Synapseudes minutus Miller, 1940

Heard, Richard W., Stępień, Anna, Drumm, David T., Błażewicz, Magdalena & Anderson, Gary, 2018, Systematic and taxonomic observations on the subfamily Synapseudinae Guţu, 1972 and related metapseudid taxa (Crustacea: Tanaidacea: Apseudomorpha), with the erection of a new genus and descriptions of three new species, Zootaxa 4370 (4), pp. 301-344: 312-319

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Synapseudes minutus Miller, 1940
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Synapseudes minutus Miller, 1940  

Figures 5–8 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE8

Synonymy. Synapseudes minutus Miller, 1940: 311   –313, fig.6; Menzies, 1949: 500, 515; Shiino, 1951: 17, 18; Menzies, 1953: 461; Pillai, 1954: 3; Lang, 1970: Tafel I, fig. d –e; Makkaveeva, 1971: 93; Gardiner, 1973: 31, 32; Riggio, 1973: 11, 15, 16, 18; Băcescu, 1976: 61; Riggio, 1977: 159; Guţu, 2006: 226–227.

Synapseudes   sp. Lang, 1970: Tafel I, fig. d –e.

Material examined. Bishop Museum: Holotype— female with oöstegites BM, Waikiki, Oahu; coll., M. A. Miller.

Other material— one adult ♀ with oöstegites (dissected), Waikiki , sta. 12, Aquarium reef, Oahu, 21 25’ 57.2 N, 157 49’ 20.3 W, coll. Bishop Museum personnel Jan 23, 2001 GoogleMaps   ; one ♀ (pre- or post- incubatory, length 1.6 mm), Kaneohe Bay , Sta 5, Waiahole Reef, Oahu, 12 29’ 14.6 N, 157 49’ 55.8 W, depth 0.5–7.5 m, coll. Bishop Museum personnel, 17 Nov 1997 GoogleMaps   ; one ♂ (length 1.1 mm) Kaneohe Bay , Sta 7, Pristine Reef, Oahu,12 28’ 42.3 N, 157 48’ 15.2 W, depth 1–8 m, coll. Bishop Museum personnel, 19 Nov 1997 GoogleMaps   ; one ♂ [Form A], 15 females (three preincubatory, nine ovigerous, three large [length 1.6–1.8 mm TL] non-incubatory), Kaneohe Bay , Sta 16, Heeia Fish Pond Reef, Oahu, 21 26’ 13.2 N, 157 48’ 15.2 W, depth 0.5–4 m, coll. Bishop Museum Personnel, 10 Nov 1997 GoogleMaps   . Bohart Museum of Entomology : one ♂, six ♀♀ (four ovigerous), Honaunau Reef, Oahu, BM I, 15 Sep 1966, coll   . M. A. Miller; two ♂♂ [Form B], Kahkoku [Kahuku?] Point, Oahu, pool lower intertidal, algae/rocks, coll. Alan Kuhn.

Revised diagnosis. Adults: lengths from 1.1 to 1.8 mm. Rostrum subquadrate with distal margin granulate, usually weakly concave. Antennular peduncular article-1 with inner margin usually bearing six, occasionally five or eight, subacute serrate-like spines. Antenna with six articles, last two minute, terminating in long simple seta and two, minute accessory setae. Maxilliped with palp article-1 with stout distolateral spiniform seta not reaching distal margin of article-2; article-2 with distolateral spiniform seta, not as stout as that of article-1, but more curved and long, reaching to end of palp article-4. Pereopods 1–2 basis usually with dorsal margin bearing two spiniform apophyses; basis of pereopod-3 usually with single spiniform apophysis. Pereopod-1 propodus ventral margin with four spiniform setae, on pereopod-2 with three or four spiniform setae, and on pereopod-3 with three spiniform setae. Pleon with pleonites 1–3 completely delineated by encircling suture; pleonites 4–5 completely fused with the pleotelson. Uropod with exopod biarticulate, endopod triarticulate.

