Dimorphostylis triplicata, Gerken, 2014

Gerken, Sarah, 2014, Eleven New Species and a New Genus of Diastylidae (Crustacea: Cumacea) from Australia and One New Species from Canada, Records of the Australian Museum 66 (1), pp. 1-62 : 43-46

Dimorphostylis triplicata n. sp.

Figs 28–29

Type material. Holotype adult male, NMV J46874 ; paratype adult male, dissected, NMV J46875 ; paratypes 1 subadult male, 1 manca NMV J46876 ; 11°06'00"S 133°00'00"E, 8 m, G. C. B. Poore, 17 Oct. 1982.

Other material examined. None.

Diagnosis. Female and subadult male. Female unknown. Carapace with 3 parallel oblique ridges, connected dorsally by short curved ridges, and terminally by short vertical ridges, serrate ridges on pseudorostral lobe. Adult male. Carapace with 3 parallel oblique lateral ridges, not connected anteriorly, not reaching anterior margin of carapace. Antennule with brush of setae covering at least half of surface of peduncle article 3. Antennae extending to posterior border of telson. Telson much longer than pleonite 6, no post-anal portion present, without stout lateral setae, with 2 tiny terminal setae.

Description

Subadult male. Paratype subadult male, NMV J46876 , 2.9 mm. —Carapace with 3 parallel ridges originating posterior dorsally, sweeping anterior and ventral to anterior ⅓ of carapace, connected by short vertical ridge terminating in tooth at corner of vertical ridge and dorsal most ridge, serrate ridge continuing anterior from tooth on pseudorostral lobe, terminating near eye lobe, dorsal fold of frontal lobe with scattered teeth, scattered long setae on carapace, antennal notch not deep; pseudorostral lobes 0.3 × carapace length; eye lobe 0.06 × carapace length, with dorsal tooth and lenses; carapace 3.9 × length of pereonites together ( Fig. 28C ).

