Gnathophausia bergstadi, Meland, Kenneth & Aas, Pål Øyvind, 2013

Meland, Kenneth & Aas, Pål Øyvind, 2013, A taxonomical review of the Gnathophausia (Crustacea, Lophogastrida), with new records from the northern mid-Atlantic ridge, Zootaxa 3664 (2), pp. 199-225 : 211-214

Gnathophausia bergstadi n.sp.

( Figs 9 & 10 )

Type locality. Mar-Eco station 18-345-1066, Charlie Gibbs Fracture Zone (52°23’87’’N, 31°48’85’’W), bottom depth: 2916m, fishing depth: 2320m, R/V “G.O. Sars”, 20 June, 2004.

Type material (in formaldehyde, transferred to ethanol). Stn 6-331-1020, 1 specimen (Ƥ 5.5cm) (ZMBN 86568); Stn 14-340-1050, 3 specimens (immature 2.5cm, 3 5.0cm, 1 damaged) (ZMBN 86569); Stn 16-343-1058, 6 specimens (immature 2.7cm, immature 3.0cm, Ƥ 3.5cm, Ƥ 4.0cm, Ƥ 5.5cm, Ƥ 6.0cm) (ZMBN 86573); Stn 16- 343-1059, 2 specimens (Ƥ 5.0cm, Ƥ 5.5cm) (ZMBN 86570); Stn 16-343-1060,1 specimen (3 4.5cm) (ZMBN 86572); Stn 16-343-1061, 3 specimens (immature 3.0cm, 3 6.0cm, 3 6.0cm) (ZMBN 86571); Stn 18-345-1066, 4 specimens (Holotype: 3 4.0cm, 3 4.0cm, Allotype: Ƥ 6.0cm, Ƥ 3.0cm) (ZMBN 86574); Stn 18-345-1067, 4 specimens (immature 2.9cm, 3 4.0cm, Ƥ 3.0cm, 1 damaged) (ZMBN 86575); Stn 18-345-1068, 3 specimens (Ƥ 3.0cm, Ƥ 3.5cm, Ƥ 5.5cm) (ZMBN 86576); Stn 18-345-1069, 2 specimens (Ƥ 3.0cm, Ƥ 5.5cm) (ZMBN 86577); Stn 20-347-1074, 3 specimens (3 7.0cm, 3 4.0cm, Ƥ 4.0cm)(ZMBN 86579); Stn 20-347-1075, 2 specimens (Ƥ 4.5cm, Ƥ 5.5cm) (ZMBN 86580); Stn 20-347-1076, 1 specimen (immature 3.0cm) (ZMBN 86578); Stn 22-349- 1083, 1 specimen (3 4.0cm) (ZMBN 86581); Stn 24-351-1090, 1 specimen (Ƥ 3.5cm) (ZMBN 86583); Stn 24- 351-1091, 1 specimen (Ƥ 5.5cm) (ZMBN 86582); Stn 28-356-1109, 1 specimen (Ƥ 6.5cm) (ZMBN 86585); Stn 28-356-1110, 1 specimen (Ƥ 6.0cm) (ZMBN 86584); Stn 30-358-1118, 2 specimens (Ƥ 5.0cm, 3 5.0cm) (ZMBN 86586); Stn 30-358-1119, 2 specimens (Ƥ 5.0cm, 3 3.0cm) (ZMBN 86587); Stn 34-363-1133, 1 specimen (Ƥ 5.5cm) (ZMBN 86588); Stn 36-365-1141, 1 specimen (immature 3.0cm) (ZMBN 86589).

