Moll. Res. 17: 111-114 (1996). 
A note on the egg capsule of Nodilittorina unifasciata 
from eastern Australia. 
W.B. Rudman 
The Australian Museum 
6-8 College St, Sydney, New South Wales 2000 
Internet: billr@amsg.Austmus.oz.au 
Keywords: Littorinidae, Nodilittorina, egg capsule, Australia, New Zealand 
Introduction 
This is the first published description of the planktonic egg capsule of Nodilittorina unifasciata 
(Gray, 1826), a common littorinid snail living high on rocky shores of southern Australia from 
Northern New South Wales to southwestern Western Australia. It is a dominant animal on many 
Shores and has been the subject of many biological and ecological studies (— as Littorina unifasciata: 
Branch & Branch, 1981; Chen & Richardson, 1987; Underwood, 1974; Underwood & Chapman, 
1989; Wells, 1984). The transfer of this species to Nodilittorina was proposed by Bandel & Kadolsky 
(1982), and supported by Reid (1989). Our understanding of the life history of N. unifasciata, is 
based on histological studies of the gonad (Underwood, 1974) and structure of the pallial oviduct 
(Reid, 1989). Murray (in an unpublished letter in Pilkington, 1971) reports that both N. unifasciata 
and N. praetermissa (May, 1908) liberate egg capsules (presumably planktonic) with the veliger 
Stage already well-developed, and these were also studied by Tin Nwe (1974). The planktonic egg 
capsules of N. antipoda (Philippi, 1847) (as Melarapha oliveri Finlay, 1930), a supposed subspecies 
of N. unifasciata from New Zealand, and another New Zealand species, N. cincta (Quoy & Gaimard, 
1833), have been described (Pilkington, 1971). 
Many studies have shown that the ability to identify accurately littorinid egg capsules from inshore 
Plankton samples, or high tidal pools, is a valuable tool in studying the life history and ecology of 
these animals (Habe, 1956; Kojima, 1957a,b, 1958; Borkowski, 1971; Pilkington, 1971; Ohgaki, 
1981). Reid (1989) has discussed the value of capsule morphology in understanding the phylogeny and 
taxonomy of the Littorinidae. 
D 
Methods & Results 
Snails ranging in shell height from 15-19mm were collected from supra-littoral aggregations at 
Harbord, Sydney, NSW (at low tide, 6 October 1995) and placed in groups of 12-15 in glass jars half 
filled with sea water, at 4pm the same day. The jars were left until ат, 9 October, when four out of 
Six jars contained a few free swimming veligers and up to 10-12 egg capsules (Figs 1, 2c). The 
Seawater was changed daily and a similar number of eggs were laid each day, until observations 
Ceased 10 days later. In a few cases 3-4 capsules adhered together in a string for a few hours after 
hatching but separated with moderate water movement. No attempt was made to time or study 
development, but eggs were laid at the single cell stage and within 12 hours were fully developed 
Veligers, hatching within 18 hours. The ambient room temperature was maintained between 22-24?C. 
The observation by Murray (in Pilkington, 1971) that capsules were laid with fully developed veligers 
Was not confirmed. 
Egg capsules appear disc, or dome-shaped (‘cupola’ type of Reid, 1989), and almost completely 
transparent. There is a prominent central dome on the convex face of the capsule, and there is a central 
Swelling on the concave face to accommodate the egg. During hatching, the veliger breaks free in this 
