Acetes omorii Hanamura, Imai, 2024

Alamri, Nasser & Alotaiby, Faraj, 2024, Taxonomic Assessment of Acetes indicus H. Milne Edwards, 1830 (Crustacea, Decapoda, Sergestoidea) as Revealed from Molecular and Morphological Analyses: Re-validation of A. spiniger Hansen, 1919 and Designation of a New Species, Bulletin of the National Museum of Nature and Science. Series A, Zoology 50 (2), pp. 49-68 : 60-63

Acetes omorii Hanamura, Imai

and Hardianto sp. nov.

( Figs 5, 6)

urn:lsid:zoobank.org:act:1199DE94-F3F4-477F-9E5B-

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Acetes indicus ; Omori, 1975: 15 (in part; at least fig. 15c, e, i); Pérez Farfante and Kensley, 1997: 187, figs 128–130 (not H. Milne Edwards, 1830).? Acetes indicus : Kemp 1917: 47 (in part): Boone, 1935:

101, fig. 9.

Material examined. Holotype: male (cl 5.3 mm), stn R 2 , Matang Mangrove Estuary , Malaysia, sledge, 25 Nov. 2012, coll. Y. Hanamura & Faizul (NSMT-Cr 31621) (transferred from formalin to 70% ethanol) . Paratypes: 1 male (4.8 mm), 3 females (cl 5.9–6.2 mm), data same as holotype (NSMT-Cr 31622) (transferred from formalin to 70% ethanol) ; 5 males (cl 3.5– 5.3 mm), 9 females (cl 5.5–6.0 mm), 2 individuals (sex & size undetermined), sledge, 25 Nov 2008, coll. Y. Hanamura & Faizul (NSMT-Cr 31623); 2 specimens used for DNA analysis (sex and size undetermined), data same as previous (NSMT-Cr 31624, 31625); 2 males (cl 4.7, 5.5 mm), 3 females (cl 6.4–7.0 mm), stn R2 , sledge, 29 Aug 2012, coll. Y. Hanamura & Faizul ( FRI CR0011 ) .

Other non-type materials. Malaysia. Mouth of Merbok Mangrove Estuary : 5 males (cl 4.5– 5.0 mm), sledge, July 2005, coll. Y. Hanamura & Faizul (NSMT-Cr 31626): Matang Mangrove Estuary. 2 males (cl 4.8, 5.0 mm), 2 females (cl 5.9, 6.9 mm), sledge, 18 Aug 2005, coll. Y. Hanamura & Faizul (transferred from formalin to ethanol) (NSMT-Cr 31627): 14 males (cl 3.7– 4.6 mm), 7 females (cl 3.7–6.4 mm), 3 juveniles (cl 1.5–2.3 mm), sledge, 25 Nov 2008, coll. Y. Hanamura & Faizul (NSMT-Cr 31628) .

Indonesia. Setrap River Estuary , Kalimantan Island : 2 males (cl 6.5, 7.5 mm), 13 females (cl 7.0–10.0 mm), 30°48.005′S, 115°31.337′E, hand net, 19 Sept 2019, coll. E. Hardianto & H. Imai (NSMT-Cr 31631); 4 specimens used for DNA analysis (sex and size undetermined), data same as previous (NSMT-Cr 31632–31635) .

Thailand. Bam Bo Village, Samut Prakan ( Gulf of Thailand): 1 male (cl 4.7 mm), commercial catch, June 2016, coll. K. Nakahara, part of appendages used for DNA analysis (NSMT-Cr 31636) .

Description. Male. Rostrum ( Fig. 5a, b) sub-triangular, elevated slightly from dorsal margin of carapace, with sharply pointed terminal tooth and small anterior tooth in addition to somewhat larger posterior tooth on its dorsal margin. Carapace entirely smooth on surface, except for post-orbital and hepatic teeth.

Abdomen with first somite possessing pro- curved sharp tooth at median part of ventral sternite between right and left pleopods. Sixth somite ( Fig. 5c) twice length of fifth, postero-dorsal part ending in small tooth, no red spot on postero-ventral part. Telson ( Fig. 5c, d) 0.7–0.8 times as long as sixth somite, posterior end narrowly rounded or sub-triangular with rounded distal part.

