Family CRISINIDAE D'Orbigny, 1853

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Family CRISINIDAE D'Orbigny, 1853

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Crisinidae was first proposed by d'Orbigny (1853) for the genus Crisina d'Orbigny 1850. The genus was defined for eight species of fossils, but no type species was designated. Harmer (1915) nominated the Australian Recent species Retepora radians Lamarck (1816) as the type species, although this was not one of the species included in the original definition. Canu & Bassler (1920) proposed that the type species be Crisina normaniana (d'Orbigny 1853), and established a new genus Mesonea, with M. radians as type species. The status of the genus Mesonea was clarified by Gordon & Parker (1991), who showed that Crisina lacks both the pores on the frontal surfaces, and the porous areas of the gonozooid which are characteristic of Mesonea.

The family is represented in Australian waters by Mesonea radians (Lamarck), which is found in eastern Australia, Torres Strait and the Paternoster Islands (Harmer 1915). The records indicating a wider distribution for Mesonea radians are based upon other species with similar colony forms (Gordon & Parker 1991).

Colonies are erect, with numerous branches bifurcating from a narrow encrusting base; with the colonies often forming a low inverted cone. A spotty purple colouration is often seen, but the nature of this colouration has not been investigated. The branches are about 1 mm wide, and are formed of zooids in series alternately to the left and right of the midline of the frontal surface. The frontal surface of the branch has numerous minute pseudopores, which are often set singly or as groups of two or three in larger oval depressions. These depressions are particularly well-defined away from the zooidal tubes, towards the sides of the frontal surface. The branch basal surface has several longitudinal ridges and grooves, (see Horneridae) with regularly placed pores in the grooves. The pores on both the frontal and basal surface have been identified as cancelli (Borg 1941), but examination with the scanning electron microscope suggests that the pores on the opposing surfaces have different origins. The gonozooids are large elongate raised chambers on the frontal side of the branch, located just proximal to a bifurcation (Gordon & Parker 1991). The gonozooids are pierced by two to four series of autozooids, with the ooeciostome located proximal to one of the zooid tubes. Distinctive minutely porous areas, with raised rims, occupy the area between autozooid series.

Although Mesonea radians is often found growing on algae in shallow water, it is also recorded at depths of over 100 metres. It is found from southern Australia (Bock 1982) to the tropical region (Harmer 1915).

The family has a fossil record from the Cretaceous of Europe, and from the Miocene of Victoria (Voigt 1984, MacGillivray 1895).

Diagnosis

Colony well calcified, erect, arising from a small encrusting base, with numerous bifurcating branches, often forming a cone. Zooid peristomes alternating on either side of a mid-line, walls sometimes pigmented, with pseudopores, basal surface with ridges and grooves. Gonozooids elongated, frontal, proximal to a branch bifurcation, incorporating several zooid series, ooeciostome proximal to a zooid peristome.