Bathytanais fragilis, Larsen & Heard, 2001

Larsen, Kim & Heard, Richard W., 2001, A new tanaidacean subfamily, Bathytanaidinae (Crustacea: Paratanaididae), from the Australian continental shelf and slope, Zootaxa 19, pp. 1-22 : 12-16

Bathytanais fragilis n. sp. ( Figs. 5­7 )

Material examined: 1 non­ovigerous female holotype, bl. 3.75 mm, NMV­J37854 , Slope Sta. 21 , 36°57.40’S, 150°18.80’E. Depth 220 m . 1 non­ovigerous female paratype, NMV­J37855 , Sta. MSL­EG 70 , 37°53.39’S, 148°14.40’E. Depth 43 m . 2 non­ovigerous female paratypes, mouthparts and limbs dissected from, NMV­J28449 & J37875 , Slope sta. 40 , 38°17.70’S, 149°11.30’E. Depth 400m. Collected by Drs. Poore, Coleman and Lew Ton .

Other material: 3 non­ovigerous females, Slope Sta. 21, 36°57.40‘S, 150°18.80’E. Depth 220 m . 3 ovigerous females, 12 non­ovigerous females, 10 manca III. MSL©EG Sta. 70 , 37°53.39’S, 148°14.40’E. Depth 43 m . 14 non­ovigerous females, Grip Point survey CPBS Sta. 22N , 38°20.60’S, 145°13.46’E. Depth 13 m .

Diagnosis: Antenna article 2 ventral extension thin and transparent. Antenna article 3 with anteriorly directed dorsal spiniform seta. Uropod endopod uniarticulated.

Description (adult female).

Body ( Fig. 5 A, B): Slender, subcylindrical, approximately 8 times as long as broad.

Carapace ( Fig. 5 D): As long as pereonite 1 and 2 combined, width 0.75 times length, anterolateral corners curving anteriorly, consisting of 8 plates. Eye­lobes square and blunt.

Pereonites: Smooth. Pereonite 1 wider than long. Pereonites 2­4 length subequal width. Pereonite 5 similar in length and width, shorter than anterior pereonites. Pereonite 6 length and width subequal, shorter than anterior pereonites, ventral surface with anterolateral punctuated lobe.

Pleonites: 1­5 subequal, approximately 4.0 times wider than long.

Pleotelson ( Fig. 5 C): Marginally exceeds length of last pleonite.

Antennule ( Fig. 6 A): 1.2 times as long as cephalothorax. Article 1 longer than rest of antennule, 2 simple setae medially. Article 2 less than 0.3 times length of article 1, distal margin with 1 long simple seta. Article 3 half as long as article 4, with 1 long setulose seta. Article 4 as long as article 2, with 1 simple short proximal seta, 1 distal simple seta and 3 distal setulose setae twice as long as antennule itself.

Antenna ( Fig. 6 B): Only marginally longer than that of antennule article 1. Article 1 smooth, wider than long. Article 2 with thin transparent ventral extension, 2 simple medial setae and 1 simple distal seta. Article 3 as long as article 4, with dorsal spiniform seta. Article 4 as long as article 5, with 1 long serrated distal seta on ventral margin, 3 short sensory setae and 1 simple distal seta. Article 5 twice as long as article 1, with 4 long setulose distal setae longer than antenna as a whole. Article 6 minute without any visible features.

Mouthparts: Labrum ( Fig. 6 C) smooth, with pointed apex. Left mandible ( Fig. 6 E) with strongly defined lacina mobilis with several denticulations, incisor unidentate. Right mandible ( Fig. 6 F) incisor bidentate. Maxillule ( Fig. 6 G) with 7 thick terminal setae and row of setae, palp not recovered. Maxilla ( Fig. 6 H) ovoid and smooth. Labium ( Fig. 6 D) with indent on anterolateral corners. Maxilliped ( Fig. 6 I) endites with 2 short flat setae; palp article 1, square and smooth; article 2, inner margin longer than outer, 3 setulated setae on inner distal margin; article 3 with 4 setulated setae; article 4, oval, inner margin with 4 setulated distal setae and several fine setules, outer margin with 1 setulated seta. Epignath not recovered.

