Type locality. Station MT 5 (27°33’28′′ N, 88°65’60′′ W) in the northern Gulf of Mexico, depth 2280 m, on 4 June 2000. Muddy sediment.
Material examined. Holotype: 1 ♀ (CR00233171) dissected on 4 slides from the type locality. Paratypes: 1 ♂ dissected on 5 slides (CR00233176) from Station S37; 4 ♀♀ (CR0023172-CR00233175) dissected on 1 (S36), 3 (S42), 2 (S44) and 6 (S36) slides; 2 ♂♂ (CR0000233177-CR00233178) dissected on 6 (S36) and 2 (S44) slides, respectively. All specimens were collected by W. Lee and R. Kalke. All other details are provided in Table 1
Etymology. The specific name refers to the type locality, near the Texan coast.
Descriptions. Female: Total body length ranging from 354 to 415 µm (n
= 5, mean = 374 µm; measured from rostral anterior distal margin to posterior margin of caudal rami). Largest width measured at posterior margin of cephalothorax: 108 µm. Urosome slightly narrower than prosome (Figure 1
Cephalothorax with folded lateral sides and with pair of longitudinal ridges dorsally; dorsal surface with serrate posterior margin and few sensilla, covered with minute spinules as illustrated in Figure 1
Prosomites (Figure 1
A,C) covered with minute spinules and with serrate posterior margins.
Rostrum (Figure 1
A–D) well-developed, fused to cephalothorax, triangular, recurved dorsally in lateral view (Figure 1
D); round at tip and bearing two sensilla (Figure 1
B); median pore on dorsal surface.
Urosomites (Figure 1
A,C,E,F) ornamented as illustrated. Dorsal surface and posterior margin of first urosomite ornamented as preceding somites. Second and third urosomites not completely fused and forming genital double-somite. Genital double-somite covered with minute spinules dorsally, with dorsolateral division between second (genital somite) and third urosomites, posterior margin of each urosomites serrate dorsally; each urosomite with several sensilla arising from distinct cones dorsally and laterally as illustrated.
Genital area (Figure 1
E) located near anterior margin, with single copulatory pore present medially and covered by integumental fold. P6 located in proximal half of first genital somite with small protuberance bearing 1 pinnate seta on each side. First and second genital somites fused mid-ventrally; ventral surface of second genital somite plain, with rows of spinules along posterior and lateral margins.
Anal somite (Figure 1
E,F) with patches of minute spinules and fine ridges on dorsal median surface as illustrated. Operculum semicircular, with dentate margin and one sensillum arising from one short socle on each side. Ventral surface smooth without ornamentation, and row of spinules along distal margin.
Caudal rami (Figure 1
E,F) as long as anal somite, and 3.5 times longer than wide; setae I and II arising laterally halfway along outer margin, seta II as long as seta I; seta III twice as long as setae I and II; seta IV small and fused to seta V; seta VI longer than seta II and located on distal inner corner; seta VII bare, located halfway along inner margin of caudal ramus, tri-articulated.
Antennule (Figure 2
A,B) 5-segmented. Segment 1 with lateral and distal row of spinules around anterior margin. Segment 2 largest. Segment 3 with aesthetasc fused basally to 1 seta. All setae smooth except for 1, 1 and 3 pinnate spines on first, third and last segments, respectively. Armature formula: 1-[1 pinnate], 2-[7
], 3-[6+1 pinnate+(1+ae)], 4-[1
], 5-[8+3 pinnate+1 acrothek]. Apical acrothek consisting of one well-developed aesthetasc fused basally to two slender naked setae.
Antenna (Figure 2
C) 3-segmented, comprising coxa, allobasis and free 1-segmented endopod. Coxa with one row of spinules along inner margin and one naked abexopodal seta. Exopod 1-segmented, small and bifurcate, with one pinnate seta laterally and one pinnate seta apically; ornamented with spinules. Endopod with row of stout spinules on anterior margin and row of spinules around outer lateral margin; apical armature consisting of one stout pinnate and two naked spines and two geniculate spines; one naked spine and one unipinnate spine laterally.
