Soft corals of the genus Dendronephthya are among the most visually spectacular animals on tropical reefs. Lacking the symbiotic algae called zooxanthellae that power most reef-building corals, they cannot rely on photosynthesis and instead feed by capturing tiny particles from the water column. Their polyps bear comb-like pinnules along the borders of their tentacles, an adaptation that improves their ability to strain phytoplankton from passing currents, and research has shown they absorb considerable amounts of dissolved organic matter in addition to their planktonic diet. Because they depend entirely on external food, these corals thrive on flow-exposed reef slopes, where their bushy, tree-like colonies sway in the current in shades of red, pink, orange and purple. Their vibrant colours and branching forms have also made them popular in the aquarium trade, adding commercial pressure to a group that remains poorly understood scientifically.

Taxonomically, Dendronephthya is a nightmare. The genus comprises more than 247 species whose distinguishing characters, chiefly the form, size and arrangement of their microscopic calcium carbonate skeletal elements known as sclerites, are subtle and frequently overlap between species. This morphological ambiguity has long frustrated efforts to delimit species boundaries, and the problem is compounded by the slow evolutionary rate of the genetic markers traditionally used in octocoral systematics. The species at the centre of the new study, Dendronephthya sinaiensis, was originally described by the Dutch taxonomist Jan Verseveldt from the Gulf of Aqaba in the northern Red Sea, and every subsequent record has come from Red Sea localities, where the species inhabits current-swept reef slopes at mesophotic depths. No confirmed occurrence outside the Red Sea had ever been documented, which is precisely why the Lakshadweep specimen is biogeographically noteworthy.

The research team, led by Nayana Narayanankutty with C. A. Riyas, K. K. Idreesbabu and S. Sureshkumar, collected a single colony fragment from the reef slope at Suheli Par using SCUBA. Portions of the colony were preserved in 75 percent ethyl alcohol for morphological examination and in 100 percent molecular-grade alcohol for genetic analysis, and the specimen was deposited and curated in the Biodiversity Laboratory at Kerala University of Fisheries and Ocean Studies under the catalogue number BDLKUFOS-03-001. The colony itself was an arborescent, tree-like form roughly 75 millimetres tall with a polypary spread of about 55 millimetres, displaying a divaricate growth pattern with long, slender terminal twigs bearing polyps grouped into bundles of five to six. The overall colouration was wine-red, with whitish to greyish stems and branches, white polyps, and wine-red sclerites within the stem.

The morphological work focused on the sclerites, the microscopic skeletal spicules that serve as primary diagnostic characters in octocoral taxonomy. The researchers dissolved small tissue fragments from different colony regions in 10 percent sodium hypochlorite, rinsed the liberated sclerites repeatedly with distilled water, and treated them with neutralised hydrogen peroxide to remove residual organic debris. Under light microscopy, the specimen revealed large, slender, spindle-shaped sclerites measuring approximately 1.7 to 2.5 millimetres in length within the supporting bundles, smaller spindles of 0.1 to 0.3 millimetres, tiny spiny rods of 0.05 to 0.1 millimetres in the tentacles, and characteristic antler-shaped sclerites up to 0.03 millimetres in the stalk. The anthocodiae, the cup-shaped feeding portions of the polyps, carried well-developed point sclerites arranged in longitudinal rows around the anthocodial wall, a configuration corresponding to a Grade II anthocodial armature, while crown sclerites were conspicuously absent.

These characters collectively matched Verseveldt’s original description of Dendronephthya sinaiensis with striking fidelity: the colony colouration, the polyp arrangement, the antler-shaped stalk sclerites, the anthocodial armature, the absence of crown sclerites, and the strongly developed supporting bundles that project beyond the anthocodial apex all agreed. The specimen could be distinguished from morphologically similar relatives such as D. hemprichi, which forms larger, more robust colonies with densely aggregated polyps, D. klunzingeri, which exhibits bushier colonies with different coenenchymal sclerite composition, and D. cervicornis, which shows a distinctly dichotomous branching pattern and lacks the combination of wine-red colouration and antler-shaped stalk sclerites. Nevertheless, the authors could not unequivocally verify the complete anthocodial formula reported by Verseveldt, because overlapping point rows and the inability to fully flatten the anthocodia prevented an exact count of point pairs and intermediate sclerites. Combined with the absence of a direct comparison with type material, this led the team to a deliberately conservative identification: Dendronephthya cf. sinaiensis, with the abbreviation cf. signalling a close but provisional match.