Male: Similar to female, but distinctly heterochelate, with major cheliped massive; minor cheliped similar in size and shape to that of female.

Redescription of adult female (based primarily on 1.2 mm holotype and 1.2 mm topotypic specimen):

Body ( Fig. 5 A, B View FIGURE 5 ). Sub-cylindrical, 1.2 mm total length.

Cephalothorax ( Fig. 5A, B View FIGURE 5 ). Length subequal to width at posterior margin. Carapace pigmented (not illustrated). Ocular lobes rounded, eyes with pigment and ommatidia. Rostrum sub-rectangular, rugose, slightly indented medially. Mid-lateral dorsal surface of carapace with one pair of long simple setae; anteromedial region with pair of short simple setae behind eye lobes.

Epistome ( Fig. 5B View FIGURE 5 ). With well-developed, slightly down-turned, acute spine.

Pereonites ( Fig. 5A, B View FIGURE 5 ). Wider than long, gradually decreasing in width posteriorly, combined length of pereonites 1–2 slightly less than that of cephalothorax. All with one pair anterolateral and one pair of anterodorsal setae, except for pereonite-6 that has three pairs anterodorsal setae.

Pleon ( Fig. 5A, B View FIGURE 5 ). Pleonites 1–3 indicated by circular sutures. Pleonite-1 twice length as other two, latter two being subequal. Pleonites 1–2 with several simple setae; pleonite-3 asetose.

Pleotelson ( Fig. 5A, B View FIGURE 5 ). Length in lateral aspect about that of pereonite-4, representing fusion of telson and last three pleonites; constricted posteriorly to form small, upturned, pointed terminus bearing pair of minute medial subapical setae. Dorsal surface relatively smooth; anterior half with one pair lateral and one pair of sub-medial setae and single medial seta; posterior half with on pair of submedial setae and single medial seta.

Antennule ( Figs 5A, B View FIGURE 5 ; 7A). Peduncle with four articles, article-1 stout, approximately twice as long as wide, inner margin with row of six or seven similarly shaped, but of variable size, subacute, tooth-like spines; outer margin with at least two broom setae and several simple setae on dorsal surface. Article-2 about half length of article-1, with three subdistal broom setae and two subdistal simple setae. Article-3 much narrower and about half length of article-2, inner distal corner with one simple seta and one small seta on outer distal corner. Article-4 about half length of article-3, with notch for insertion of outer flagellum, one distal simple seta on dorsal surface. Flagella subequal; outer flagellum with three articles. Articles 1–2 with one or two simple setae and one aesthetasc on inner distal corner of each article; article-3 terminating in four long simple setae. Inner flagellum with two articles; article-1 nearly twice as long as terminal article, with one simple seta on inner distal margin; terminal article-2 with two broom setae and three distal simple setae.

Antenna ( Fig. 5C View FIGURE 5 ). Small, distinctly shorter (excluding terminal seta) than antennular peduncular article-1, with six apparent articles, squama absent. Article-1 strongly developed, nearly as wide as long, with coarse granulate lateral margin, and pigmented. Article-2 approximately one third length of article-1, with small simple seta on lateral margin. Article-3 shorter and narrower than article-2, naked. Article-4 shorter than articles 2–3 combined, with about five distal broom setae. Article-5 asetose small, about half length of article-3. Article-6 minute, length subequal to article-5, having one long strongly central simple seta about same length as articles 1–5 combined, and two minute simple accessory setae on either side.

Labrum (damaged, not figured.). Rounded and finely setose along upper margin.

