Siriella brevicaudata Paulson 1875

Siriella brevicaudata Paulson, 1875

Figs 7–10

Siriella brevicaudata Paulson, 1875a: 123, pl. 20, fig. 1a–m.

Siriella brevicaudata – Paulson 1875b: 30, pl. 1, figs 15–16. — Czerniavsky 1882: 95; 1887: 32. — W.M. Tattersall 1922: 450, figs 3–4; 1927a: 187. — Illig 1930: 561 (key). — Coifmann 1937: 19, pl. 7, fig. 11a–p (illustrations of W.M. Tattersall 1922). — Gordan 1957: 378 (catalogue). — Băcescu 1973a: 173; 1973b: 645, fig. 1l. — Mauchline & Murano 1977: 76 (checklist). — Almeida Prado-Por 1980: 189. — Müller 1993: 34 (catalogue). — Ariani et al. 1993: 396. — Murano 1998: 45, fig. 2a. — Wooldridge & Mees 2003: 32. — Grabe et al. 2004: 2323. — Murano & Fukuoka 2008: 33, fig. 13. — Anderson 2010: 22 (checklist). — Naser et al. 2012: 379 (list).

Siriella brevicauda – Pillai 1965: 1682 (lapsus calami), 1691 (lapsus calami), fig. 12.

Diagnosis

Carapace with anterodorsal margin rounded. Subrostral process not covered by carapace in male and covered in female. Carapace with dorsal cephalic tubercle and postcervical elevation, particularly wellestablished in female. Eye cornea black. Telson 0.9 times as long as last abdominal somite; posterior margin truncated; length 1.5–1.7 times anterior width; anterior width 1.5–1.7 times posterior width. Lateral margins of telson with three anterior and four to seven posterior spiniform setae, among latter three to four short and two to three apical pairs very long; terminal posterolateral pair of spiniform setae 0.36–0.53 times as long as telson and 1.2–1.6 times as long as subterminal pair; subterminal spiniform setae 1.4–3.1 times as long as preceding pair of posterolateral spiniform setae. Telson apically with slight emargination, bearing three small, dorsally invisible spinules, 0.03–0.08 times as long as terminal spiniform setae. Labrum with very short, barely visible, anterior spine, <0.1 times as long as rest of labrum. Maxilla 1: outer ramus robust setae smooth. Maxilla 2: endopod with five lateral setae. Endopod of pereopods 1–3, merus 3.0–3.3 times as long as wide. Uropodal exopod 3.1–3.4 times as long as wide; segment 1 is 2.8–3.0 times as long as segment 2, with three to five distolateral spiniform setae. Uropodal; endopod with 10 to 12 medial spiniform setae in both sexes, along almost entire margin, with terminal spiniform seta not reaching apex of ramus.

* Posterior width of telson is considered to be between the first pair of posterolateral spiniform setae.

* Posterior width of telson is considered to be between the first pair of posterolateral spiniform setae.

Type material

Syntypes

UNKNOWN COUNTRY: 9 specimens, Red Sea (Zoological Museum of the University of Kiev, Ukraine; Czerniavsky 1887). The specimens, as well as the entire collection of Paulson were lost during World War II (Bidzilya, museum curator, pers. comm.).

Material examined

BAHRAIN: 9 ♂♂, 3 ♀♀, 4–4.5 mm long, 2 juveniles, 3.5 mm long, Arabian Gulf, Tubli Bay, st. 16, 1991 (exact date unknown), J. A. Mansoor and H. Sulman leg. (USNM 1459141); 1 ♂ (+ slide), 4.5 mm long, 1 ♀ (+ slide), 4 mm long, same collection data as for preceding (USNM 1459142); 4 ♂♂, 5– 5.5 mm long, 11 ♀♀, 5.5–6.5 mm long, Arabian Gulf, Tubli Bay, st. 73, 1991 (exact date unknown), J.A. Mansoor and H. Sulman leg. (USNM 1459143); 2 subadult specimens with parasitic Isopoda, Arabian Gulf, Tubli Bay, st. 29, 1991 (exact date unknown), J. A. Mansoor and H. Sulman leg. (USNM 1459144).