Mandible (Figure 2
D) with well-developed gnathobase bearing multicuspidate teeth and one naked seta at distal corner. Mandibular palp bifurcate1-segmented with one lateral and two distal bipinnate setae; a row of spinules along each ramus; lateral seta originating from cylindrical peduncle.
Maxillule (Figure 2
E) praecoxa with row of spinules along outer lateral margin. Arthrite with three teeth and three strong apical spines and one surface seta. Coxa-basis with three apical and one lateral naked seta; endopod represented by single pinnate seta and one row of spinules along outer lateral surface.
Maxilla (Figure 2
F). Syncoxa with one spinular row on anterior surface and two endites; proximal endite with one pinnate spine and two smooth setae; distal endite with one pinnate seta, with distal corner an acute outgrowth. Allobasis produced into long naked curved claw; accessory armature consisting of two slender lateral setae proximally and close to base of endopod. Endopod incorporated into allobasis and represented by two slender setae fused at their base.
Maxilliped (Figure 2
G). Syncoxa with one row of spinules. Basis with one row of spinules on palmar region. Endopod small with 1 long, sparsely pinnate claw. Accessory armature consisting of one naked seta.
Swimming legs 1–4 (Figure 3
A,B and Figure 4
A,B) biramous, with 3-segmented exopod and 2-segmented endopod and with wide intercoxal sclerites and well-developed praecoxae. Coxae and bases with anterior rows of surface spinules as illustrated.
P1 (Figure 3
A). Praecoxa triangular with row of short spinules along distal margin. Coxa are large with several rows of spinules on anterior surface and close to outer and inner distal corners.
Basis with one strong, pinnate seta and spinules along inner margin and with one naked seta and several spinules along outer margin. Exopod 3 segmented; exp-1 and exp-2 with one pinnate spine and outer spinular row without inner spine, respectively; exp-3 with two pinnate outer spines and two pinnate distal setae. Endopod 2-segmented; Enp-1 without seta. Enp-2 about three times longer than enp-1 and with one pinnate stout spine and one slender pinnate seta.
P2–P4 (Figure 3
B and Figure 4
A,B). Coxae and bases with spinular rows along outer margin. Outer margin of basis with naked seta (P2 and P4) or pinnate seta (P3). Each exopodal segment-1 and -2 with coarse frills at inner distal margin. All segments with rows of spinules and setules as illustrated, especially inner margins of exopod and endopod segments with long setules or spinules.
P2 (Figure 3
B) basis with row of spinules on anterior surface. Exopod 3-segmented; exp-3 with two pinnate spines and two plumose setae. Endopod 2-segmented and distal margin of enp-2 reaching to distal margin of exp-3; enp-1 small, with outer spinules and some apical inner spinules; enp-2 with two pinnate setae, outer spinular row, with one row of setules along inner margin and one patch of small spinules inner distally.
P3 (Figure 4
A) exp-1 longest with 1 patch of spinules along inner distal margin; exp-2 and exp-3 with row of setules along inner margin. Endopod reaching to middle of exp-3. Enp-2 three times longer than enp-1, with one outer spine and two long apical pinnate setae; both setae subequal in length; one row of setules along inner margin and one row of spinules along outer margin; inner distal corner of enp-2 with one patch of short setules.
P4 (Figure 4
B) exopod segments subequal in length; exp-2 and exp-3 with inner row of setules. Endopod reaching to just beyond distal margin of exp-2. Enp-2 three times longer than enp-1. Inner distal corner of enp-2 with 1 patch of short spinules.
Armature formula is as follows:
P2 0.0.022 0.020
P3 0.0.122 0.021
P4 0.0.122 0.021
P5 (Figure 4
C). Baseoendopod with one long cylindrical outer setophore bearing one terminal seta and one small pore near boundary with exopod. Endopodal lobe reaching about the proximal third of the exopod, ornamented with three transverse rows of long spinules, with one pinnate apical and two pinnate lateral setae. Exopod elongate, somewhat rectangular with row of spinules at base of apical pinnate spine, with two outer setae and one inner tube-pore.
