Two new species of poecilostomatoid copepods symbiotic on the venomous echinoid Toxopneustes pileolus (Lamarck) (Echinodermata) from Vietnam

New Myzostomids (Annelida) in Symbiosis with Feather Stars in the Shallow Waters of the South China Sea (Hainan Island)

This research delves into the molecular and morphological characteristics of myzostomid worms associated with common shallow-water feather stars (Echinodermata: Crinoidea: Comatulidae) in the coastal waters near Sanya, Hainan Island. Through the examination of specimens collected at depths of up to 10 m using scuba diving techniques, we describe three new species (Myzostoma ordinatum sp. nov., M. scopus sp. nov., and M. solare sp. nov.) and report the first record of Myzostoma polycyclus Atkins, 1927 in the South China Sea. The absence of overlap with the seven previously documented Myzostomida species in the shallow waters of Hong Kong and Shenzhen reveals significant gaps in our understanding of marine biodiversity in the South China Sea. These findings, combined with an analysis of available molecular data, underscore the potential existence of unexplored and diverse symbiotic relationships among marine invertebrates within the region.

Morphological and Molecular Evidence of an Intergeneric Host-Range in Clavisodalis sentifer (Crustacea: Copepoda: Taeniacanthidae) Associated with Diadematid Sea Urchins from the Western Pacific

Sea urchins have a wide variety of symbionts on their body surfaces and inside their bodies. Copepods of the genus Clavisodalis (Taeniacanthidae) collected from the esophagus of sea urchins of the genera Diadema and Echinothrix in southern Japan were identified based on their morphological characteristics, and molecular analysis was conducted to determine whether genetic variation occurs in copepods from different localities and hosts. Morphological observations identified individuals from southern Japan as Clavisodalis sentifer Dojiri and Humes, 1982, making this the first record of this species in the northern hemisphere and the first record of its genus in Japan. Morphological and molecular analysis suggested that the copepod specimens collected from multiple hosts across two genera would be the same species. Considering the typically observed high level of host specificity among taeniacanthid copepods, the utilization of hosts from two genera by C. sentifer is noteworthy.

From Microscale Interactions to Macroscale Patterns in Copepod-Crinoid Symbiosis

Crinoids (Echinodermata) exhibit unique morphological and behavioral characteristics that facilitate a wide range of symbiotic relationships with diverse organisms. Our comprehension of their interactions with microscopic copepod crustaceans is, however, still in a nascent and fragmented state. Here, we review and discuss the 166 literature records to date in which a total of 39 copepod species in 6 families have been reported in association with 33 species of the crinoid order Comatulida. Many of these associations have been reported just once. The respective localities cover 5 of the World Ocean's 12 ecoregions, with a notable concentration of both host and symbiont diversity in the Central and Western Indo-Pacific. In contrast, the documentation of copepod-crinoid associations in the Atlantic appears markedly limited. Copepods have been found predominantly in ectosymbiotic relationships with crinoids, with a lower incidence of endosymbiosis. Copepods of the genera Collocheres Canu, 1893 and Pseudanthessius Claus, 1889 are particularly prominent in the list, and the comatulid family Comatulidae displays the most diverse assortment of copepod associations. The current scope of knowledge encompasses a mere 5% of the potential crinoid host diversity, underscoring the need for more extensive research in this area.

Cephalotrichella echinicola, sp. nov. (Palaeonemertea : Cephalotrichellidae), a new nemertean associated with sea urchins from Nha Trang Bay (South China Sea)

About 50 nemertean species have been reported to live in symbiotic relationships with other invertebrates, but only two hoplonemertean species are associated with echinoderms (starfish). The palaeonemertean Cephalotrichella echinicola, sp. nov. is described from samples collected in Nha Trang Bay, Vietnam, South China Sea. The species is the first known nemertean associated with sea urchins (Metalia sternalis and M. spatagus), living on both the oral and the aboral surfaces of the host and freely moving among its spines. The internal morphology of the new species is described based on histological sections and confocal laser scanning microscopy with phalloidin and antibody labelling. Sequences of three nuclear gene markers (18S rRNA, 28S rRNA, and histone H3) and two mitochondrial gene markers (16S rRNA and COI) were compared with those of other palaeonemertean species, and a phylogenetic analysis suggested that C. echinicola is closest to the free-living Cephalotrichella alba Gibson & Sundberg, 1992. Both the morphological data and the phylogenetic analysis provide additional evidence for distinguishing the families Cephalotrichidae and Cephalotrichellidae and support the rejection of Cephalotrichella as a junior synonym of Cephalothrix. A new diagnosis of the genus Cephalotrichella is given. http://zoobank.org/urn:lsid:zoobank.org:pub:091B5D56-71B2-4F4C-9AD8-F666B4610DE2

Dumbbell-Shaped Ossicles Discovered in Pedicellaria of Flower Sea Urchins

Sea urchins have a globiferous pedicellaria that stands from a test with a stalk on which lies a head made of three movable jaws with venom-injecting teeth. The globiferous pedicellariae of the flower sea urchin Toxopneustes pileolus, one of the most developed among sea urchins, are unique in that the jaws are provided with a jaw membrane that gives the pedicellaria an appearance of a flower when the jaws are open. We observed this membrane in an ionic liquid that does not require processes, such as fixation, dehydration, or coating with conductive materials, for observation with a scanning electron microscope. Using this technique, we discovered dumbbell-shaped ossicles, which consist of two spheres of similar size connected by a cylinder. The diameter of the sphere is 4-8 µm, and the total length of the ossicle is 10-20 µm. The jaw membrane is trimmed with an edge zone. The ossicles were found sparsely in the connective tissue of general part of the membrane, but in the edge zone their density was so high that neighboring ossicles were in close contact with each other. Some neighboring ossicles crossed their cylinders and some inserted one of their spheres to snugly fit in the gap between the spheres of neighboring ossicles. Their structural role is very likely in strengthening the jaw membrane, probably serving as fillers in the general part of the membrane; in the edge zone the interlocking of adjacent ossicles forms a loose network providing a firm frame for the head of the globiferous pedicellaria. When opened, the stiff frame prevents the membrane from sagging. When clasped, it works as a closed door, firmly keeping prey trapped.