Despite the fact that South East (SE) Asia is considered as a biodiversity hotspot, knowledge of sessile invertebrates such as freshwater sponges (Porifera: Haplosclerida: Spongillina)

Only six species (four genera, one family) of freshwater sponges are known until now from Thailand. A first record of thegenus Corvospongilla Annandale, 1911 with the description of a new species is here reported from the Pong River in the LowerMekong Basin. The taxonomic status of Corvospongilla siamensis nov. sp. is discussed in comparison to the 18 speciesassigned to the genus. The new species is characterised by i) alveolate, paucispicular skeletal network with scanty spongin,thick ascending tracts towards the sponge surface to support conules; ii) skeleton of stout microspined strongyles, andextremely rare, abruptly pointed oxeas usually with a few tubercles, plus micropseudobirotules with smooth shaft; iii) gem-mules belonging to a single gemmular morph, typically sessile; iv) gemmular cage notably stout, of tangentially arrangedstrongyles of variable length from tubercled to spiny; v) gemmular theca with abundant laminar compact spongin, lackingpneumatic layer, armed by short, tubercled to spiny strongyles tangentially embedded; vi) larvae armed by spiny oxeas. Corvo-spongilla siamensis nov. sp. differs from all the other known species of the genus in its unique combination of diagnostic traits,particularly a) acanthostrongyles (megascleres), b) gemmuloscleres, both in the cage and in the theca, as strongyles showing the tendency towards ring-shape and button-like shape, and c) larval spiny oxeas.

Taxonomic richness of Thai Spongillina numbers so far seven species (five genera, one family). The first record of the genusOncosclera Volkmer-Ribeiro, 1970 belonging to the family Potamolepidae Brien, 1967 is here reported with the description ofa new species from the Pong River (NE Thailand, Oriental Region) in the framework of a biodiversity assessment in the LowerMekong Basin. An emended diagnosis of the genus is also provided. The new species, ascribed to the genus Oncosclera fordiagnostic traits of the skeleton and the gemmular architecture, differs from all the other known species of the genus in itsunique combination of diagnostic traits. O. asiatica sp. nov. is characterised by i) more or less alveolate skeleton, ii) conulosesurface with a network of branched subdermal canals, iii) acanthoxeas as dominant megascleres and less frequentacanthostrongyles, iv) gemmular theca sublaminar of compact spongin with a scantly developed pneumatic layer of fibrousspongin, and v) gemmuloscleres as acanthostrongyles from elongated to ovoid with tubercles/spines particularly dense towardsthe tips. Despite the extremely disjunct distribution O. asiatica is morphologically similar to O. intermedia and O. jewelli fromthe Neotropical Region and O. gilsoni from Pacific Islands, from which the former diverges for megascleres and/or gemmuloscleres traits.

Umborotula bogorensis (Weber, 1890) is a freshwater sponge species that is recorded occasionally, mainly on islands and peninsulas of Australasia. Less than 10 records with morphological descriptions and illustrations have been published so far, and the most recent record is dated 1978. A list of the few voucher specimens from museum collections is provided here together with the rich unpublished Sasaki collection from Japan, Korea, and Taiwan, recently deposited in a Japanese museum. The present new record from Northeast Thailand enlarges the geographic range of U. bogorensis to the Indochina mainland. A comparison of historical data vs present Thai records is performed by morpho-analysis (SEM) as well as biogeographic, ecological and climatic data. Results show low variability in shape and size of the diagnostic morphotraits in populations scattered over the wide geographic range. Here we also formally accept the new taxonomic status (rank elevation) of the previous suborder Spongillina as a new order Spongillida. The presence of this potentially threatened species in the Sakaerat Biosphere Reserve, together with its possible long-term persistence in the Bogor Botanical Garden, may support its conservation. Only a census of the known, extremely scattered populations will define the status of this species.

Shallow water sponges settled on a raft along the Pong River (Lower Mekong Basin, Thailand) were investigated to highlight the taxonomic richness, composition, relative abundance and lifestyle of sponge-dwelling aquatic Insecta. The three-dimensional biogenic structures of the model sponges hosted 4 orders of Insecta, belonging to 10 families and 19 genera/species, able to strictly coexist at the level of the sponges in aquiferous canals and/or at the body surface, and/or dwelling in the extracellular matrix. On the basis of the identified 379 larvae and pupae, Trichoptera and Diptera were found to be the dominant inhabitants of Corvospongilla siamensis (Demospongiae: Spongillida), endemic to Southeast Asia. In the focused lotic ecosystem, dominated by soft bottoms, sponges play a functional role. Insecta use sponges as a substratum, nursery ground, food source, and shelter microhabitat, protecting them from predation and environmental aggression. Moreover, their feeding behavior indicates the insects’ adaptive traits to recycle sponge siliceous spicules as a source of exogenous material to strengthen the larval–pupal cases and the digestive system. The results of the Thai sponge model contribute to the inventory of global engineering species richness, ecosystem types, and biogeographic diversity, thus raising awareness for freshwater biodiversity conservation. In this regard, the present data, along with the worldwide inventory, focus on sponges as (a) key habitat-forming species for aquatic insect assemblages, (b) ecosystem engineers in river/lake/wetland ecosystems, providing water purification, the processing of organic matter, recycling of nutrients, and freshwater–terrestrial coupling, and (c) promising candidates in restoration projects of tropical freshwater ecosystems by bioremediation.