Thorunna daniellae - radula

October 4, 2003
From: Bill Rudman

To accompany Rebecca Johnson's message about the radula of Thorunna kahuna here is a description of the radula of the very similarly looking T. daniellae from Rudman (1990).

The oral tube is five or six times the length of the buccal bulb, the radular sac being a small rounded bump between the muscle blocks in the postero ventral midline. The radular formula of the specimen 6mm long alive (AM C154376) is 14.0.14 x 17(+1)[from New South Wales, Australia]. The innermost right tooth has an elongate flattened blade with a rounded terminal cusp flanked by a similar but smaller rounded denticle on each side. All the other lateral teeth on the right side have an elongate shaft with a bifid tip formed from the reduction of the cusp to a rounded but elongate projection with a similar shaped outer denticle alongside.
The innermost lateral tooth on the left is quite different in shape and is apparently aberrant. It consists of a short quadrangular plate with a small triangular recurved hook on each of the upper corners (Fig. C). The other left lateral teeth mirror those on the right.
The jaw plates are not heavily chitinised and they are armed with scattered clusters of tapering unicuspid rodlets.

Like all species of the genus, the buccal armature is extremely small, when compared with other chromodorids. The oral tube is five or six times the length of the buccal bulb, and the radular sac is a small rounded bump between the muscle blocks in the postero ventral midline. The radular formula of a specimen 6mm long alive (AM C154376) was 14.0.14 x 17(+1). The radular teeth illustrated here are somewhat aberrant. The innermost right tooth has an elongate flattened blade with a rounded terminal cusp flanked by a similar but smaller rounded denticle on each side. All the other lateral teeth on the right side have an elongate shaft with a bifid tip formed from the reduction of the cusp to a rounded but elongate projection with a similar shaped outer denticle alongside. The innermost lateral tooth on the left side is quite different in shape and is apparently aberrant. It consists of a short quadrangular plate with a small triangular recurved hook on each of the upper corners Fig.C). The other left lateral teeth mirror those on the right. The jaw plates are not heavily chitinised and they are armed with scattered clusters of tapering unicuspid rodlets.

PHOTOS: A, whole radular ribbon. B, C, central and inner right region. D, mid-lateral teeth on right. E, outermost left lateral teeth. F, Jaw rodlets. Scale bars: A = 100 microns. B-F = 10 microns. Photos: G. J. Avern.

• Rudman, W.B. (1990) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: further species of Glossodoris, Thorunna and the Chromodoris aureomarginata colour group. Zoological Journal of the Linnean Society, 100(3): 263-326.

Rudman, W.B., 2003 (Oct 4) Thorunna daniellae - radula. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11111

In the earlier account (Rudman, 1984) description of Australian specimens, the innermost lateral teeth were quite different in shape from those described by Kay & Young (1969) from Hawaii. The radula of the specimen illustrated here dissected is fortuitously aberrant, with the innermost right laterals being as described by me before from Australian material while the innermost left lateral teeth are very similar to those described by Kay & Young for their one specimen from Hawaii. As most species of Thorunna have innermost lateral teeth similar to those on the right side of this specimen (T. africana, T. furtiva, T. horologia - see Rudman, 1984), it would seem that the innermost left teeth of this specimen and the innermost right and left teeth of the Hawaiian specimen described by Kay & Young are aberrant.

Bill Rudman

Rudman, W.B., 2003 (Oct 4). Comment on Thorunna daniellae - radula by Bill Rudman. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11111

Factsheet

Thorunna daniellae

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