Life - History Studies on New Zealand Brachyura (Crustacea, Decapoda)
Authors:   , Wear Robert George 
Published: November 2021

<p>1. Abbreviated or direct development is described in Pilumnus novaezelandiae Filhol, 1886 and P. lumpinus Bennett, 1964 (Xanthidae, Pilumninae) from New Zealand. Embryonic development is separated into Nauplius, Metanauplius, and embryonic Zoea stages. In P. novaezelandiae, larvae hatch at a Megalopa stage and are retained beneath the pleon of the female crab. The Megalopa larva and first five juvenile crab stages are described. In P. lumpinus emergent larvae are advanced, much-modified, and non-natatory Zoeae which are not retained by the parent. The Zoea and Megalopa larvae of this species are described. Abbreviated development has little phylogenetic significance among Brachyura, and has probably evolved as a response to habitat requirements of adult crabs. 2. A brief account is given of the systematics and distribution of the New Zealand xanthid crabs Heterozius rotundifrons A. Milne Edwards, 1867, Ozius truncatus H. Milne Edwards, 1834, and of Heteropanope (Pilumnopeus) serratifrons (Kinahan, xanthid Brachyura and to the Megalopa larvae of Heterozius rotundifrons and Ozius truncatus. Notes are given on the seasonal breeding cycle of Heterozius rotundifrons, and the pre-Zoea larva, two Zoea larval stages, and the Megalopa larva reared in the laboratory are described. Ozius truncatus possesses a pre-Zoea larva, four Zoea larval stages, and a Megalopa larva. These have been reared and are described. A key is given for the separation of the Zoea larval stages. The pre-Zoea larva and first stage Zoea larva of Heteropanope Pilumnopeus serratifrons are described. There are probably four zoeal stages in the larval development of this species. 3. The characters of Zoea larvae of the family Xanthidae described up of the present time are critically analysed and considered in relation to the status of currently accepted adult genera and species, the generic groupings used by Monod (1956), and the generic composition of the subfamilies proposed by Balss (1957). Xanthid Zoea larvae fall into two natural groups of genera based on larval characters, the most important being the length of the antennal exopod in relation to that of the spinous process. The first group is equivalent to the subfamily Xanthinae as reconstituted by Balss (1957), but there is no larval evidence suggesting that the "Panopean" genera should be separated from the "Xanthian" genera as suggested by Monod (1956). A second natural group is formed by larvae of the subfamily Menippinae as in Balss (1932, 1957), the subfamily Pilumninae of Balss (1957), and the genus Geryon. Larvae of genera in the subfamily Trapeziinae Miers should be removed from the section Hyperolissa and included in this second natural group. Zoea larvae described from the genera Heteropanope and Pilumnopeus form a separate branch of the second group. Zoea larval evidence does not support Monod's (1956) separation of Eriphia from the "Menippian" group of genera. 4. The first stage Zoea larva Hemiplax hirtipes (Jacquinot, 1853) is described, and present knowledge concerning larvae of crabs of the family Ocypodidae is summarized discussed. No diagnostic character is common to all ocypodid Zoea larvae, but affinities are shown with those of the families Hymenosomidae, Pinnotheridae, and Grapsidae. 5. Pre-Zoea and first stage Zoea larvae hatched from the grapsid crabs Leptograpsus variegatus (Fabricius, 1793), Planes marinus Rathbun, 1915, Hemigrapsus crenulatus (H. Milne Edwards, 1837), H. edwardsi (Hilgendorf, 1882), Cyclograpsus lavauxi H. Milne Edwards, 1853, Helice crassa Dana, 1851, and Plagusia chabrus (Linnaeus, 1764) from New Zealand are described. A key is given for the separation of these larvae. Known Zoea larvae of the family Grapsidae show close affinities with those of the brachyrhynchous families Ocypodidae and Gecarcinidae, and fall into four groups based on larval characters. This system of larval classification agrees with the present arrangement of adult genera into subfamilies except for a division among larvae of the subfamilies Varuninae and Sesarminae. The length of larval life and larval dispersal probably has no bearing on the presence or absence of certain New Zealand species at the Chatham Islands.</p>