P6 (Figure 1
E), vestigial; each P6 represented by one protuberance bearing one pinnate seta and one row of spinules close to seta insertion area. Copulatory pore located at slightly distal region from median line of genital double somite.
Male: Total body length 364–432 µm (n = 3, measured from tip of rostrum to posterior margin of caudal rami). Greatest width measured at posterior margin of cephalic shield: 102 µm.
Prosomites (Figure 5
A) slightly narrower than in female, with similar pattern of minute spinules on dorsal surface of each segment as in female. Rostrum less developed than in female, with a smooth and slightly bifid apical margin and one pair of sensilla, as in female (Figure 5
Urosomites (Figure 5
A,B). Surface ornamentation pattern consisting of patches of minute denticles present dorsally and laterally, with posterior margin irregularly serrate dorsally and laterally. Caudal ramus slightly shorter than in female and three times as long as wide. Sexual dimorphism expressed in A1, P3, P5, P6 and genital field.
Antennule (Figure 6
C–F) 7-segmented. Subchirocer. Geniculation present between segments 5 and 6. Segment 1 with two rows of spinules along anterior surface medially and distally. Segment 4 shaped as one small sclerite along anterior margin. Segment 5 swollen and largest. Segment 7 triangular with spinous apical tip. Armature formula: 1-[1 bipinnate], 2-[8
], 5-[6 + 2 pinnate + (1 + ae)], 6-[2
], 7-[5 + acrothek]. Distal acrothek consisted of minute aesthetasc and 2 naked setae.
Mouthparts, P1, P2 and P4, as in female.
P3 (Figure 6
A,B) basis, exp-1 and exp-3 as in female. Exp-2 with one robust and slightly hardened outer spine. Endopod 3-segmented; enp-2 2.2 times longer than enp-1, with one long, outer distal apophysis reaching to tip of third exopodal segment; enp-3 subequal to enp-1 in length, separated from enp-2 with clear surface suture (arrowed in Figure 6
A) but internal articulation obscure, with two long pinnate apical setae.
P5 (Figure 5
D,E) baseoendopod same as in female, except for two strong elements only in male P5 and two transverse rows of long spinules; apical pinnate spine overlapped by exopod in ventral view and only reaching to near lateral outer seta of exopod. Exopod elongate, 3.6-times longer than width, with one lateral pinnate outer seta, one apical pinnate strong spine and one inner tube pore (arrowed in Figure 5
D,E); one row of setules along outer margin and one spinular row along posterior apical margin.
P6 (Figure 5
B), vestigial, represented on both sides by one spinulose ventral plate close to posterior margin of somite; each plate bearing one pinnate apical spine. P6 bearing somite produced into cylindrical process bearing sensillum at each distal outer corner.
