Structural–functional Aspects in the Evolution of Operculate Corals (Rugosa)

Abstract

ABSTRACT. Among the Rugosa operculae were developed by only a few genera. One is the slipper-shaped Calceola and another is the pyramidal shaped Goniophyllum. On the basis of biological and morphological knowledge of recent corals, the two different bauplans of the soft bodies of Calceola and Goniophyllum have been reconstructed. The soft body (i.e. the polyp) of a rugose coral is thought to have all the basic structures of anthozoan polyps: a barrel-like body shape, a¯at oral disc with tentacles, and a mouth from which a pharynx reaches inside the gastric cavity. Furthermore, as in all Anthozoa, Rugosa had internal mesenteries that act as tensile cords; during growth in the diameter further mesenteries were inserted. In contrast to all other Anthozoa, in the Rugosa new single mesenteries were added in four insertion sectors. The bauplans of Calceola and Goniophyllum differ in the pattern of mesentery insertion into these four sectors. Calceola had a serial insertion pattern and Goniophyllum had a symmetrical insertion pattern. They are representatives of the two different bauplans within the Rugosa. The lid corals are examples of convergent evolved genera; Calceola as well as Goniophyllum originated by quite simple modi®cations of the ancestral type. The peculiar shapes, the operculae and especially the straight hinges between the calyx and the lid(s) result only from mechanical necessity. Under special conditions (such as high sedimentation rates) these modi®cations of the corallites represent suitable tactics for survival.

Soft body reconstructions of Palaeozoic corals: implications for the system of Anthozoa (Coelenterata)

“…Although many Rugosa show these serial insertion patterns, some other patterns have been found in Palaeozoic corals: Schindewolf (1942Schindewolf ( , 1950) mentioned a sym- metric pattern for the pleurophylliids and scleractinian-like patterns were mentioned in Numidiaphillida and Kilbuchophyllida (Ezaki 1997(Ezaki , 1998(Ezaki , 2000Scrutton & Clarkson 1991;Sorauf 1966). Examples of the serial pattern are well known (Hill 1981a, b): examples for the symmetric pattern are Argutastrea (Gudo & Hubmann 2001), Goniophyllum (Gudo 1999(Gudo , 2001(Gudo , 2002 and several genera of the pleurophylliids (Figs 2, 3). The latter pattern with exponential insertion of septa in six sectors, which has been found in the Ordovician Kilbuchophyllidae (Scrutton & Clarkson 1991;Sorauf 1966) and in the Numidiaphyllidae (Ezaki 1997), is also present in several genera of the Streptelasmatida, e.g.…”

“…Accordingly, these corals show a radial septal pattern, and deep calyces such as can be found in Argutastrea (Gudo & Hubmann 2001). Other specimens that belong in this group are Goniophyllum, Araeopoma (Gudo 1999(Gudo , 2002 and Polycoelia (Gudo 2001).…”

“…counter side and the corallum changed into a slipperlike shape by mechanical necessity due to opening and closing of the lid (Gudo 1998(Gudo , 2000a(Gudo , 2002Richter 1929). In the Symmetricales, the formation of four lids was possible because they have symmetric growth zones and mesenteries are shifted to both lateral sides and to both perpendicular sides.…”

“…In the Symmetricales, the formation of four lids was possible because they have symmetric growth zones and mesenteries are shifted to both lateral sides and to both perpendicular sides. Consequently, four lids developed and the corallum changed into a pyramidal shape, again by mechanical necessity due to opening and closing of the lids (Gudo 1998(Gudo , 2000a(Gudo , 2002Richter 1929). In a more traditional view, the operculate corals are joined together in one monophyletic group (Stolarski 1993).…”

“…The polyps, which have only four zones in which to grow (Seriales, Symmetricales, Heterocorallia), were constrained to having a round circumference. The only exceptions are external deformations caused by closely growing neighbours or autodefor-mations resulting from mechanical necessity, as is true of the lidded corals (Gudo 1998(Gudo , 1999(Gudo , 2000a(Gudo , 2002Richter 1929). Due to having a serial or a symmetrical pattern of mesentery insertion, the Seriales can build Calceola-like corals with one lid and the Symmetricales can build Goniophyllum-like corals with four lids (Gudo 1999(Gudo , 2001(Gudo , 2002.…”