Echinodermes: Crinoïdes Pentacrinidae (MUSORSTOM 2 & CORINDON 2)
Bourseau, J.-P. (1989). Echinodermes: Crinoïdes Pentacrinidae (MUSORSTOM 2 & CORINDON 2), in: Forest, J. (Ed.) Résultats des Campagnes MUSORSTOM 4. Mémoires du Muséum national d'Histoire naturelle. Série A, Zoologie, 143: pp. 113-201
In: Forest, J. (Ed.) (1989). Résultats des Campagnes MUSORSTOM 4. Mémoires du Muséum national d'Histoire naturelle. Série A, Zoologie, 143. Editions du Muséum: Paris. ISBN 2-85653-150-4. 260 pp., more
In: Mémoires du Muséum national d'Histoire naturelle. Série A, Zoologie. Editions du Muséum: Paris. ISSN 0078-9747, more
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| Keywords |
Classification > Taxonomy
Distribution
Crinoidea [WoRMS]
ISEW, Philippines [Marine Regions]
Marine/Coastal |
| Abstract |
During MUSORSTOM 2 and CORINDON 2 expeditions (West Philippines for the former, Makassar channel for the latter) many stalked crinoids of the family Pentacrinidae were sampled. They are more diversified and comparatively more abundant than the fauna which was collected during the MUSORSTOM 1 expedition. The samplings come from depths between 170 and 970 meters. Four genera are represented: Diplocrinus, Hypalocrinus, Metacrinus and Saracrinus. Detailed descriptions of the ten following species are given: D. alternicirrus, D. sibogae, H. naresianus, M. interruptus, M. musorstomae, M. nodosus, M. serratus, M. wyvillii, S. angulatus and S. superbus. For each specimen, data on morphological features, biometry, arm branching and ossicle articulations are given. Stalk and arm joints were observed under scanning electron microscope, especially stem synostosis with regard to their importance for taxonomy. Sometimes, some peculiar growth patterns appear to be a consequence of fast regeneration. Such features are illustrated by the proximal part of the stalk of a few specimens belonging to S. angulatus and M. wyvillii. As numerous individuals of each species were collected, it was possible to study the variation of crown and stem characters. The morphological features and their variability seem to be depth related. The bathymetrical distribution of Pentacrinidae in the Western Pacific province is examined and discussed. Intraspecific polymorphism with regard to external stem morphology and arm organization is suggested for a few species of this biogeographical province. The number of recognized species might be reduced because some of them might be interpreted as a consequence of ecophenotypic or geographical variations. So, in the subfamily Metacrininae, S. acutus, S. cingulatus, S. batheri and S. suluensis might be synonyms of S. angulatus. It is also suggested that S. nobilis (S. varians and S. superbus included) shows intraspecific polymorphism or large morphological variations through a wide depth range. For the genus Metacrinus, simplification of the species number is more difficult to effect because each phenotype frequently seems to be clearly distinguished. Nevertheless, M. interruptus and M. musorstomae are very similar and the latter might be an ecophenotype of the former. M. costatus and M. serratus are also two species with large morphological affinities ; the first species seems to be a morph living in deeper environment. M. rotundus might include M. multisegmentatus and M. cyaneus. Stem and arm morphological variations linked to bathymetry are also interpreted in terms of adaptive strategy (r and K selection). For pentacrinids, two unstability limits are suggested from their depth repartition: the upper boundary (about 100 meters) could correspond to hydrodynamic vulnerability threshold, the lower (about 1500-2500 meters) to the trophic vulnerability limit, the food becoming too scarce. In one genus, species living close to these two unstability limits have a very important morphological variability (for example: M. rotundus, M. wyvillii). In the Western Pacific, the most stable depth range for these crinoids could be situated between 300 and 600 meters with development of K strategy (M. serratus). Biogeographical repartition of these species is analysed from such a point of view. Typical r strategy species (M. rotundus. M. wyvillii, S. nobilis, H. naresianus) have the largest geographical repartition. S. nobilis seems to be the species with the most eurybathic pattern with polymorphic characters. Taxonomy, paleoecology and biostratigraphy of fossil stalked crinoids must be reconsidered and discussed as a consequence of these results. |
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