Additional material examined. In formaldehyde, transferred to ethanol. Stn 14-341-1054, 1 specimen (Ƥ 5.5cm) (ZMBN 81297); Stn 18-346-1071, 3 specimens (immature 3.5cm, immature 4.0cm, immature 4.5 cm) (ZMBN 81298); Stn 20-348-1079, 2 specimens (immature 2.5cm, Ƥ 5.5cm) (ZMBN 81299); Stn 22-350-1087, 3 specimens (Ƥ 5.0cm, Ƥ 6.0cm, 3 6.5cm (ZMBN 81300); Stn 22-350-1088, 3 specimens (immature 5.0cm, immature 5.0cm, 3 5.5cm) (ZMBN 81301); Stn 24-352-1095, 8 specimens (immature 3.0cm, immature 4.5cm, immature 5.0cm, Ƥ 5.5cm, Ƥ 5.5cm, Ƥ 6.0cm, Ƥ 6.0cm, Ƥ 6.0cm) (ZMBN 81302); Stn 26-354-1103, 7 specimens (immature 5.0cm, Ƥ 5.5cm, Ƥ 6.0cm, Ƥ 6.0cm, Ƥ 6.0cm, 3 6.5cm, 1 damaged) (ZMBN 81303, ZMBN 81304); Stn 36-366-1146, 4 specimens (immature 4.5cm, immature 5.0cm, Ƥ 5.0cm, Ƥ 5.5cm) (ZMBN 81306); Stn 40- 367-1149, 1 specimen (Ƥ 5.5cm) (ZMBN 81307); Stn 50-373-1155, 3 specimens (immature 5.5cm, Ƥ 5.0cm, Ƥ 5.0cm) (ZMBN 81308); Stn 54-377-1159, 1 specimen (3 6.0cm) (ZMBN 81309); Stn 74-387-1169, 1 specimen (3 6.0cm) (ZMBN 81310).

In ethanol. Stn 2-326-1001, 1 specimen (Ƥ 5.5cm) (ZMBN 81296); Stn 22-350-1087, 8 specimens (immature 2.2cm, immature 3.7cm, Ƥ 5.0cm, Ƥ 6.0cm, Ƥ 6.5cm, Ƥ 6.5cm, 3 5.5cm, 3 6.5cm) (ZMBN 86617, ZMBN 86628, ZMBN 86590, ZMBN 86591).

Description. Body slender. Carapace soft and fragile, extending over first abdominal somite; rostrum shorter than carapace, three-sided, denticulate; median dorsal keel continuous, extends anteriorly onto rostrum and posteriorly onto posterodorsal spine, forms raised keel proximal to rostrum; posterodorsal spine three-sided, denticulate, less then half length of carapace; posterolateral corners rounded ( Fig. 9 A); upper lateral keels continuous extend onto posterodorsal spine; lower lateral keels continuous, curves upwards towards posterolateral margins, becomes slightly obsolete and does not merge with upper lateral keels ( Fig. 9 A, B); supra-orbital spines acute ( Fig. 9 B); branchiostegal expansions broad, antennal spines small ( Fig. 9 A, B).

Antennule peduncle broad and robust, second segment short; outer flagellum long, exceeding length of whole animal ( Fig. 9 B).

Antenna sympod large and broad, outer distal margin produced into pointed lobe; peduncle small and slender, third segment equal in length to first and second segments combined; scale at least twice as long as broad, inner margin curved and narrowing distally, divided by oblique distal suture, outer lateral margin terminates in strong spine that extends past terminal lobe, outer margin without setae, inner margin densely setose ( Fig. 9 C).

Eyes pyriform in shape; small spine-like ocular papilla on dorsal surface of stalk; cornea broad.

Mandibles; large molar process on left mandible; three-segmented palp, first segment short and broad, second and third segments long and slender, almost equal in length, third segment with dense row of short setae along outer margin and much longer setae on inner margin at distal end. Labrum extends anteriorly taking on pyriform appearance.

Maxillule with two-segmented endopod (palp), distal end of precoxal lobe armed with with long setae; distal end of basis armed with rows of cuspidate setae ( Fig. 9 D).

Maxilla large, coxal endite large and broad at base, basal endite bifid and slender, first segment of endopod twice as broad as second segment, exopod large and oval shaped ( Fig. 9 E).

First thoracopod takes on form of maxilliped; exopod absent, indicated by shallow depression; epipod slightly longer than endopod, membranous and backwardly directed; endopod richly furnished with long setae; short and slender endites set with short setae on ventral distal ends of basis and ischium; dactylus short and triangular, ventral margin armed with short setae ( Fig. 10 A).

