Cabangus, Korshunova & Bakken & GrØtan & Johnson & Lundin & Martynov, 2021

Korshunova, Tatiana, Bakken, Torkild, GrØtan, Viktor V., Johnson, Kjetil B., Lundin, Kennet & Martynov, Alexander, 2021, A synoptic review of the family Dendronotidae (Mollusca: Nudibranchia): a multilevel organismal diversity approach, Contributions to Zoology 90 (1), pp. 93-153 : 131-132

Genus Cabangus gen. nov.

ZooBank: http:// urn:lsid:zoobank.org:act:3B779CBF-A310-4B47-85B1-488104FAD541 Type species. Dendronotus regius Pola & Stout, 2008

Etymology. From the Indonesian word “cabang” meaning “branch” in reference to this genus as “dendronotids of the tropics” and to respect the great contribution of the Indonesian fauna to global marine biodiversity (e.g., Hoeksema, 2007).

Diagnosis. Dorsolateral appendages with distinct tertiary branches. Oral veil with branched appendages. Radula with at least up to nine lateral teeth in adult specimens. Central teeth with cusp integrated within lateral denticles. Denticle-bearing part of central teeth not separated from lateral sides, distinct shoulders absent, thus central teeth triangular in outline. Prostate represented by a thickenedstructurewithoutevidentalveolar glands and disk. Copulative organ conical.

Remarks. According to the present molecular phylogenetic analysis, thetropical Dendronotus regius Pola & Stout, 2008 comesas a most basal clade, distinctfrom allpresentlyknown species of the genera Dendronotus and Pseudobornella . Morphologically, D. regius differs from any known species of the genus by the presence of a homogenous, fine prostate, which is externally smooth and does not show any alveoles. Pola and Stout (2008: Fig. 4 ) evidently did not indicate any alveols in the prostate of their D. regius , but in the text they ( Pola & Stout, 2008: 48) mentioned a “large prostate with the proximal limit being marked by a closely set ring of alveolar glands”. To clear this contradiction between this figure and the text in the original description, we checked several adult specimens of D. regius and confirm that there are no externally or internally conspicous alveols, otherwise so characteristic for a majority of true Dendronotus species. There is another striking difference between both strictly tropical species of Dendronotus ( D. regius plus D. noahi ) and any other known species of this genus, namely that the denticle-bearing part of the central teeth is not separated from the lateral sides by a distinct shoulder.Thusthe centralteethhaveasquarish base and a triangular top. This makes the radula of both species more similar (though not identical) to that of the family Bornellidae , whosespecies are alsopartlysimilarin external morphology. However, details of the stomach and the reproductive systems are different. Therefore, takingmolecularandmorphological evidence into account, we propose here the new genus Cabangus gen. nov. with as type species Dendronotus regius Pola & Stout, 2008 . The holotype of the only other tropical species described so far, D. noahi , is likely a juvenile since it possesses only four rows of lateral teeth and immature reproductive system. Although this species is now included in the genus Cabangus gen. nov., this needs further study. Externally, Cabangus spp. aredifferentfromthe common external appearance of Dendronotus spp. by a combination of a very narrow body and short dorsolateral appendages. By these characters, Cabangus gen. nov. is also somewhat similar to the family Bornellidae , which is phylogenetically distant from the Dendronotidae . Cabangus gen. nov. represents a basalmost clade within the Dendronotidae and hence may retain some features of the common ancestorswith phylogenetically more distantly related families. Cabangus gen. nov. is also well supported by biogeographic data because the majority of its species inhabits Arcticandtemperatewaters,whereas Cabangus gen. nov. represents a distinct tropical lineage.

Figures

FIGURE 4 Dendronotus yrjargul sp.nov.(a–n) and D.kalikal (o–t), external and internal morphology.a–c: living holotype of D.yrjargul NTNU-VM-76306 (a) and its habitat (b, c), dorsal,ventral and lateral views with egg mass and associated hydroid Abietinaria fusca, respectively; d: Dendronotus yrjargul, habitat of living paratype NTNU-VM-76302;e: jaw of holotype; f:denticles on the masticatory edge of the holotype; g: jaws of paratype NTNU-VM-76302; h:discoid ridge-like structures on the masticatory edge of paratype NTNU-VM-76302;i: details of discoid structures on the masticatory edge of paratype NTNU-VM-76302; j: anterior part of radula of holotype; k:central teeth of radula of holotype;l:lateral teeth of radula of holotype; m:central teeth of radula of paratype NTNU-VM-76302; n: lateral teeth of radula of holotype; o: living holotype of D.kalikal; p: jaw of D.kalikal, specimen from Kurile Islands;