Mandibles ( Fig. 5D, E View FIGURE 5 ). Left mandible ( Fig. 5D View FIGURE 5 ) with incisor process weakly tridentate distally; lacinia mobilis palmate, with three distal lobes; setiferous lobe with four irregularly setulate setae; inner face of molar process not observed. Right mandible ( Fig. 5E View FIGURE 5 ) appearing non-dentate; lacinia mobilis bidentate; setiferous lobe with four irregularly setulate setae; molar with marginal setation obscured. Palp with three articles, articles 1–2 asetose; article-3 short, less than half length of article-2, with two terminal (one long and short), finely pectinate, setae.

Labium. Not recovered.

Maxillule ( Fig. 5F View FIGURE 5 ). Outer endite with apparently eight terminal spiniform setae, outer margin with setules; inner endite bearing four distally setulose setae, outer margin with setules. Palp biarticulate with two long terminal setulate setae.

Maxilla ( Fig. 5G View FIGURE 5 ). Moveable endite with outer lobe with distal margin bearing five (1.2 mm female) to six 1.8 mm female) long setae; inner lobe with four setulate setae. Fixed endite with outer lobe from outer to inner margin appearing to have three simple setae, two stout setae, and one stout setulate seta; inner lobe with subdistal row of about eight (1.2 mm female) basally swollen, distally setulate setae, and two subdistal straight, stiff, simple setae on dorsal face.

Maxilliped ( Fig. 5H View FIGURE 5 ). Basis sub-rectilinear in ventral view, appearing asetose. Palp article-1 outer margin with narrow distolateral elongation bearing robust spiniform seta not reaching to distal margin of article-2; shortened inner margin with long, simple seta. Article-2 with outer margin having distolateral lobe bearing long, curved, spiniform seta, not as robust as that on article-1, but reaching to or near tip of palp article-4; inner subdistal margin with row of four short, stout simple setae; with four basally swollen setae in between long simple proximal seta and long simple distal seta; minute seta present proximally. Article-3 with several marginal proximally-swollen simple and pectinate setae and inner sub margin with two basally swollen pectinate setae and two small, stout curved setae. Article-4 with three pectinate setae and four proximally swollen simple setae, and one, minute simple distal seta. Endite with two simple setae (innermost longest) on inner distal margin, distal margin with row of setulate setae decreasing in size laterally, lateral sub margin with row of four or five small basally swollen setulate seta; inner margin with two functional coupling hooks (retinacula).

Epignath ( Fig. 5H View FIGURE 5 ). Narrow, boat shaped, tapering, margin with fine hirsute setae, terminal seta large with length little shorter than main body of epignath.

Cheliped ( Fig. 5 I, J View FIGURE 5 ). Basis swollen, suboval in lateral view, with small seta on subdistal, ventral margin; dorsal margin granular, with one small and one minute short seta. Merus appearing “V shaped in lateral view, extending ventrally about half way along ventral margin of carpus, armed with four subdistal, simple, marginal, or sub-marginal setae. Carpus about twice as long as broad, with three distal/subdistal simple setae (one on apex of shallow ventral apophysis). Propodus having ventral margin with one subdistal and one smaller medial simple seta; palm with inner face having two short pectinate setae just proximal to articulation with dactylus (movable finger), one simple seta between fixed and movable fingers; fixed finger inner face with two sub marginal setae just proximal to sclerotized claw ( Fig. 5I View FIGURE 5 ); outer face of propodus with distal half having four sub marginal simple setae, distal smallest, and one simple seta adjacent to base of moveable finger ( Fig. 5J View FIGURE 5 ). Dactylus longer than fixed finger and three fourths length of palm, grasping margin irregularly pectinate, three subdistal simple setae just proximal to well-developed, sclerotized, orange-brown claw, claw with weakly bidentate tip.

Pereopods 1–6 ( Figs 6 View FIGURE 6 ; 7B). Ambulatory, pereopods 1–3 oriented anteriorly, pereopod-4 cable of pivoting both anteriorly and posteriorly; pereopods 5–6 oriented posteriorly. All having basis with proximal third bearing at least two broom setae (often broken off preserved specimens); propodus having dorsal margin with broom seta; dactylus ventrally with small tubercle and associated minute seta just proximal to unguis and another more proximal minute seta to tubercle; dorsally with minute medial simple seta.