Type locality

The exact type locality in the Red Sea is unknown.

Description

Body length of males 4–5.5 mm, of females 4–6.5 mm.

Male (Arabian Gulf)

CARAPACE. With anterodorsal margin rounded (Fig. 7B). Subrostral process visible from under carapace. Cephalic part of carapace with slight, barely visible dorsal tubercle.

TELSON. Slightly shorter than last abdominal somite (0.88 times as long) (Fig. 7A), trapezoidal (Fig. 7E), 1.5–1.7 times as long as wide anteriorly and 1.5–1.7 times as wide anteriorly as posteriorly; lateral margins with three anterior and four to five posterior spiniform setae, among latter two apical pairs especially long; terminal pair of posterolateral spiniform setae 1.4–1.6 times as long as subterminal; subterminal pair 1.9–3.1 times as long as preceding posterolateral pair of spiniform setae; apically with slight emargination, bearing three small, dorsally invisible spinules (Fig. 7F), 0.03–0.04 times as long as terminal posterolateral pair of spiniform setae, and a pair of long plumose setae flanking them.

HEAD APPENDAGES. Eyes protruding beyond carapace sides (Fig. 7B), 1.3 times as long as wide and 0.6 times as long as width of anterior part of carapace; peduncle slightly wider than long; cornea slightly wider than peduncle. Peduncle of antenna 1 about twice as long as peduncle of antenna 2; segment 3 swollen dorsally, 1.2 times as long as segment 1, with short conical posterior processus masculinus, slightly advanced forward and covered by fine setae (Fig. 8A). Antennular inner flagellum normal, not dilated or meandering in proximal part. Antennal scale not reaching distal margin of antenna 1 peduncle (Fig. 7B), with or without distal joint (sometimes in same specimen); 2.7–2.8 times as long as wide; 1.3 times as long as distance from scale base to base of outer spine (Fig 8C). Labrum with very short, barely visible, anterior spine, <0.1 times as long as rest of labrum (Fig. 8E). Mandibular palp (Fig. 8F): segment 1 without setae; segment 2 with 10 to 12 medial and four to eight lateral setae, about as long as width of segment; among medial setae, longer alternating with shorter; segment 3 is 0.6–0.7 times as long as segment 2, with three lateral, two long distal, seven to eight rather long and robust serrated proximomedial, five to seven distomedial setae and 10 or 11 distal anterior plumose setae. Maxilla 1 (Fig. 8H): inner process with three lateral and four apical setae; outer process with about 10 robust smooth apical setae. Maxilla 2 (Fig. 9A): exopod narrowly oval, 2.5 times as long as wide, with 12 plumose setae; segment 2 of endopod about as long as and as wide as exopod, with five lateral setae and many robust medial setae; apical medial setae distally finely serrated; endites with robust setae; apical setae of distal endite distally finely serrated.

MAXILLIPEDS. Thoracopodal exopod 9-segmented (Fig. 9B). Maxilliped 1 endopod (Fig. 9C): bases of preischium and ischium with rudimentary endites; merus widest and longest segment, nearly as long as wide; carpopropodus with anterior bunch of four serrated setae; dactylus with strong unguis, 2.7 times as long as dactylus. Maxilliped 2 endopod (Fig. 9D): ischium as wide as merus; merus 1.5 times as long as wide; carpopropodus slightly longer and narrower than merus, with three medial bunches of setae; dactylus rather small, with four anteromedial serrated setae and four posteromedial long setae; dactylar unguis 4.5 times as long as dactylus.

