Synapseudes 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 : 311-312

Genus Synapseudes Miller, 1940

Diagnosis (emended). Body 0.9–3 mm length, length 3.8–4.7 times width. Cephalothorax length 2.0–3.6 times length of antennular peduncle article-1. Pleon with segments appearing functionally fused; but with vestiges of one to three pleonites delineated by sutures, at least dorsally. Antenna lacking squama; with five or six articles (four peduncular and one or two flagella articles). Antennule peduncle article-1 with inner row of spiniform apophyses or single distinct spine; article-2 with or without apophyses on distal corners. Outer flagellum usually with three articles, rarely fewer; inner flagellum usually with two articles, rarely with one. Mandible palp articles 1–2 asetose, article-3 bearing two finely pectinate, unequal terminal setae. Pleopods absent. Uropodal exopod with one or two articles, endopod with three or four articles.

Remarks. Most of the meristic characters used in distinguishing the 26 species now retained within Synapseudes are listed in Table 3. Guţu & Ortiz (2009) considered the vestiges of two pleonites as a primary criterion for the erection of a new monotypic genus to accommodate Synapseudoides pinosensis from Cuban waters. Synapseudoides was diagnosed as having (1) a pleon with the indications of two pleonites, (2) pereonites with rounded margins, (3) an antennule with inner flagellum being biarticulate and the outer being triarticulate, (4) an antenna with six articles, terminating in a single long seta, (5) uropod with exopod biarticulate and an endopod triarticulate. All these characters fall within the range of those presently ascribed here for Synapseudes , especially the variation in the number of vestigial pleonites as originally indicated by Lang (1970). Based on our systematic analyses, we here subsume Synapseudoides into the genus Synapseudes . Hence, its type species becomes Synapseudes pinosensis ( Guţu & Ortiz 2009) , n. comb.

Also, besides S. pinosensis , over a third of the other previously described species of Synapseudes (i.e., S. acroporae , S. cystoseirae , S. erici , S. intumescens , S. menziesi , S. mediterraneus , S. rectifrons , S. setoensis , and S. shiinoi ) exhibit the presence of just two pleonites (see Table 3). There is one character that appears to be unique to S. pinosensis that may be systematically important. Article-3 of its antenna appears to be more than three times longer than article-4, whereas in all other members of the genus for which the antenna has been described, article-4 is significantly longer than article-3. As discussed earlier, S. heterocheles generally only exhibits one pleonite, but two can be present (see Bamber 2012).

The systematic status of four nominal species, S. acroporae , S. aflagellatus , S. mediterraneus , and S. shiinoi , which we have tentatively retained within Synapseudes , remains problematical. These four species each possess unique characters, possibly of generic significance, which are not exhibited by other members of the genus.

Synapseudes aflagellatus , remains the only cold-water (sub-Antarctic) member of the genus within the Synapseudinae . The distinctive combination of characters separating this species from the others in the genus include: (1) the greatly reduced condition of both antennular flagella ( Fig. 4A ), (2) the inner margin of antennular peduncle article lacking spiniform apophyses ( Fig. 4A ), (3) the presence of five or six long terminal setae on the antenna ( Fig. 4B ), (4) a maxilla with a reduced number of similar setulate setae on the endites ( Fig. 4C ), and (5) the presence of five stout, spiniform setae on the posteroventral margin of the propodus of pereopods 1–3 ( Fig. 4D ). This unique set of characters may warrant the elevation of Synapseudes aflagellatus to a new monotypic genus; however, we tentatively retain it within Synapseudes , pending re-examination of the type material and further systematic analysis.

The Tasmanian species, S. acroporae , appears to exhibit several unique features, including (1) the subproximal outer face of propodus (palm) of female chela armed with a stout spiniform seta ( Fig. 4M ), the dorsal surface of each of the pereonites and cephalothorax with long plumose setae (not simple setae as in the other know members of the genus) ( Fig. 4K, L ), and the surface of its body appearing to be covered with fine setules ( Fig. 4K, L ). None of these characters appear to be shared with other members of the genus. It should also be mentioned that another atypical Tasmanian species, S. violaceus , is illustrated with a long terminal plumose seta on the uropodal endopod ( Fig. 4N ).

Synapseudes mediterraneus appears, possibly apart from S. shiinoi and S. aflagellatus , to be unique among the described members of the genus by having a combination of only two articles in the outer antennular flagella plus an antenna terminating in “three long setae; however, four terminal setae appear to be present on the illustration of the antenna ( Băcescu 1977: fig. 2E). If substantiated, the most systematically significant feature of S. mediterraneus is the presence of a pair of small elongate, ventrolateral, protuberances on pleonites 1–2. Băcescu considered these structures as possible vestiges of pleopods; however, based on his illustrations ( Fig. 4H ) we believe that these structures appear to represent the lateral spines of the reduced pleura associated with pleonites 1– 2. They are somewhat similar to lateral processes on the partially fused pleonites of R. idios , which has the pair of pleopods on pleonite-1 inserted more ventrally ( Fig. 3I ).

