Microprosthema tortugasensis, Goy, Joseph W. & Martin, Joel W., 2013

Goy, Joseph W. & Martin, Joel W., 2013, Redescription of Microprosthema semilaeve (von Martens, 1872) (Decapoda: Stenopodidea: Spongicolidae) and description of a new species of Microprosthema from Dry Tortugas, Florida, Zootaxa 3630 (3), pp. 467-488 : 481-486

Microprosthema tortugasensis sp. nov.

( Figs. 10–12 )

Material examined. female holotype, USNM 1153608, cl 5.6, male allotype, USNM 1153609, cl 3.4, south of Loggerhead Key, Dry Tortugas, depth 91.4 m, 7 August 1939.

Diagnosis. Moderately small spongicolid shrimp, with subcylindrical, depressed body, with few spinous processes; carapace covered with few small spines and long setae, cervical groove distinct; propodus of third pereiopod with distinct dorsal crista, numerous spinules along dorsal margin; dorsal surface of abdominal somites glabrous third abdominal somite with distodorsal longitudinal median carina; all pereiopods with numerous long setae; dactyli of fourth and fifth pereiopods triunguiculate; scaphocerite lobate with 5 strong teeth on outer margin; uropodal endopodite with median longitudinal ridge ending in distal tooth.

Description. (holotype, female USNM 1153608). Rostrum ( Figs. 10 A, B) short, straight, reaching end of last segment of antennular peduncle. Dorsally with long setae; dorsal margin with 4 spines, ventrally small spine, laterally without spines.

Carapace ( Fig. 10 A, B) with few anteriorly directed spinules, dorsally with numerous long setae. Cervical groove distinct with 11 spinules around its border.

Large antennal spine, superior and inferior orbital spines, branchiostegal, and hepatic spines present; 4 small pterygostomial spines present. Ventrolateral carapacial angle rounded with row of 5 spinules.

Abdomen ( Fig. 10 B) broad, depressed, dorsally glabrous. First pleomere with anterior transverse ridge dorsally provided with row of setae, pleuron rounded. Second pleomere with median transverse ridge, pleuron broadly rounded. Third pleomere with distodorsal longitudinal carina, pleuron broadly rounded. Last 3 abdominal pleomeres ending with rounded overlapping pleura.

Telson ( Fig. 10 B) slightly longer than uropods, triangular. Dorsal surface with 2 longitudinal ridges, ending considerable distance before posterior margin, bearing 3 strong teeth; 2 small anterior spines present at telson base, large spine present anteriorly between longitudinal ridges. Lateral margin at each side provided with large median spine; posterior margin with 3 small spines; posterior half of telson fringed with plumose setae.

Eyes ( Fig. 10 A, B) well developed, cornea smaller than peduncle; facets, pigments distinct in cornea. Ophthalmic peduncle broad, with 3 dorsomesial spinules.

Basal segment of antennular peduncle ( Fig. 10 C) with short, straight stylocerite; ventrally distal spine, small rounded laminate process proximally.

Both flagella short, provided with numerous plumose setae; upper flagellum with 16 aesthetascs, 2 on articles 5–12.

Antennal peduncle ( Fig. 10 D) 2-segmented, basal segment strong, outer margin with 4 setae, inner margin with distinct rounded laminate process; distal segment with outer margin bearing 3 spines. Scaphocerite reaching far past tip of rostrum, lobate, narrow at base, outer margin slightly concave with 5 strong teeth; inner margin strongly convex, fringed with long plumose setae. Dorsal surface with straight longitudinal carina reaching about half its length. Antennal flagellum well developed, extending slightly beyond telson, covered with numerous long short plumose setae.

Epistome ( Fig. 10 E) straight anteriorly with 4 submedian spines separating median process with small knob. Labrum normally developed. Paragnath bilobed with spinose lobes separated by median fissure. Thoracic sternites broadening from front to back with 2 submedian blunt spinules on segments 4–6, none on segments 7–8. Mandible ( Figs. 10 F, G) robust with short, fused molar and incisor processes. Molar surface with 2 small teeth; incisor thickened with 3 large, 6 small submedian teeth. Palp well developed, 3-segmented; proximal segment naked, middle and distal segments covered with plumose setae.

