
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Glycymeris stellata (Bruguière, 1789)
- where?: Madeira, Canary Islands, Mauritania, Senegal, Sierra Leone, Gulf of Guinea, Cameroon, Angola;
- outline: nearly circular, broader than high, valves obtusely truncated;
- ligament: amphidetic;
- microsculpture: dense reticulated structure of irregular concentric cords crossed by very fine radiating threads, clear growth stages;
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- periostracum: velvety, dark olive-brown;
- colour: many concentric undulating brown zigzag lines merging in a nearly brown zone at the bottom of the valves;
- measurements: 50-70 mm;
- differs from G. formosa by the larger number of shorter internal crenulations
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Glycymeris stellata Senegal
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Glycymeris stellata Senegal
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Glycymeris sp.
- Locus typicus: Sumba, Angola;
- shell: small, solid with flattened valves;
- outline: subovate, posteriorly truncated;
- ligament: prosodetic;
- hinge plate: 2 series of taxodont teeth, anterior part with 10 teeth nearly continuously proceeding in a posterior series with 14-15 smaller teeth;
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- microsculpture: practically no traces of a pattern (external surface of valves is glossy with only faint radial ribs and microscopic concentric threads);
- periostracum: absent;
- colour: bluish grey with brown streaks and zigzag markings; dark blotch posteriorly; interior of valves brilliant with a well-defined central brown blotch.
- Remark: only 1 (juvenile?) specimen (coll. F. Nolf)
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Glycymeris sp. Angola
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Glycymeris sp. Angola
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Comparison of the microsculpture
G. concentrica
G. rafaelmesai
G. formosa
G. scripta G. stellata
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G. concentrica G. formosa G. rafaelmesai
G. scripta Glycymeris sp. G. stellata
Geographic distribution