Cetoconcha Dall, 1886

Pacheco, Leonel I., Teso, Valeria & Pastorino, Guido, 2024, Use of traditional tools and micro-computed tomography for the taxonomy of carnivorous bivalves from the deep waters of Southwestern Atlantic, Zoological Journal of the Linnean Society 202, pp. 1-23 : 9-11

publication ID

https://doi.org/ 10.1093/zoolinnean/zlae118

publication LSID

lsid:zoobank.org:pub:1C0D753-0F6F-4D0C-BD1D-8D1C6D588F30

DOI

https://doi.org/10.5281/zenodo.14269307

persistent identifier

https://treatment.plazi.org/id/03857E58-A108-FF81-FBAD-FDB7FF30FC0B

treatment provided by

Plazi

scientific name

Cetoconcha Dall, 1886
status

 

Cetoconcha Dall, 1886 View in CoL

Type species: Lyonsia bulla Dall, 1881 , by original designation.

Desciption

Shell: Globular to ovate. Inequivalve; right valve overlaps less anterodorsally and posterodorsally. Inequilateral, posterior region with siphonal gape. Surface granulated, covered by numerous radial lines. Hinge of less valve edentulous and right sometimes with weak cardinal tooth corresponding to a socket in less valve. Inner ligament supported by elongated and superficial resilifer (over hinge margin), delimited by angular ridges. Lithodesma absent. Posterior hinge margin covered by a layer of fused periostracum.

Remarks

Ŋe following description of the soss parts of Cetoconcha is based on the information taken from the studied specimens of Cetoconcha spinulosa , and the bibliography ( Pelseneer 1888 b, Allen and Morgan 1981, Krylova 2001, Leal 2008).

Ŋe body is completely sealed, except for two siphonal and one pedal gape, similar to Cardiomya . However, the pedal gape in Cetoconcha is larger, running from the anterior adductor muscle to two-thirds of the ventral margin. Internally, the palial cavity is compartmentalized into an infraseptal and a supraseptal cavity by the muscular septum and connected through three pairs of groups of septal pores. Ŋe number of septal pores varies subtly, sometimes even between sides of the same specimen, and each one contains gill filaments lacking interfilamental connections. Ŋe cavities connect to the exterior through the siphonal gaps, as described in Cardiomya .

In Cetoconcha View in CoL , both siphons are exposed, instead of being inside a siphonal sheath, and they are separated by the intersiphonal septum ( Fig. 5B View Figure 5 ). Ŋe inhalant siphon is modified into a large raptorial sac invaginated inside the pallial cavity, and the exhalant siphon is short, conical, and slightly prominent. In the scanned specimen, the raptorial inhalant siphon was fixed, contracted, and semi-evaginated near the siphonal tentacles, hence its shape cannot be understood fully ( Fig. 5A–C View Figure 5 ). Ŋe siphonal tentacles are tapered and surround the siphons with an irregular distribution, with one dorsal to the exhalant siphon and 12–14 lateral and ventral to the inhalant siphon. Machado et al. (2019) reported 13 siphonal tentacles, but this number tends to vary among Poromyoidea, even within a species, commonly ranging between 13 and 15 ( Krylova 2001). Ŋis numerical variation is evident among the studied specimens of Cetoconcha spinulosa . A pair of structures that seem to correspond to the pair of internal tentacles described by Allen and Morgan (1981) for Poromya View in CoL and Cetoconcha species is located ventral to the posterior adductor muscle, anterior to the exhalant siphon and lateral to the visceral ganglion ( Fig. 5B View Figure 5 ). Although Machado et al. (2019) did not mention any internal siphonal tentacles, they were observed in ZUEC 7002. Allen and Morgan (1981) proposed the cleaning of the supraseptal cavity from faecal material as a possible function.

Ŋe septum is connected anteriorly to the mantle margin between the anterior adductor muscle and the anterior labial palps and, posteriorly, to the intersiphonal septum. One pair each of fine anterior, posterior, and lateral muscles provide aưachment to the shell. Ŋe anterior and posterior septal muscles in Cetoconcha View in CoL are much thinner and more rod shaped compared with Cardiomya View in CoL . Ŋe lateral septal muscles are concentrated on the posterior side of the body, aưaching to the shell at a single point. Posterior to the septal muscles, the septum becomes more membranous. At this point, a swollen and hollow bilobate sac, apparently associated with the eversion of the inhalant siphon ( Morton 1981), is visible.

Foot hatchet-shaped, large, with a shallow byssal groove, attached to the shell through one pair of anterior retractor muscles and one posterior muscle that bifurcates near the attachment site. The anterior palps are well developed, and the posterior palps are reduced in comparison but still noticeable ( Fig. 5A, B, D View Figure 5 ). The digestive tube remains the same as in Cardiomya . The stomach is covered anterodorsally by the digestive diverticula, posterodorsally by the ovaries, and posteroventrally by the testes ( Fig. 5A, B View Figure 5 ), because this genus is hermaphroditic. Only the visceral ganglia could be observed ( Fig. 5E, F View Figure 5 ).

‘Visceral muscles’ are also present and can be seen in Figure 5A, B, F View Figure 5 in our scanned specimen (MACN-In 44329) and in Figure 5G View Figure 5 in the specimen from the study by Machado et al. (2019) (ZUEC 7002). These muscles are visible to the naked eye ( Fig. 7F View Figure 7 ), and instead of forming a group of scarce muscle bundles, as in Cardiomya , they form a rod-shaped structure.

Kingdom

Animalia

Phylum

Mollusca

Class

Bivalvia

Family

Cetoconchidae

Loc

Cetoconcha Dall, 1886

Pacheco, Leonel I., Teso, Valeria & Pastorino, Guido 2024
2024
Loc

Cetoconcha

Dall 1886
1886
Loc

Cetoconcha

Dall 1886
1886
Loc

Cardiomya

Fagilissima (E. A. Smith 1885
1885
Loc

Poromya

Forbes 1844
1844
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