We placed the new species in the genus Enhydrosoma
on account of two setae on the antennary exopod, one segmented mandibular palp having three elements, the medially elongated segments of the maxilliped, the seta formula and segmentation of swimming legs, the well-developed exopod and enopodal lobe of P5 in both sexes and the well-developed apophysis on P3 enp-2 of the male. All the above character sets can be found from the congeners [1
sp. nov. is clearly distinguishable from the type species of the genus, Enhydrosoma curticauda
Boeck, 1872, by several character states: (1) the round apical margin of the rostrum in the female (bifid in E. curticauda
, see [1
], p.86, Figure 1A; P. 89, Figure 4A), (2) the elongated, cylindrical caudal ramus (ovoid in E. curticauda
, see [1
], p.86–87, Figures 1A,B and 2B), (3) three setae and an inner lateral tube pore on P5 exopod in the female (only four setae in E. curticauda
, see [1
], p.88, Figure 3A, in addition a long tube pore present on endopodal lobe inner laterally), (4) two setae and an inner lateral tube pore on the exopod in the male (only three setae in E. curticauda
, see [1
], p.87, Figure 2D, its endopodal lobe has a long tube pore as in the female and elongated with a characteristic triangular shape), (5) a naked abexopodal seta on the antenna (no seta in E. curticauda
, see [1
], p. 89, Figure 4C), (6) three setae on the mandibular palp (four setae in E. curticauda
, see [1
], p.89, Figure 4D), (7) no seta on the syncoxa of the maxilliped (a strong pinnate seta in E. curticauda
, see [1
], p.90, Figure 5E), (8) a pinnate seta on the P6 in the female (two elements in E. curticauda
, see [1
], p.91, Figure 6C), (9) two setae on the P1 enp-2 (three elements in E. curticauda
, see [1
], p.93, Figure 7A) and (10) three-segmented endopod and the third segment of P3 at least separated by a surface suture (See Figure 6A) in the male (two-segmented in E. curticauda
, see [1
], p.93, Figure 7B). The oligomerization of seta numbers on the mandibular palp and the syncoxa of maxillipeds, P1, P5 and P6 may be interpreted to mean that E. texana
sp. nov. is a more advanced lineage than the type species within the genus. However, E. texana
sp. nov. can be accommodated to a primitive basal group within the genus, displaying a combination of plesiomorphic characters: (1) the presence of abexopodal seta on A2, (2) the presence of maxillipedal claw seta, (3) the 3-segmented endopod of male P3, (4) the clearly defined (not fused) exopod and endopod of P5 in both sexes.
Using Wells’ key [5
], Enhydrosoma texana
sp. nov. appears to be most closely related to E. parapropinquum
Gómez, 2003. The close relationship between both species is indicated by the following combination of shared character states: (1) an elongated, cylindrical caudal ramus, (2) an abexopodal seta of antennae, (3) the structure of mouth-part appendages including mandible, maxillule, maxilla and maxilliped, (4) seta formula of P1–P4, (5) three setae on the endopod of P5 in the female, (6) overlapping position of the exopod with the endopod in P5 of the male and their setation, (7) only one seta on P6 in the female and (8) the apophysis structure of P3 in the male. Mouthpart appendages, the apophysis of P3 in the male and the appearance of P5 in both sexes is very similar between the two species. These shared characters or potential synapomorphies might reflect a close sister relationship between these two taxa. However, they can be distinguished from one another by the following features. (1) Rostrum: E. texana
sp. nov. has a round apical margin in the female (Figure 1A,B) and a bifid apical margin in the male (Figure 5A), while E. parapropinquum
has a bifid apical margin in both sexes (See [8
], p.96, Figure 1A and p.103, Figure 7). (2) Antennule: the second segment is longest in E. texana
sp. nov. (Figure 2A); however, the same segment is clearly shorter than the fifth segment in E. paraproqinquum
], p.98, Figure 3A). (3) Antenna: abexopodal seta is naked in T. texana
sp. nov. (Figure 2C), while it is pinnate in E. paraproqinquum
], p.98, Figure 3B). (4) Mandibular palp: the lateral peduncle arming the lateral seta is clearly elongate in E. texana
sp. nov. (Figure 2D), while it is barely separated and short in E. paraproqinquum
], p.99, Figure 4A). (5) Maxilliped: the accessory seta on the endopod is slightly shorter than the syncoxa in E. texana
