HOMOLIDAE De Haan, 1839 Homolid

Manikandan, K, Megalaa, N, Valliappan, Subramanian, Nandini, K, Rani, Lourdu V, Dakshinamurthi, Senthil & Nagappan, Nagappan, 2022, Crabs (Crustacea, Decapoda) from the Seas of East and Southeast Asia Collected by the RV Hakuhō Maru (KH- 72 - 1 Cruise) 3. Sahul Shelf, Bulletin of the National Museum of Nature and Science. Series A, Zoology 48 (2), pp. 35-83 : 40-42

Family HOMOLIDAE De Haan, 1839 Homolid megalopa

( Figs. 2–3 )

Material examined. RV Hakuhō Maru KH-72-1 cruise, sta. 33, 1 specimen ( CB 4.5 mm excluding lateral spines×CL 5.0 mm excluding frontal spines; length of dorsal spine, 9.0 mm; length of lateral spine, 11.2 mm; length of frontal spine, 7.7 mm; length of protogastric spine, 0.8 mm) , NSMT-Cr 30699.

Remarks. The specimen was found in the samples trawled up from station 33, but the exact capture depth is not known. The specimen is different from usual megalopae in having remarkably long frontal, dorsal and lateral carapace spines ( Fig. 2 ). The frontal spines are horizontal and parallel throughout their length, tapering distally; each lateral spine is directed posterolaterally and weakly downwards, and slightly longer than the frontal spines, tapering very weakly towards the tips; the dorsal spine is nearly erect or only weakly inclined posteriorly, and slightly shorter than the lateral spines. The carapace is otherwise armed with a pair of the short protogastric spines weakly directed outwards.

The megalopa at hand was not dissected, but externally agrees well with a megalopa from off Port Hacking, New South Wales, Australia, tentatively attributed to Dagnaudus petterdi (Grant, 1905) by Williamson (1965) (as Paromola ). The original line drawings of this Australian megalopa were given by Rice (1981: fig. 2a, dorsal view), Wear and Fielder (1985: figs. 41, 42, dorsal and lateral views), Konishi (2017: fig. 119I, dorsal view), and also in this paper ( Fig. 3A ) for explanation of and comparison with the homolid megalopae.

Sakai (1965) recorded a megalopa of Homola orientalis Henderson, 1888 from Sagami Bay, Japan, with an illustration of dorsal view, but without comment on the species identification. The frontal and dorsal carapace spines are long and similar to those of the Australian megalopa, but both of the lateral spines were mentioned and figured as short and obtuse at the tips. Later, however, Rice (1971) examined the same specimen from Sagami Bay, and showed that the lateral spines were shortened as a result of damage over time. As far as the descriptions and figures are concerned, the megalopa from Sagami Bay ( Fig. 3B–C ) appears to be indistinguishable from the Australian megalopa ( Fig. 3A ) and also from the Sahul Shelf megalopa ( Fig. 2 ). Dagnaudus petterdi is, however, restricted to New Caledonia, New Zealand and off northeastern Australia, and unknown from Japanese waters.

Considering the wide distribution and common occurrence of Homola orientalis in the Indo-West Pacific waters including Australia and Japan, the identification of the homolid megalopa from Sagami Bay by Sakai (1965) may be reasonable. Although Williamson (1965) initially thought his Australian megalopa to be Dagnaudus petterdi (as Paromola ), Williamson (1967) reidentified the megalopa as H. orientalis , and Rice (1971) concluded, after examination of Japanese megalopa, that it belongs to Paromola , not to Homola . Paromola megalopae are unknown to date, so Rice`s (1971) conclusion is not always accepted as it is. However, his conclusion that the Australian and Japanese megalopae are not referable to Homola is reasonable, because Rice (1964) and Rice and Provenzano (1970) studied the complete developmental stages of Homola barbata (Fabricius, 1783) , revealing a quite different, but rather usual type of megalopa without long frontal and dorsal carapace spines. As the zoeal and megalopal stages are generally thought to be similar among the congeneric species, Rice`s (1964) conclusion can be considered reasonable that the Australian and Japanese megalopae belong to Paromola , which is related to, but distinct from Homola . Only the Paromola zoeae of three species have hitherto been reported: P. japonica Parisi, 1915 by Aikawa (1937), P. cuvieri (Risso, 1816) by Samuelsen (1976), and P. macrochira Sakai, 1961 by Konishi et al. (1995), but as mentioned above, no information about the megalopae is available to date.

Recent systematic, taxonomic and biogeographic studies on the family Homolidae by Guinot and Richer de Forges (1981, 1995), Richer de Forges and Ng (2007), Ahyong et al. (2009), and Ng and Richer de Forges (2017) recognized 14 genera mostly from Indo-West Pacific waters, the species of which are, in general, rather restricted biogeographically. There is no information about their larvae, especially megalopae, even from planktonic samples, and therefore it is difficult at present to reliably refer the megalopa in question to a genus.

Figures

Fig. 2.ɹA homolid megalopa (NSMT-Cr 30699; CB 4.5mm excluding lateral spines×CL 5.0mm excluding frontal spines) from sta. 33, in different views.

Fig. 3.ɹA: Homolid megalopa of? Paromola petterdi (Grant), from off Port Hacking, N.S.W., Australia [after Williamson (1965, fig. 2A, B)]. B–C: Homolid megalopa from Sagami Bay, Japan [after Rice (1971, fig. 1a, b)]. Scale bars:A=2mm; B, C=5mm.