Maxillule ( Fig. 10 H) with slender undivided endopodite bearing plumose setae. Proximal endite moderately broad, distally truncate with 3 plumose setae laterally, 8 compound plumose setae, 13 simple setae distally. Distal endite slightly broader, rounded with 4 compound plumose setae, numerous simple setae distally.

Maxilla ( Fig. 10 I) with setose coxal and basal endites. Endopodite long, slender with 26 long plumose setae laterally and distally. Scaphognathite long, narrow, fringed with numerous plumose setae.

First maxilliped ( Fig.11 A) with 2-segmented endopodite; proximal segment long with 13 long plumose setae laterally, 7 shorter plumose setae on inner margin. Distal segment ovate with 9 long plumose setae. Basipodite large, rounded anteriorly, with straight outer border bearing dense fringe of plumose setae; coxopodite, bilobed, with each lobe bearing numerous plumose setae. Exopodite well developed, bearing 24 long plumose setae distally. Large epipod with slender pxoximal and distal lobes.

Second maxilliped ( Fig.11 B) with 4-segmented endopodite. Dactylus suboval with dense fringe of setae along distodorsal margin. Propodus same length as dactylus, densely setose on dorsal margin. Carpus short with 9 simple setae distodorsally, few simple setae mesially. Merus twice dactylar length, with straight inner border bearing 6 simple setae; outer border convex with numerous long simple setae. Ischium and basis fused into setose lobe; coxa lobate with dense fringe of setae. Exopodite long, slender, undivided with distal third bearing 21 plumose setae, 12 long simple proximal setae.

Third maxilliped ( Fig. 11 C) endopodite strongly developed, 5-segmented. Dactylus slender with dense fringe of setae. Propodus slightly longer than dactylus, with numerous simple setae, setiferous organ distally on inner margin. Carpus equal to dactylar length, with numerous simple setae. Merus 1.5 carpal length, strong, with 3 spines, few simple setae on outer margin; inner margin with numerous simple setae. Ischium robust, almost twice meral length, with 2 small spines at distodorsal margin, numerous short simple setae along outer margin length; inner margin fringed with numerous long simple setae. Coxa short with dense fringe of setae. Exopodite long, slender, extending to middle of merus, with distal half bearing long plumose setae.

First pereiopod ( Figs. 11 D, E) small, slender, reaching past scaphocerite, all segments without spines. Fingers slightly compressed, with hooked tips, cutting edges provided with 8 or 9 peg-like teeth. Fingers and distodorsal extremity of palm bearing small tufts of long setae. Distoventral part of carpus and proximoventral part of propodus with well developed setiferous organ, 3 long setae extending over carpal part of organ. Carpus longest segment, about twice propodal length, merus slightly shorter than carpus, ischium about half meral length. All segments bear numerous long simple setae.

Second pereiopod ( Fig. 11 F) similarly built as first, including setation and lack of spines, but longer. No setiferous organ present. Carpus longest segment, about 1.5 times longer than propodus, merus slightly longer than propodus, ischium about 0.7 propodal length.

Third pereiopod ( Figs. 11 G, H) robust, largest, strongest, reaching with entire carpus beyond scaphocerite, covered with numerous long simple setae. Palm of chela longest segment with dorsal crista bearing 4 or 5 small spines. Fingers elongate, with sharp, crossing tips, distally bearing small tufts of long setae. Dactylar cutting edge with distal chitinous ridge followed by large triangular tooth. Cutting edge of propodus with distal chitinous ridge with indentation to receive dactylar triangular tooth followed by elevated ridge bearing 5–8 tiny teeth. Carpus less than half propodal length, narrowing proximally, distodorsal margin with rounded tubercle; ventral margin with 1–3 spines. Merus slightly longer than carpus, dorsal margin with distal spine; ventral margin with 4 spines. Ischium half meral length with large spine at distodorsal margin. Basis and coxa short with no spines but few long simple setae.

Fourth and fifth pereiopods ( Figs. 12 A, B) long, slender, propodus and carpus undivided. Dactyli triunguiculate with dorsal and ventral equal, accessory tooth on ventral margin half length of ventral unguis. Propodi with ventral row of 14 or 15 movable spines. Carpus longest segment, with 2 ventral movable spines. Merus almost as long as carpus; ischium, basis, and coxa short.

