Typhlotanais incognitus, Larsen & Błażewicz-Paszkowycz & Cunha, 2006

Larsen, Kim, Błażewicz-Paszkowycz, Magdalena & Cunha, Marina R., 2006, Tanaidacean (Crustacea: Peracarida) fauna from chemically reduced habitats-the lucky strike hydrothermal vent system, mid-atlantic ridge, Zootaxa 1187, pp. 1-36 : 21-26

Typhlotanais incognitus n. sp. ( Figs. 7 , 8 )

Material examined

Holotype: non­ovigerous female ( ZMUC CRU­4906 ), inside the vent field, 37°17.289’ N, 32º16.522’ W, 1718 m, RV Prof. Logachev, TV­assisted grab, TTR­12, station AT­428­GR, August 2002, body length 1.05 mm . Paratypes, 1 non­ovigerous female in poor condition ( ZMUC CRU­4907 ), same data . 1 non­ovigerous female (dissected), same data .

Diagnosis, female. Carapace oval (1.25 times as long as wide), narrowing anteriorly. All pereonites wider than long. Pereonites 1–3 clearly separated. Pereonites 2–5 with rounded margins. Chelipeds basis do not reach the edge of pereonite 1, wide groove at the cheliped insertion. Mandible molar with ring of terminal blunt denticles. Maxillule with eight spines distally; one of them bifurcated. Chela shorter than carpus. Pereopods 4–6 not stouter than pereopods 1–3; dactylus and unguis fused but not into a claw, not bifurcate. Uropods longer than pleotelson; endopod and exopod with two articles and almost subequal length.

Etymology

Named after ‘inconspicoulous’ characters of this species.

Description

Female. Body length 1.5 mm.

Body ( Fig. 7A, B ). Cylindrical, about 6 times as long as broad.

Cephalothorax. Longer than combined length of pereonites1 and 2. Narrowing anterior, rounded posteriorly. Eyelobes absent.

Pereonites. All wider than long. Pereonite 1 shortest. Pereonite 5 longest.

Pleon. Marginally wider than pereon, short (including pleotelson about 20% of total body length). All pleonites subequal, carrying pleopods. Pleotelson shorter than combined length of two pleonites, apex smoothly rounded.

Antennule ( Fig. 7C ). As long as cephalothorax. Article 1 longer than rest of antennule and four times as wide as article 3, with several setules along both margins and four simple distal setae. Article 2 less than 0.25 times as long as article 1, with one simple distal seta. Article 3 more than twice as long as article 2, with one pinnate and six simple distal setae.

Antenna ( Fig. 7D ). Three­quarters length of antennule and one­quarter as wide as proximal part of antennule. Articles 1 and 2 broken but not broader than following articles. Article 3 marginally longer than article 6, with one minute dorsal seta. Article 4 longer than other articles, with three simple and two pinnate dorsodistal setae. Article 5 more than twice as long as article 3, with one distal seta. Article 6 minute, with five distal setae.

Mouthparts. Labrum ( Fig. 7E ) flat and with several setules. Mandibular molar broad and longer than incisor, with terminal ring of denticles. Left mandible ( Fig. 7F ) lacinia mobilis longer than incisor, in shape of a single spine; incisor broad, with two denticles. Right mandible not recovered. Labium ( Fig. 7G ) with inner and outer processes, both with a few setules. Maxillule ( Fig. 7H ) endite with eight distal spiniform setae, one of which is bifurcate; palp not recovered. Maxilla not recovered. Maxilliped ( Fig. 8A ) basis with one long seta at palp insertion. Endites with inner medial and outer distal processes and two setae, almost as wide as basis. Palp article 1 naked; article 2 with one outer and three inner setae, one of which is serrated; article 3 with four inner setae; article 4 with one outer and five inner setae. Epignath not recovered.

Cheliped ( Fig. 8B ). Basis divided unequally by small sclerite attached to the proximal part of basis, shorter than carpus. Merus with one ventral seta. Carpus longer and wider than propodus including fixed finger, with three ventral and two small dorsal setae. Propodus with two setae at dactylus insertion. Fixed finger with two ventral setae and three on inner margin, with two visible denticles on inner margin. Dactylus longer than fixed finger.

Pereopod 1 ( Fig. 8C ). Coxa with one simple seta. Basis longer than three succeeding articles combined, with three setae. Ischium with one seta. Merus as long as carpus, widening distally, with two distal setae. Carpus three­quarters length of propodus, with four distal setae. Propodus longer than half of basis, with three robust distal setae. Dactylus and unguis shorter than propodus, not fused to a claw. Dactylus shorter than unguis.

Pereopod 2 ( Fig. 8D ). As pereopod 1 except: basis naked. Carpus half as long as propodus. Propodus with two dorsodistal setae and one ventral spiniform seta.

Pereopod 3 ( Fig. 8E ). As pereopod 2 except: basis with one dorsal seta. Carpus with three simple distal setae. Dactylus longer than unguis. Both dactylus and unguis stouter than that on pereopods 1 and 2.

