Synapseudes mediterraneus Băcescu, 1977

Bâlcu, Maxim-J., Motoc, Rozalia M., Ștefan, Andrei, Murariu, Dumitru & Popa, Oana P., 2025, Synapseudes marinae (Tanaidacea, Apseudomorpha, Metapseudidae) the first metapseudid species from the Sea of Crete, and redescription of S. mediterraneus from Israel, Zoosystematics and Evolution 101 (4), pp. 1423-1443 : 1423-1443

Synapseudes mediterraneus Băcescu, 1977

Figs 2 , 3 , 4 , Table 2

Material examined.

Holotype • 1 male, length 1.7 mm (No. 49211 / 372) . Allotype • 1 female with empty marsupium (No. TAN 054/373 ) . Paratypes • 10 males (No. TAN 056/373 b) and 7 adult females (No. TAN 055/373 b), from which 1 non-ovigerous female was dissected (permanent slide) . Non-types • 5 juveniles (No. TAN 057), from Mediterranean waters of Israel, Bat Yam, 3 km south of Tel Aviv, station TM 15 , depth 1 m, 1 November 1976, on a subtidal sandstone platform, in algae Jania sp. , leg. Prof. Lev Fishelson .

Other material.

(determined by Maxim-Jean Bâlcu in the museum’s scientific crustacean collection) • 1 adult female, 1 male, and 1 manca II, Station T 80-31 , Israel, without other collection data (from Prof. Dr. Mihai Băcescu Collection) .

Revised diagnosis.

Adult body length: females 1.3–1.9 mm, males 1.5–1.8 mm. Rostrum short, wide, anterior margin slightly concave and rugose. Pereonites 1–6 with one simple seta on each anterolateral corner; pereonites 4–6 with one simple seta on each posterolateral corner. Pereonites 2 and 3 longest. Each pereonite much wider than long, laterally rounded. Pleonite 1 slightly longer and wider than second. Pleotelson with about six dorsal simple setae, three posterolateral simple setae on each side, two caudo-dorsal simple setae on apex. Antennule peduncle with four articles, articles 2–4 wider than long; first article longer than following ones combined, inner margin with six sharp small denticles. Inner flagellum with two articles; second article with three simple setae, one aesthetasc terminally. Outer flagellum with three articles; second article with one aesthetasc, two simple setae; last article with four long simple setae, terminally. Antenna peduncle with four articles; flagellum uniarticulate, small, with four long simple setae terminally. Maxilliped first palp article with one small simple seta on inner side, one long thick seta on outer distal corner; article 2 largest, with eight stout and two long simple setae on inner margin, distally; one long thick seta on outer distal corner. Pereopod 1 basis with two or three dorsal apophyses; pereopod 2 basis with one, two, or rarely three dorsal apophyses; pereopod 3 basis with one dorsal apophysis. Pereopods 1–3 propodus with four ventral spines. Pereopods 4–5 carpus with four ventral spines; pereopod 6 carpus with three ventral spines. Pereopods 4–6 propodus with two small ventral spines.

Redescription of non-ovigerous female (dissected paratype).

Body (Fig. 2 A ) short, thick, relatively cylindrical, approximately 4.5 times as long as wide; length about 1.3 mm.

Cephalothorax (Fig. 2 A ) (including rostrum) approximately 28 % of body length, about 1.4 times as long as wide. Rostrum short, wide, anterior margin slightly concave and rugose. Ocular lobes undefined; visual elements with dark pigment. One very small, simple seta under eyes. Two medial simple setae on both sides of carapace.

Pereon (Fig. 2 A ) approximately 59 % of body length, about 2.1 times as long as carapace length; each pereonite much wider than long, laterally rounded. Pereonites 2 and 3 longest, each 0.5 times as long as wide. All pereonites with one simple seta on each anterolateral corner; pereonites 4–6 with one simple seta on each posterolateral corner. Pereonite 1 with two pairs of mid-dorsal simple setae; pereonites 2, 3, and 6 with three pairs of dorsal simple setae; pereonites 4 and 5 with four pairs of dorsal simple setae.

Pleon (Fig. 2 A ) approximately 13 % of body length, composed of two free pleonites and pleotelson. First pleonite slightly longer and wider than second. Each pleonite with four mid-dorsal simple setae and one lateral seta (latter appears to be plumose seta, as in Băcescu 1977; see fig. 2 D). Each pleonite expanded posterolaterally by small spiniform process.