First pleopod ( Fig. 12 C) uniramous, second ( Fig. 12 D) to fifth biramous, all lacking appendices. First pleopod smallest, with exopodite about twice length of basipodite, dorsal surface of exopodite with longitudinal ridge, margin with dense fringe of plumose setae. Rami of second pleopod more than twice length of basipodite; basipodite with dorsal longitudinal ridge, margins of basipodite, rami fringed with plumose setae. Third to fifth pleopods generally similar, third largest of all pleopods, decreasing in size posteriorly.

Uropods ( Fig. 10 B) well developed, almost reaching end of telson. Exopodite with straight outer margin bearing 8 or 9 teeth; inner margin semicircular fringed with plumose setae; dorsal surface with 2 distinct longitudinal ridges without spinules. Endopodite subovate, outer margin with 6 or 7 teeth; inner margin fringed with plumose setae; dorsal surface with distinct median longitudinal ridge ending with strong spine.

Branchial formula same as M. semilaeve given above.

Allotype. (male USNM 1153609, Fig. 12 F). Smaller than holotype, carapace spination not as dense as holotype, only 2 pterygostomian spines; abdominal pleura more acute, ventral median spine on each male abdominal pleomere; telson oblong; thoracic sternites 4–6 bear 3 submedian acute spines, 2 on sternites 7–8; rostrum with 3 dorsal spines; ophthalmic peduncle with 4 dorsal spinules; 3 spines on outer margin of 3rd maxilliped; 12–16 ventral movable spines on 4th and 5th pereiopods; uropodal exopodite with 9 or 10 outer margin teeth, endopodite with 8 outer margin teeth.

Measurements. (mm) Postorbital carapace length: female 4.4, male 3.2; carapace and rostrum length: female 5.6, male 3.4; total body length: female 10.1, male 7.0.

Development. The female holotype was carrying 71 eggs ( Fig.12 E) that were in a late stage of embryonic development measuring 0.53 × 0.73 mm in size.

Type locality. Presently known only from south of Loggerhead Key, Dry Tortugas, Florida, U.S.A. at a depth of 91.4 m.

Remarks. Microprosthema tortugasensis closely follows the definition of the genus Microprosthema Stimpson given by Holthuis (1946). It is most closely related to the M. inornatum Manning & Chace 1990 but differs in the presence of transverse ridges in the 1st, 2nd, and 3rd abdominal pleomeres, teeth on uropodal margins, and spination of the 3rd maxillipeds and pereiopods. Among the other species in the genus Microprosthema , M. tortugasensis is similar to M. granatense Criales 1997 but differs by having stouter carapacial spines, less uropodal marginal teeth, and biunguiculate dactyli on the 4th and 5th pereiopods. The triunguiculate 4th and 5th pereiopod dactyli seen in M. tortugasensis is unique for the genus, but is present in some members of the spongicolid genera Spongicola and Paraspongicola . Most species of Microprosthema have been collected in shallow reefal habitats of less than 10 m. The type material of M. tortugasensis was collected at 91.4 m depth and the previous depth record for the genus was M. validum from 70 m depth (Holthuis 1946). However, a specimen of M. inornatum (ULLZ 7423) was recently collected at depths from 100– 63 m from the northwest Gulf of Mexico, extending this species’ range from Ascension Island in the South Atlantic Ocean.

Figures

FIGURE 10. Microprosthema tortugasensis n. sp., female holotype, USNM 1153608: A, carapace, lateral view; B, dorsal view; C, antennule, dorsal view; D, antenna, dorsal view; E, epistome and labrum, ventral view; F, mandible, dorsal view; G, mandible, ventral view; H, maxillule; I, Maxilla. Scale bars = 1.0 mm.

FIGURE 11. Microprosthema tortugasensis n. sp., female holotype, USNM 1153608: A, first maxilliped; B. second maxilliped; C, third maxilliped; D, first pereiopod: E, first pereiopod enlarged; F, second pereiopod; G, left third pereiopod; H, right third pereiopod. Scale bars = 1.0 mm.

FIGURE 12. Microprosthema tortugasensis n. sp., female holotype, USNM 1153608: A, fourth pereiopod; B, fifth pereiopod; C, first pleopod; D, second pleopod; E, embryonated egg; male allotype, USNM 1153609: F, dorsal view; G, left third pereiopod. Scale bars = 1.0 mm.