Cimaria

Høisaeter, Tore, 2012, Cimaria vargasi n. gen, n. sp. (Gastropoda: Pyramidellidae: Odostomiinae) from the Pacific Coast of Costa Rica, Central America, Zootaxa 3178, pp. 63-67 : 66-67

Cimaria sp.

( Fig. 3 C)

In addition to the material from Costa Rica, a single worn shell was found in a sample from a mangrove creek in Macau, 5°05'S, 36°30'W, Rio Grande do Norte, Brazil (ZMBN 87911). This shell may or may not belong to the same species as the ones from Costa Rica, and is here called Cimaria sp.

Cimaria vargasi is characterized by an unusually thick shell with a pitted surface, unknown among pyramidellids described to date. Representatives of the genus Adelactaeon Cossmann, 1895 , have spiral grooves with pits along their bottom (see van Aartsen et al. 1998).

Of the known pyramidellids from the tropical eastern Pacific, Egila poppei Dall & Bartsch, 1909 is perhaps the one most similar to the new species. An unnamed species from the west coast of southern Mexico have axial sculpture above the periphery and pits below, and is thus intermediate in sculpture between Egila poppei and Cimaria vargasi (Patrick LaFolette, pers. comm.)

Seven specimens were collected alive, but could unfortunately not be observed alive, or properly preserved for description of the soft parts. The eyes are exceptionally close-set, however, even for a pyramidellid, and are thus reminiscent of Odostomia lukisi Jeffreys, 1848 , from the north-east Atlantic. There are not many further clues available as to its closest relatives among pyramidellids. The shell characters, however, seems to rule out any close relationship to any so far described tropical, west American species. The thick shell and the very prominent columellar tooth indicates a placement within the subfamily Odostomiinae .

The microhabitat of the new species is unknown. The different frequency of the new species in the five samples from Punta Morales, does not eliminate any of several possibilities. The most parsimonious conclusion is that the species lives in a narrow zone close to the beach, maybe on the borderline between the beach dominated by coarse shell debris and the mud flat proper. Much coarse shell debris was present in the sample with 16 shells ( Table 1 ), indicating a thin layer of sandy mud on top of coarser sediment. Four living specimens, all juveniles, together with three empty shells, were found in a sample where all bottom material went through the 500 µm mesh sieve. This sample was incredibly rich in living gastropods (dominating species seemed to belong to Crepidula , Natica , Nassarius , Anachis, Epitonium , and several small pyramidellids), and the limited number of specimens might indicate that C. vargasi does not live uniformly throughout the transect covered by this sample. In another rich sample, which was taken about 100 m from the beach, no living specimens were found and it is unlikely that many were overlooked. This contrasts starkly with the richness of other species. The solid, thick shell is rather untypical for pyramidellids living in muddy sediment. Thus patches of hard substrate on the mud flat, or a narrow zone close to the beach, may be the preferred habitat of this species. A plausible hypothesis is that the pyramidellid may be loosely associated with one or more of the Crepidula or Calyptraea species found scattered in the samples.

The thick shell may be an adaptation to heavy predation pressure. A majority (i.e., 10 of 16 from station CoRi 34) of the empty shells were found with the outer lip broken in a characteristic way, as by the claw of a crab. Many of these scars were almost identical in shape and position on the lower part of the outer lip, and several had old, repaired scars of the same shape. Only three shells had naticid bore-holes, although many naticids were found in the samples.

The shell from Brazil presents a particular challenge. Although the possibility of the shell being conspecific with the population from Costa Rica cannot be completely excluded, I agree with e.g. Pimenta et al. (2009) that this is very unlikely, and since only a single, worn shell is found, I provisionally call it Cimaria sp.

Logistic help was provided by the director, Dr. José Vargas, and the staff of CIMAR. Also my most sincere thanks to Franklin Guillén for invaluable assistance in the field, and to Rita Vargas at the Museo de Zoologia at the University of Costa Rica, for pleasant company and help during the sorting and working up of the material. The SEM photographs were taken at the Laboratory for Electron Microscopy at the University of Bergen, by Chief Engineer Egil Sev. Erichsen, whose help has been most appreciated. I also thank Patrick I. LaFolette for constructive comments on the manuscript. Elin Holm has drawn the maps and helped with the editorial arrangement of the other illustrations.

Figures

FIGURE 3. Light microscopy. A & B - Cimaria vargasi. Two views of largest shell found (ZMBN 87909); 2.7 mm long. Showing the thickened outer lip in fully grown shells. C - Cimaria sp. Shell from Macau, Brazil (ZMBN 87911); 1.4 mm long.