Synapseudes shiinoi , also described from the Mediterranean, appears to have affinities with S. mediterraneus by having three terminal setae on the antenna and reduced flagella articles ( Fig. 4I ), but is unique in having the last article of the mandibular palp terminating in a tight, broom-like cluster of about ten long setae ( Fig. 4J ), a character not exhibited by any other known members of the Metapseudidae .

Another Mediterranean species, S. cystoseirae , which has four long terminal setae on the antenna, may be related to S. mediterraneus and S. shiinoi , but like most species of Synapseudes , differs by having two and three articles, respectively, in the inner and outer antennular flagella and a mandibular palp with two terminal setae. It would be useful using molecular markers to attempt to determine if S. mediterraneus and S. shiinoi were derived from isolated populations of S. cystoseirae , which had been dispersed into the Mediterranean Basin when it was breached by the Atlantic Ocean 5.3 million years ago during the catastrophic formation of the present-day Mediterranean Sea ( Blanc 2002).

Several other species within Synapseudes are inadequately described and illustrated. In the case of S. comorinensis , which is very briefly described from Indian waters, Pillai (1954) specifically describes it as having a distinctly five jointed pleon and three articles (segments) in the uropodal exopod, features not present in other species of Synapseudinae as defined here. Though not discussing the taxonomic status of S. comorinensis, Lang (1970) presented a photograph showing the dorsal view of its pleon and pleotelson, which shows the vestiges of the first three pleonites. Băcescu (1977) also considered S. comorinensis as referable to Synapseudes based on drawings sent to him by Pillai, which indicated the presence of just two recognizable pleonites. According to Băcescu, however, Pillai’s drawings also depicted a transverse row of dense setae on the first two pleonites, which is characteristic of some parapseudid and tanaidid genera, but unknown for the other described species of Synapseudes . Notwithstanding the apparent errors in the original description, Lang’s photograph supports the original generic designation for S. comorinensis .

Besides Synapseudes comorinensis , other nominal species including S. makkaveevae , S. hancocki , and S. tomescui need redescription or supplemental description based on type and/or topotypic material. Of these two species, S. hancocki can be grouped with those species having a combination of two antennal flagella articles terminating in a single long seta, and an uropodal endopod with three articles. Synapseudes tomescui is generally well-described and illustrated, except for the maxilliped and antenna, which are both important taxonomic and systematic characters, are not described or illustrated. As with S. comorinensis , the description and illustrations for S. makkaveevae are too incomplete and poorly executed to allow for any meaningful taxonomic comment.

Figures

FIGURE 3. Metapseudes wilsoni. A, antenna; C, right mandible with palp; H, uropod, endopod biarticulate. Metapseudes aucklandiae. E, abdomen, pleonites completely delineated (five pairs of biramous pleopods not illustrated); F, biramous pleopod with terminal setulate setae; G, pleonites 4–5 and pleotelson, dorsal aspect. Ronabus idios. B, antenna; D, left mandible with palp.I, male pleon and pleotelson, lateral aspect,showing partially fused pleonites1–5 and biramous pleopod-1; J, female, uniramous pleopod-1; K, partially fused pleonites and pleotelson, dorsal aspect; L, uropod, endopod triarticulate. A, C, H from Błażewicz-Paszkowycz & Bamber (2007); B, D–G, I–L from, or modified from, Gardiner (1973).

FIGURE 4. Some atypical species of Synapseudes. Synapseudes aflagellatus: A, antennule; B, antenna; C, maxilla; D, pereopod-1. Synapseudes mediterraneus: E, antennule; F, antenna; G, pleon and pleotelson, dorsal aspect; H, pleon andpleotelson, lateral aspect. Synapseudes shiinoi: I, antennule; J, right mandible with palp terminating in multiple setae. Synapseudes acroporae. K, carapace with lateral setulate setae and minute setae covering surface; L, pereonite-6, pleon and pleotelson, lateral aspect, showing same types of setation; M, chela of female with spiniform setae on mid-proximal region of propodus. Synapseudes violaceus: N, uropod with endopod bearing long setulate terminal seta. A–D modified from Sieg (1986); E–H; modified after Băcescu (1977); I–Jmodified from Riggio (1977); K–N modified from Băcescu (1976).