Parapenaeopsis maxillipedo Alcock 1906

Parapenaeopsis maxillipedo Alcock, 1906 Figs 1 b, 2 b, 3 b, 4 b, 5 b, 6 b, 7 c Parapenaeopsis maxillipedo Alcock 1906: 40, pl. VIII – fig. 24, 24 a – b (type-locality: Bombay and Madras, India and Arakan, Myanmar); Holthuis 1984: PEN Para 8, 4 unnumbered figs; De Bruin et al. 1995: 32, 3 unnumbered figs; Chan 1998: 944, 3 unnumbered figs. Parapenaeopsis (Kishinouyepenaeopsis) maxillipedo – Psomadakis et al. 2019: 39, 4 unnumbered figs. Kishinouyepenaeopsis maxillipedo – De Grave and Fransen 2011: 216. Material examined. India • [NTOU M 02625]: Tamil Nadu, Tuticorin fishing harbor, commercial trawler, 18 Mar. 2017, 2 ♂♂, cl 14.4–16.0 mm, 3 ♀♀, cl 11.4–22.3 mm • [NTOU M 02626]: Tamil Nadu, Tuticorin fishing harbor, commercial trawler, 22 Mar. 2017, 1 ♂, cl 11.9 mm, 1 ♀, cl 19.0 mm • [NTOU M 02627]: Tamil Nadu, Tuticorin fishing harbor, commercial trawler, 22 Mar. 2017, 1 ♂, cl 12.1 mm, 1 ♀, cl 15.4 mm • [NTOU M 02628]: Muttom, Jeppiaar fishing harbor, commercial trawler, Sep. 2018, 2 ♂♂, cl 13.9–14.0 mm. Malaysia • [USM_INV 1006]: Strait of Malacca, Pantai Remis, Perak, 10 Aug. 2023, 1 ♂, cl 18.6 mm • [USM_INV 1009]: Strait of Malacca, Pantai Remis, Perak, 10 Aug. 2023, 1 ♂, cl 22.5 mm • [USM_INV 1010]: Strait of Malacca, Pantai Remis, Perak, 10 Aug. 2023, 1 ♂, cl 18.9 mm • [USM_INV 1011]: Strait of Malacca, Pantai Remis, Perak, 10 Aug. 2023, 1 ♀, cl 26.8 mm • [USM_INV 1012]: Strait of Malacca, Pantai Remis, Perak, 10 Aug. 2023, 1 ♀, cl 25.7 mm. Diagnosis. Rostrum generally straight and horizontal, reaching between base and middle of distal antennular peduncle segment, bearing 8–10 (avg. 8.9, n = 15) dorsal teeth (excluding epigastric tooth), tip without tooth, and slightly curved upwards. Postrostral carina distinct and similar width along entire length but often with a weak median pit, almost reaching posterior margin of carapace and being 0.91–0.97 (avg. 0.96, n = 16) of carapace length. Longitudinal suture short and extending to about level of epigastric tooth. Pereiopods I and II bearing basial spines and epipods. Pereiopod III generally armed with distinct basial spine. Abdominal somites I and II without dorsal carina. Telson without movable lateral spinules. Males with endopod of pleopod II strongly modified into boot-like shape, distal margin straight or slightly concave medially, median part of distal margin concealed by tuft of dense long stiff setae arose from anterodistal part of endopod; petasma horn-like with distolateral projections strongly elongated, tip of horn bearing distinct protuberance only at outer side. Female thelycum, anterior plate generally semi-quadrate or sometimes semi-circular, 0.79–1.03 (avg. 0.91, n = 7) as long as wide, surface slightly sunken and lacking median longitudinal furrow; posterior plate with distinct and often high median ovate boss, lateral parts semicircular; tuft of setae behind posterior plate long and thick. Coloration. (Fig. 7 b) Body greenish yellow and covered with dense yellowish to dark green dots. Eyes black gray. Antennal flagellae pinkish to yellowish and alternated with dark bands. Rostrum with tip reddish to dark reddish brown, bases of rostral teeth sometimes black and continuous as thick black line. Thoracic appendages whitish to pinkish white and greenish yellow. Abdomen with dense dark green dots arranged as distinct transverse bands, last somite (or somite VI) bearing a large black or brown posterolateral spot anteriorly accompanied with thick white margin. Uropods of tailfan reddish to dark red and with yellowish green margins or distal parts yellowish green. Pleopods pale white to pale yellow or reddish, outer parts of peduncles sometimes whitish. Tuft of long setae behind thelycum bluish. Color photograph belonging to this species given in Chaitiamvong and Supongpan (1992: pl. 43). Distribution. Known with certainties from India to Thailand and Strait of Malacca, shallow water less than 30 m deep (Chan 1998). Perhaps more widely distributed eastwards to the Philippines and northern Australia (see Remarks). Remarks. The relationships between P. maxillipedo and P. cornuta are extremely confusing in literature. Parapenaeopsis maxillipedo was suspected to belong to the same species as P. cornuta in the original description (Alcock 1906), and some authors also suspected or considered these two names to be synonyms (e. g., Dall 1957; Dall and Rothlisberg 1990; De Man 1911; Hall 1961). Other workers, however, considered that P. maxillipedo is a distinct species or subspecies (e. g., Chaitiamvong and Supongpan 1992; Chan 1998; Chanda 2016 b; Holthuis 1980, 1984; Kubo 1949; Liu and Wang 1987; Liu and Zhong 1988; Motoh and Buri 1984; Muthu 1968; Racek and Dall 1965; Racek and Yaldwyn 1971) and proposed many characters to separate it from P. cornuta. Careful comparisons and molecular analyses of materials assigned to P. maxillipedo and P. cornuta in this work reveal that there are large nucleotide divergences (13.5–16.0 %, Table 