Acetes spiniger Hansen, 1919

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 : 63-66

Acetes spiniger Hansen, 1919

( Fig. 7)

Acetes spiniger Hansen, 1919 ; pl. 4, fig. 5a–f. Acetes indicus : Kemp, 1917: 47 (in part); Omori, 1975:

(in part; at least fig. 15a, b, d, f, g–i); Ravindranath,

1980: 255, figs 1–3; Pathan and Jalihal, 1997: 510.? Acetes indicus : Tirmizi and Ghani, 1982: 44, figs 1, 2.

Material examined. Malaysia. Off Kuala Selangor, Selangor (Malacca Straits): 31 males (cl 3.2–4.3 mm), 38 females (cl 3.3–5.8 mm), 9 juveniles and damaged specimens (cl 2.8–4.0 mm), several body parts, off-shore commercial catch, 23 Sept 2012, coll. Y. Hanamura & Faizul (NSMT-Cr 31637); 2 specimens used for DNA analysis (sex and size undetermined), data same as previous (NSMT-Cr 31638, 31639): 7 males (cl 3.5–4.4 mm), 10 females (cl 3.5–5.8 mm), 2 abdomens, data same as previous (NSMT-Cr 31640); 3 males (cl 3.7–4.0 mm), 2 females (cl 5.2, 5.8 mm), data same as previous (NSMT-Cr 31641) . Malacca: 1 male (cl 3.8 mm), 13 females (cl 3.5–6.3 mm), fish market (dried products), 5 Aug 2005, coll. Y. Hanamura & Faizul (NSMT- Cr 31642) .

India. Off Calangule , Goa; 4 males (cl 3.9–4.8 mm), 1 female (cl 6.4 mm), 1 Dec 1972, coll. C. T. Achuthanktty, id. M. Omori (NSMT-Cr 22267) .

Description. Male. Rostrum ( Fig. 7a) subtriangular, elevated slightly from dorsal margin of carapace, apex ending into sharp tooth, and armed dorsally with 2 teeth, posterior tooth larger than anterior one. Carapace (Fig. 9a) smooth, with small post-orbital and hepatic teeth.

Abdomen with first sternite possessing pro- curved sharp tooth at mid-part between right and left pleopods; sixth somite ( Fig. 7b) somewhat compressed, 2.1–2.3 times as long as fifth, bear- ing small tooth or point at postero-median part, without red spot on postero-ventral part. Telson ( Fig. 7b, i) 0.6–0.7 times as long as sixth abdominal somite, posterior part somewhat narrowing, then forming sub-triangular end.

Eye ( Fig. 7a) with well pigmented cornea, latter wider than ocular peduncle in dorsal aspect.

Antennule ( Fig. 7a) with elongate peduncle in adults, particularly in third segment, latter 0.92– 1.10 times as long as combined length of first and second segments: lower flagellum ( Fig. 7c) modified into clasping organ, most commonly with 12 sub-segments, distal part of first segment of trunk part forming nearly vertical or weak conjunction with second one; major clasping setal-spine somewhat slender, extending as far as mid-length of fourth segment of main branch, with single line of serrated denticles and rudimentary clasping spine placed near base of major spine; first segment of main branch with or with- out setal-spine; second and third segments with single setal-spine, fourth segment 0.5–0.7 times as long as combined length of anterior 2 segments, bearing 4–6 setal-spines on distal half.

Antennal scale ( Fig. 7a) 0.70–0.81 times as long as carapace, barely reaching end of second segment of antennular peduncle but not extending beyond it, outer margin with small tooth at distal end.

Third maxilliped reaching mid-length of third segment of antennular peduncle, distal segment two-thirds times as long as penultimate segment. First pereopod shortest, falling slightly short of cornea of eye; second pereopod falling short of anterior end of antennal scale; third pereopod ( Fig. 7d) longest, reaching mid-length of third segment of antennular peduncle; coxa with stout tooth or projection on distal inner margin; basis with obtuse tooth near distal inner part. Genital coxa narrowly tapering distally in lateral aspect, but widely truncated or weakly grooved in ventral aspect.

Petasma ( Fig. 7e) with capitulum robust and somewhat rounded distally, bearing numerous hooks on distal and lateral surfaces; processus ventralis narrow, reaching as far as distal end of capitulum; pars astringen occasionally noticeable as weak elevation or vestigial lobule. Appendix masculina with 2 or 3 hooks on distal margin.

Uropod ( Fig. 7b) with exopod bearing small but distinct tooth at distal 0.64–0.76 on lateral margin, basal part from which is naked while setose in distal part; no confident data for its number of red spots, but at least 1 or 2 spots present in preserved specimens.

Female. Usually larger in body size than males and also differing in several sexual charac- ters.

Antennule ( Fig. 7f) with first segment longest, and third segment of peduncle not elongated as in male, 0.33–0.47 times as long as combined length of second and third segments; lower fla- gellum simple and not modified, composed of 19 or 20 sub-segments.

Antennal scale ( Fig. 7f) 0.64–0.73 times as long as carapace, reaching about basal 2/5–1/3 length of third segment of antennule peduncle.

Third maxilliped extending beyond antennular peduncle by distal and 1/2–1/3 of penultimate segment, distal segment 0.70–0.75 times as long as penultimate.

First pereopod shortest, fully reaching cornea of eye; second pereopod falling slightly short of distal end of antennular peduncle; third pereopod extending beyond antennular peduncle by length of propodus and dactylus.

Third and fourth thoracic sternites forming longitudinal groove rather wide and shallow, not conspicuously narrowing anteriorly and not swelling markedly ( Fig. 7g, h)

Body size. Largest male cl 4.8 mm and female cl 6.4 mm from Goa, India.

Type locality. The type locality of this species should be off Rangoon, Burma (now Yan- gon, Myanmar), based on which materials Omori (1975) evidently noted the morphological traits of this species .

Remarks. Tirmizi and Ghani (1982) reported A. indicus from Pakistan, as a species resembling Omori`s llarge formz (= A. omorii sp. nov.). The male lower flagellum figured by these authors appeared to show an unusual form for the l A. indicus z species complex in having an extremely elongated first segment of the main branch as well as a relatively short clasping tooth. However, the form of the female genital area seemed similar to A. spiniger rather than the latter by a broad sternal groove, although future confirma- tion is in need for specimens occurring in Pakistan.

Distribution. This species is known with certainty in the peripheral region of the north-eastern part of the Indian Ocean, from the Malacca Straits and off Galangule, Goa, India (and proba- bly to Pakistan). In the Malacca Straits, A. spiniger is commercially fished by offshore trawls. Contrary to this, A. omorii sp. nov. occur in great abundance in the inshore waters including mangrove estuaries, suggesting that the two closest relatives are sharing their major habitats ( Fig. 3).