Alpheus cf. djiboutensis De Man, 1909

Anker, Arthur, 2024, Preliminary revision of Alpheus djeddensis Coutière, 1897 species complex, with description of three new species of goby-associated snapping shrimps and taxonomic notes on A. macellarius Chace, 1988 and A. djiboutensis De Man, 1909 (Decapoda: Alpheidae), Zootaxa 5472 (1), pp. 1-63 : 50-55

publication ID	https://doi.org/ 10.11646/zootaxa.5472.1.1
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scientific name	Alpheus cf. djiboutensis De Man, 1909
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Alpheus cf. djiboutensis De Man, 1909 View in CoL

Figs. 1D–K View FIGURE 1 , 32–35 View FIGURE 32 View FIGURE 33 View FIGURE 34 View FIGURE 35

Alpheus djiboutensis De Man, 1909: 160 View in CoL , pl. 8, figs. 17–24.

(?) Alpheus djiboutensis View in CoL . — Balss 1915: 23; Abel 1960: 459; Klausewitz 1960: 152; Polunin & Lubbock 1977: 93 [identity cannot be confirmed without examining material].

Not Alpheus djiboutensis View in CoL . — Karplus et al. 1972a: 95, figs. 1–13; Karplus et al. 1972b: 275; Karplus et al. 1974: 259 ( A. djiboutensis View in CoL 1); Karplus et al. 1981: 6, fig. 2G; Karplus 1987: 514, fig. 2G [all = A. djeddensis Coutière, 1897 View in CoL and/or A. shukran sp. nov.]; Karplus et al. 1974: 260 [= A. berumeni sp. nov.]; Debelius 1998: 273, colour photograph; Debelius 2001: 152, 2 colour photographs [= A. tigrinus sp. nov. (small photograph) and A. aff. tigrinus (large photograph), see text]; Humann & DeLoach 2010: 84 (colour photograph) [= Alpheus sp. , probably undescribed, see below].

Not Alpheus cf. djiboutensis View in CoL .— Kuiter & Debelius 2009: 152, colour photographs [= A. aff. tigrinus , see text].

Not Alpheus djiboutensis View in CoL . — Harada 1972: 1, fig. 1E, F; Banner & Banner 1979: 26; Banner & Banner 1982 (part.?): 180, fig. 55; Banner & Banner 1985: 15 [most likely not A. djiboutensis sensu De Man (1909) View in CoL , however, identity cannot be ascertained without examining material].

Material examined. 1 male (cl 16.7 mm, specimen dried out, broken in pieces after examination), 1 ovig. female (cl 16.9 mm, specimen dried out), FLMNH UF 36942 , Red Sea , Saudi Arabia, Farasan Islands , Abulad (Abu Lad), 16°47’51.7”N / 42°11’56.8”E, fringing reef / slope, depth 1–10 m, leg. A. Anker et al., 10.03.2013 (BDJRS-2562); 1 ovig. female (cl 11.9 mm), FLMNH UF 37013 , Red Sea, Saudi Arabia, Farasan Islands, Zahrat Durakah (Zahirah), 16°50’09.2”N / 42°18’22.7”E, fringing reef / slope, depth 2–6 m, leg. A. Anker et al., 11.03.2013 (BDJRS-2703) GoogleMaps ; 1 female (cl indet., specimen examined in 2019, not located in 2023), FLMNH UF 37000 , same collection data as for previous specimen (BDJRS-2687) GoogleMaps ; 1 juvenile (cl indet., missing major cheliped, photographed and released), Red Sea , Saudi Arabia, Thuwal, KAUST, near King Abdullah Monument, 22°20’32.2”N / 39°05’03.1”E, sandflat with rubble and sparse seagrass near channel, depth 0.5–1 m, leg. V.N. Peinemann, 30.09.22 (AA-22-533) GoogleMaps .

Description. See De Man (1909) for description and illustrations of A. djiboutensis and Figs. 33–35 View FIGURE 33 View FIGURE 34 View FIGURE 35 for colour photographs of specimens from the Red Sea tentatively identified as A. cf. djiboutensis .