To strengthen the case, the team turned to genetics. Genomic DNA was extracted from the ethanol-preserved tissue and two gene fragments were amplified and sequenced: a 735-base-pair segment of the mitochondrial mtMutS gene, widely used in octocoral systematics, and an approximately 810-base-pair fragment of the nuclear 28S rRNA gene. The sequences were deposited in GenBank under accession numbers PV469418 and PZ568242 respectively. The results were remarkable. The mtMutS sequence showed 100 percent identity, with a Kimura two-parameter genetic distance of zero, to three published sequences attributed to Dendronephthya sinaiensis from the Red Sea, while intrageneric distances to other Dendronephthya species ranged from 0.4 to 0.5 percent and intergeneric distances to outgroup species of Sinularia reached 10.0 to 10.4 percent. The 28S rRNA dataset told the same story, showing complete identity to two reference sequences of D. sinaiensis.

Phylogenetic analyses reinforced the genetic evidence. Maximum likelihood trees constructed with IQ-TREE placed the Lakshadweep specimen squarely within the Dendronephthya clade, and the mtMutS sequence clustered directly with the published Red Sea D. sinaiensis sequences with a bootstrap support value of 97 percent, while remaining clearly separate from congeners such as D. hemprichi, D. putteri and D. suensoni. The 28S rRNA analysis produced a congruent topology, with the new sequence forming a distinct lineage with the D. sinaiensis references and the Sinularia outgroups forming a well-supported sister clade with 100 percent bootstrap support. Yet the authors caution that these markers, though among the most informative currently available for octocorals, often fail to reliably distinguish closely related nephtheid species, and public databases contain limited Dendronephthya sequences, many unverified against type specimens. The molecular data therefore support a close relationship with D. sinaiensis rather than serving as the sole basis for species confirmation, which is why the cf. designation stands pending further examination of fully dissected anthocodiae and comparison with type material.

Beyond taxonomy, the occurrence raises fascinating questions about how a Red Sea-affiliated soft coral reached an atoll in the Arabian Sea, roughly two thousand kilometres away. Several mechanisms could theoretically facilitate dispersal across such distances: transport of larvae on ocean currents, rafting of asexually detached fragments, which Dendronephthya species are known to produce through autonomous fragmentation, or human-mediated vectors such as ballast water and hull fouling on ships. Global maritime traffic is a well-documented conveyor of marine organisms, and the Lakshadweep reefs lie close to major international shipping routes connected through the Bab-el-Mandeb Strait at the southern entrance to the Red Sea, suggesting that both natural and anthropogenic dispersal could be involved. The authors stress, however, that in the absence of direct evidence these mechanisms remain speculative, and resolving them will require population-level genetic studies and broader spatial sampling across the Indian Ocean.

The study also underscores how little is known about soft coral diversity in the Lakshadweep Islands compared with other Indo-Pacific reef systems. While hard corals of the archipelago have received substantial attention, systematic studies of its soft corals remain scarce, with only a handful of historical works documenting the region’s octocoral fauna. The first molecular record of Dendronephthya from the archipelago therefore fills a genuine gap and provides a foundation for future taxonomic and biogeographic research on nephtheid octocorals in the northern Indian Ocean. The authors, whose work was supported by a Core Research Grant from the Department of Science and Technology, Government of India, argue that accurately delineating species in this challenging genus will demand a fully integrative approach combining SEM-based sclerite analysis, nuclear genetic markers, expanded reference datasets and much wider sampling. For now, a wine-red fragment from a Lakshadweep reef slope stands as a reminder that the distributions of even familiar reef animals may be far less settled than the textbooks suggest.

