Sunday, May 13, 2018

[Cnidaria • 2018] Conglomeratusclera coerulea & Caementabunda simplex • Evaluating the Genus Cespitularia Milne Edwards & Haime, 1850 with Descriptions of New Genera of the Family Xeniidae (Octocorallia, Alcyonacea)

 Conglomeratusclera coerulea (May, 1898)

Caementabunda simplex (Thomson & Dean, 1931)  

in Benayahu, van Ofwegen & McFadden, 2018.

Several species of the family Xeniidae, previously assigned to the genus Cespitularia Milne Edwards & Haime, 1850 are revised. Based on the problematical identity and status of the type of this genus, it became apparent that the literature has introduced misperceptions concerning its diagnosis. A consequent examination of the type colonies of Cespitularia coerulea May, 1898 has led to the establishment of the new genus Conglomeratusclera gen. n. and similarly to the assignment of Cespitularia simplex Thomson & Dean, 1931 to the new genus, Caementabunda gen. n. Both new genera are described and depicted and both feature unique sclerite morphology, further highlighting the importance of sclerite microstructure for generic position among Xeniidae. Freshly collected material was subjected to molecular phylogenetic analysis, whose results substantiated the taxonomic assignment of the new genera, as well as the synonymies of several others.

Keywords: Indo-Pacific Ocean, new genera, phylogeny, sclerite microstructure, taxonomy

Figure 5. Live colonies on the reefs of Green Is. Taiwan.
A–B Conglomeratusclera coerulea (May, 1898).
Caementabunda simplex (Thomson & Dean, 1931) with expanded polyps D C. simplex (Thomson & Dean, 1931) with partially retracted polyps.

Photo credit Chang-Feng Dai, National Taiwan University, Taiwan.

Class Anthozoa Ehrenberg, 1831
Subclass Octocorallia Haeckel, 1866
Order Alcyonacea Lamouroux, 1812
Family Xeniidae Ehrenberg, 1828

Conglomeratusclera gen. n.

Type species: Cespitularia coerulea May, 1898: 21

Diagnosis: Colonies soft with a short but distinct stalk, ramified into primary branches and occasionally into secondary ones. Polyps monomorphic, found along the branches, sometimes down on the stalk; most are non-retractile. Sclerites of a wide diversity of forms and dimensions, many lacking a distinct repetitive morphology. They include spheres, spherules, and small dumbbell-like sclerites. They are commonly cemented together, forming heterogeneous morphologies of various shapes and sizes. Occasionally, the aggregates form plate-like structures, embedded with spheres and/or spherules. The abundance of sclerites can vary greatly; in some specimens they are rare and then mostly found only at the colony base, and occasionally they may be found in all parts of the colonies, or may even be entirely absent. Zooxanthellate.

Etymology: The generic name is derived from Latin conglomerātus, which refers to anything composed of heterogeneous materials or elements and sclera from Greek meaning sclerite. Here it denotes the sclerites that resemble the geological structures termed conglomerates, a feature comprising rounded to sub-angular clast of granules, pebbles or cobbles cemented together. Gender female.

Conglomeratusclera coerulea (May, 1898)

Distribution: Kenya; Zanzibar; Tanzania; Glorioso Islands; Mauritius; Seychelles; Mayotte; Taiwan; Philippines; Japan (Tanabe, Wakayama, Shikoku); Ryukyu Archipelago; Indonesia.

Conglomeratusclera robusta (Tixier-Durivault, 1966)
Cespitularia robusta Tixier-Durivault, 1966: 335–356; Janes 2008: 604–605.

Distribution Mayotte; Aride Island, Seychelles.

Caementabunda gen. n.

 Type species: Cespitularia simplex Thomson & Dean, 1931

Diagnosis: Colonies quite flaccid with a distinct but short encrusting base bearing primary lobes, sometimes divided into secondary ones. Non-retractile monomorphic polyps found on the lobes and occasionally down on some parts of the base. The spherical-oval sclerites are composed of a myriad of densely packed chip-like microscleres. Zooxanthellate.

Etymology: The generic name refers to the microstructure of the sclerites, which are composed of multitudes of microscleres, resembling aggregates of cement chips. The name is derived from the Latin caementumcement, and abunda meaning copious. Gender feminine.

Caementabunda simplex (Thomson & Dean, 1931)

Distribution: Green Island, Taiwan; Philippines; Great Barrier Reef; Sulawesi; Madagascar; Seychelles.

Morphological and molecular phylogenetic analyses support the reassignment of the former species Cespitularia coerulea and C. simplex into two separate genera; Conglomeratusclera n. gen. and Caementabunda n. gen., respectively. They are distinguished by differences in sclerite microstructure as well as genetic distances comparable to those among other well-defined genera of the family Xeniidae. In addition, the findings justify synonymy of C. taeniata and C. turgida with each of these two new genera, respectively. We are at present only able to distinguish a single species in each of the new genera, based on both morphology and genetics. It should be noted that the status of C. robusta as a second species of Conglomeratusclera remains to be verified genetically. A recent study of the xeniid genus Ovabunda found a lack of congruence between the morphological characters traditionally used to diagnose species, in particular the number of rows of pinnules and pinnules per row, and genetic evidence of species boundaries (McFadden et al. 2017). In that case, evidence from multiple segregating nuclear markers was necessary to delineate species that shared identical or very similar mitochondrial haplotypes. Therefore, it is possible that data from additional genetic markers might detect further differences among those individuals with variant 28S rDNA genotypes that we have assigned here to Conglomeratusclera coerulea and Caementabunda simplex. As currently circumscribed, both of these new genera and in particular the respective species occur over a wide geographic range from the south-western Indian Ocean (Madagascar) to Japan.

 Yehuda Benayahu, Leen P. van Ofwegen and Catherine S. McFadden. 2018. Evaluating the Genus Cespitularia Milne Edwards & Haime, 1850 with Descriptions of New Genera of the Family Xeniidae (Octocorallia, Alcyonacea). ZooKeys. 754: 63-101. DOI: 10.3897/zookeys.754.23368

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