Colour pattern. Background colour whitish; both carapace and pleon with pale greenish brown or olive green, irregular patches, short bands and spots, most arranged in diffuse, interrupted, longitudinal bands or chains; rostral carina darker olive green with white blotches; saddle on first pleonite usually conspicuous, white; saddle on fourth pleonite much smaller, white; white dorsal blotch also present on fifth pleonite; telson white with green-brown blotches; antennular and antennal peduncles white or yellowish with green-brown patches; antennular and antennal flagella pale greenish blue; chelipeds white with green-brown or olive green patches or mottling on merus, carpus and mesial face of chela; calcified distal portion of chela fingers pinkish; lateral face of chelae largely white; second to fifth pereiopods whitish with yellowish tinge and conspicuous reddish markings; uropods white with pale green-brown mottling ( Figs. 33–35 View FIGURE 33 View FIGURE 34 View FIGURE 35 ).

Common name. Djibouti goby shrimp (if confirmed as A. djiboutensis ).

Type locality. Djibouti, Gulf of Aden .

Distribution. Western Indian Ocean: Red Sea ( A. cf. djiboutensis ) and Gulf of Aden; may be more widespread in the Indo-West Pacific (see below).

Ecology. Red Sea: fringing reefs and slopes at depths of 1 to 10 m; recorded partner gobies are Cryptocentrus caeruleomaculatus and C. cryptocentrus ( Fig. 35 View FIGURE 35 ) and Ctenogobiops spp. , including C. crocineus ( Fig. 34C View FIGURE 34 ) and possibly C. maculosus ( V.N. Peinemann, pers. comm.).

Remarks. The present specimens from the Farasan Islands, Saudi Arabia, especially the fully grown male (FLMNH UF 36942), correspond rather well to the original description of A. djiboutensis provided by De Man (1909), which was largely based on a medium-sized male (estimated cl 14 mm, based on tl 35.5 mm) from Djibouti. However, whether they actually represent A. djiboutensis sensu De Man (1909) remains to be shown in the future. Unfortunately, two of the originally collected four specimens, including the only complete adult male (FLMNH UF 36942), were found in dry condition after a loan return in 2022, making preparation of line drawings impossible, whereas the fourth specimen examined by the author in 2019 was not located in the FLMNH in 2023. Nonetheless, photographs of the now dry male ( Fig. 32A–I View FIGURE 32 ) and female ( Fig. 32J View FIGURE 32 ), as well as colour photographs of these two specimens (FLMNH UF 36942) taken alive or shortly after death ( Figs. 33 View FIGURE 33 , 34A, B View FIGURE 34 ), are provided, in addition to some in situ photographs of the species ( Figs. 34C, D View FIGURE 34 , 35 View FIGURE 35 ).

The two perhaps most important features of A. cf. djiboutensis distinguishing it from A. djeddensis , A. shukran sp. nov., A. tigrinus sp. nov. and A. berumeni sp. nov. are the more protruding rostro-orbital region of the carapace (cf. Figs. 1B, D View FIGURE 1 , 9A View FIGURE 9 , 32A View FIGURE 32 , 34B View FIGURE 34 ), and the presence of a sharp distomesial tooth on each of the cheliped meri (cf. Figs. 2D View FIGURE 2 , 3F View FIGURE 3 , 8A View FIGURE 8 , 9G View FIGURE 9 , 32G View FIGURE 32 , 33C View FIGURE 33 ). In A. djeddensis and other species the distomesial margin of the merus is typically somewhat protruding, sometimes forming a small blunt tooth (visible in Fig. 10C View FIGURE 10 ), but never forming a stout sharp tooth, as in the male of A. cf. djiboutensis (well visible on both cheliped meri in Fig. 33C View FIGURE 33 and on the major cheliped merus in Fig. 32G View FIGURE 32 ). However, in two female specimens from the Farasan Islands, the meral tooth is rather obsolete, making its use in the distinction between these taxa ambiguous. Therefore, other possible distinguishing characters must be included. For instance, the telson of A. djiboutensis and A. cf. djiboutensis appears to be noticeably more slender than the telson of A. djeddensis or its closest relatives (cf. Figs. 1F View FIGURE 1 , 2I View FIGURE 2 , 3C View FIGURE 3 , 12B View FIGURE 12 , 18C View FIGURE 18 , 26C View FIGURE 26 ; see also Chace 1988; Purushothaman et al. 2021; Anker 2022 a, 2022b). Furthermore, the merus and the chela of the major cheliped of A. djiboutensis and A. cf. djiboutensis appears to be stouter than in A. djeddensis (cf. Figs. 1G View FIGURE 1 , 2C, E View FIGURE 2 , 3F, G View FIGURE 3 , 8 View FIGURE 8 , 32G, F View FIGURE 32 ), which was also noted by De Man (1909). However, due to sexual dimorphism and frequent regeneration of the chelipeds resulting in abnormal proportions of the chelae, this last feature may be more problematic to use. Nevertheless, in the proportions of the major and minor chelae, and the minor chela fingers only slightly gaping, distally strongly curved and furnished with rows of balaeniceps setae, the male from the Farasan Islands ( Figs. 32D–G View FIGURE 32 , 33 View FIGURE 33 ) is much closer to A. djiboutensis than to A. djeddensis .