Pereopod-1 ( Figs 6A, B View FIGURE 6 ; 7B). Basis with dorsal margin armed with two, occasionally three, blunt spiniform apophyses, longer than ischium, merus, and carpus combined; distodorsal margin with acute spiniform seta margin; ventral margin with small spiniform seta and one distal simple setae. Ischium with one simple seta on ventrodistal corner. Merus with one dorsodistal, acuminate, spiniform and one short, simple setae, one long and two short ventral/subventral simple setae, and one spiniform seta on subventral corner. Carpus slightly less than half length of merus, subquadrate, about as broad as long, ventral margin with two spiniform setae, two dorsodistal simple setae and one dorsodistal pectinate seta, and one dorsodistal spiniform seta. Propodus relatively narrow, about 1.5 times length of carpus; distodorsal margin with long simple and spiniform setae; inner subdorsal face with subdistal short stout pectinate seta ( Fig. 6B View FIGURE 6 ); ventral margin with four stout spiniform setae becoming larger distally, stout bipectinate seta on inner face adjacent to distal most spiniform seta. Dactylus slightly shorter than propodus, curved ventrally; ventral margin sinuous unguis slightly less than half total length.

Pereopod-2 ( Fig. 6C View FIGURE 6 ). Basis longer than combined length of merus, ischium, and carpus; with two blunt spinelike apophyses (sometimes with only one or with smaller third), one simple seta and two broom setae on dorsal/ subdorsal margin; ventral margin with two short simple setae. Ischium with ventrodistal margin bearing single simple seta. Merus about half length of basis, with narrow, spiniform seta on dorsodistal margin, and five simple setae. Carpus as wide as long, with four stout spiniform setae, and three simple setae. Propodus, depending on size, having ventral margin with three or four, stout spiniform setae. Dactylus as in pereopod-1.

Pereopod-3 ( Fig. 6D View FIGURE 6 ). Generally similar to pereopod-2, but with basis having one spiniform apophysis on anterior margin of basis. Carpus with five spiniform setae. Propodus having ventral margin with three stout spiniform setae.

Pereopod-4 ( Fig. 6E View FIGURE 6 ). Fixable, capable of both anterior and posterior orientation. Basis longer than ischium, merus, and carpus combined, dorsal margin with two broom setae; ventral margin with two simple setae. Ischium with simple seta on ventrodistal margin. Merus with one subdistal spiniform and one subdistal simple setae, one simple seta on dorsal margin. Carpus shorter than merus; ventral margin with two on subdistal spiniform setae; dorsodistal margin with strongly developed spiniform seta; medial distal margin with long stiff simple seta; lateral face subdistally with one small curved seta and one stout short spiniform seta; dorsodistal margin with stronglydeveloped spiniform seta. Propodus with dorsodistal margin with three stiff finely bipectinate setae, inner distal medial margin with stout bipectinate seta; ventral margin with two spiniform setae, largest distally. Dactylus similar to those of pereopods 1–3.

Pereopod -5 ( Fig. 6F View FIGURE 6 ). Basis longer than combined length of ischium, merus, and carpus, setation as in pereopod-4. Ischium as in pereopod-4. Merus about 1.5 times length of carpus, with two simple setae on ventral and one simple seta on dorsodistal margin. Carpus slightly longer than broad, with three spiniform setae, and two simple setae (one long ventrodistal and dorsodistal). Propodus elongate, more than twice length of carpus, distal/ subdistal dorsal margin with one well-developed finely pectinate and smaller simple setae; inner medial with stout bipectinate seta distally; ventral margin with two spiniform setae, one subproximal and largest distal. Dactylus similar to that of pereopod-4, but larger.