Adult male. Holotype adult male, NMV J46874 , 3.4 mm; paratype adult male, NMV J46875 , 3.4 mm. —Carapace longer and less deep than subadult male, with 3 parallel ridges originating posterior dorsally, sweeping anterior and ventral, without vertical ridge connecting parallel ridges; pseudorostral lobes 0.4–0.5 × carapace length; eye lobe 0.1 × carapace length, with lenses; carapace 2.8 × length of pereonites together ( Figs 28A–B ). — Paratype adult male, NMV J46875 , 3.4 mm. —Antennule peduncle article 1 1.0 × length of articles 2 and 3 together, with simple seta, margin lined with fine hair-like setae; article 2 0.4 × article 1 length, with 4 pappose setae, margins lined with simple setae; article 3 1.4 × article 2 length, with thick brush of simple setae on lateral face, with pedunculate seta; main flagellum of 5 articles, with 1 aesthetasc and 2 simple setae; accessory flagellum of 3 articles, 0.6 × main flagellum length, with 2 simple setae terminally ( Figs 28D–E ). —Antenna extending to end of uropod peduncles; article 5 with ranks of short setae incompletely circling article, and pappose seta; flagellum with long articles, each with several groups of short setae ( Fig. 28F ). — Mandible navicular, with 11 microserrate setae medially ( Fig. 29A ). —Maxillule with 2 endites; outer endite with double row of stout simple setae; inner endite broken off; palp with 2 microserrate setae ( Fig. 29B ). —Maxilla with 3 endites; broad endite distal margin with pappose seta, row of simple setae and 4 pappose setae, medial margin lined with row of pedunculate setae and 2 pappose setae; medial narrow endite with 4 microserrate setae terminally; distal narrow endite with 5 microserrate setae terminally; inner endite not extending past distal corner of broad endite, outer narrow endite extending to distal corner of broad endite ( Fig. 29C ). —Maxilliped 1 basis produced as lobe with 2 simple, 7 pappose, 2 hook and 1 stout beak-like setae; ischium absent; merus distal margin lined with fine hair-like setae; carpus 1.5 × merus length, with 4 beak setae and simple setae medially, lateral margin lined with fine hair-like setae, with plumose seta; propodus 0.8 × carpus length, with 4 plumose, 1 pappose and 2 serrate setae; dactylus 0.4 × propodus length, with 4 simple setae terminally ( Fig. 29D ). —Maxilliped 2 basis 1.0 × length of all other articles together, with 2 simple and 3 plumose setae distally; ischium 0.03 × basis length, unarmed; merus 6.0 × ischium length, with 1 plumose and 1 pappose setae; carpus 2.2 × merus length, with 5 plumose setae medially, plumose seta laterally; propodus 1.0 × carpus length, with 3 serrate and 4 plumose setae medially, plumose seta laterally; dactylus 0.3 × propodus length, with 2 simple setae terminally ( Fig. 29E ). —Maxilliped 3 basis 1.9 × length of all other articles together, with 7 plumose and 1 pappose setae medially, distal corner broad, with 5 plumose setae; ischium 0.05 × basis length, with pappose seta; merus 2.0 × ischium length, with 3 pappose setae medially; carpus 1.3 × merus length, with 2 simple setae medially; propodus 1.1 × carpus length, with 4 simple setae medially, plumose seta laterally; dactylus 0.6 × propodus length, with 5 simple setae terminally; exopod 0.7 × basis length, basal article unarmed, flagellum with plumo-annulate setae ( Fig. 29F ). —Pereopod 1 basis 0.6 × length of all other articles together, with 4 plumose setae distally; ischium 0.1 × basis length, unarmed; merus 1.7 × ischium length, with simple seta; carpus 3.3 × merus length, with simple seta; propodus 1.4 × carpus length, with 21 simple setae; dactylus 0.3 × propodus length, with 2 simple setae and 6 simple setae terminally; exopod 0.7 × basis length, basal article with 2 simple setae, flagellum with plumo-annulate setae ( Fig. 29G ). —Pereopod 2 basis 1.1 × length of all other articles together, expanded distally to midpoint of carpus, with 14 plumose setae; ischium 0.1 × basis length, unarmed; merus 2.8 × ischium length, with 3 simple setae; carpus 1.0 × merus length, with 5 simple setae; propodus 0.5 × carpus length, with simple seta; dactylus 1.8 × propodus length, with 5 simple setae terminally; exopod 1.0 × basis length, basal article unarmed, flagellum with plumo-annulate setae ( Fig. 29H ). —Pereopod 3 basis 1.3 × length of all other articles together, expanded distally past ischium, with 1 simple and 9 plumose setae; ischium 0.07 × basis length, unarmed; merus 4.0 × ischium length, with simple seta; carpus 0.8 × merus length, with 3 simple and 1 annulate setae; propodus 0.6 × carpus length, with 1 pedunculate and 1 annulate setae; dactylus 0.6 × propodus length, with 3 simple setae terminally; exopod 1.0 × basis length, basal article unarmed, flagellum with plumo-annulate setae ( Fig. 29I ). —Pereopod 4 basis 1.0 × length of all other articles together, expanded distally past ischium, with 6 plumose setae; ischium 0.1 × basis length, with 2 simple setae; merus 4.0 × ischium length, with 6 simple setae; carpus 0.8 × merus length, with 4 simple and 1 annulate setae; propodus 0.4 × carpus length, with annulate seta; dactylus 1.0 × propodus length, with 2 simple setae terminally; exopod 1.1 × basis length, basal article unarmed, flagellum with plumo-annulate setae ( Fig. 29J ). —Pereopod 5 basis 0.7 × length of all other articles together, with 4 simple setae; ischium 0.2 × basis length, with 2 simple setae; merus 3.0 × ischium length, with 3 simple setae; carpus 0.9 × merus length, with 6 simple setae; propodus 0.6 × carpus length, with 1 pedunculate and 1 annulate setae; dactylus 0.8 × propodus length, with 3 simple setae terminally ( Fig. 29K ). —Pleopod 1 peduncle with 4 simple and 4 plumose setae; endopod uniarticulate, with 3 plumose setae; exopod biarticulate with 4 plumose setae ( Fig. 29L ). —Pleopod 2 peduncle with 4 simple setae; endopod uniarticulate, with 3 plumose setae; exopod biarticulate with 3 plumose setae ( Fig. 29M ). —Telson 1.7 × length of pleonite 6, without lateral stout setae, 2 tiny terminal setae ( Fig. 29N ). — Uropod peduncles 2.9 × pleonite 6 length, 1.7 × telson length, with 1 simple and 23–24 simple setae with single subterminal setule medially, medial margin lined with fine hair-like setae. Uropod endopod of 3 articles, 0.4 × peduncle length; article 1 1.2 × length of articles 2 and 3 together, with 6 simple setae with single subterminal setule medially, medial margin lined with fine hair-like setae, pedunculate seta laterally; article 2 0.5 × article 1 length, with 2 simple setae with single subterminal setule medially, medial margin lined with fine hair-like setae, simple seta laterally; article 3 0.7 × article 2 length, with simple seta with single subterminal setule medially, medial margin lined with fine hair-like setae, simple seta laterally, terminal seta simple. Uropod exopod 0.8 × length of endopod; article 1 0.3 × article 2 length, unarmed; article 2 with 3 simple setae, terminal seta broken ( Fig. 29N ).

