Marine symbiotic Palaemonidae, comprising over 600 species, live in association with marine invertebrates of different phyla, like Cnidaria, Echinodermata, Mollusca, Porifera, and Tunicata. A phylogenetic study is performed on a clade of bivalve- and ascidian-associated endosymbiotic shrimp species (Caridea: Palaemonidae), using morphological and molecular data. A Total Evidence approach is used in order to include all currently known ingroup species in an evolutionary framework. Ancestral state reconstruction analyses are performed to identify host-switching events and ancestral ranges. The clade, including Ascidonia, Conchodytes, Dactylonia, Odontonia, and Pontonia, and various smaller genera, is recovered as monophyletic, with an ascidian-associated ancestral host state. At least six interphylum host switches are tentatively identified, with members of Odontonia and Notopontonia switching back to an ascidian host affiliation after the ancestral host switch of the clade including Conchodytes, Odontonia and related genera, from an ascidian- to a bivalve host. The clade including Ascidonia and Pontonia was recovered to have an ancestor with an East Pacific/Atlantic distribution. The other studied genera remained in the original ancestral Indo-West Pacific range. We hypothesize that similar internal environments of shrimp hosts from different phyla will function as hot spots for interphylum host switching in various lineages of symbionts.

Almost all pea crab species in the subfamily Pinnotherinae (Decapoda: Brachyura: Pinnotheridae) are considered obligatory endo- or ectosymbionts, living in a mutualistic or parasitic relationship with a wide variety of invertebrate hosts, including bivalves, gastropods, echinoids, holothurians, and ascidians. While the subfamily is regarded as one of the most morphologically adapted groups of symbiotic crabs, the functionality of these adaptations in relation to their lifestyles has not been reviewed before. Available information on the ecomorphological adaptations of various pinnotherine crab species and their functionality was compiled in order to clarify their ecological diversity. These include the size, shape, and ornamentations of the carapace, the frontal appendages and mouthparts, the cheliped morphology, the ambulatory legs, and the reproductive anatomy and larval characters. The phylogenetic relevance of the adaptations is also reviewed and suggestions for future studies are made. Based on an updated list of all known pinnotherine symbiont–host associations and the available phylogenetic reconstructions, it is concluded that, due to convergent evolution, unrelated species with a similar host interaction might display the same morphological adaptations.

Most marine shrimp species of the family Palaemonidae are characterized by symbiotic associations with hosts that belong to a wide range of invertebrate phyla. One clade of related endosymbiotic species has evolved to live inside the branchial chambers of ascidians and the mantle cavities of bivalve molluscs. The phylogeny of this clade (comprising 15 bivalve-associated species in the genera Anchistus, Neoanchistus, and Paranchistus, and three species of ascidian-associated species in the genus Dasella) is the topic of the present study, which is based on both morphological and molecular data. A concatenated phylogeny reconstruction was built by using the markers coi and 16S. With the help of a total evidence approach (with a scored morphological datamatrix), species could be added for which no molecular data were available. An ancestral character state analysis was performed to detect host switches. In contrast to another endosymbiotic clade, the ancestral host state was found to be slightly in favour of bivalves. The phylogenetic relevance of morphological features is discussed with a focus on a tympanal organ located in the major chelipeds of some bivalve-associated shrimp species. This little-known anatomical structure is illustrated by sem and µCT scans. Its possible function is discussed. In the phylogeny reconstructions, both Anchistus and Paranchistus were found to be polyphyletic. They were reclassified to obtain a more natural classification: Anchistus custoides and Anchistus custos were transferred to the resurrected genus Ensiger. Paranchistus liui, P. nobilii, P. pycnodontae, and P. spondylis were transferred to Polkamenes gen. nov. Anchistus pectinis and P. ornatus were transferred to Tympanicheles gen. nov. Per genus, a key to the species is provided.

Two new species of palaemonid shrimp associated with ascidian hosts, Odontonia bagginsi sp. n. from Tidore and Odontonia plurellicola sp. n., from Ternate, Indonesia are described and figured. Through phylogenetic analyses based on both morphological and molecular datasets (mitochondrial Cytochrome c oxidase subunit I gene and the 16S mitochondrial ribosomal gene) of the genus Odontonia, the phylogenetic positions of the new species have been reconstructed. Scanning Electron Microscopy has been used to observe additional characters on dactyli of the ambulatory pereiopods. Odontonia plurellicola sp. n. appears to be more closely related to O. simplicipes and O. seychellensis, but it differs most notably in the morphology of the rostrum and mouthparts. Odontonia plurellicola sp. n. appears to be the only Odontonia species living inside a phlebobranch ascidian Plurella sp. Odontonia bagginsi sp. n. is closely related to O. sibogae, but differs markedly in the abundance of setae on the propodi of the ambulatory pereiopods. In the present paper, O. maldivensis Fransen, 2006 is regarded as a junior synonym of O. rufopunctata Fransen, 2002 based on both morphological and molecular aspects.

