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Gacella

Strophomenata - Orthotetida - Chilidiopsidae

Taxonomy
Gacella was named by Williams (1962) [Sepkoski's age data: O Llde Sepkoski's reference number: 1066]. Its type is Gacella insolita. It is the type genus of Gacellinae.

It was assigned to Orthotetidae by Williams (1962); to Gacellinae by Williams et al. (2000); and to Strophomenida by Sepkoski (2002).

Synonymy list
YearName and author
1962Gacella Williams pp. 222 - 223
2000Gacella Williams et al. p. 671
2002Gacella Sepkoski, Jr.

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RankNameAuthor
kingdomAnimalia()
Triploblastica
Eutriploblastica
Neotriploblastica
Eucoelomata
superphylumLophotrochozoa
Lophophorata
phylumBrachiopodaCuvier 1805
RankNameAuthor
subphylumRhynchonelliformeaWilliams et al. 1996
classStrophomenataWilliams et al 1996
orderOrthotetidaWaagen 1884
suborderOrthotetidina
superfamilyChilidiopsoideaBoucot 1959
familyChilidiopsidaeBoucot 1959
subfamilyGacellinae
genusGacella

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

Diagnosis
ReferenceDiagnosis
A. Williams 1962Biconvex, transversely semi-oval shells with a dorsal median fold and a complementary ventral sulcus projected dorso-anteriorly as a pronounced tongue so that the anterior commissure is uniplicate; ornamentation consisting of differentially accentuated costellae arising by intercalation and fine, closely spaced, concentric lamellae; ventral interarea long, procline to apsacline in disposition, pseudodeltidium strongly arched, almost completely covering the deltidium, foramen large and supra-apical; dorsal interarea anacline, chilidium convex and well developed; shell substance impunctate.

Teeth small, supported by a pair of long, deep, subparallel dental lamellae; pedicle callist well developed supra-apically; muscle-scar confined by the dental lamellae and orthoid in appearance with a lanceolate adductor field divided medianly by a faint ridge and surrounded by a pair of narrow diductor scars, lobate and discrete anteriorly; vascula media emerging anterior to the muscle-field as parallel impressions on either side of the sulcus, the rest of the pallial sinus pattern unknown.

Cardinal process bilobed, projecting ventrally and with the attachment area for the diductor muscles facing ventro-posteriorly, socket ridges well developed, parallel with the hinge-line and, like the cardinal process, overhanging the visceral chamber and unsupported by any definite notothyrial platform; adductor muscle-scars not deeply impressed but quadripartite about a pair of divergent septa flanking a low median ridge which bifurcates anteriorly to subtend an additional discrete and slender median ridge.