1) between these two species and they can be separated by the following characters. As commented on by many workers (Chan 1998; Chanda 2016 b; Dall 1957; De Man 1911; Hall 1961; Holthuis 1984; Kubo 1949; Liu and Wang 1987; Liu and Zhong 1988; Motoh and Buri 1984; Muthu 1968; Racek and Dall 1965; Racek and Yaldwyn 1971), the pereiopod III generally bears a distinct basial spine in P. maxillipedo (Fig. 6 b) but lacks a basial spine in P. cornuta (Fig. 6 a). Nevertheless, as pointed out by Kubo (1949) as well as Racek and Dall (1965), there are variations in this character. Of the 16 specimens (including nine males and seven females) of P. maxillipedo examined in this work, a male [NTOU M 02625] and a female [NTOU M 02627] from India lack a basial spine at the pereiopod III on both sides. Another female [NTOU M 02625], also from India, only has a small basial spine at the pereiopod III. On the other hand, only two (both males) of the 100 specimens (including 27 males) examined in P. cornuta have small ischial spines present on the pereiopods III. The rostrum is generally shorter (maximum extending to the middle of the distal antennular segment) but armed with more teeth (8–10, avg. 8.9) in P. maxillipedo (Fig. 1 b). The rostrum of P. cornuta (Fig. 1 a) is relatively longer (maximum reaching tip of antennular peduncle) and bears fewer teeth (6–8, avg. 7.0). The postrostral carina is distinct along the entire length and almost reaches the posterior margin of the carapace (postrostral carina / cl: 0.91–0.97, avg. 0.96) in P. maxillipedo (Figs 1 b, 2 b), but it is faded and broadened at posterior 1 / 4 and terminates with a distinct distance from the posterior carapace (postrostral carina / cl: 0.72–0.92, avg. 0.85) in P. cornuta (Figs 1 a, 2 a). The median boss at the posterior plate of the thelycum is strongly elevated in P. maxillipedo (Fig. 5 b) but weak in P. cornuta (Fig. 5 a). However, as the development of the thelycum is related to size, the median bosses in some juveniles of P. maxillipedo are sometimes low and rather similar to that of P. cornuta. The most distinct difference between P. maxillipedo and P. cornuta is body coloration. Some of the Indian specimens and all Malaysian specimens of P. maxillipedo examined in this study are accompanied by color photographs showing the same color pattern. The abdomen is distinctly banded and bears a large dark spot with an anterior thick white margin on the lateral surfaces of the last somite in P. maxillipedo (Fig. 7 c). In P. cornuta, the bandings on the abdomen are obscure, and there is no large spot on the last abdominal somite (Figs 7 a, b; see also Hayashi 1986; Hsu and Chan 2023). Although P. cornuta has been reported from India (Chanda 2016 b; Muthu 1968), the original description of P. maxillipedo described from India and Myanmar clearly mentioned that this species has more rostral teeth (8–10 excluding epigastric tooth), a postrostral carina as “ … continued right up to the posterior border of the carapace, is sharp and particularly prominent …., ” the pereiopod III bearing a big basial spine, and the middle of the posterior plate of the thelycum with “ … a globous tubercle … ” (Alcock 1906). The present Indian specimens with characteristics described in the previous paragraph fit well with the original description of P. maxillipedo and can be considered as typical of this species. As the basial spine is occasionally absent or small at the pereiopod III in P. maxillipedo, the records of P. cornuta from India based only on males (Chanda 2016 b; Muthu 1968) become doubtful. Even those Indian records of P. cornuta represent a species different from P. maxillipedo; there are possibilities that they may be P. amicus or P. incisa because these two species also lack a basial spine at the pereiopod III, and the latter species has recently been suggested to occur off Bangladesh (Fakhruddin et al. 2024). Actually, most of the characters used in separating P. maxillipedo from P. cornuta can also be applied to distinguish it from P. amicus or P. incisa (Table 2). Parapenaeopsis maxillipedo is unique in the “ P. cornuta ” species group as it has the postrostral carina distinct along the entire length (Fig. 2 b) and likely also in its coloration (Fig. 7 c, P. incisa still without information on coloration but probably similar to P. cornuta and P. amicus). Moreover, P. maxillipedo differs from the other species of the “ P. cornuta ” group by generally having more rostral teeth (Fig. 1 b), longer postrostral carina (Figs 1 b, 2 b), bearing a large basial spine at the pereiopod III (Fig. 6 b), and posterior plate of thelycum having a high median boss (Fig. 5 b). Nevertheless, the petasma and endopod of pleopod II in males are almost identical between P. maxillipedo and P. cornuta (Figs 3 a, b, 4 a, b). The thelycum of these two species is also rather similar, but with the median boss at the posterior plate more developed and the anterior plate somewhat more elongated (0.79–1.03, avg. 0.91