Holthuis (1958) identified a large female from Sudan as A. djiboutensis and this identification was initially followed by the present author. Later, during the review of the A. djeddensis complex, Holthuis’ specimen was reassigned to A. tigrinus sp. nov., together with the Saudi Arabian material, based on the somewhat broader telson and rather moderately protruding rostro-orbital region of the carapace. Nevertheless, it must be noted that in the proportions and general shape of the major and minor chelipeds (including the development of the balaeniceps setae), De Man’s (1909) type specimen of A. djiboutensis corresponds well to the material herein identified as A. cf. djiboutensis , but also to larger male specimens of A. tigrinus sp. nov. and A. berumeni sp. nov., except for the distal armature of the merus. In the absence of type material of A. djiboutensis (see above) and fresh material from Djibouti, as well as taking into account the relatively high degree of endemism in the Red Sea (e.g., DiBattista et al. 2016a, 2016b; Bogorodsky & Randall 2019), the present identification of the Red Sea material as A. cf. djiboutensis must be treated with some caution. Therefore, a formal redescription of A. djiboutensis , as well as confirmation of the identity of the present specimens, must await a recollection of at least one adult and complete male specimen in Djibouti, morphologically corresponding to the larger male described and illustrated by De Man (1909).

Some morphological characters of the Red Sea material herein identified as A. cf. djiboutensis , such as the cheliped merus armed with a strong distomesial tooth, somewhat gaping minor chela fingers and the marbledspotted type of colour pattern, suggest a closer phylogenetic relationship of this species, or at least some affinities, with A. rapax (probably also a species complex, A. Anker, pers. obs.). However, A. djiboutensis (including A. cf. djiboutensis ) and all afore-mentioned species can be easily separated from A. rapax (or a species currently identified as A. rapax ) by the less gaping fingers of the male minor chela, a noticeably blunter rostral carina, and some features of the colour pattern (cf. Figs. 33–35 View FIGURE 33 View FIGURE 34 View FIGURE 35 ; Anker & De Grave 2006: figs. 26, 27). A species preliminarily identified as A. rapax cooccurs with A. cf. djiboutensis in the Red Sea, where it prefers shallow seagrass flats and associations with gobies of the genus Ctenogobiops , and is also common in Oman (A. Anker, pers. obs.). Another species with morphological and possibly phylogenetic links to A. djiboutensis is A. brevirostris . The author’s recent reexamination of Olivier’s holotype of A. brevirostris (MNHN-IU-2014-5115), which is in fair condition, will serve as a base for a detailed redescription of this taxon (A. Anker, in prep.). Nevertheless, it can be already stated that the specimens from the northern Red Sea identified as A. brevirostris in Karplus et al. (1981) and Karplus (1987) are likely not A. brevirostris sensu Olivier (1811) . Some shrimps identified as “ Alpheus spec. ”, which could belong to A. rapax , A. djiboutensis or A. cf. brevirostris , were reported in associations with Cryptocentrus caeruleopunctatus and Vanderhorstia delagoae (Barnard) ( Magnus 1967) .