Maslakova, S. A. | Search bioRxiv

bioRxiv2021

A New Genus Of Microsporidian Parasite (Hepatosporidae; Microsporidia) Found In The Oocytes Of Ribbon Worms From The North Pacific Genus Maculaura (Heteronemertea; Nemertea)

An intracellular microsporidian parasite was first observed within oocytes of Maculaura alaskensis, a small pilidiophoran nemertean, commonly found on sandflats along the Pacific coast of North America. Infected oocytes have large vesicles containing dozens to hundreds of diplokaryotic, ellipsoid spores measuring 1.3 by 2.3 m. A partial small subunit nuclear ribosomal 18S gene sequence isolated from the microsporidian does not match any known microsporidian sequences in the public databases. Phylogenetic analysis groups it with Hepatospora eriocheir in a sister clade to the Enterocytozoonidae. All the known life stages of this parasite are contained within a membranous envelope. This microsporidian was identified in M. alaskensis, Maculaura aquilonia, Maculaura oregonensis, and Maculaura cerebrosa in Coos Bay, Oregon, in M. alaskensis from Newport, Oregon, and in M. aquilonia collected in Juneau, Alaska. This is, to our knowledge, the first species of microsporidia found to directly infect nemertean host cells. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=180 SRC="FIGDIR/small/438387v1_ufig1.gif" ALT="Figure 1"> View larger version (81K): org.highwire.dtl.DTLVardef@1b89feaorg.highwire.dtl.DTLVardef@aedc5org.highwire.dtl.DTLVardef@18030f2org.highwire.dtl.DTLVardef@10d7734_HPS_FORMAT_FIGEXP M_FIG C_FIG

zoology↗

bioRxiv2021

Hoplonemertean larvae are planktonic predators that capture and devour active animal prey

The superficially-simple ciliated planktonic larvae of hoplonemerteans have been assumed to be lecithotrophic direct developers, even though many develop from such small eggs that it is hard to imagine how they could give rise to a viable juvenile without some phase of larval feeding. Indeed, attempts to raise such larvae to settlement without food invariably fail. Observations that some hoplonemertean larvae are found in plankton samples at a range of sizes, and much larger than hatchlings, suggests they must indeed feed somehow. Since these "planuliform" larvae lack apparent means to concentrate suspended algae or other unicellular food, one alternative hypothesis is that they are planktonic predators that hunt large prey. Here we provide direct evidence that this is indeed the case for six distinct species of hoplonemerteans. We recorded wild-caught larvae of Paranemertes californica, Paranemertes sp., Gurjanovella littoralis, Emplectonema viride, Carcinonemertes epialti, and Ototyphlonemertes sp. attacking, subduing, and devouring pelagic crustaceans, including barnacle nauplii, cyprids, copepods and their nauplii, and others. While there is no doubt that some hoplonemerteans are genuine lecithotrophs, our evidence suggests that many species in this group both feed and grow during an extended planktonic larval period. This conclusion has important consequences for biogeographic and life-history studies in this group, because it implies enhanced potential for long-distance dispersal. More broadly, the possibility that many animal larvae are actually carnivores invites reconsideration of prevailing stereotypes about metazoan developmental modes and the trade-offs between them.

zoology↗