Pereopod 4 ( Fig. 8F ). Coxa not present. Basis twice as wide as on pereopods 1–3, with one simple and one setulose ventromedial seta. Ischium with one seta. Merus with one spiniform distal seta and cuticular scales. Carpus with one simple dorsodistal seta, one ventrodistal spiniform seta, and two tubercles covered with minute spines (clinging apparatus). Propodus with two ventrodistal spiniform setae, one dorsodistal robust seta and dorsal spine. Dactylus and unguis shorter than propodus and incompletely fused into an elongate claw. Unguis with simple apex, shorter than dactylus.

Pereopod 5 ( Fig. 8G ). As pereopod 4 except: merus with two ventrodistal setae. Carpus with one tubercle covered with minute spines and one simple and one spiniform distal seta.

Pereopod 6 ( Fig. 8H ). As pereopod 5 except: basis naked. Propodus with three dorsodistal setae.

Pleopod ( Fig. 8I ). Basal article naked. Exopod with one outer and seven inner plumose setae (setulation not illustrated). Endopod with twelve inner plumose setae, large gap between proximal seta and other setae.

Uropods ( Fig. 7I ). Basal article shorter than first endopod article, naked. Endopod with two articles, longer than pleotelson; article 1 with one simple and two pinnate distal setae; article 2 with five distal setae. Exopod with two articles, article 1 with one medial seta; article 2 with one short simple and one long thick specialized distal seta.

Remarks

Typhlotanais incognitus n. sp. somewhat resembles Typhlotanais vaiabilis Hansen, 1913 from the deep North Atlantic. These species display a number of shared characters such as: the same habitus (oval head, slim body and clearly separated pereonites 1–3); similar mandible molar; a slim cheliped basis not reaching pereonite 1; relatively slim pereopods 4–6 which have simple­tipped unguis; uropodal endites biarticulated. Typhlotanais incognitus however differs from T. variabilis possessing a cheliped propodus shorter than carpus and a distal seta on pereopod 4 and 5 propodus which is only reaching halfway of dactylus. In contrast the chela of T. variabilis is clearly longer than the carpus while the distal setae on pereopod 4 and 5 propodus reaches beyond the unguis.

To some extent, a similar habitus can be observed in Typhlotanais mucronatus Hansen, 1913 . However, this species has an elongated antennule equipped with especially long terminal setae and a bifurcated unguis of pereopod 4–6.

Family Indet

Genus Armaturatanais Larsen, 2005

Diagnosis

Female (modified from Larsen 2005). Body slightly dorso­ventrally flattened. Cuticle heavily calcified. Pleotelson acorn­shaped in lateral view. Antennule with four articles. Antenna with six articles and fusion line on article 4. Mandibles small; molar fairly broad with flat distal crushing area surrounded by small denticles Maxilliped endites without denticles, processes or flat setae. Pereopods and pleopods attached on the inner side of the lateral shield. Pereopods with coxa; Pereopods 1–3 merus and carpus without spiniform setae; dactylus and unguis not fused to a claw; unguis longer than dactylus. Pereopods 4–6 dactylus longer than unguis. Pleopods present in female, with simple or plumose setae. Uropods biramous, endopod with two articles; exopod with one article.

Male. Pleon marginally longer than in female. Antennular article 3 shorter than in female and without fusion line. Functional mouthparts retained. Alle pleonites bearing pleopods with plumose setae, pleopods larger than in female.

Gender Masculine.

Type species

Armaturatanais minipodus Larsen, 2005 (by monotype).

Remarks. This genus was only recently described from the Gulf of Mexico ( Larsen 2005) and yet another species, A. trispinipodus Larsen, 2006 was recently described from the hydrothermal vent system at the Juan de Fuca Ridge. The systematic position of this genus is not yet resolved.

Key to the species of Armaturatanais

1. Pereopods 4–6 dactylus and unguis trifurcate ........................................ A.trispinipodus Pereopods 4–6 dactylus naked and unguis in the shape of a single spine..................... 2 2. Antennular article 2 short (shorter than half of article 1). Uropodal exopod not reaching endopod article 2 ......................................................................... A. atlanticus n. sp. Antennular article 2 long (longer than half of article 1). Uropodal exopod reaching endopod article 2 ........................................................................................ A. minipodus

Figures

FIGURE 7. Typhlotanais incognitus n.sp. A, holotype, lateral view; B, holotype, dorsal view; C, antennule; D, antenna; E, labrum; F, left mandible; G, labium; H, maxillule; I, uropod. Scale bars 0.1 mm.

FIGURE 8. Typhlotanais incognitus n.sp. A, maxilliped; B, cheliped; C, pereopod 1; D, pereopod 2; E, pereopod 3; F, pereopod 4; G, pereopod 5; H, pereopod 6; I, pleopod. Scale bars 0.1 mm.