Paranaspides Smith, 1908

Ahyong, Shane T., Schwentner, Martin & Richter, Stefan, 2017, The Tasmanian Lake Shrimps, Paranaspides Smith, 1908 (Crustacea, Syncarida, Anaspidesidae), Records of the Australian Museum 69 (4), pp. 259-275 : 261-262

Paranaspides Smith, 1908

Paranaspides Smith, 1908: 470 (type species: Paranaspides lacustris, 1908 , by monotypy).

Diagnosis. Rostrum prominent, well-developed. Cephalothorax without fenestra dorsalis. Body subcylindrical in cross-section, with prominent obtusely angled flexure at pleonite 1, appearing obtusely bent in lateral view. Free pereonites length subequal, shorter than pleonites. Pleonites 1–5 lower midlateral surface with vertical or near vertical row of minute spines; pleonite 6 lower mid-lateral surface with arcuate row of prominent spines. Pleonite 6 longer than twice length of pleonite 5. Telson dorsoventrally compressed; longer than wide, subquadrate; posterior margin and posterior half of lateral margin spinose. Antennal peduncles unarmed. Scaphocerite with lateral spine. Thoracopod 1 (maxilliped) with epipods. Thoracopod 7 with exopod. Uropodal endopod about two-thirds length of exopod; exopod with row of fixed spines proximal to diaraesis.

Description. Body subcylindrical in cross-section; prominent, obtuse flexure at pleonite 1. Rostrum triangular, apex blunt, slightly deflexed ventrally; few distal setae, arising submarginally. Head (cephalothorax) comprising fused cephalon and pereonite 1; cervical groove distinct; dorsal organ present on dorsal midline anterior to cervical groove; midlateral surface posterior to cervical groove with shallow diagonal groove. Pereonites 2–8 length slightly increasing posteriorly, subparallel, shorter than pleonites. Female gonopore (spermatheca) on pereonite 8 sternum between coxae; bulbous, directed anteriorly, anterior surface with genital orifice as narrow transverse slit.

Pleonite 1 enlarged, wedge-shaped in lateral view, dorsal margin rounded, forming prominent, obtuse flexure; longer than pleonite 2. Pleonites 2–5 length subequal; subparallel, dorsal margin straight. Pleonites 1–5 lower lateral tergal surface with vertical row of minute, close-set spines. Pleura 1–5 rounded; pleuron 1 margin unarmed, those of 2–5 posteriorly multispinose. Pleonites 1–2 upper posterior tergal margins unarmed, of pleonites 3–5 multispinose. Pleonite 6 longer than twice length of pleonite 5; lower midlateral surface of integument with arcuate row of prominent, well-spaced posteriorly directed spines, extending from slightly below mid-height almost to ventral surface; upper posterior margin multispinose; posterolateral angle spinose; posteroventral angle anterior to uropod articulation multispinose. Pleonal sternites 3–5 with low, broadly curved to truncate median processes between pleopod bases.

Telson elongate, subquadrate, dorsoventrally compressed, with low, broad median prominence proximally; posterior margin truncate to slightly concave; posterior margin and posterior half of lateral margins prominently spinose, lengths uneven.

Eyes pedunculate; cornea well-developed, rounded, distinctly wider than peduncle, dorsoventrally compressed; peduncle slightly longer than cornea, distally divergent.

Antennular peduncle 3-articulate, unarmed, dorsoventrally compressed; article 1 with statocyst, longer than article 2; article 2 longer than article 3, with rounded distomesial lappet; biflagellate, mesial (= accessory) flagellum shorter than lateral, similar in both sexes.

Antenna uniflagellate, flagellum slightly shorter than lateral antennular flagellum; protopod 2-articulate, coxa with splayed row of spines on lateral margin, basis with 2 lateral spines; exopod (scaphocerite) laminar, longer than wide, subovate, reaching end of antennular peduncle, distinct lateral spine, mesial and distal margin setose to base of lateral spine; endopod peduncle 2-articulate, unarmed, proximal article longer than distal article.

Labrum with shallow proximal constriction; distal margin slightly concave, finely setose.

Mandibular corpus (apophysis) robust; molar process and incisor process well-developed; molar with elongate, ovate, triturating surface, surrounded by spiniform setae; incisor process diagonal to axis of mandibular corpus. Left incisor process with 8 triangular teeth in sinuous row, proximal tooth largest; proximally with spine row between proximal incisor tooth and molar process. Right incisor process similar to left except with 6 triangular teeth, proximalmost tooth usually apically bifid, widely separated from adjacent tooth. Palp 3-articulate, setose, article 1 short, subquadrate, with 2 setae, article 2 slender, longer than articles 1 and 3.

Paragnaths widely separated by deep V-shaped incision, without lobes, distal half finely setose, especially mesially.

Maxillule with 2 endites; proximal endite distally setose; distal endite spinose distally, lateral surface with small conical palp.

Maxilla with 4 endites, proximal 2 endites with plumose setae, distal 2 endites densely arrayed with serrulate setae.

Thoracopods 1–8 protopod with coxa, basis, preischium, ischium, merus, carpus, propodus and dactylus; flexure at carpus-merus articulation.