Etymology. The species is named triplicata for the three lateral ridges or plica present on the carapace.

Remarks. The female of Dimorphostylis triplicata is not currently known, thus it is possible that the species should be placed in Paradiastylis . Differentiation between Paradiastylis and Dimorphostylis is impossible without the females, as the only consistent differences are the lack of an exopod on maxilliped 3 and the presence of rudimentary exopods on pereopods 3–4 in the Paradiastylis female, while the females of Dimorphostylis have an exopod on maxilliped 3 and no exopods on pereopods 3–4.

The subadult male Dimorphostylis triplicata is similar in carapace ornamentation and the long telson to the female of the new species Paradiastylis occidensaustralis . However, the species can be differentiated by the proportions of pereopod 1. In P. occidensaustralis the propodus of pereopod 1 is distinctly longer than the basis, while in D. triplicata the propodus of pereopod 1 is distinctly shorter than the basis. As the adult male of P. occidensaustralis is not currently known, it may be confused with the male of D. triplicata . The carapace architecture of the female of D. triplicata is expected to be similar to the subadult male.

The adult male of the new species is similar to the adult male illustrated by Hale (1945) for Dimorphostylis australis ; however, the proportions of the articles of pereopod 1 vary, with a relatively longer carpus and dactylus in D. australis , and a relatively shorter carpus and dactylus in D. triplicata . The carapace of the subadult male, collected at the same time and place as the adult male, is quite different from that illustrated by Foxon (1932) for the female of D. australis . Despite the poor quality of the Foxon illustrations, it is clear that in his female specimen the three ridges on the carapace continued forward to the anterior margin of the carapace, there is no indication of a vertical ridge, and there are four tubercles shown dorsally. In contrast, the subadult male of the new species has three lateral ridges that meet a vertical ridge well posterior of the anterior margin. As subadult male and female cumaceans typically have very similar carapace morphology, it is expected that the female of this species will resemble the subadult male, and thus be quite different from the female of D. australis .

Figures

Figure 28. Dimorphostylis triplicata n. sp. male. Holotype adult male, 3.4 mm, NMV J46874: (A), side view. Paratype adult male, 3.4 mm, NMV J46875: (B), side view; (D), antennule without setal brush; (E), antennule article 3 with setal brush; (F), antenna. Paratype subadult male, 2.9 mm, NMV J46876: (C), side view. Scale bars A–C = 1.0 mm, D–F = 0.5 mm.

Figure 29. Dimorphostylis triplicata n. sp. male. Paratype adult male, 3.4 mm, NMV J46875: (A), mandible; (B), maxillule; (C), maxilla; (D), maxilliped 1; (E), maxilliped 2; (F), maxilliped 3; (G), pereopod 1; (H), pereopod 2; (I), pereopod 3; (J), pereopod 4; (K), pereopod 5; (L), pleopods 1; (M), pleopods 2; (N), pleonite 6, telson and uropods. Scale bars = 0.5 mm.