Phylogenetics, systematics and biogeography of deep-sea Pennatulacea (Anthozoa: Octocorallia): evidence from molecules and morphology

Abstract

Despite its extreme environmental conditions, the deep sea harbours a unique and
species-rich fauna of mostly unknown age and phylogeny. Pennatulids (Anthozoa:
Octocorallia) are a group whose taxonomy and phylogenetic relationships remain poorly
known and little studied, in spite of their abundance and ecological importance in softbottom
communities. Phylogenetic analysis of a combination of partial ND2 and msh1
sequences produced well-supported phylogenetic relationships for representative deepsea
(and shallow-water) pennatulids at familial, generic and specific taxonomic levels.
Generally, molecular data were congruent with current classification and previous
phylogenetic reconstructions of the O. Pennatulacea based on morphology.
Discrepancies were evident concerning the finer details for some families and genera: this
can be attributable to the high frequency of homoplasy in pennatulids where reversals in
evolution have led to taxa that possess apomorphic character states that are analogous
with plesiomorphic traits. Genetic analysis gave strong support that highly-derived taxa
occur in both shallow and deep water and that many may have differentiated and
dispersed from the deep sea to the shallows. The Renillidae, which is considered one of
the most primitive shallow-water families, evolved recently from deep-water ancestors.
Conversely, the bathyal Anthoptilidae was the most primitive of families, and although
more evidence is required, pennatulids as a group may have originated in deep water.
The systematics of the exclusively deep-sea genus Umbellula, which contains fortytwo
species, remains unclear despite the repeated attempts of revision. Incorporating
new morphological and distributional data from the examination of recently collected
material, together with type specimens, genetic analysis, and a critical study of the
literature, fifteen Umbellula species are here considered valid, including three new to
science. Eight species lack sclerites in the autozooids, U. magniflora, U. encrinus, U.
antarctica, U. carpenteri and Umbellula sp.1 n. sp. (quadrangular axes), and U. huxleyi and
U. pellucida (round axes); and seven possess autozooid sclerites, U. thomsoni and U.
hemigymna (quadrangular axes), and U. monocephalus, U. aciculifera, U. durissima,
Umbellula sp.2 n. sp. and Umbellula sp.3 n. sp. (round axes).
Biogeographic data and genetic evidence supported the hypothesis that species of
Umbellula differentiated in the Indo-Pacific. Many radiated southwards to the Antarctic
and later north into the Atlantic, E Pacific, Indian and Arctic oceans, occupying bathyal
and abyssal depths. Other, older species that evolved via a separate evolutionary
pathway, may have originated in the Indo-Pacific, and dispersed to the Subantarctic (U.
sp.2 n. sp.) or Indian and Atlantic oceans (U. monocephalus). Further, morphological
examination of Umbellula showed it adapted to the oligotrophic conditions of the deep
sea by reducing the number but increasing the size of the autozooids, and in doing so,
enlarged the food-catchment area; abyssal species have done so even more extremely.

More information

Identifiers

Catalogue record

Export record