Subject of Research: First molecular record of a Dendronephthya sinaiensis-like azooxanthellate soft coral from the Lakshadweep Archipelago, Arabian Sea

Article Title: Occurrence of a Dendronephthya cf. sinaiensis-like nephtheid octocoral in the Arabian Sea, India

Article References: Narayanankutty, N., Riyas, C. A., Idreesbabu, K. K., & Sureshkumar, S. (2026). Occurrence of a Dendronephthya cf. sinaiensis-like nephtheid octocoral in the Arabian Sea, India. Discover Oceans, 3(1), Article 60. https://doi.org/10.1007/s44289-026-00175-9

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00175-9

Keywords: Dendronephthya, Nephtheidae, octocoral, soft coral, azooxanthellate, Lakshadweep, Arabian Sea, Red Sea, mtMutS, 28S rRNA, integrative taxonomy, biogeography

Marine sponges are notoriously difficult to identify. Many species lack fixed, easily readable external characteristics, and their morphological traits can be ambiguous, variable with environment, or shared misleadingly among unrelated lineages. This has produced a long history of taxonomic confusion, misidentifications and inconsistent classification, particularly among so-called cryptic species that look nearly identical but differ genetically. In recent years, sponge systematics has been transformed by integrative approaches that pair careful morphological description with molecular tools, allowing researchers to delimit species and reconstruct evolutionary relationships with far greater confidence than morphology alone permits.

The new study focuses on the order Scopalinida, a group erected and redefined only in the last decade using both morphological and molecular evidence. Scopalinida contains a single family, Scopalinidae, which in turn holds just three genera: Scopalina, Stylissa and Svenzea. The genus Svenzea, named in honor of the Colombian spongiologist Sven Zea, was established in 2002 for reef-associated sponges whose classification had long bounced between the former order Halichondrida and the family Dictyonellidae. Its defining features include distinctive microanatomy, the arrangement of skeletal elements, the composition and shape of spicules, and the presence of granular cells observed in both adults and larvae, along with a larva of extraordinary size. The larvae of Svenzea zeai, at up to six millimeters long, are regarded as the largest documented for the entire phylum Porifera.

Despite decades of study, only seven species of Svenzea had ever been described, and none had been recorded anywhere along the Eastern Tropical Pacific. That gap made the Mexican Pacific an intriguing frontier. Between July and November 2024, a team led by Eric Bautista-Guerrero of the Universidad de Guadalajara collected samples by SCUBA diving at depths of three to eight meters in the coral community known as Plataforma Pavonas, within Islas Marietas National Park in Bahía de Banderas. The site, where live pocilloporid coral cover is roughly eleven percent and sponges account for only about one percent, proved to host an abundant, widely distributed sponge growing over semi-shaded substrates, cave walls and vertical rock formations.

Underwater, the sponge is unmistakable: a thickly encrusting, irregularly massive animal ten to twenty-five centimeters across and two to three centimeters high, glowing bright orange in life and fading to beige in alcohol preservation. Its surface is smooth but microscopically hispid, densely pierced with incurrent pores and marked by bifurcated exhalant channels that lead to elevated, translucent chimney-like oscula. Under the microscope, the internal architecture revealed a cavernous choanosomal skeleton of disorganized, multispicular tracts, bundles of three to six needle-like spicules cemented by spongin fibers, ascending toward the surface. The spicules themselves, slender styles in two size categories measuring roughly 413 to 551 micrometers long, proved to be significantly larger than those of any previously known Svenzea species, and the complete absence of oxea, a second spicule type common in relatives, provided another decisive clue.

The team did not stop at adults. Using plankton nets towed by a diver around the coral community, they captured free-swimming larvae in full planktonic condition and raised them for observation. The larvae are bright orange, elongated to ovoid, and slightly flattened at the posterior pole, giving them a pyriform, or pear-shaped, appearance. Measuring 710 to 766 micrometers in length, they are uniformly covered in fine cilia about 24 micrometers long and swim in counterclockwise spirals, sometimes pausing or sinking before resuming their corkscrew journey. Their clear anterior-posterior polarity and cylindro-conical body plan echo the unusual parenchymella larvae documented in other scopalinid sponges, although the new species’ larvae are far smaller than the giant larvae of the Caribbean Svenzea zeai, which reach over six millimeters in length.

To place the new species on the sponge tree of life, the researchers extracted DNA from three adults and two larvae and amplified two independent genetic markers: the mitochondrial cytochrome c oxidase subunit I gene, COI, and the nuclear small-subunit ribosomal RNA gene, 18S. Sequences were aligned against a comprehensive set of Scopalinidae sequences from public databases, and phylogenetic trees were reconstructed using both maximum likelihood and Bayesian inference methods. The two approaches produced congruent topologies, and both markers placed Svenzea marialmae firmly within a well-supported clade containing Svenzea, Scopalina and Stylissa, confirming its membership in the family Scopalinidae and its distinction from the family Dictyonellidae, to which some of its relatives were once assigned.