Pereopod-6 ( Fig. 6G View FIGURE 6 ). Similar to pereopod-5, but with single finely pectinate on distodorsal margin.

Uropod ( Fig. 7C View FIGURE 7 ). Peduncle expanded with distal inner margin forming subacute dorsolateral apophysis. Exopod biarticulate, extending to distal margin of endopodal article-1; article-1 with small, single subdistal seta, article-2 with two terminal setae of different lengths. Endopod with three articles, subequal in length; article-1 with one short simple seta on inner distal corner; article-2 with one subdistal seta and two broom setae on inner distal margin; article-3 with four terminal simple setae (three long and one short) and two distal broom setae.

Subadult male (1.2 mm TL) ( Fig. 8A –E View FIGURE8 ). Similar to adult female, but smaller (length 1.1 mm) with slenderer body. Chelae heterochelate with major cheliped beginning to develop, but not exhibiting marked sexual dimorphism of adult male forms. Minor cheliped similar in size and setation to female of same size. Body setation, antennule, antenna, mouth parts, maxilliped, pereopods, and uropods similar to those of female.

Subterminal adult male? (1.3 mm TL) ( Fig. 8F –H View FIGURE8 ). Similar to subadult 1.1 mm male, but with more massive major chela and less defined pleonite-3.

Terminal adult. Not determined.

Variation. Ovigerous females attributed to S. minutus   in the Oahu materials varied in length between 1.2 and 1.8 mm, suggesting that at least two reproductive instars may be present. As previously mentioned, some of the smaller (1.2–1.3 mm) preincubatory and incubatory females had the ventral margin of the propodus of pereopod-2 with three, instead of four, spiniform setae. When we examined the 1.2 mm female holotype, it was not feasible to illustrate pereopod-2. Hence, we do not know if the holotype has three or four ventral setae on the propodus of this pereopod. Several large females (1.6–1.8 mm in length) lacking oöstegites were observed in the collection from Kaneohe Bay. These specimens may indicate a resting stage between broods, or a terminal senescent stage. None of the seven females over 1.6 mm in length that we examined were ovigerous or had oöstegites.

Distribution. Oahu Island, Hawaii.

Remarks. The females of Synapseudes minutus   and S. rudis   can be separated from those of the other 24 species of the genus recognized here by the following general combination of characters: (1) antenna with four peduncular and two minute flagella articles, (2) antenna terminating in a long primary seta, (3) pereopods 1 and 2 with dorsal margin of basis having two spiniform apophyses and pereopod-3 with dorsal margin of basis bearing one spiniform apophysis (4) presence of three partially fused, but completely delineated, pleonites, and (5) uropodal endopod with three articles.

Synapseudes minutus   differs from S. rudis   , which is known from the northeastern Pacific coast of the Americas ( Menzies 1953), by having palp article-2 of the maxilliped with well-developed distolateral seta being relatively narrow, but extending to the distal margin of palp article-4; in S. rudis   this seta is short and robust, but not extending past palp article-3. Synapseudes minutus   can be further distinguished from S. rudis   by lacking a distinctly cleft rostrum, and by the better developed and relatively larger spines along the inner margin of antennular peduncle article-1. Refer to the Synapseudes   Key and Table 3 for further comparative morphological information differentiating S. minutus   from its congeners.

The type material of S. minutus   is represented by a single female holotype. We examined the type and topotypic specimens housed in the Bernice Bishop Museum, and were able to study additional specimens of S. minutus   formerly in M. A. Miller’s personal collection and now housed in the Bohart Museum of Entomology, University of California at Davis. Though Miller’s specimens were not topotypic, they came from Oahu with some collections made just a few miles from the type locality. Based on our examination of the holotype, topotypic specimens, and the additional material from Oahu, Miller (1940) apparently misinterpreted the articulation of the antenna and uropod. He described the antenna as having three, instead of six articles, the uropodal endopod being biarticulate instead of triarticulate, and the exopod being uniarticulate instead of biarticulate. Miller briefly mentioned the adult male, but did not illustrate it and only mentioned that it was heterochelate with the larger chela being over half the length of the body. The adult male or males reported by Miller from the type locality were not found in either the collections of Bishop or Bohart Museums.