Cheliped ( Fig. 6 J): Basis with depression midlength, smooth, twice as long as wide. Merus ovoid, 1 simple medial seta on ventral margin. Carpus oval, longer than basis, 2 simple setae on ventral margin and 1seta on dorsal margin. Propodus ( Fig. 6 K) expanded distally beyond attachment of dactylus, row of serrated setae flanking dactylus insertion. Fixed finger with strong apex, 2 simple setae on ventral margin and 3 setae on cutting edge. Dactylus narrow.

Oostegites: originating from pereonites 1­4.

Pereopod 1 ( Fig. 7 A): Coxa but distinct. Basis width increasing distally, with 3 simple dorsal setae. Ischium with 1 simple seta. Merus with 2 simple ventral distal setae and 1 simple dorsal seta. Carpus half as long as merus, with 1 short simple ventral seta and 1 longer dorsal seta. Propodus as long as merus, tapering distally, with 1 short simple ventral distal seta and 2 long dorsal setae. Dactylus and terminal seta not fused, combined longer than propodus. Terminal seta 2.0 times longer than dactylus.

Pereopod 2 ( Fig. 7 B): Similar to pereopod 1 except: Ischium, and carpus smooth. Merus about 0.3 times length of that of pereopod 1. Propodus less elongated, with 1 simple seta on each margin.

Pereopod 3 ( Fig. 7 C): Similar to pereopod 2 except: Basis with 2 setae. Ischium and merus each with 1 seta. Propodus with 2 short and 3 long simple distal setae.

Pereopod 4 ( Fig. 7 D): Lateral coxa absent, but a ventral plate is interpreted as coxa. Basis stout, length approximately 1.5 times width, with 1 simple dorsal seta and 2 sensory ventral setae. Ischium width 3.0 times length, with 2 simple ventral setae. Merus ovoid, shorter than carpus, with 2 short stout denticulated ventral setae. Carpus as long as ischium and merus together, with denticulate cuticular scales and 2 short stout denticulated distal setae. Propodus as long as carpus, with 1 short thick dorsal distal seta, 1 sensory and 1 flat serrated dorsal setae, Dactylus and terminal seta fused into a claw with denticles.

Pereopod 5 ( Fig. 7 E): Similar to pereopod 4 except: Basis longer and with several simple setae and only 1 sensory seta. Merus quadrate and with denticulated scales. Propodus without sensory seta.

Pereopod 6 ( Fig. 7 F): Similar to pereopod 4 except: Basis longer and smooth. Merus with denticulated scale and 1 short stout seta. Carpus with 1 short stout denticulated seta and scales as well as paired short thick bifurcate distal setae. Propodus with 1 short stout denticulated seta and 3 thick hook­shaped distal setae.

Pleopods ( Fig. 7 G): All 5 pairs similar. Protopod trapezoidal. Exopod armed with 13 plumose setae, 2 distal setae shorter and stouter than rest. Endopod with 12 plumose setae.

Uropods ( Fig. 7 H): Protopod smooth, quadrate. Endopod with 1 article, width decreasing 30% midlength, with 1 simple seta and 2 sensory setae midlength and 5 long simple distal setae. Exopod with 1 article, with 1 simple seta at midlength and 2 long simple distal setae.

Etymology: Named after the fragile, ventral extension on antenna article 2, which is transparent and much less rigid as compared to other species in the genus (Latin: fragilis = fragile).

Remarks: Bathytanais fragilis is easily separated from other species of Bathytanais by the thin, transparent ventral extension of antenna article 2. The weakness of this process indicate that this species is the link between Bathytanais and Pseudobathytanais .

Figures

FIGURE 5. Bathytanais fragilis, holotype, female scale bar 2.5 mm. A) Dorsal view. B) Lateral view. C) Pleotelson. D) Cephalothorax.

FIGURE 6. Bathytanais fragilis, female paratype scale bars A­B 1 mm, E­I 0.02 mm, J 0.5 mm. A) Antennule. B) Antenna. C) Labrum. D, Labium. E) Left mandible. F) Right mandible. G) Maxillule. H) Maxilla. I) Maxilliped. J) Cheliped. K) Cheliped propodus.

FIGURE 7. Bathytanais fragilis, female paratype, scale bar A­F 0.25 mm, G­H 0.1 mm. A) Pereopod 1. B) Pereopod 2. C) Pereopod 3. D) Pereopod 4. E) Pereopod 5. F) Pereopod 6. G) Pleopod. H) Uropod.