Jukesena foveolata (Dell, 1964)

J. foveolata View in CoL in Cyamioidea and that the species is not closely related to Gomphina undulosa (type species of Gomphina ) or other Veneroidea, as previously thought.

Considering the number, morphology and degree of development of cardinal teeth, the presence of an internal and an external ligament, the numerous tentacles at the posterior part of mantle margin, the long byssus groove and the left and right inner demibranchs being posteroventrally fused by a short distance, J. foveolata shows greater similarity to Cyamiidae than to Gaimardiidae . However, it differs clearly from all other Cyamiidae studied herein by having both inhalant and exhalant apertures projected as siphons and crowned by tentacles, related to the presence of a well-marked pallial sinus, and by having the series of posterior tentacles arising from the distal part of the middle mantle fold instead of arising from the base of the inner mantle fold as in Cyamiocardium , Cyamium , Gaimardia , Heteromactra , Kidderia , Pseudokellya and Ptychocardia . Furthermore, the anterior labial palps are subquadrate, and the foot appears to lack a differentiated stalk, a condition not seen in any other Cyamiidae . In contrast, unlike any other Cyamiidae and Gaimardiidae , the foot of J. foveolata is compressed and has a narrow base. The molecular information obtained from the two markers considered herein does not allow us to be conclusive whether J. foveolata is a Cyamiidae or belongs to a different family in Cyamioidea . It is interesting to note the similarity in shell morphology and gross anatomy of this species to Cyamiomactra problematica (type species of the genus), although the restricted knowledge of that species does not allow us to be conclusive regarding whether both taxa should be reunited into the same genus.

OTHER TAXA PREVIOUSLY ASSIGNED TO CYAMIOIDEA

Besides the taxa considered above, 11 other (sub) genera ( Costokidderia , Cyamiomactra , Cyamionema , Dicranodesma, Eugaimardia , Legrandina , Lutetina , Neogaimardia , Perrierina, Progaimardia and Reloncavia ) were previously mentioned in the literature as belonging to either Cyamiidae or Gaimardiidae , and seven other families ( Bernardinidae , Basterotiidae , Galatheavalvidae , Juliidae , Neoleptonidae , Sportellidae and Turtoniidae ) were assigned to Cyamioidea /Gaimardioidea.

TAXA HERE REGARDED AS PROBABLY BELONGING TO CYAMIOIDEA

Reloncavia View in CoL (type species: Kingiella chilenica Soot-Ryen, 1959 View in CoL )

The hinge of this genus (figured by Soot-Ryen, 1959: figs 14, 15; and Chavan, 1969: fig. E39, 3 b, 3c) shows great similarity with that of Cyamium View in CoL . Soot-Ryen (1957, 1959) described the gross anatomy of Reloncavia chilenica View in CoL , reporting the presence of a large pedal opening and two smaller (inhalant and exhalant) openings, a large foot, small labial palps and small posterior ‘papillae’. Gallardo (1993) described how ‘each embryo is contained in a small capsule attached to a branchial filament by a short peduncle’. The ‘capsule’ and ‘peduncle’ are likely to correspond to the follicular epithelium recognized here as diagnostic for Cyamioidea . All morphological and anatomical characters suggest Reloncavia View in CoL to be a Cyamiidae View in CoL .

Cyamiomactra View in CoL (type species: Cyamiomactra problematica Bernard, 1897 View in CoL )

The description of this genus was not given separately from that of the type species. Bernard (1897) emphasized the similarity of this genus to Cyamium View in CoL , pointing out as the main differences the shell outline (‘ Cyamium View in CoL is much more elongated’) and the presence of posterior cardinal teeth in the left valve (regarded as absent in Cyamium View in CoL , but as a consequence of an erroneous interpretation of the hinge; see above). After studying the gross anatomy of Cyamiomactra problematica, Ponder (1971) View in CoL concluded that it ‘agrees closely with Cyamium antarcticum View in CoL ’. In fact, the author considered Cyamiomactra View in CoL as a subgenus of Cyamium View in CoL . In its shell outline, Cyamiomactra View in CoL does not show great morphological differences from Cyamium View in CoL .

Perrierina View in CoL (type species: Perrierina taxodonta Bernard, 1897 View in CoL )

The genus has the same number, morphology and arrangement of cardinal teeth as Cyamiomactra problematica View in CoL . This fact was pointed out in its description ( Bernard, 1897) and ratified by subsequent authors (e.g. Fleming, 1948). The only difference is the presence of several lateral ‘crests’ along the dorsal margin in Perrierina View in CoL (diversely referred as lateral teeth, marginal denticles, lateral lamellae, taxodontlike laterals or taxodont lamellae). Ponder (1971) studied the gross anatomy of the type species of Perrierina View in CoL , which, although similar to that of Cyamium View in CoL and Cyamiomactra View in CoL , was described as lacking a byssus groove in the foot and tentacles at the posterior end of the mantle margin (two characters present in the other species of Cyamioidea studied herein). Despite that, Ponder (1971) concluded that Perrierina View in CoL ‘is clearly derived from a Cyamium View in CoL or Cyamiomactra View in CoL - like ancestor’. In addition, he considered Legrandina View in CoL to be a subgenus of Perrierina View in CoL . We have no additional evidence to confirm or reject Ponder’s (1971) opinion. Consequently, we follow the family placement proposed by Ponder (1971) for those taxa.

