Keijella multisulcus Whatley & Zhao, 1988

Chitnarin, Anisong, Forel, Marie-Béatrice & Tepnarong, Prachya, 2023, Holocene ostracods (Crustacea) from a whale-fall excavation site from the Chao Phraya delta, Central Thailand, European Journal of Taxonomy 856 (1), pp. 120-151 : 136

Keijella multisulcus Whatley & Zhao, 1988

Figs 7J–O , 8A–I , 9

Keijella multisulcus Whatley & Zao, 1988: 15 , fig. d.

Dimensions

L = 0.325 –0.875 millimeters; H = 0.175 –0.444 millimeters; H/L = 0.45–0.59 ( Fig. 9 ).

Distribution

Modern distribution: Malacca Strait ( Whatley & Zhao 1988b); Malaysia ( Omar et al. 2017); Mae Khlong River mouth, north west Gulf of Thailand ( Montenegro et al. 2004); southwestern coast of Peninsular Thaiand, Ao Nun, Satun Province, Andaman Sea ( Forel 2021).

Fossil distribution: Bangkok Clay (samples 20SS01B, 02A, 02B, 03A, 04A, 04B), whale excavation site, Samut Sakhon Province, Thailand, Late Holocene (this work, Fig. 4 ).

Remark

Dimorphism of Keijella multisulcus can be recognized by the subrectangular shape with H/L ratio less than 0.50 in the male ( Fig. 7L ) and the subovate shape with a higher H/L ratio in the female ( Fig. 7M–O ). The juvenile carapaces are sub-triangular in lateral view with Hmax located anteriorly at one third of L, Lmax is located below midH in both valves. The ventral longitudinal carina is prominent in young juveniles ( Fig. 8G–H ) and extends into a small spine (posteroventral spine). The ventral longitudinal carina is faint and becomes obscured in the larger juvenile stage ( Fig. 8A–F ). Small conical posterior marginal denticles and a large terminal posteroventral spine are observed in juveniles. Figure 9 shows H and L plot of the species which clearly demonstrates that sexual dimorphism can be differentiated in adult specimens.

Figures

Fig. 7. Holocene ostracods from Samut Sakhon Province, Central Thailand. A–E. Keijella gonia Zhao & Whatley, 1989. A. Carapace, left lateral view, SUT-20SS-C310. B. Carapace, left lateral view, SUT-20SS-C311. C. Carapace, left lateral view, SUT-20SS-C312. D. Carapace, right lateral view, SUT- 20SS-C288. E. Carapace, right lateral view, SUT-20SS-C286. – F. Pistocythereis sp. Carapace, right lateral view, SUT-20SS-C305. –G–I. Stigmatocythere bona Chen in Hou, Chen, Yang, Ho, Zhou & Tian, 1982. G. Carapace, right lateral view, SUT-20SS-C201. H. Carapace, left lateral view, SUT-20SS-C200. I. Valve, internal view of right valve, SUT-20SS-C190. – J–O. Keijella multisulcus Whatley & Zhao, 1988. J. Valve, juvenile, right lateral view, SUT-20SS-C231. K. Valve, juvenile, internal view of right valve, SUT-20SS-C213. L. Carapace, male, left lateral view, SUT-20SS-C225. M. Carapace, female, left lateral view, SUT-20SS-C242.N. Carapace, female, left lateral view, SUT-20SS-C206. O. Carapace, female, left lateral view, SUT-20SS-C243. Scale bars = 0.1. mm.

Fig. 8. Holocene ostracods from Samut Sakhon Province, Central Thailand. A–I. Keijella multisulcus Whatley & Zhao, 1988. A. Valve, juvenile, right lateral view, SUT-20SS-C254. B. Valve, female, left lateral view, SUT-20SS-C269. C. Carapace, juvenile, left lateral view, SUT-20SS-C270. D. Valve, juvenile, right lateral view, SUT-20SS-C267. E. Valve, juvenile, left lateral view, SUT-20SS-C286. F. Valve, juvenile, right lateral view, SUT-20SS-C253. G. Valve, juvenile, right lateral view, SUT- 20SS-C272. H. Valve, juvenile, left lateral view, SUT-20SS-C273. I. Valve, female, right lateral view, SUT-20SS-C257. – J–L. Ammonia tepida (Cushman, 1926), spiral side, SUT-20SS-F001. – M. Spiroloculina sp., side view, SUT-20SS-F002. – N. Quinqueloculina sp., side view, SUT-20SS-F003. – O–Q. Asterorotalia pulchella (d’Orbigny, 1839), side view, SUT-20SS-F004-6. Scale bars = 0.1 mm.

Fig. 9. Height and length scatter plot of Keijella multisulcus Whatley & Zhao, 1988 found at the whalefall excavation site in Samut Sakhon Province, north of the Gulf of Thailand. Scale bars = 0.1 mm.

Fig. 4. Distribution of Holocene ostracods below and above the whale skeleton level at the whale-fall excavation site in Samut Sakhon Province, north of Gulf of Thailand.