Pleotelson (Fig. 2 A ) about 1.6 times as long as combined pleonites, triangular; apex acute in dorsal view, crest-like in lateral view; with about six unequal dorsal simple setae, three posterolateral simple setae on each side, two caudo-dorsal simple setae on apex.

Antennule (Fig. 2 B ). Peduncle with four articles; first article longer than following ones combined, about 1.7 times as long as wide; inner margin with six sharp small denticles and one small simple seta on dentiform prolongation; outer margin with four penicillate and four simple setae; three simple and two penicillate setae on dorsal surface. Articles 2–4 wider than long. Article 2 narrow, 0.3 times as long as article 1, with two simple setae on inner and three simple setae on outer margin, distally; five penicillate setae subterminally. Article 3 much narrower, 0.6 times as long as article 2, with two simple setae on inner and one simple seta on outer margin, distally. Article 4 (common) 0.7 times as long as article 3, with two simple setae inner distally, small notch for insertion of outer flagellum. Inner flagellum with two articles; first article with one inner small simple seta; second article about equal in length to first, with two long thick simple setae, one small simple seta, one aesthetasc terminally. Outer flagellum slightly longer than inner, with three articles; first article with one outer simple seta; second with one aesthetasc and two simple setae on inner distal corner; third article with four long simple setae, terminally.

Antenna (Fig. 2 C ) (without terminal setae) smaller than first peduncular article of antennule. Peduncle with four articles. First article with inner dentiform expansion, naked. Articles 2 and 3 wider than long. Article 2 about 0.6 times as long as article 1, with one small simple seta on outer distal corner. Article 3 shortest, about 0.9 times as long as article 2, naked. Article 4 longer than articles 2 or 3, with one inner penicillate seta, about four penicillate setae and one long simple seta, distally. Flagellum uniarticulate, small, with four long simple setae, terminally. Squama absent.

Labrum (unfigured) with conical projection.

Mandibles (Figs 2 D, E ) with three-articled palp; article 1 about 2.6 times as long as wide, naked; article 2 about 2.5 times as long as wide, naked; article 3 smallest, with two unequal setulated setae, terminally. Pars molaris without special features. Pars incisiva of left mandible (Fig. 2 D ) wide, lacking conspicuous denticles; lacinia mobilis with three rounded denticles; setiferous lobe with three serrated setae. Pars incisiva of right mandible (Fig. 2 E ) wide, lacking conspicuous denticles; setiferous lobe with three serrated setae and one stout furcate seta.

Labium unstudied.

Maxillule palp broken and lost. Outer endite (Fig. 2 F ) with about eight narrow spines terminally; inner endite with four setulate setae, terminally.

Maxilla (Fig. 2 G ) with outer lobe of movable endite with six long simple setae distally. Inner lobe of movable endite with about three simple setae. Outer lobe of fixed endite with three setae and one stout furcate seta. Inner lobe of fixed endite with row of 10 setae (thicker at the base), distally.

Maxilliped (Fig. 2 H ) with basis about 1.4 times as long as wide, naked. First palp article short and broad, with one small simple seta on inner side and one long and thick seta on outer distal corner. Article 2 largest, narrower proximally, with eight stout simple setae in two rows and two long simple setae on inner margin, distally; one long thick seta on outer denticled distal corner. Article 3 smaller than article 2, with three unequal simple setae, one finely serrated seta and four stout curved setae on inner margin. Article 4 smallest, with two small finely serrated setae, subterminally, five serrated setae and one simple seta on inner side. Endite (Fig. 2 I ) with four simple and three truncate thick setae on rostral side; inner margin with four setae and three coupling hooks.

Epignath unstudied.

Cheliped (Fig. 3 A ). Basis 1.3 times as long as wide, broad; rounded ventrally; with one mid-ventral and one disto-ventral simple seta. Exopod absent. Merus subtriangular; 3.7 times as long as wide; extended ventrally about half length of carpal margin; with one small proximal and two long distal simple setae, ventrally. Carpus approximately two times as long as wide; with two distal simple setae, ventrally; one distal simple seta, dorsally. Propodus as long as carpus; palm with one long and one small simple seta on outer face; one long simple seta and two small serrated setae near dactylus joint on inner face; fixed finger thick; outer face with eight simple setae (two ventral, six submarginal in distal third of fixed finger); cutting edge with about four sharp denticles. Claw small; orange-brown colour. Dactylus as wide as fixed finger; three thick inner simple setae near claw; claw stout; orange-brown colour; stronger than that of fixed finger; weakly bidentate tip.