Neogaimardia (type species: Kellia rostellata Tate , 1889)

Since its description, Neogaimardia has been considered a member of the Gaimardiidae . Odhler (1924) compared it with Gaimardia , and Ponder (1971) and Huber (2010) considered it to be a subgenus of Gaimardia . Morton (1979) provided valuable anatomical information of Neogaimardia finlayi Powell, 1933 , a species very similar to N. rostellata . The main differences of Neogaimardia (with respect to Gaimardia ) are the presence of a short internal ligament, well-defined posterior lateral teeth, accessory ‘marginal teeth’ and the presence of only one (the inner) demibranch at each side. Furthermore, judging from Morton’s (1979) figure 5, the laterofrontal cilia of ctenidia in Neogaimardia do not form hornlike structures. In all other aspects, Neogaimardia appears similar to Gaimardia . In fact, both taxa also have similar modes of life, attached to floating algae. Odhler (1924) described how N. rostellata brood ‘large eggs … in follicles which are formed as in Pseudokellya (cf. Pelseneer, 1903)’. Considering the very peculiar structure described by Pelseneer (1903), it seems clear that Odhner’s description refers to the follicular epithelium considered here as diagnostic for Cyamioidea .

Progaimardia (type species: Modiolarca minutissima Iredale, 1908)

The general shell morphology of the type species closely resembles that of Gaimardia . In fact, this genus was originally proposed as a subgenus of Gaimardia , from which it was distinguished by the presence of a large, internal ligament and a strong hinge plate, bearing one large tooth in each valve and moderately long anterior and posterior teeth ( Ponder, 1971). No additional anatomical or reproductive information is available for this genus.

Eugaimardia (type species: Neogaimardia perplexa Cotton, 1931 )

Cotton (1931a) described a new species of gaimardiid, erecting Neogaimardia as a new genus for its placement, but had overlooked that this name was preoccupied by Neogaimardia Odhler, 1924 . Cotton (1931b) proposed Eugaimardia as a replacement name for the former. Cotton (1931a) distinguished his new genus from Gaimardia by the absence of a concavity in the ventral margin and by its different ‘dentition of the hinge’, namely the presence of a ‘U-shaped tooth, and a small tooth between the arms of the U’ in the right valve. The morphology of the teeth he described does not appear as discrepant from the one we find in G. trapesina . Furthermore, in G. trapesina , the concavity of the ventral margin proves to be variable among specimens. Thus, from a morphological point of view, we find no evidence to consider Eugaimardia to be distinct from Gaimardia . Unfortunately, nothing is known about the anatomy or reproduction of Eugaimardia perplexa . Despite that, Eugaimardia was considered a valid genus by Huber (2010).

Costokidderia View in CoL (type species: Kidderia costata Odhler, 1924 View in CoL )

The type species of this genus has a shell outline that closely resembles that of Kidderia View in CoL . Odhler (1924) described for that species the presence of strong radial sculpture and strong cardinals. The first of these characters led Finlay (1926) to propose the genus Costokidderia View in CoL , a name currently regarded as a subgenus of Kidderia View in CoL (e.g. Ponder, 1971).

Cyamionema (type species: Cyamium (Cyamionema) decoratum Melvill & Standen, 1914 )

Despite having originally been compared with Cyamium View in CoL , the general shell outline and morphology of the hinge teeth of Cyamium decoratum appear more similar to those of K. minuta View in CoL (type species of Kidderia View in CoL ) than to those of Cyamium antarcticum View in CoL (type species of Cyamium View in CoL ). Cyamionema decoratum View in CoL differs from Cyamium antarcticum View in CoL (and from other Cyamiidae View in CoL ) by lacking an internal ligament, by having only one tooth in the left valve and by the presence of thin radial sculpture in the central part of the shell ( Melvill & Standen, 1914). The significance of these differences and the relationship of Cyamionema to Kidderia View in CoL deserve further studies. Scarlato & Starobogatov (1979) proposed a new family, Cyamionematidae (in Galeommatoidea ), based on this genus. Cyamionema appears listed as a subgenus of Kidderia View in CoL by Huber (2010).

TAXA HERE EXCLUDED FROM CYAMIOIDEA