Calamyzinae, Hartmann-Schroder, 1971

Watson, Charlotte & Faulwetter, Sarah, 2017, Stylet jaws of Chrysopetalidae (Annelida), Journal of Natural History 51 (47 - 48), pp. 2863-2924 : 2912-2914

Subfamily Calamyzinae

Free-living. The Calamyzinae comprises a number of free-living taxa that form a grade with respect to a symbiotic clade ( Watson et al. 2016). The calamyzin buccal cavity, comprising a muscular pharynx with terminal papillae and jaws with tanned distal tips, mid-way flange and longitudinal groove, has similarities to that observed in taxa of Chrysopetalinae and Dysponetinae . The planktonic larvae of Vigtorniella zaikai possess a platelet/stylet form of jaw which is also seen in the larvae of Boudemos flokati ( Dahlgren, Glover, Baco & Smith, 2004) ( Watson et al. 2016). The stylet jaw is only present in larvae, then entirely lost (e.g. Boudemos flokati ) or very modified in the adult (e.g. Vigtorniella zaikai ), indicating that hard jaw structures are not essential for adult feeding. It is not known if presence of jaws in larvae is indicative of larval feeding or, more likely, a phylogenetic remnant ( Dahlgren et al. 2004; Watson et al. 2016).

Free living calamyzins have been successful in exploiting chemosynthetic ecosystems such as anoxic basins, hydrocarbon seeps and whale falls and have been documented vigorously sucking up lipid-rich remains in microbial mats of sedimented areas around whalefalls ( Dahlgren et al. 2004), and robust sucking and ingestion of bacteria growing on whale bones by larvae raised in the laboratory has been observed (Wiklund, pers. comm.). Micospina , a new jawless clade, is found associated with cold seeps with an isotope signature indicative of feeding on sulphide oxide bacteria ( Watson et al. 2016).

Sensory characters observed in free-living calamyzins include very small, simple lateral antennae, pair of small ventral palps (the latter two structures undifferentiated), ciliated nuchal patches and segmental ciliation. The prostomium has been reduced to a simple half-lobe and eyes and median antenna are absent. Slender fascicles of spinous notochaetae originate laterally, leaving the dorsum bare, e.g. Micospina ( Figure 1c ). Freeliving calamyzins are epibenthic and mobile, especially larger taxa, e.g. Boudemos (~ 40 mm L), whereas the smaller taxa, e.g. Vigtorniella (2 mm L) burrow in flocculent bacterial mats and may be considered partly meiofaunal.

A modified platelet/stylet jaw is a single unique character observed in free-living Calamyzinae ; otherwise the group is characterized by reduction in character form and complexity (e.g. lateral antennae, palps, proboscis) or absence of characters (e.g. eyes, median antenna and mouth cover). The inhabitation of extreme environments has led to a shift of more simplified morphology and a bacteriovore feeding mode, reflected in ontogenetic jaw forms, including complete loss of jaw types in some adult taxa ( Watson et al. 2016).

Ectoparasitic/symbiont. Modified jaws are found in the adults of two symbiont clades: Calamyzas , a monotypic clade, and the former nautiliniellid, Shinkai . Shinkai longipedata was previously considered to have an unarmed pharynx ( Aguado and Rouse 2011; Aguado et al. 2013; Watson et al. 2016) but micro-CT scans taken in this current study indicate the presence of jaws.

Shinkai longipedata is coloured deep pink in life and lives within the gills of deep-sea, chemosynthetic bivalves ( Figure 1e ). This taxon is very long bodied (200 mm L, ~ 400 segments) but possesses a relatively small proboscis and muscular pharynx (the buccal cavity reaches to segment 6) and a very small pair of jaws. Jaws resemble a little the platelet/stylet jaws seen in the larvae of free-living calamyzins, although Shinkai stylets also possess a sharp pointed distal structure which could function well as a piercing and scraping structure used for partial predation on bivalve tissue. Consumption of other host bivalve products such as mucous, gametes and pseudofaeces is also suggested for obligate symbiont nautiliniellids by Becker et al. (2013).

Cryptic body coloration is here reported for the first time in the Chrysopetalidae . Calamyzas amphictenicola , a very small ectoparasite (2 mm L), often found nestled in the gill groove of its host polychaete, Amphicteis , is successfully camouflaged by the presence of dark body stripes which mimic the striped gills of its host ( Figure 1d ). Calamyzas possesses a small muscular pharynx, a modified mouth opening ringed by fine denticles, and a very small pair of extremely attenuated stylet jaws, ostensibly used for piercing and sucking fluids from the tissue of its host polychaete ( Aguado et al. 2013; this study).

Reduction and loss of sensory characters are observed in the symbiont taxa Calamyzas and Shinkai : lateral antennae and pair of palps are undifferentiated and reduced to two very small structures, more laterally positioned. Terminal proboscidial papillae, eyes, median antenna, nuchal and body ciliation, and anal cirri are absent and the loss of notochaetae in both taxa renders the dorsum completely bare and exposed.

Unique adaptive characters in Calamyzas and Shinkai are related to a symbiont lifestyle that provides a lipid-rich and reliant food source from the host. Calamyzas has a modified mouth opening with rings of denticles useful for rasping and gaining entry into host tissue; it has been found in different locations on its host body when attached for feeding, which indicates a certain mobility aided by the presence of camerate compound neurochaetae. In comparison, the endosymbiont Shinkai leads a sedentary existence and has simple neurochaetae with apparent loss of compound joints along with internal cameration, thereby transforming neurochaetae into stout, simple chaetae with hooked distal ends, useful for purchase within tissue of host bivalves while feeding. The tendency of reduction in locomotor appendages and size of mouth parts observed in Shinkai , as adaptations to an obligate symbiont mode of life, is recorded in other parasitic polychaetes ( Martin and Britayev 1998).

Figures

Figure 1. Live photos: (a) Chrysopetalinae. Arichlidon gathofi Watson Russell, 2000a (~5 mm L); (b) Dysponetinae. Dysponetus pygmaeus (~3 mm L); (c–e) Calamyzinae: (c) free-living Micospina aureobohnorum Watson et al., 2016 (~4mm L); (d) ectoparasite Calamyzas amphictenicola (~ 2 mm L); (e) symbiont Shinkai longipedata (~ 250 mm L). Copyright: a, c, e: © Greg Rouse; b: © Monika Kedra/ Slawomira Gromisz; d: © Fredrik Pleijel. All photos reproduced with permission by the copyright holders.