This research presents the early life history stages of Malo maxima, a recently described tropical Australian cubozoan from the family Carukiidae, from sexual fertilisation to metamorphosis including planula, polyp, asexual reproductive strategies and young medusa. We discuss the similarities between M. maxima and two closely related carukiid species from Japan and Australia including morphology and behaviours previously undocumented in the class Cubozoa. All three carukiids can reproduce by mono-disk strobilation, a strategy common to all other orders of the class Scyphozoa but only recently described in Cubozoa.

Scale-dependent spatial patterns of coastal benthic assemblages have been analyzed in many studies, especially in temperate regions, but such analyses are scarce in tropical waters. Hierarchical analysis of variance was performed using data from a nested sampling design to test whether variability in assemblages of midshore macrofauna from rocky intertidal ecosystems on the southern Thailand coastline differs over different spatial scales and whether assemblages on natural and artificial rocky reefs are similar. Analyses revealed that the composition of macrofaunal groups on the coastline facing the Andaman Sea did not differ from that of the assemblage on the Gulf of Thailand coastline; however, significant variation was detected on the scale of region (within coast) and shore (within region). The abundance of some macrofaunal groups differed among coasts and regions, but all groups exhibited high variation between shores. High variation between shores may mask larger-scale patterns in the composition of macrofaunal groups. Interestingly, the composition of macrofaunal groups and abundance of each group were not influenced by the type of habitat, suggesting that artificial structures may provide a habitat for hard-bottom species where the natural hard substrate is lacking.

The freshwater calanoid copepod Mongolodiaptomus malaindosinensis is an endemic species of the lower Mekong basin, including Malaysia. The relationships between environmental factors and life history traits have been reported for many copepods, while they have never been assessed in this tropical species. Post-embryonic development time (post-EDT), body size and survival rate of M. malaindosinensis were determined under different algal concentrations of Chlamydomonas reinhardtii and Cryptomonas tetrapyrenoidosa at 25°C, to clarify the effects of algal species and carbon supply on their somatic growth and survival. Post-EDT until adult in M. malaindosinensis decreased with increasing food carbon supply regardless of the algal species tested. Although naupliar developments were the shortest at 10⁴ cells mL⁻¹ of C. reinhardtii, food shortage delayed the development time and also induced high mortality during the copepodid stages. The highest survival rate of 93% was obtained in the copepods fed on C. tetrapyrenoidosa at 5×10⁴ cells mL⁻¹, whereas the survival rates in the remaining lower carbon supply were <23%. The most sensitive stages were the 1st copepodid stage, as indicated by high stage-specific mortalities, because of large morphological and physiological changes in this transitional stage. Prosome length of adult M. malaindosinensis positively correlated with food carbon supplies, though females were larger than males. Somatic growth rate exponentially increased with increasing food carbon supplies with a threshold at around 4.0 mgC L⁻¹. These results suggest that tropical copepods may be adapted to higher food quantities due to their high metabolic rates under high temperature conditions.

Pseudodiaptomus inopinus, a common estuarine calanoid copepod in the Northwest Pacific, has been suggested to be a species complex. The population of the mainland of Japan consists of two allopatric forms that are distinguishable by the length of the posterior processes of the genital operculum; the forms with short and long processes are tentatively called SP- and LP-forms, respectively. We analyzed the mitochondrial cytochrome c oxidase subunit I (COI) gene and the nuclear ribosomal internal transcribed spacer 1 (ITS1) gene of 34 individuals (12 SP- and 22 LP-forms) collected from various localities. The genetic differences between the two forms were 12–15% for COI and 7–10% for ITS1. They were clearly separated into different clades in both COI and ITS1 trees. These results confirmed that the two forms belong to different species. The SP-form is a distinct species because the shape of the genital operculum of P. inopinus s. str. has long posterior processes as in the LP-form. Pseudodiaptomus japonicus Kikuchi, 1928, which is the SP-form and was once synonymized with P. inopinus, is revived. The genetic comparison using available sequence data indicates that Pseudodiaptomus koreanus Soh et al., 2012 is the same species as P. japonicus.

A total of 113 and 73 individuals of the North Pacific lightfish Maurolicus japonicus were collected from the Japan Sea and the Pacific Ocean off the Japanese Islands, respectively. Based on nucleotide sequences of mitochondrial genes for cytochrome oxidase c subunit I (COI) and 16S ribosomal RNA, they were classified into the ‘Southern’ clade by Rees et al. (2017). Taken together, the previous results and our present findings suggest that the individuals examined should be treated as a single species, Maurolicus australis, and that this species exhibits the highest genetic diversity in the North Western Pacific Ocean. The Japanese population consisted of three genetically distinct groups. Individuals of one group are also distributed in the South Eastern Atlantic and the Southern Pacific Oceans, and individuals of another group are also distributed in the North Eastern Pacific Ocean. The remaining group has not yet been reported from other sea areas and might be endemic to the North Western Pacific. Although no significant genetic structure was detected around the Japanese Islands, the frequencies of these three groups seemed to show a latitudinal trend.