Hexabathynella monoaesthetasca Cho & Schminke 2006, SP. NOV.
Creators: name: Cho, Joo-Lae
name: Schminke, Horst Kurt
Publisher: name: Zenodo
Year: 2006
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Bathynellacea
Parabathynellidae
Hexabathynella
Hexabathynella monoaesthetasca

description: HEXABATHYNELLA MONOAESTHETASCA SP. NOV.   Diagnosis: Parabathynellid of small size (1.0– 1.5 mm). Antennal organ protruded and bearing a hairpin-shaped dorsal seta and a simple ventral seta. Fifth antennular segment bearing two aesthetascs. Third antennular segment sexual dimorphic: male bears one seta on inner distal margin in addition to two lateral setae and with one ventral seta. Sixth antennular segment bearing one aesthetasc. Distal spine of mandibular spine row needle-shaped. Basipodal seta absent in thoracopods II–VI. Pleotelson with two setae. Uropodal exopod drawn out inner distally into a chitinous projection, with one seta at base of projection, one dorsal subterminal seta, and one long seta on outer distal margin.   
Holotype ♀, South Africa, Olifants River, 400 m above the bridge Citrusdal, Kaapprovinsie. Pit 85 cm deep, 16 m from the shore, temperature 14°C. 25 September 1973, leg. Schminke, coll. Iziko Museums of Cape Town (A45277). Allotype ♂ (A45278), same data as for holotype. Paratype four ♀♀, two ♂♂, and 11 juveniles (A45279–A45285). Other localities: Olifants River, on the street between Citrusdal and Clanwilliams, Kaapprovinsie. Pit 85 cm deep, 95 m from the shore, temperature 13.5°C. 25 September 1973; Olifants River, 1.25 km above the bridge Citrusdal, Kaapprovinsie. Two pits of 95 and 105 cm deep, and 28 and 62 m from the shore, temperature 14°C. 26 September 1973.  
 Etymology: The species name refers to the presence of only one aesthetasc in sixth antennular segment.   
 Description of the female (holotype): Body (Fig. 1A) length 1.42 mm, approximately 15 times as long as wide. Body length of other females (paratypes) 1.40, 1.37, 1.37, 1.35 mm.   
Antennule (Fig. 1F) six-segmented. First segment with one seta on inner distal margin, one simple dorsal seta, and one lateral and one ventromedial plumose seta. Second segment with one group of four plumose setae and one seta on inner distal margin and one ventral seta. Third segment with two setae on outer margin and two ventral setae. Peduncle of third segment half fused with fourth segment, with three simple setae. Fourth segment with one stub seta on dorsal margin and three plumose setae. Fifth segment with two setae on inner margin, one aesthetasc and one simple on dorsal margin, and one lateral aesthetasc. Sixth segment with four terminal setae and one subterminal aesthetasc.  
Antenna (Fig. 1G) five-segmented, 60% as long as antennule, setal formula: 0/0+0/0+0/1+1/3(1).  
Labrum (Fig. 2A) flat, with seven (eight in other females) main teeth flanked by one smaller tooth on both lateral sides.  
Mandible (Fig. 2B) with incisor process of four teeth. Tooth of ventral edge triangular. Spine row consisting of five spines. Distal spine narrow, needle-shaped. Palp of one segment, with one apical seta being three times as long as palp.  
Paragnaths (Fig. 2B, arrow) represented by a plate with lateral protrusions, bearing ctenidia.  
Maxillule (Fig. 2C) two-segmented. Proximal segment with four setae on inner distal margin. Distal segment with three terminal claws, with two claws and one seta on inner edge, and with three simple setae on outer distal margin.  
Maxilla (Fig. 2D) three-segmented, setal formula 2-4-13.  
Thoracopods I–IV (Fig. 2E–J) increasing in length posteriorly. Thoracopods IV–VI equal in length. Protopods of thoracopods I–VI each bearing one epipodite. Only thoracopod I bearing one basipodal seta. Exopod of thoracopod I one-segmented, with one terminal seta. Exopod of thoracopods II–VI two-segmented, with one terminal seta on distal segment, and one dorsal and one ventral seta on proximal segment. Endopod of thoracopods I–VI four-segmented, setal formulae: thoracopod I 1+0/0+1/1+0/2(1); thoracopods II–VI 0+0/0+1/0+0/1(0).  
Thoracopod VIII (Fig. 3A) tiny, cone-shaped.  
First pleopod in form of a seta.  
Uropod (Fig. 3C, D) bearing five (right uropod) or six (left uropod) spines on inner distal margin of sympod. Distal spine 2.5 times as long as proximal spine. Endopod approximately 50% as long as sympod, drawn out distally into slightly curved spur, with one dorsal plumose seta and two simple setae at base of spur. Exopod as long as endopod, drawn out inner distally into a chitinous projection, with one seta at the base of the projection, one dorsal subterminal seta, and one long seta on outer distal margin.  
Pleotelson (Fig. 3C, D) with two setae at base of fucal rami. Anal operculum projected, with round tip.  
Furcal rami (Fig. 3C, D) as long as wide, with three spines and two dorsal setae of equal length. The outer seta is plumose.  
 Description of the male (allotype): The male differs from the female in body length, second and third antennular segments, and thoracopod VIII. Body length 1.05 mm. Body length of other males (paratypes) 1.05, 1.04 mm.   
Second antennular segment (Fig. 1B, D) with one group of four plumose setae, one ventral seta and antennal organ on inner distal margin. Antennal organ (Fig. 1C, E) represented by a protrusion bearing a hairpin-shaped dorsal seta and simple ventral seta.  
Third antennular segment (Fig. 1B, D) with one seta on inner distal margin in addition to two lateral setae and one ventral seta.  
Thoracopod VIII (Fig. 3B) massive. Penial region three-lobed. Middle lobe with three to four teeth distally. Epipod absent. Basipod with one seta at base of endopod. Inner margin of basipodite drawn out into a chitinous projection. Exopod triangular, bottle-shaped, bearing two tiny spines in the region of the bottleneck and four distal denticles. Endopod 1.5 times as long as basipod, drawn out in round tip. With two setae at base of tip.  
 Variability: The labrum of a female paratype from type locality is equipped with eight main teeth flanked by one smaller tooth on both lateral sides. A paratype from the third locality bears three spines on the uropodal sympodite.
description: Published as part of Cho, Joo-Lae & Schminke, Horst Kurt, 2006, A phylogenetic review of the genus Hexabathynella Schminke, 1972 (Crustacea, Malacostraca, Bathynellacea): with a description of four new species, pp. 71-96 in Zoological Journal of the Linnean Society 147 (1) on pages 72-73, DOI: 10.1111/j.1096-3642.2006.00215.x, http://zenodo.org/record/10114560