Development of Rhincalanus nasutus (Giesbrecht, 1888) (Copepoda, Rhincalanidae) from the Humboldt Current System

Abstract

Morphological changes in the exoskeleton of naupliar stages 2-6 and copepodid stages I-V of Rhincalanus nasutus are described. On the distal segment of nauphar antennule, one lateral seta and two medial setae are added during each molt to nauplius 3-6. A naupliar arthrite is a thick, distinctive structure on the coxa of antenna, and the exopod of this limb is patterned from the large proximal segment of that ramus. The coxal gnathobase of the mandible appears at nauplius 4. Buds of maxillule and maxilla are added during the molt to nauplius 5, and buds of maxilhped and sviiimming legs 1-2 are added during the molt to nauplius 6. The somite bearing maxilla clearly articulates completely with the somite bearing the maxilhped on the last two naupliar stages. This unusual articulation does not appear during copepodid development, and the somite bearing swimming leg 2 is the anterior articulating somite during this later phase. One articulating somite is added during molts to copepodid 11-V. Segmentation of the antennule is completed by copepodid IV. Segmentation of the exopod of antenna does not change during the copepodid phase, but one segment is added to the endopod of maxilla. Segmentation and setation of the maxilhped follow the usual calanoid pattern. Buds of swimming legs 3-5 are ventrolateral on their somite. Their presumptive exopod has two attenuations; their presumptive endopod bears an attenuation and a seta. Segmentation of the rami of swimming legs 1-4 follows the common pattern for copepods except for the exopod and endopod of swimming leg 1 which are only 2-segmented.PAMELA HIDALGO ET AL. RESUMENCambios morfológicos en el exoesqueleto de estadios naupliares 2-6 y estadios copepoditos de Rhincalanus nasutus son descritos. El segmento distal de la anténula naupliar, muestra que una seta lateral y dos setas intermedias son adicionadas durante cada muda desde el naupUus 3 al nauplius 6. El artrito naupliar presenta una gruesa estructura distintiva sobre la coxa de la antena y el exopodito está marcado desde el mayor segmento proximal de esta rama. La gnatobase de la coxa de la mandíbula aparece en el nauplius 4. Inicios de la maxilula y maxilla aparecen durante la muda hacia el nauplius 5, e inicios del maxilipedo y los apéndices natatorios 1 y 2 aparecen durante la muda del nauplius 5 al nauplius 6. El somito presenta la maxila claramente y completamente articulada y el maxilipedo aparece en los dos últimos estadios naupliares. Esta inusual articulación no aparece durante el desarrollo de copepoditos y el somito presenta la pata nadadora 2 en la articulación anterior en esta fase. Articulaciones del somito aparecen durante las mudas de copepodito II a copepodito V. La segmentación de la antenula es completada en el copepodito IV. La segmentación del exopodito de la antena no cambia durante la fase de copepodito, pero un segmento es adicionado en el endopodito de la maxila. La segmentación y setación de los maxilipedos sigue el normal patrón de calanoideos. Los crecimientos de las patas natatorias 3-5 se ...