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In many decapod crustaceans, escape tailflips are triggered by lateral giant (LG) and medial giant (MG) interneurons, which connect to motor giant (MoG) abdominal flexor neurons. Several decapods have lost some or all of these giant neurons, however. Because escape-related giant neurons have not been documented in palinurans, I examined tailflipping and abdominal nerve cords for giant neurons in two scyllarid lobster species, Ibacus peronii and Ibacus alticrenatus. Unlike decapods with giant neurons, Ibacus do not tailflip in response to sudden taps. Ibacus can perform non-giant tailflipping: the frequency of tailflips during swimming is adjusted by altering the gap between each individual tailflip. Abdominal nerve cord sections show no LG or MG interneurons. Backfilling nerve 3 of abdominal ganglia revealed no MoG neurons, and the fast flexor motor neuron population is otherwise identical to that described for crayfish. The loss of giant neurons in Ibacus represents an independent deletion of these cells compared to other reptantian decapods known to have lost these giant neurons. This loss is correlated with the normal posture in scyllarids, in which the last two abdominal segments are flexed, and an alternative defensive strategy, concealment by digging into sand.

Ibacus peronii were captured, tagged and released off the east coast of Australia during 1993 and 1994 to study their patterns of growth and movements. Ten long-term recaptures have been reported since 1996, representing the longest recorded times at liberty for any tagged Scyllarid lobsters. Times at liberty for these 10 animals ranged between 1802 and 3417 days. Growth increments for all recaptured animals were within the ranges expected from shorter term recaptures, and all were recaptured from the same areas where they were tagged. These long-term recaptures reinforce previous conclusions on growth and movements of I. peronii, and are important in demonstrating to fishers and fishery managers that they are long-lived, do not move long distances and are susceptible to overfishing. The ratio of all recaptured tagged male and female I. peronii since 1993 was approximately 3:2. However, there were no differences in the recapture rates of males and females for small (less than 65 mm carapace length (CL)) and large (≥65 mm CL) individuals at tagging. The overall skewed recapture rate between sexes is likely to have been due to females being, on average, larger than males at the time of tagging and tag-loss being greater in these larger animals. These long-term recaptures show that, when properly inserted, the standard Hallprint T-bar tags used are retained through moulting events for many years.

The growth rates of the morphologically similar scyllarid lobsters Ibacus peronii (Leach, 1815) and I. chacei (Brown and Holthuis, 1998) are described using data from a tag/recapture study and from tagged lobsters kept in captivity. Within particular size classes, we found no differences in moult increments between male and female I. peronii nor between male and female I. chacei. Small individuals of both species always had larger moult increments than larger individuals. For I. peronii, females moulted more frequently than males, and smaller size classes moulted more frequently than larger size classes. Female I. peronii therefore grew more quickly than males and reached their estimated size at sexual maturity (51 mm carapace length) after ∼2 yr. Moulting of I. peronii was seasonal, with most lobsters (96.3%) moulting between October and January. We found no differences in growth rates of I. peronii at two locations along the east coast of Australia: Coffs Harbour in New South Wales (30°18′S; 153°08′E), and Lakes Entrance in Victoria (37°53′S; 148°00′E). For I. chacei, we found no differences in the frequency of moulting between males and females and, because we also found no differences in the moult increments between males and females, the growth rates of both sexes were the same.

Data from a tag/recapture study were used to describe patterns of movement in the commercially exploited Scyllarid lobsters Balmain bugs (Ibacus peronii) and the undescribed smooth bug (Ibacus sp.), off the east coast of Australia. The results showed that these morphologically similar lobsters, which overlap in their distributions, displayed contrasting patterns of movement: I. peronii exhibited a classic nomadic pattern of movement and Ibacus sp. underwent a long migration northward. The largest distance travelled by a recaptured tagged Ibacus sp. was 310 km in 655 days at liberty. This northward movement, combined with information on the reproductive biology of Ibacus sp. suggests that this species may migrate to spawn, with larvae recruiting to more southern areas via the southerly flowing East Australian Current.

Various aspects of the reproductive biology of the Australian scyllarid lobsters Ibacus peronii and Ibacus sp. were studied for the first time. Sizes at physiological and physical maturity were estimated for males and females of each species and we provide the first documented observations of their reproductive anatomy, mating, oviposition and hatching. Size at physiological maturity was determined via histological examination of ovaries and testes and by identifying the smallest ovigerous females captured in the field. This was estimated (±95% confidence intervals) as 50.4 mm±0.7 mm carapace length (C.L.) for female I. peronii from Coffs Harbour and 50.2 mm± 0.4 mm C.L. for female I. peronii from Lakes Entrance. Male I. peronii and Ibacus sp. were estimated to be physiologically mature when as small as 38.5 mm and 47.4 mm C.L., respectively. All female Ibacus sp. sampled in the study were found to be immature. Size at physical maturity was estimated by examining changes in the relative growth rates of various body parts and, for female I. peronii, was estimated as 54.9 mm±4.0 mm C.L. from Coffs Harbour and 56.6 mm±3.1 mm C.L. from Lakes Entrance. For male I. peronii, size at physical maturity may be approximately 55 mm C.L. The results are discussed in terms of the similarity of these species' reproductive biology with other species of scyllarid and palinurid lobsters, and the consequences of their sizes at sexual maturity for setting a minimum legal size for the fishery of these species.