sp. nov. (Figure 2G), while it is minute in E. paraproqinquum
], p.99, Figure 3D). (6) P1–P4: enp-2 of P1 and P2 reach to the tip of the exp-3 in E. texana
sp. nov. (Figure 4A,B), while these are shorter than their exopods in E. paraproqinquum
], p.100, Figure 5A,B). (7) P3 in males: the shape of the apophysis is sharper apically and smoother laterally in E. texana
sp. nov. (Figure 6A,B) than in E. paraproqinquum
], p.105, Figure 9B). (8) P5 in the female: the exopod has one apical and two lateral setae in E. texana
sp. nov. (Figure 4C), while it has one apical and three lateral setae in E. paraproqinquum
], p.102, Figure 6C). In addition, the tube pore is inserted laterally in E. texana
sp. nov., but it is located rather distally near the proximal area of the apical seta. (9) P5 in the male: exopod located anteriorly against the baseoendopod, the tip of the apical seta reaches only to the middle of the third urosomal somite, and the exopod arises from the apical margin of the baseoendopod in E. texana
sp. nov. (Figure 5B–D), while the exopod is located posteriorly, the tip of the apical seta elongates and reaches the middle of the fourth urosomal somite (see [8
], p.104, Figure 8), and the exopod arises from the posterior surface in E. paraproqinquum
], p.105, Figure 9C). (10) Caudal ramus: the length of the caudal ramus is 3.5-times longer than the width in the female and 3.0-times longer in the male in E. texana
sp. nov. (Figure 1E,F, female; Figure 5A–C, male), while there is no significant difference in the length ratio of the caudal ramus between the female and male in E. paraproqinquum
], p. 97, Figure 2, female; p.104, Figure 8, male).
There are several species that have a P3 with a three-segmented endopod in the male, namely E. texana, E. parapropinquum, E. stylicaudatum
Willey, 1935, E. hopkinsi
Lang, 1965, E. vicinum
Por, 1967, E. littorale
Wells, 1967, E. brauchi
Coull, 1975, E. herrerai
Bell and Kern, 1983 and E. pericoense
Mielke, 1990. Gee [1
] claimed that the description of the endopod in some species is probably a misinterpretation. Gómez [8
] consequently accepted Gee’s claim, and he described E. parapropinquum
as having a two-segmented endopod, although it displays a three-segmented endopod in the published figure (see [8
], p.105, Figure 9B). However, we regard the segment as the separated third segment, because it was clearly separated based on our observations of E. texana
sp. nov. (Figure 6A,B). Indeed, E. brauchi
displays separation of the third endopodal segment marked at the very least by a surface suture (see [12
], p.120, Figure 4), as does E. herrerai
], p.902, Figure 3D) and E. pericoense
], P.154, Figure 11A). As Gee (1994) claimed, separation of the third segment can be incomplete; however, it is still quite different from the two-segmented endopods of E. curticauda
], p.93, Figure 7B) and E. coreana
Kim, Trebukhova, Lee and Karanovic, 2014 (see [7
], P. 259, Figure 8A).
species have been described mainly from shallow neritic waters. Gee [1
] redescribed E. curticuda
based on specimens collected from the muddy sand bottom at depths between 5–50 m from various localities including fjords in Norway and Gullmarfjorden in Sweden. Coull [15
] reported E. propinquum
from the North Carolina continental shelf at the depth range of 17–41 m. E. brauchi
has been reported from the muddy sediment of shallow estuary in the North inlet estuary, Georgetown, South Carolina by Coull [12
]. He did not mention the sampling depths of E. brauchi
, but the samples are from muddy sediment. Enhydrosoma herrerai
is from shallow subtidal habitats in Tampa bay [13
]. Enhydrosoma herrerai
is collected from fine sands and also Thalassia
seagrass beds approximately 0.8m deep [13
]. Thistle reported two species, E. franklini
from subtidal sand of 2 m depth, Florida and E. woodini
from an intertidal Spartina
marsh, North Carolina [16
]. Based on the previous reports, the genus Enhydrosoma
inhabits mainly the shallow subtidal and intertidal zone and adapts to various environments including seagrass beds, sandy and muddy sediments. However, the new species described here was collected from muddy sediment of deep-sea between 213 m and 2382 m (Table 1
), the deepest habitat that the genus Enhydrosoma
has ever been recorded at. The present report enlarges distributional depth of Enhydorosoma
from shallow subtidal to deep-sea bathyal zone.