Second to eighth thoracic limbs slender; with small, densely setose, club-shaped epipods; well developed natatory exopods, distal end covered with long setae; endopods developed as pereopods, ventral margins supporting dense rows of setae ( Fig. 10 B).

Pleopods, five pairs in both males and females, well developed sympods, exopods, and endopods. Natatory, as type normal for genus.

Abdominal somites ( Fig. 9 A, B) keeled dorsally; posterodorsal border on first, second, third, and fourth somites, produced into short median spines; posteroventral margins produced into acutely pointed spines; ventral margins of sixth somite posteriorly produced into three spines.

Uropods as type normal for genus, exopods broader than the endopods, with transverse subapical suture; endopod fringed with setae; exopod setose on inner and distal margins, entire on outer proximal margin up towards subapical suture ( Fig. 10 C).

Telson large and linguiform, extends beyond uropods, dorsal surface with longitudinal ridges on each side of mid-dorsal line, between them shallow channel is formed, lateral margins armed with spiniform setae that become more dense towards apex, lateral margins at distal end slightly concave ( Fig 10 D); apex of telson heart shaped, apex corners armed with one small and one large spiniform seta on each side and armed with a row of small spiniform setae along posterior margin ( Fig. 10 E).

Obtains lengths up to 70 mm (from base of rostrum to distal end of telson).

Etymology. Species is named in honour of Dr. Odd Aksel Bergstad in recognition of his contribution to the Mar-Eco program.

Distribution. A total of 46 specimens were captured from 170 m to 2900 m depths, being most abundant below 1500 m. Comparable to Gnathophausia affinis , G. bergstadi , seems to inhabit the deepest stations, and is most abundant below 1500 m. In the shallowest trawls it was absent, here being replaced by G. z o e a. G. bergstadi was distributed along the entire sampling area between Iceland and the Azores islands, but the largest numbers of specimens were collected in central stations near the Charlie Gibbs fracture zone. In the northernmost stations only a single specimen was captured and in the southernmost stations we obtained seven specimens.

Remarks. Gnathophausia bergstadi bears close resemblance to G. z o e a and G. affinis , but is distinguished from these species by the following morphological traits:

1. The majority of mature G. b e rg s t a d i specimens were measured to less then 60 mm in length, mature specimens where identified down to 30 mm, and did not exceed lengths of 70 mm. G. affinis is somewhat similar in size, but both the rostrum and posterodorsal spine are comparably shorter than that observed in G. bergstadi . Also, in G.affinis there is dorsal depression marking the cervical groove, this is not seen in G. bergstadi . As for G. z o e a, mature specimens in this study were never smaller than 50 mm, and reached lengths up to 100 mm.

2. At the posterior end of the carapace, the upper lateral keels, of both G. bergstadi and G. z o e a, extend onto the posterodorsal spine, but in G. z o e a the upper and lower lateral keels fuse in the mid region of the spine, this is not seen in G. bergstadi . Instead the lower lateral keels in G. bergstadi gradually grow weaker before reaching the posterodorsal spine and there is no fusion. In G. affinis the lower lateral keels do not curve upward but stop before reaching the posterior margin of the carapace.

3. Compared to G. affinis , the anterolateral spines (eye-, antennal-, branchiostegal-) are more pronounced in G. bergstadi and G. z o e a, being most conspicuous in G. z o e a.

4. Opposed to the crescent shaped apex of the telson seen in G. affinis and G. z o e a, the apex in G. b e rg s t a d i is heart-shaped, bearing resemblance to that of two Pacific species, G. elegans and G. fagei , but may be distinguished by these two species in that the upper lateral keels of the carapace in G. elegans and G. f a g e i are fused too, and not distinct from, the median dorsal keel.

Figures

FIGURE 9. Gnathophausia bergstadi n. sp. A – B: allotype (adult female, 5, 5 cm), C – E: paratype from type locality (adult male, 4, 0 cm). A, lateral view; B, dorsal view; C, antenna; D, maxillule; E, maxilla.

FIGURE 10. Gnathophausia bergstadi n. sp. Paratype from type locality (adult male, 4, 0 cm). A, first thoracopod (maxilliped 1); B, second thoracopod; C, uropod; D, telson; E, telson (apex).