Samples of egg-bearing female Balmain Bugs Ibacus peronii were collected from Coffs Harbour, NSW, and Lakes Entrance, Victoria, to estimate their fecundity and egg-size. Fecundities ranged between 5 500 and 37 000 eggs per brood with a mean egg diameter of 1.18 mm ±0.013 mm. Fecundity did not vary significantly between the two locations and the data were combined to provide a general fecundity-size relationship for I. peronii. This relationship is similar to those described for other scyllarid and palinurid lobsters in that it can be described by a positive linear regression.

The original figures of Scyllaridae by Lesueur and manuscript descriptions and notes by Péron, made during the 1800-1804 French Expedition to Australia, are now kept in the Museum d'Histoire Naturelle du Havre, and shed new light on the identity, type locality and whereabouts of these species. The figures and part of the descriptive material are reproduced here.

Summary Optimal numbers of replicates to estimate mean oocyte sizes in female Balmain Bugs (Ibacus peronii) were determined using analyses of variance of data from a pilot study. Mean oocyte size was different in different pans of the ovary in some animals, but there were no differences within sections from the same part of each ovary. The optimal numbers of oocytes to measure was 219 or 55 per section to produce a standard error that was 5% or 10% of the mean, respectively, and for some purposes, only 20 oocytes per section needed to be measured. It is recommended that as many animals be sampled as possible, and that only a single section be taken from several parts of the ovary.

The original figures of Scyllaridae by Lesueur and manuscript descriptions and notes by Péron, made during the 1800-1804 French Expedition to Australia, are now kept in the Museum d'Histoire Naturelle du Havre, and shed new light on the identity, type locality and whereabouts of these species. The figures and part of the descriptive material are reproduced here.

Larvae from 3 adult Ibacus peronii were reared through 6 phyllosomal instars and a nisto before metamorphosing into juveniles. Two phyllosoma instars previously attributed to /. peronii (see Ritz and Thomas, 1973) were not observed during the present studies. We suggest that these belong to Ibacus alticrenatus. Six larvae successfully metamorphosed into nisto larvae and subsequently into juvenile stages. Of these juveniles, 3 were successfully cultured for 1 year on a diet of fresh mussels (Mytilus edulis). In a second experiment, larvae were reared at 2 temperature regimes (20.7° and 23.3°C). Considerably higher survival rates were achieved at the lower regime, although molting frequency decreased. During 1 year at ambient temperatures the juveniles developed from a mean carapace length of 12.2 mm at the first molt to 39.8 mm at the sixth molt. The mean intermolt period was 49 days.

The swimming of two scyllarid lobsters Ibacus peronii Leach and Thenus orientalis Lund was studied and compared with the swimming of the palinurid lobster Jasus novaehollandiae Holthuis. In the two scyllarid lobsters significant lift is created during backward tail flips. Articulation of the flattened antennal plates alters the distribution of this lift so that pitching and rolling moments are created which are used in continuous swimming and in performing manoeuvres. By contrast J. novaehollandiae generates a negligible amount of lift during each tail flip and its antennae are not shaped or positioned to control any lift that is created, consequently backward tail flips in these animals cannot be used to produce efficient continuous swimming or manoeuvering.

I. Peronii is a scavenger on small benthic invertebrates and animal remains. The mouthparts are less complex than those of some palinurans, as shown by their simple setation and fusion of endites, but have a broad endopod on the third maxillipeds. In the maceration and ingestion of soft animal remains, the mouthparts function as in other palinurans. How the mouthparts collect small prey is not yet known. The proventriculus of I. Peronii is simplified in the number, size and structure of its ossicles as compared with Jasus novaehollandiae and J. lalandei. The action of the gastric mill in I. Peronii is described. The relation between mouthpart structure, proventriculus structure and diet is discussed for I. Peronii and other palinurans. I. Peronii is specialized by simplification of the masticatory structures in relation to the soft and small animal food available at the surface of sublittoral sands and muds.

Plankton samples from the south-eastern Indian Ocean between 25�30's. and 35�00'S. and from the Western Australian coast out to 99� 00'E., showed the presence of several species in three genera of the Scyllaridae; Scyllarides sp. a; Scyllarus demani; Scyllarus bicuspidatus; Scyllarus spp. a, b, and c; Ibacus peronii and Ibacus sp, a. The final (gilled) phyllosoma and nisto stages of previously undescribed species are described. A generic key to the final phyllosoma of the Palinuridae, Scyllaridae and Synaxidae recorded from the southern Indian Ocean is presented. The distribution of the catches of the phyllosoma of Scyllarus bicuspidatus, Scyllarus sp. b, Ibacus peronii and Scyllarides sp. a and data on the seasonal catches of all scyllarid species are presented. The phyllosoma of S. bicuspidatus undergo diel migrations. Early-stage densities peak at depths of 40-80 m during the day, and mid and late stages peak at 80-100 m. At night the early stages are found at the surface, independent of moonlight intensity. Mid and late stages peak at the surface only on moonless nights. On moonlit nights the density of mid and late stages peak at 15-25 m depth.

[Description des stades phyllosome et puerulus du Scyllaride Ibacus peronii, ainsi que des jeunes stades post-larvaires. Parmi les phyllosomes prises dans le plancton cotier de l'Australie occidentale, l'une a ete elevee en laboratoire jusqu'a un stade juvenile, mais bien reconnaissable, de cette espece. La distribution des larves et celle de l'adulte sont toutes deux brievement indiquees., Description des stades phyllosome et puerulus du Scyllaride Ibacus peronii, ainsi que des jeunes stades post-larvaires. Parmi les phyllosomes prises dans le plancton cotier de l'Australie occidentale, l'une a ete elevee en laboratoire jusqu'a un stade juvenile, mais bien reconnaissable, de cette espece. La distribution des larves et celle de l'adulte sont toutes deux brievement indiquees.]