OKINAWAN
OPISTHOBRANCH OF THE WEEK

Okenia purpureolineata Gosliner, 2004 (15mm)
[Holotype*: CASIZ** 168020]

Opisthobranch of the Week Data

Taxonomy:

Frequency on Okinawa: Collection Data:
[brackets indicate range for all Okinawa-collected specimens of the species]


Species Account:

        Okenia purpureolineata was originally listed on this site as Okenia sp. 1, however the recent publication by Gosliner (2004) has now named the former undescribed species as O. purpureolineata. The animal is considered to be rare in Okinawan waters as I have collected a total of seven individuals collected between 30 April, 1989 and 12 March, 1994. As of the current date, O. purpureolineata is only found in the waters off Okinawa's main island.

        The above featured animal was collected from a 10cm3 ctenostome bryozoan colony (in a recent personal communication with Phil Bock he mentions that he feels the animal is an undescribed Amathia sp.) in 49m amid strewn coral rubble during a mid-morning SCUBA excursion. The above image is of the holotype * specimen. All seven of the specimens have been collected from the same general site in approximately the same environment, ranging between 49m and 58m. In all cases the animals were found in similar-appearing colonies of the ctenostome bryozoan. These bryozoan colonies were found in shallow depressions of mixed sand, and coral/shell rubble, in areas frequently experiencing high bottom currents. In several instances these attractive little goniodorids were found with another fascinating little goniodorid, O. japonica, in the same bryozoan colony. I've added a second page showing several additional specimens of O. purpureolineata and the host bryozoan upon which they were collected.

        The following description of external morphology and discussion are taken from Gosliner (2004):

        EXTERNAL MORPHOLOGY. - The living animals are 10–12 mm in length. The body is moderately elongate and relatively high. There is a well–developed, distinct notal border. The foot extends posteriorly and is devoid of notal papillae. The body color is uniformly translucent purple. There is an irregular network of darker purple lines on the dorsal surface of the notum. Darker purple pigment is also present on the gill lamellae. The rhinophores are dark purple basally and red throughout most of their length. There are seven pairs of elongate notal papillae along the sides of the body. The two anteriormost pairs of papillae are situated in front of the rhinophores and are anteriorly directed. Two medial papillae are present mid-dorsally anterior to the gill. The gill consists of 4–5 unipinnate branches. The rhinophores are elongate with 18–21 congested lamellae. The anterior end of the foot contains two elongate triangular lobes that are united medially. The genital aperture is situated on the right side of the body approximately a third of the length of the body posterior to the head. The foot is narrow and is wider anteriorly. The oral tentacles are broadly triangular and extend beyond the lateral margins of the foot.

        DISCUSSION. - Okenia purpureolineata is similar to O. japonica in its external body shape. Both species occur sympatrically in relatively deep water from Okinawa. Although O. japonica is uniformly white in color, O. purpureolineata is purple with darker purple lines on the notum and red rhinophores. Okenia purpureolineata has two mid-dorsal papillae but only one is present in O. japonica. Both species have large oral glands surrounding the anterior end of the buccal mass, but there are more numerous glands in O. purpureolineata, that are smaller in size. The inner lateral teeth of O. purpureolineata have 9–12 large denticles along the masticatory border whereas there are 19–22 finer denticles on the inner laterals of O. japonica. In the reproductive system of O. purpureolineata, the receptaculum seminis and bursa copulatrix are well separated from each other whereas in O. japonica they are immediately adjacent to each other.

        *Holotype/Paratype: See "Type" Dictionary for explanation.
        **CASIZ: California Academy of Sciences Department of Invertebrate Zoology

Etymology:

Literature Cited:


Page Date: 17 May '04
Page Modification Date: 18 May '04
Digitally manipulated photo
Copyright © 2004 Robert F. Bolland