Thoracopod 1 (maxilliped) coxa mesial margin with setose coxal endites, lateral margin with 2 lamellar epipods, proximal wider than distal; basis with slender, flattened, liguliform exopod; coxa-basis demarcation often ill-defined; preischium rectangular, more than quadruple length of quadrate ischium, expanded mesially, projecting beyond mesial margin of ischium; merus slightly tapering distally, distinctly longer than ischium; carpus triangular, longer than high, half length of merus; propodus slender, as long as merus; dactylus short, terminating in slender claw, with 2 slender movable spines on either side.

Thoracopods 2–8 (pereopods) as ambulatory legs. Thoracopods 2–6 structurally similar, distal 4 articles with tufts of setae, primarily along flexor margins, dactylus strongly setose; thoracopods 4–5 longest; coxa lateral margin with 2 ovate, lamelliform epipods, proximal epipod more pointed distally than distal epipod; coxa mesial margin in adult females with setose endite; basis short, partially fused with preischium; exopod articulating with lateral margin of basis, with elongate basal article and setose multi-annulate flagellum; ischium about as long as basis-preischium; merus elongate, slightly tapering distally, about twice ischium length; carpus triangular, longer than high, about half merus length or slightly less; propodus elongate, slender, shorter than merus; dactylus short, terminating in long, slender claw, with slender movable spine on lateral side, 2 movable spines on mesial side. Thoracopod 7 similar to thoracopods 2–6 except epipods proportionally more slender; exopod a single narrow lamella; dactylus with movable spine on either side. Thoracopod 8 structurally similar to preceding thoracopods but lacking epipods or exopod; basis and preischium indistinguishably fused; longer than thoracopod 7; dactylus with movable spine on either side.

Pleopods 1–5 exopod long, slender, setose, multi-annulate. Pleopods 1–2 endopod always present; unmodified endopod ovate, lamellar, short, length subequal to first exopod annulation in females and juvenile males; endopod always present on pleopods 3, present or absent on pleopods 4–5; adult male pleopods 1–2 endopod modified as copulatory structures (petasma).Adult male pleopod 1 elongate, directed anteriorly, reaching beyond thoracopod 8 coxa; slender proximally, expanded distally, hollowed mesially, deepest near midlength; distally bluntly rounded to subtruncate, lateral margin thin, lamellate; dorsomesial margin with short row of retinacula near midlength and distally; proximo-mesial surface with long scattered setae and spinules; midventral margin bluntly triangular, incurved mesially; left and right pleopods united by retinacula, together forming scoop-like structure. Male pleopod 2 endopod of 2 articles, slightly longer than pleopod 1, directed anteriorly, reaching to thoracopod 8 coxa; proximal article slightly longer than distal article, mesial proximal margin with row of retinacula; distal article straight, mesially hollowed, with short scattered spinules, apex blunt.

Uropods forming tail-fan with telson. Uropodal exopod elongate, spatulate, distolateral spine row of fixed graded spines; indistinct, partial diaeresis extending from base of distalmost spine; spine row preceded by straight margin; mesial margin and lateral margin distal to spine row setose. Uropodal endopod distinctly shorter than exopod, reaching to distal two-thirds of exopod; mesial margin to distal half of lateral margin setose.

Remarks. Paranaspides is readily distinguished from Anaspides and Allanspides by the distinct flexure at pleonite 1, the presence of a vertical row of minute spines on the lower midlateral surface of pleonites 1–5, an arcuate row of prominent spines on the midlateral surface of pleonite 6, a spinose basal antennal article, a more pronounced distomesial lobe on the maxilliped ischium, absence of sexually dimorphic antennules, a proportionally larger, more elongate scaphocerite, presence of the triangular ventromesial lobe of the male pleopod 1 endopod, a rectangular versus polygonal or linguiform telson, and more elongate uropods. In other respects, Anaspides and Paranaspides closely agree. Note that Ahyong (2016) inadvertently described Anaspides as having a 3-articulate antennal protopod; both Anaspides and Paranaspides have only two free protopod articles. Like Anaspides , Paranaspides further differs from Allanaspides by lacking the fenestra dorsalis on the cephalothorax.

When first described, Paranaspides immediately attracted controversy with its apparent possession of a biramous mandibular palp, a feature otherwise unknown in malacostracans ( Smith 1908, 1909b; Hansen, 1925). Gordon (1961), however, showed Smith’s mandibular observations to be based on an aberrant specimen; the palp of P. lacustris is uniramous and 3-articulate as in Anaspides . Phylogenetic analyses indicate a close relationship between Anaspides and Paranaspides , as sister groups or with the latter possibly even nested within the former (Jarman & Elliott, 2000).

Species of Paranaspides differ ecologically from those of Anaspides and Allanaspides , which are epibenthic and pholeteric, respectively. Instead, species of Paranaspides are frequently natatory and occur only in association with aquatic vegetation, amongst and above which they freely swim. Some morphological differences between Paranaspides and other anaspidesid genera, such as the enlarged scaphocerite and more elongated uropods may relate to the primarily pelagic or natatory rather than benthic habits of other anaspidesids.

Subsequent to Smith’s (1908, 1909b) accounts of Paranaspides lacustris , other studies have examined pleonal musculature ( Daniel, 1931), functional morphology and excretion (Cannon & Manton, 1929; Manton, 1930, 1931), internal reproductive organs and the alimentary canal (Nicholls & Spargo, 1932), ommatidial structure ( Richter, 1999) and cuticular sclerites ( Kutschera et al., 2015).