OKINAWAN
OPISTHOBRANCH OF THE WEEK

Costasiella vegae Ichikawa, 1993 (2~5mm)

Opisthobranch of the Week Data

Taxonomy:

Frequency on Okinawa: Collection Data:


Species Account:

        Costasiella vegae is considered to be uncommon in the waters of Okinawa's main island. The above image shows five of the nine individuals collected during this particular collecting dive. Several collections have been made of these animals which number in excess of fifteen individuals. The animals were collected from an area of mixed coral rubble and sand in the presence of numerous thallophytes.

        The following description of the holotype specimen of C. vegae is taken from Ichikawa (1993):

       The brown, contiguous eyes are situated between the bases of the rhinophores. The anterior corners of the foot are not extended. The rhinophores are white with black tips. The white head bears a conspicuous red mark behind the eyes like a posteriorly pointing arrowhead. The cerata are arranged in 8 rows and all are of the same colouration, green spotted with white dots. The distal portion of each ceras has many small red spots, whose density increases distally, eventually coalescing into a red line. The pointed tips of the cerata are white. On the dorso-distal part of each ceras is an eye-shaped pattern, a white spot encircled by a dark green circle.

        Ichikawa collected six specimens of C. vegae from the waters off Ishigaki Island, between Uganzaki and Yarabuzaki during June of 1991. The animals were found between 0.5~1m on the green thallophyte, Avriavillea erecta.

        This is a drawing of C. vegae from Ichikawa's 1993 publication:

        In a recent post on the Sea Slug Forum Bill Rudman (2006) points out the confusion in naming new species on very little information, but mentions the Okinawa animals seem to fit the description of Costasiella vegae. In comparison of animals from both the Keramas and Okinawa's main island Rudman points out

"The most distinctive feature of C. vegae seems to be the eye spot on each cerata. However Ichikawa described the eyespots as being 'a white spot encircled by a dark green ring'. In both your animals and Atsushi Ono's the spots are blue, and while the ones in your upper photo are surrounded by a dark green ring, the ring is absent in Atsushi Ono's, and your lower photo. Also Ichikawa describes a distinctive mark behind the eyes as 'a conspicuous red mark behind the eyes like a posteriorly pointing arrow head' which is not clear in the drawing of the animal. I suspect the mark is the blue eye spot or mark found in your animals and Atsushi Ono's. Ichikawa also describes a red subapical band around the cerata. This is not visible in Atsushi Ono's or your animals but there is an orange subapical band around the cerata of C. ocellifera from the Caribbean. Ichikawa's description of C. vegae was based on 6 specimens collected at the Ryukyu Islands on Avrainvillea. I suspect your animals and Atusushi Ono's are part of the colour variation of C. vegae. I also suspect that C. vegae is the same as the Caribbean C. ocellifera."

        Previously I've featured several species of Costasiella on these pages and as of the current date there are several described and undescribed species of Costasiella, reported from Okinawan waters. The featured animals are as follows:

  • C. kuroshimae
  • C. paweli
  • C. usagi
  • C. vegae (the above featured animal)
  • C. sp. 1
  • C. sp. 2
  • C. sp. 3
  • Etymology:

    Literature Cited:


    Page Date: 15 Jan '07
    Page Modification Date: 15 Jan '07
    Digitally manipulated photo
    Copyright © 2007 Robert F. Bolland