Pereopod 1 (Fig. 4 A ) largest. Exopod absent. Basis 2.8 times as long as wide; ventral margin with one proximal and two distal small simple setae; two proximal small simple setae and two distal apophyses dorsally. Ischium very short; 0.2 times as long as wide; with one ventral simple seta. Merus 1.2 times as long as wide; three simple setae and one distal spine ventrally; one simple seta and one distal spine dorsally. Carpus shorter than merus; about as long as wide; with two spines and one simple seta ventrally; two outer subdistal spines; one distal robust spine and one long simple seta dorsally. Propodus 1.9 times as long as wide; with four ventral spines (increasing in size distally); two outer subdistal spines; one penicillate seta, one robust spine and one simple seta dorsally; one small subdistal inner serrated seta near dactylus articulation. Dactylus with two small ventral setae; unguis short and curved.

Pereopod 2 (Fig. 4 B ). Basis 2.5 times as long as wide; ventral margin with two distal small simple setae; one small simple seta and two apophyses mid-dorsally. Ischium very short; 0.2 times as long as wide; with one ventral simple seta. Merus 1.2 times as long as wide; with one long and three small simple setae ventrally; one outer subdistal simple seta; one distal spine dorsally. Carpus shorter than merus; wider than long; with one small simple seta and two spines ventrally; two outer subdistal spines; two outer long simple setae; one distal spine dorsally. Propodus 1.6 times as long as wide; with four ventral spines (increasing in size distally); two outer subdistal spines; one penicillate seta, one robust distal spine and one simple seta dorsally; one small subdistal inner serrated seta near dactylus articulation. Dactylus and unguis as in pereopod 1, but shorter.

Pereopod 3 (Fig. 4 C ) smaller than pereopod 2. Basis three times as long as wide; ventral margin with one proximal and two distal small simple setae; one small simple seta and one small apophysis mid-dorsally. Ischium very short; 0.2 times as long as wide; with one ventral simple seta. Merus 1.3 times as long as wide; with three simple setae ventrally; one distal simple seta and one distal slender spine dorsally. Carpus shorter than merus; wider than long; with two ventral spines; two mid-outer spines; one subdistal spine and two subdistal simple setae dorsally. Propodus 2.3 times as long as wide; with four ventral spines (increasing in size distally); two outer subdistal spines; one penicillate seta, one distal robust spine and one distal long simple seta dorsally; one small subdistal inner serrated seta near dactylus articulation. Dactylus and unguis similar to those of pereopod 2, but smaller.

Pereopod 4 (Fig. 4 D ). Basis about 2.2 times as long as wide; with one small distal seta ventrally; two small (one proximal, one mid) simple setae dorsally. Ischium very short; 0.3 times as long as wide; with one ventral simple seta. Merus 1.3 times as long as wide; with two simple setae and one subdistal small spine ventrally; one slender spine dorsally. Carpus as long as merus; with one small simple seta and four spines ventrally; one outer subdistal spine and one outer simple seta; one spine and two simple setae dorsally. Propodus two times as long as wide; with two small (one mid, one subdistal) spines ventrally; one penicillate seta and four serrated setae dorsally. Dactylus and unguis similar to those of pereopod 3, but larger.

Pereopod 5 (Fig. 4 E ). Basis about 2.5 times as long as wide; with three small (two proximal, one distal) simple setae ventrally. Ischium short; 0.4 times as long as wide; with one ventral simple seta. Merus 1.5 times as long as wide; with three simple setae ventrally; one distal slender spine dorsally. Carpus shorter than merus; wider than long; with one simple seta and four spines ventrally; one distal spine and two unequal simple setae dorsally. Propodus three times as long as wide; with two small (one mid, one subdistal) spines ventrally; one outer simple seta subdistally; one penicillate and one subdistal serrated seta dorsally. Dactylus and unguis similar to those of pereopod 4, but thinner and longer.

Pereopod 6 (Fig. 4 F ). Basis about three times as long as wide; with three small simple setae ventrally. Ischium short; 0.3 times as long as wide; with one ventral simple seta. Merus 1.6 times as long as wide; with two simple setae ventrally; one distal spine dorsally. Carpus shorter than merus; about as long as wide; with one simple seta and three spines ventrally; one distal spine and two unequal simple setae dorsally. Propodus 2.7 times as long as wide; with two small (one mid, one subdistal) spines ventrally; one penicillate, one subdistal serrated, and one subdistal simple seta dorsally. Dactylus and unguis similar to those of pereopod 5, but thick and longer.

