Description and life cycle of a new species of the genus Arachnanthus (Cnidaria: Anthozoa: Ceriantharia) from the Southwestern Atlantic Ocean

LOPES S.S., CELINE; SCARABINO, FABRIZIO; CARRANZA, ALVAR; GONZÁLEZ-MUÑOZ, RICARDO; MORANDINI, ANDRÉ C.; NAGATA, RENATO MITSUO; STAMPAR, SÉRGIO, N.

PeerJ

PeerJ

Lugar: San Diego; Año: 2023 vol. 11

Background. Ceriantharia is a subclass of the phylum Cnidaria, which comprises tubedwellingmarine invertebrates. This subclass is composed of three families, includingArachnactidae, with two known genera. Currently, the genus Arachnanthus has fivevalid species recorded from Australia, the Mediterranean Sea and both the Southernand Northern Pacific Ocean. However, at the moment, there is no record of organismsof this family from the South Atlantic Ocean. Besides that, the life cycle of any speciesof the genus Arachnanthus is known. The present study describes a new species of thegenus Arachnanthus and its life cycle, based on specimens from Uruguay and South ofBrazil.Methods. Larvae were collected by plankton net in Rio Grande—Brazil and thedevelopment and external morphology of these specimens were observed in thelaboratory during two years, and subsequently described. Additionally, nine adultceriantharians correspondent to the larvae from Rio Grande were collected in Uruguayand their external and internal anatomies, and cnidome were described.Results. Arachnanthus errans sp. nov. exhibited a free-swimming, short-lived cerinulalarvae that spent short-time on the plankton. The larva developed into small andtranslucent polyps with a short actinopharynx, one pair of mesenteries attached toa siphonoglyph, and a medium first pair of metamesenteries. Further, the adult polypdisplayed an unprecedented locomotion behavior in Ceriantharia that is first reportedhere, it can crawl under and in between the sediment.