Zoological Studies

Vol. 62, 2023

(update: 2023.4.25)

Understanding the Symbiotic Relationship between the Sea Urchin Loxechinus albus (Molina, 1782) and the Pea Crab Pinnaxodes chilensis (H. Milne Edwards, 1837): a Potential Parasitism

Hans N. Jaramillo1, Luis P. Salas-Yanquin1, Joseline A. Büchner-Miranda1, Víctor M. Cubillos1, Jaime A. Montory2,
Jan A. Pechenik
3, Luis M. Pardo1, and Oscar R. Chaparro1,*

1Universidad Austral de Chile, Instituto de Ciencias Marinas y Limnológicas, Valdivia, Chile. *Correspondence: E-mail: ochaparr@uach.cl (Chaparro).
E-mail: h.jaramillog@gmail.com (Jaramillo); luis.salas.y@gmail.com (Salas-Yanquin); joseline.a.buchner@gmail.com (Büchner-Miranda); victor.cubillos@uach.cl (Cubillos); luispardo@uach.cl (Pardo)
2Universidad de Los Lagos, Centro i~mar, Camino a Chinquihue km 6, Puerto Montt, Chile. E-mail: jaime.montory@ulagos.cl (Montory)
3Biology Department, Tufts University, Medford, MA 02155, USA. E-mail: Jan.Pechenik@tufts.edu (Pechenik)

(Received 1 July 2022 / Accepted 27 January 2023 / Published 25 April 2023)
Communicated by James D. Reimer

The echinoderm Loxechinus albus has a symbiotic relationship with the pinnotherid crustacean Pinnaxodes chilensis. Females of the crustacean develop in the terminal section of the sea urchin’s digestive system, remaining there for life. This relationship has been suggested as commensalism. However, a potential negative impact on gonadal development and on the morphology of the sea urchin’s digestive system suggest that it is instead parasitic. To study if there is a negative impact of the crustacean symbiont on the host, specimens of L. albus of all sizes were collected from a rocky shore in southern Chile. The gonadal and somatic tissues of sea urchins that were and were not harboring the pinnotherid were weighed and compared. Our results show that the presence of the pinnotherid was related to sea urchin gonads of lower biomass, decreased gonadosomatic index levels, and alterations in the morphology of the terminal portion of the host digestive system. The lower gonadal biomass suggests a negative impact on gamete production as well as a diversion of energy due to changes of the digestive system tissues and the potential consumption of algal food by the resident crustacean. These results suggest that the prolonged relationship between these two species is one of parasitism rather than one of commensalism.

Key words: Parasitism, Symbiosis, Sea urchins, Pinnotherid, Crustacean.

Citation: Jaramillo HN, Salas-Yanquin LP, Büchner-Miranda JA, Cubillos VM, Montory JA, Pechenik JA, Pardo LM, Chaparro OR. 2023. Understanding the symbiotic relationship between the sea urchin Loxechinus albus (Molina, 1782) and the pea crab Pinnaxodes chilensis (H. Milne Edwards, 1837): a potential parasitism. Zool Stud 62:18. doi:10.6620/ZS.2023.62-18.

Supplementary materials: Fig. S1Fig. S2Fig. S3