PEREOPODS. Carpopropodus segments separated by clear articulation; proximal segment 0.3–0.5 times as long as distal. Dactylus with strong unguis and subungulary robust seta. Pereopod 1 (Fig. 10A): ratio of ischium, merus, carpopropodus and dactylus (including unguis) length 1.3: 2.3: 2: 1; ischium 1.7 times as long as wide, with one–two lateral and multiple short medial setae; merus 3.0 times as long as wide, with multiple medial setae; carpopropodus with clear proximal joint, five times as long as wide; paradactylary setae slightly shorter than unguis. Pereopod 2 (Fig. 10B): ratio of ischium, merus, carpopropodus and dactylus length 1.5:2.2: 2: 1; ischium 1.9 times as long as wide, with three lateral and multiple short and long medial setae; merus 3.3 times as long as wide; carpopropodus with clear proximal joint, five times as long as wide, and 0.9 times as long as merus; paradactylary setae slightly shorter than unguis. Pereopods 5 and 6 thinner than pereopods 1–4. Pereopod 5 (Fig. 10C): ratio of ischium, merus, carpopropodus and dactylus length 1.1: 2: 2.1: 1; ischium 2.5 times as long as wide, with distomedial bunch of setae and distolateral seta; merus five times as long as wide, with about eight medial setae in proximal half; carpopropodus with clear proximal joint, six times as long as wide; paradactylary setae reaching half of unguis. Pereopod 6 (Fig. 10D): ratio of ischium, merus, carpopropodus and dactylus length 1: 2.5: 2.7: 1.2; ischium with distomedial bunch of setae; merus about 5.5 times as long as wide, with four medial setae; carpopropodus about nine times as long as wide, proximal joint barely visible; paradactylary setae reaching only half unguis. Penis cylindrical, with 2 long, thick apical setae (Fig. 10E).

PLEOPODS. Pleopods 2–4 (Fig. 10F, H): pseudobranchia spirally coiled; rami 10–11 segmented; proximal segments wider than longer; distal setae not modified. Pleopod 5 (Fig. 10G) with 11-segmented rami; proximal segments of rami about as long as wide; pseudobranchia not coiled.

UROPODS. Uropodal exopod (Fig. 7G) with joint, visible only in lateral half, 3.1–3.4 times as long as wide; segment 1 about three times as long as segment 2, with three–four distolateral spiniform setae. Uropodal endopod with 10 about equally long medial spiniform setae along almost entire margin, with terminal one not reaching apex of ramus.

Female (Arabian Gulf)

Anterodorsal margin of carapace covering subrostral process (Fig. 7C). Carapace with dorsal cephalic tubercle and high postcervical elevation (Fig. 7D). Peduncle of antenna 1 shorter and narrower than in male; segment 3 is 0.5 times length of segment 1, with one medial and three rather long medial setae (Figs 7C, 8B). Antennal scale reaching distal margin of antenna 1 peduncle, with distal joint; total length 3.1 times width (Figs 7C, 8D). Mandibular palp (Fig. 8G): segment 3 is 0.5 times as long as segment 2, with three rather long and robust serrated proximomedial setae.

Comparison

Siriella brevicaudata is readily distinguished from all species of the brevicaudata group by having a telson with the longest terminal spiniform setae, which can sometimes be as long as half of the telson length, as well as by the general pattern of posterior armature of the telson: three to four short and two to three very long pairs of setae, and terminal setae distinctly longer than subterminal. In addition, the distinction between the subterminal pair of spiniform setae and the preceding posterolateral setae is the greatest (up to three times as long) for any species in the group. Unique also is the sexual dimorphism of the anterodorsal margin of the carapace, which covers the subrostral process in females, but not in males.

Siriella brevicaudata is most closely related to S. gibbosa (see differences in the comparison section for S. gibbosa); these two species have telsons with the fewest posterolateral spiniform setae (four to seven compared to 9 to 20 in other species of the group) and the widest uropodal exopods (3.1–3.4 times as long as wide, compared to about 4 times as long as wide for other species). Siriella brevicaudata is also similar to S. occulta sp. nov. (see differences in the comparison section of S. occulta sp. nov.). For additional morphological differences between S. brevicaudata and other species in the group, see Table 1.

