Cypris morphology in the barnacles Ibla and Paralepas (Crustacea: Cirripedia Thoracica) implications for cirripede evolution

We used scanning electron microscopy (SEM) to describe cypris morphology in species of the barnacles Ibla and Paralepas, both of which are pivotal in understanding cirripede evolution. In Ibla, we also studied late naupliar stages with video and SEM. Special emphasis was put on the lattice organs, the antennules and the thorax and telson. In Paralepas we had settled specimens only and could therefore only investigate the carapace with the lattice organs. Cyprids of Ibla quadrivalvis and Paralepas dannevigi have five sets of lattice organs, grouped as two anterior and three posterior pairs. The organs are of the pore‐field type and the terminal pore is situated anteriorly in the first pair, just as in the Rhizocephala and the Thoracica. In Ibla the armament of antennular sensilla resembles that found in the Thoracica but differs from the Rhizocephala. The absence of setules on the A and B setae sited terminally on the fourth antennular segment is a similarity with the Acrothoracica. The attachment disc is angled rather than facing distally and is encircled by a low cuticular velum. The thoracopods have two‐segmented endopods and exopods as in the Thoracica, but the number, shape, and position of thoracopodal setae differ somewhat from other species of that superorder. Both Ibla and Paralepas cyprids have a deeply cleaved telson, but no independent abdominal part. In cypris morphology, Ibla and Paralepas show several synapomorphies with the clade comprising Rhizocephala and Thoracica and there are no specific apomorphies with either the Acrothoracica, the Rhizocephala or any particular subgroup within the Thoracica. This is in agreement with recent molecular evidence that Ibla (Ibliformes) is the sister taxon to all other Thoracica and the ibliforms therefore become the outgroup of choice for studying character evolution within the superorder. Paralepas, and other pedunculated barnacles without shell plates, are apparently not primitive but are secondarily evolved and nested within the Thoracica. J. Morphol., 2009. © 2008 Wiley‐Liss, Inc.     

Floral ontogeny of the Afro-Madagascan genus Mitrasacmopsis with comments on the development of superior ovaries in Rubiaceae

BACKGROUND AND AIMS: Members of Rubiaceae are generally characterized by an inferior ovary. However, Mitrasacmopsis is cited in the literature as having a semi-inferior to superior ovary. It has previously been hypothesized that the gynoecial development of Rubiaceae with semi-inferior to superior ovaries takes place in the same way as in Gaertnera, one of the most commonly cited rubiaceous genera with a superior ovary. To test this hypothesis, a floral ontogenetic study of Mitrasacmopsis was carried out with special attention paid to the gynoecial development. METHODS: Floral ontogeny and anatomy of Mitrasacmopsis were examined using scanning electron and light microscopy. KEY RESULTS: At an early developmental stage, a concavity becomes visible in the centre of the floral apex simultaneously with the perianth initiation. A ring primordium surrounding this concavity expands vertically forming the corolla tube (early sympetaly). Stamen primordia develop inside the corolla. From the bicarpellate gynoecium only two carpel tips are visible because the ovary is formed by a gynoecial hypanthium. In the basal part of each carpel, a placenta primordium is initiated. Two septa divide the ovary into two locules. In each locule, the placenta becomes mushroom shaped and distinctly stalked. Eventually, the inferior ovary of Mitrasacmopsis develops into a beaked capsule. Only very late in the fruiting stage, the continuously expanding ovary is raised above the insertion point of the persistent calyx, changing the ovary position of Mitrasacmopsis from basically inferior to secondarily semi-inferior. CONCLUSIONS: Mitrasacmopsis follows an epigynous pattern of floral development. However, the presence of a prominent beak in the fruiting stage gives the whole ovary a semi-inferior appearance. This kind of secondarily semi-inferior ovary is shown to be different from the secondarily superior ovary observed in Gaertnera.