Lang (1970) presented a photographic image of the dorsal aspect of the abdomen and pleotelson for both S. minutus   and a supposedly second Hawaiian species of Synapseudes   , but he gave no specific details regarding the sex or morphology of the second Hawaiian species. It would be useful to know the sex of Lang’s second Hawaiian “species, but we were unable to trace the location of the specimen or specimens in question. The taxonomic status of some of the males co-occurring with the females, which we attribute to S. minutus   from Oahu, is problematical and requires further study. No males occurred in the material that we examined from Waikiki, but they were present in collections from other sites on Oahu.

Though small (1.1 mm), a single immature male attributable to S. minutus   occurred among the specimens from Kaneohe Bay. The major cheliped of the specimen appeared to be that of a subadult or the first recognizable male stage ( Fig. 8A, B View FIGURE8 ); but pereopod-1 had four stout spiniform on the ventral margin of the propodus and the complete delineation of the pleonites as in the females examined from Oahu ( Fig. 8E View FIGURE8 ). Like the smaller females pereopods-2 and 3 have three spiniform setae on the ventral margin of the propodus. These features are also shared by the 1.3 mm subterminal male collected Oahu ( Fig. 8F –H View FIGURE8 ), though in this specimen the suture indicating the third pleonite appears to be more indistinct than for the 1.1 mm subadult male. It appears that the larger subadult male ( Fig. 8F – H View FIGURE8 ), which we tentatively attribute to S. minutus   , is sexually mature. Based on the major chela, however, this specimen, appears not to have the size and degree of morphological development exhibited by other known terminal males of Synapseudes   (e.g., S. caleyi   n. sp.: see Fig. 12 View FIGURE 12 ).

In contrast, the three other males, all larger than those attributed herein to S. minutus   , occurring in the Oahu collections have only three instead of four spiniform setae on the propodal inner margin of pereopod-1 and the pleon with only incomplete dorsal vestiges of the pleonites 2 and 3 being present. Compared to the 1.3 mm male we tentatively attribute to S. minutus   , these males exhibit differences in setation, as well as, the development and dentition of the major cheliped; two of the specimens exhibited a huge major chela similar to the terminal male of S. caleyi   (see Fig. 12 View FIGURE 12 ), which were nearly as massive as the rest of their bodies. These specimens appeared to represent at least two different morphotypes. Examination of additional topotypic material is needed to determine if there are two different terminal male forms represented within the S. minutus   populations on Oahu or if a cryptic species having nearly identical females may be present.

We examined specimens of Synapseudes   resembling S. minutus   from other islands within the greater Hawaiian Archipelago, including Midway, Maui, Molokai, and Hawaii (Big Island). Those specimens appear very similar to and possibly conspecific with S. minutus   sensu lato and are similar to the “atypical large specimens examined on Oahu by Miller in that they have the ventral margin of the propodus of pereopod-1 armed with only three stout spiniform setae instead of four as in females, and pleonites 2–3 are incompletely delineated ventrolaterally. As in the specimens from Oahu, we did not observe any females exhibiting a pereopod-1 and pleon similar to those of the “atypical males. The larger females examined from Oahu had more setae in the maxilla than the 1.2 mm female, but this could be attributed to ontogenetic development. It is possible that the atypical male forms and possibly some of the larger females are conspecific with S. minutus   sensu lato or as previously mentioned may represent a closely related cryptic species. However, addressing these issues with only the limited amount of material presently available to us is beyond the scope of this investigation and awaits future detailed morphological studies in conjunction with those on molecular genetics of populations attributable to S. minutus   within the confines of the Hawaiian Archipelago.