Pleopods absent.

Uropod (Fig. 2 J ) short; peduncle about 1.3 times as long as wide; with strong inner apophysis and two unequal outer simple setae subdistally. Exopod with two articles; first article 1.6 times longer than second; with one simple seta; second article with two long unequal terminal setae. Endopod with three articles; article 1 longest, with one distal simple seta; article 2 with one distal simple seta; article 3 with three long setae and one penicillate seta terminally.

Redescription of male cheliped (paratype).

Cheliped (Fig. 3 B ) symmetrical; larger than female cheliped. Basis 1.1 times as long as wide; broad; rounded ventrally; with one mid-ventral simple seta. Exopod absent. Merus subtriangular; about 2.6 times as long as wide; extended ventrally more than half length of carpal margin; with three small simple setae ventrally. Carpus approximately 1.2 times as long as wide; with two distal simple setae ventrally; one distal simple seta dorsally. Propodus about 1.8 times as long as carpus; with large space between fingers; palm with one long outer and one long inner simple seta in gap between fixed finger and dactylus; two small serrated setae near dactylus joint on inner face. Fixed finger thinner, slightly curved; with 11 simple setae around inner and outer margins (three ventral, six outer submarginal in distal third, two inner near claw); tip slightly denticled. Claw small; orange-brown colour. Dactylus thicker than fixed finger; with proximal apophysis and one outer simple seta; three thick inner simple setae near claw; claw stout; bidentate tip (Fig. 3 C ); orange-brown colour; stronger than that of fixed finger.

Some remarks about juveniles and manca II.

Juveniles length 0.9–1.3 mm. Pereopods 1, 2 basis with two dorsal apophyses; pereopod 3 basis with one dorsal apophysis. Pereopods 1–3 propodus with three ventral spines (proximal ones very small); one dorsal spine; one or two outer subdistal spines. Pereopods 4–6 basis without apophyses; propodus with two ventral spines.

Only in one juvenile out of five: pereopod 1 basis with two dorsal apophyses; pereopods 2 and 3 basis with one dorsal apophysis; pereopods 1–3 propodus with four ventral spines, one dorsal spine, and two outer subdistal spines.

Manca II length 0.8 mm. Pereopod 1 basis with two dorsal apophyses; pereopods 2, 3 basis with one apophysis; pereopods 1–3 propodus with two ventral spines.

Intraspecific variation.

S. mediterraneus displays some degree of variation among the individuals examined in this study and from Băcescu (1977) text and drawings: (1) out of 13 males, only one male (7.7 %) has asymmetrical chelipeds (left cheliped larger than right one), the rest have symmetrical chelipeds; (2) number of dorsal apophyses of pereopod 1 basis (in males and females) varies between two-three; (3) number of dorsal apophyses of pereopod 2 basis (in males and females) varies between one-three; (4) out of five juveniles, four (80 %) have the pereopods 1–3 propodus with three ventral spines, only one (20 %) with pereopods 1–3 propodus with four ventral spines.

All the adult females and males individuals (100 %) have the left and right pereopods 1–3 propodus with four ventral spines.

Size-distribution.

Manca II body length 0.8 mm (n = 1). Juveniles body length 0.9–1.3 mm (n = 5). Non-ovigerous females body length 1.3–1.6 mm (n = 4). Female with oostegites body length 1.4 mm (n = 1). Females with empty marsupium body length 1.4–1.5 mm (n = 2). Males body length 1.5–1.8 mm (n = 13).

Distribution and habitat.

According to Băcescu (1977): Mediterranean waters of Israel: Ras-El-Nacura (in algae); Acre (in Pterocladia algae); Bat Yam (subtidal sandstone platform, in Jania algae).

Figures

Figure 2. Synapseudes mediterraneus, paratype, non-ovigerous female: A. Body, dorsally; B. Antennule; C. Antenna; D. Left mandible; E. Right mandible; F. Maxillule, outer and inner endite; G. Maxilla; H. Maxilliped; I. Maxilliped endite; J. Uropod.

Figure 3. Synapseudes mediterraneus, paratypes: A. Non-ovigerous female cheliped, outer view; B. Male cheliped, outer view; C. Fixed finger claw and dactylus bidentate claw, detail of male cheliped.

Figure 4. Synapseudes mediterraneus, paratype, non-ovigerous female: A – F. Pereopods 1–6, outer view.