Geographic variation

In the Red Sea, judging from the original illustrations (cf. Paulson 1875a) and the illustrations of Băcescu (1973b), the telson of S. brevicautada is armed with five to seven posterior lateral spiniform setae, including three long terminal ones; while in the Arabian Gulf (cf. Murano 1998; Murano & Fukuoka 2008; our data) and Gulf of Manaar (cf. W.M. Tattersall 1922), it is armed with four to five posterior lateral spiniform setae, including two long terminal ones. Also, the terminal spiniform setae of the telson are 1.2–1.3 times as long as the subterminal ones in the Red Sea, 1.4–1.6 in the Arabian Gulf, and 1.3–1.5 in the Gulf of Manaar; the subterminal spiniform setae are 1.4–1.8 times as long as the preceding posterolateral pair of spiniform setae in the Red Sea, 1.9–3.1 in the Arabian Gulf and 1.4–1.9 in the Gulf of Manaar. The uropodal exopod has five distolateral spiniform setae in the Red Sea and Gulf of Manaar, as opposed to three–four spiniform setae in the Arabian Gulf. And last, W.M. Tattersall (1922) reported 10 to 12 spiniform setae on the uropodal endopod, and at least 10 can be counted on Paulson’s illustrations; however, a maximum of 10 was found in the Arabian Gulf.

Distribution

Red Sea (type locality) (Paulson 1875a): Ras-el-Kanisa Gulf (Băcescu 1973a), Gulf of Aqaba, Eilat (Băcescu 1973b; Ariani et al. 1993); Suez Canal and nearby Lake Timsah and Great Bitter Lake in Egypt (W.M. Tattersall 1927a); Arabian Gulf: Bahrain (Grabe et al. 2004), Tarut Bay (Saudi Arabia) (Murano 1998); Mozambique Channel: Nacala Bay (Wooldridge & Mees 2003); Gulf of Mannar (India) (W.M. Tattersall 1922) (Fig. 1).

Habitat

Upper sublittoral species, found among seaweeds, seagrasses and sand at depths of 0.5– 7 m. Salinity 42‰ (Red Sea, Gulf of Aqaba; Ariani et al. 1993).

Remarks

Based on specimens from the Arabian Gulf, Bahrain, earlier reported by Grabe et al. (2004), we provide here a detailed description of S. brevicaudata, comparing specimens with the original illustrations from the type locality, the Red Sea. The original description by Paulson (1875a) contains little information, but the illustrations allow recognition of the species. Despite the loss of the type specimens, the designation of a neotype is not, therefore, necessary for the time being. In our specimens, we did not confirm the sexual dimorphism of the antennal scale mentioned by Murano & Fukuoka (2008). The described geographical variation in telson armature in the existing fragmentary material may indicate some level of differentiation between different populations.

Bibliographic note

There is confusion concerning placement of the original description of S. brevicaudata either in Paulson (1875a) or Paulson (1875b) (cf. Murano 1998; Murano & Fukuoka 2008). We were able to obtain both rare works. The species was described in detail and illustrated in Paulson (1875a), which is the author’s doctoral dissertation on the crustaceans of the Red Sea, but the exact date of this publication was not found. In the same book Paulson (1875a: 124) noted the mistake in his illustration of the penis and referred to an update of the figure and a more detailed description of the penis in another work (Paulson 1875 b). The latter publication includes only the supplementary description of the statocyst and penis of S. brevicaudata. Paulson (1875 b), as well as other papers of the same issue, were published on 8 Jun. 1875, but the volume was not combined until 1876, as indicated on the front page of the cover. Discussing the development of the statocyst, Paulson (1875 b: 31) referred to his study of the brachyuran cuticle in his dissertation (Paulson 1875 a) and gave the exact page number, implying, probably, that it had been published previously. Therefore, this dissertation (Paulson 1875 a), with the detailed description of S. brevicaudata, is most likely the original description of the species. Murano (1998) remarked that he did not see both works, although he gave the correct order of publications and page references. Murano & Fukuoka (2008) stated that they did not see Paulson 1875 b, which they put as the first original work, but were able to obtain a translation of Paulson (1875 a), though they gave erroneous reference pages and general pagination (probably coming from the translation).