A new species of bivalve mollusk dwelling palaemonid shrimp of the genus Odontonia is described from the Berau Islands, East Kalimantan, Indonesia. This is the only Odontonia species recorded as a symbiont of a bivalve mollusk, all other congeners are known to associate with solitary ascidians. The new species belongs to the group wherein the dactylus of the ambulatory pereiopods has an accessory tooth. It differs from these species in the absence of a forward directed proximal tooth on the flexor margin of the corpus of the ambulatory dactyli. It also lacks the small denticles posterior to the distoventral accessory tooth on the dactylar corpus.

Following 3 days of gales in the North Sea off the Dutch coast, one part of the beach at Katwijk, ZuidHolland, was littered with shells (cuttlebones) of the common cuttlefish, Sepia officinalis Linné. Over 100 specimens were collected. These Sepia may have died at the same time, with the storm as the probable cause of death (=life assemblage); alternately, did it just cause dead, floating cuttlebones to wash ashore as a monospecific death assemblage? The collected cuttlebones showed a great variation not only in their dimensions, but also in their preservation. All the cuttlebones were examined in detail. About one third of the shells were broken. Most of the cuttlebones have triangular holes and V-shaped scratches, which suggest that they were carried and attacked by birds; this kind of damage can only be made after the death of Sepia. One specimen preserved a bite mark of a fish. Some of the cuttlebones have algae or barnacles growing on them, suggesting they had a lengthy post-mortem residence floating in the North Sea. The diversity and common occurrence of evidence of interactions by other organisms with the cuttlebones, predatory, scavenging, and pseudoplanktonic, leads to a conclusion that these Sepia cuttlebones represent a death assemblage, possibly left over from the previous summer season and perhaps mixed with some older specimens. Keywords Coleoidea Cuttlebones Preservation Á Pseudoplankton Á IchnologyKurzfassung Nach einem dreitägigen Sturm in der Nordsee vor der niederländischen Küste wurde ein Teil des Strandes von Katwijk in Südholland mit Schulpen des Gewöhnlichen Tintenfisches Sepia officinalis Linné über-sät. Mehr als 100 Exemplare wurden aufgesammelt. Entweder sind diese Sepien gleichzeitig (mit dem Sturm als mögliche Todesursache) gestorben, oder aber im Wasser schwebende Schulpe wurden als monospezifische Grabgemeinschaft an den Strand gespült. Die aufgesammelten Tintenfischschulpe variieren nicht nur in ihren Abmessungen, sondern auch in ihrer Erhaltung. Alle Stücke wurden im Detail untersucht, wobei etwa ein Drittel der Schulpe zerbrochen war. Die meisten Tintenfischschulpe haben dreieckige Löcher und V-förmige Kratzspuren, die daraufhin deuten, daß diese den Sepien nach dem Tode von Vögeln beigebracht wurden. Bei einem Exemplar ist die Bissspur eines Fisches erhalten. Einige andere Tintenfischschulpe besitzen Algen-oder Seepockenbewuchs, welcher auf ein längeres Schweben dieser (post mortem) in der Nordsee hinweist. Aufgrund der Diversität und der Interaktionen mit anderen Organismen läßt sich insgesamt postulieren, daß die vorliegenden Sepiaschulpe eine Taphozönose darstellen, die eventuell vom vorherigen Sommer stammt, oder mit noch älteren Exemplaren durchmischt wurde.Schlü sselwörter Coleoidea Á Tintenfischschulpe Á Erhaltung Á Pseudoplankton Á Ichnologie

Most pea crab species (Crustacea: Decapoda: Brachyura: Pinnotheridae) are characterized by their symbiotic lifestyle, often thought to be obligate parasites or commensals (Baeza, 2015). The degree of host dependency is, however, still unclear for most species. The species within the subfamily Pinnotherinae are known to be endo-or ectosymbiotic inhabitants of bivalves, polyplacophorans, gastropods, holothurians, echinoids, brachiopods, and ascidians (de Gier & Becker, 2020). Although some species have a broad host spectrum spanning across various phyla, most species of Pinnotherinae are considered to be specialists. This means that these species are only inhabiting specific genera or orders within a host phylum. Several species of the two smaller subfamilies (Pinnixinae and Pinnixulalinae) are also found in bivalve, or in/on holothurian hosts in their adult stages, but most are considered to be free-living or tube/ burrow-dwelling, sharing this habitat with a worm, ghost shrimp, or mud lobster as a host (inquilism; see Palacios Theil et al., 2016;

Christmas tree worms (Serpulidae: Spirobranchus) occur in shallow parts of coral reefs, where they live as associates of a large number of stony coral species [...]