Eye ( Fig. 5a, b) with well pigmented cornea, latter wider than eye-stalk.

Antennule ( Fig. 7a, b) noticeably elongate in mature males, particularly in third segment of peduncle, 0.70–0.86 times as long as combined length of first and second segments; lower flagel- lum ( Figs 5a, b, 6a) modified into clasping organ, commonly composed of 12-segmented; first seg- ment of trunk not noticeably long, almost uniform in width through length and utmost about twice length of its width, showing weakly oblique conjunction with second one; major clasping spine moderately stout, reaching as far as mid-length of fourth segment of main branch, with 2 aligned rows of minute serrated denticles, and rudimentary clasping spine present near base of major one; first sub-segment of main branch with single basal and single distal setal-spines, second and third each with single distal and/or sub-distal setal-spine, fourth segment 1.2–1.5 times as long as combined length of second and third segments, and usually bearing 9 or 10 setal-spines on its entire margin, fifth segment with 1–3 setal-spines.

Antennal scale ( Fig. 5a) 0.70–0.79 times as long as carapace, slightly but distinctly extending beyond anterior margin of second segment of antennular peduncle.

External maxilliped and pereopods varying in length depending on body size. Third maxilliped in larger males extending as far as anterior end of antennular peduncle, distal segment about three-fourths times as long as penultimate. First pereopod in larger males extending as far as cornea. Second pereopod in larger males reaching as far as anterior end of antennal scale. Third pereopod ( Fig. 5e) in larger males extending anterior end of antennular peduncle, distinct sharp tooth present at disto-mesial part of basis; coxa with anteriorly curving on its inner margin. Genital coxa ( Fig. 5e) often with slender or sub-acute distal part in lateral aspect, while sub-rectangular in ventral aspect, with widely truncated or widely sinuous anterior part.

Petasma ( Fig. 5f) with brunt and distally rounded capitulum bearing numerous hooks along lateral surface as well as distal part; processus ventralis slender, reaching as far as distal margin of capitulum; no trace of pars astringen, Appendix masculina ( Fig. 5 g) with 2 or 3 short hooks distally.

Endopod ( Fig. 5c) of uropod with 1–6 irregularly-shaped red-spots in fresh materials: exopod with small tooth on lateral margin demarcating non-ciliated and ciliated parts, latter about 0.7– 0.8 times as long as former.

Female. Usually larger than males.

Antennule ( Fig. 5h) not elongated as in males, first segment longest, and third segments 0.39– 0.46 times as long as combined length of second and third segments; lower flagellum ( Fig. 6b) as long as third segment of peduncle, constituted of 18–20 sub-segments.

Antennal scale ( Fig. 5h) 0.67–0.74 times as long as carapace, extending to mid-length to distal one-third of third segment of antennular peduncle.

Third and fourth thoracic sternites forming longitudinal groove rather deep and narrow, median swelling steep and well pronounced ( Fig. 6c, d).

Body size. Largest male cl 7.5 mm, female 10.0 mm, recorded from south-eastern part of Kalimantan Island, Indonesia.

Type locality. Matang Mangrove Estuary , Peninsular Malaysia .

Etymology. This species is named in honour of the late Dr. Makoto Omori (1937-2022), who first discussed the two morphological forms in Acetes indicus .

Remarks. Tirmizi and Ghani (1982) noted that specimens of A. indicus collected from Pakistan resemble Omori`s large form. However, we have the impression that their morphological features appeared to be similar to A. spiniger rather than A. omorii sp. nov.

The specimens reported from Thailand by Pérez Farfante and Kensley (1997; figs 128–130) are regarded to be A. omorii , because the male lower antennular flagellum agrees well with that of this species.

Distribution. Acetes omorii sp. nov. has been collected with certainty in the coastal waters of South-East Asia, from Kalimantan Island, Indonesia to the Malacca Straits, via the Gulf of Thailand ( Fig. 3). On the west coasts of Peninsular Malaysia, specimens of A. omorii sp. nov. were commonly captured in the inshore waters including mangrove estuaries (see also Hanamura et al., 2007; under A. indicus ).