The genetic evidence was strikingly specific. Based on COI sequences, the new species is closest to the Caribbean sponge Svenzea cristinae, with a genetic distance of just 0.052, followed by an undescribed Svenzea and Svenzea zeai, while showing much larger distances from all species of Scopalina and Stylissa. The 18S data told the same story, yielding the lowest interspecies distance, a mere 0.005, between Svenzea marialmae and Svenzea cristinae. Intriguingly, the two markers disagreed on one point: COI recovered Svenzea as monophyletic while 18S suggested it is paraphyletic, a discrepancy the authors attribute to the scarcity of Scopalinida sequences in public databases and to the possibility that some Scopalina species, such as S. goletensis and S. kuyamu, may have been misidentified. Resolving this will require additional genetic markers, but the congruence of the adult and larval sequences within a single clade provides strong evidence that both life stages belong to the same new species.

Morphologically, the new sponge walks a fascinating line between its named relatives. Its skeletal architecture, prominent dendritic spongin fibers cored by long styles over a basal spongin plate, resembles that of Scopalina species, and its thin cushions, conulose surface and bright orange color closely recall the Caribbean Scopalina ruetzleri. Yet it lacks the oxeas and other spicule modifications seen in that species, and it differs sharply from the erect, flabellate Stylissa, whose choanosome is supported by confusedly plumoreticulate spicule tracts. Against its congeners, the comparisons are equally decisive: Svenzea tubulosa is tubular with smaller styles, Svenzea flava bears blunt-ended styloids, Svenzea germanyanezi is a tiny cave-dweller with two categories of oxea, and Svenzea zeai carries short styles and a purple-brown, volcano-like form. Only the combination found in the Mexican specimens, giant styles, no oxeas and vivid orange pigmentation, defines the new species.

Beyond its taxonomic significance, the discovery carries a dedication with deep personal meaning. The species epithet marialmae honors María del Rocío Troncoso González, mother of co-author Dr. Alma Paola Rodríguez-Troncoso, a marine biologist who has spent two decades conserving and restoring the coral communities of Islas Marietas National Park and strengthening biodiversity management in this Marine Protected Area. The type specimens are deposited in the Colección de Esponjas del Pacífico Mexicano at the Institute of Marine Sciences of the National Autonomous University of Mexico, and all genetic sequences have been archived in GenBank, making the data freely available for future studies.

The broader implications reach well beyond one sponge. By raising the global count of Svenzea species to eight and establishing the first documented record of the genus in the Eastern Tropical Pacific, the study fills a conspicuous biogeographic gap and hints at unrecognized evolutionary connections across ocean basins, the new species’ closest relative after all lives on the far side of the American continent in the Caribbean. It also validates the combined use of mitochondrial and ribosomal markers alongside morphological and reproductive characters as a robust framework for testing phylogenetic hypotheses in Demospongiae, reducing the uncertainty of misidentifications that has long plagued sponge taxonomy. For the coral reefs of the Mexican Pacific, the message is clear: even in a marine protected area studied for decades, an abundant, brightly colored animal can remain formally unknown to science. As integrative taxonomy spreads to underexplored regions, researchers expect many more such surprises, each one refining our understanding of how sponge diversity evolved and how these ecologically important filter feeders are distributed across the world’s tropical seas.

Subject of Research: Taxonomic and molecular description of a new marine sponge species of the genus Svenzea from coral communities in the Eastern Tropical Pacific

Article Title: New insights into the diversity of Scopalinida (Porifera: Demospongiae) in the Eastern Tropical Pacific

Article References: Bautista-Guerrero, E., Marin-Ramirez, M. F., Carballo, J. L., Rodríguez-Troncoso, A. P., & Santiago-Valentín, J. D. (2026). New insights into the diversity of Scopalinida (Porifera: Demospongiae) in the Eastern Tropical Pacific. Discover Ecology, 2(1), Article 13. https://doi.org/10.1007/s44396-026-00031-2

Image Credits: AI Generated

DOI: 10.1007/s44396-026-00031-2

Keywords: marine sponges, Svenzea marialmae, Scopalinidae, Eastern Tropical Pacific, new species, integrative taxonomy, phylogenetics, COI, 18S rRNA, coral reefs, Islas Marietas, biodiversity