Prionocrangon incisum

Hendrickx, Michel E. & Ayón-Parente, Manuel, 2012, First record of Prionocrangon Wood Mason & Alcock, 1891 (Crustacea: Decapoda: Caridea: Crangonidae) in the East Pacific and description of a new species from western Mexico, Zootaxa 3205, pp. 63-68 : 64-67

Prionocrangon incisum sp nov.

( Fig. 1 )

Type material. Holotype. One female (CL 8.31 mm), St. 21 (29°00'53"N, 112°51'31"W), 9/April/2011, 412- 425 m, benthic sledge (EMU-8926).

Paratypes. Four females (CL 8.47–10.45 mm), St. 21 (29°00'53"N, 112°51'31"W), 9 April 2011, 412– 425 m, benthic sledge (EMU-8927); one female (CL 9.6 mm), same station (LACM-CR 2011-2); one ovigerous female (CL 9.1 mm), same station ( OUMNH.ZC.2011-09-0051). Two females (CL 6.04 and 10.60 mm), St. 22 (29°05'27"N, 112°46'44"W), 9 April 2011, 380– 390 m, benthic sledge (EMU-8929). One male (CL 8.38 mm), St. 24 (29°08'06"N, 112°58'42"W), 9 April 2011, 532– 594 m (EMU-8930). Two females (CL 9.24 and 10.68 mm), same station (EMU-8931). One male (CL 5.81 mm), St. 26 (29°02'41"N, 113°17'44"W), 10 April 2011, 1050– 1165 m, benthic sledge (EMU-8932).

Additional material. Seven females (CL 7.89-9.74 mm), and three ovigerous female (CL 8.33–10.45 mm), St. 26 (29°02'41"N, 113°17'44"W), 1050–1165 m, benthic sledge (EMU-8928).

Description. Rostrum moderately long, reaching basis of branchiostegal spine, little elevated, 0.10–0.12 times as long as carapace ( Fig. 1 A, B, C, D). Mid-dorsal carina of carapace armed with 7–11 spines, 1 or 2 spines beyond carapace mid-length ( Fig. 1 A, C, D), posteriormost spine located just behind carapace mid-length. Fourth and fifth abdominal somites without carina; sixth somite 0.50 times as long as carapace, posterior margin of posterolateral process truncated, without spine, with a tuft of setae, inferolateral angle deeply notched ( Fig. 1 G, H). Telson slightly shorter than sixth abdominal somite, 0.45 times as long as carapace, three pair of dorsal spines on posterior half, lateral margin of the latter strongly convergent; posterior margin rounded, armed with 3–6 long spines, without minute median denticle ( Fig. 2 G). Eyestalks with bluntly cylindrical extremities, curving ventrally in-between antennules ( Fig. 1 C, E, F). Antennular peduncle with proximal segment moderately long, 0.66 to 0.70 times as long as carapace ( Fig. 1 A, C). Stylocerite oval in dorsal view, with tip elongate, sharp ( Fig. 1 C, 2H, I). Scaphocerite equaling or slightly shorter than proximal segment of antennular peduncle, 0.55–0.60 times as long as carapace ( Fig. 1 A, C). Palm of first pereopod moderately stout, 4.30–5.30 times as long as wide; distomesial spine long ( Fig. 1 I). Dactyli of fourth and fifth pereopods short, 0.40-0.50 times as long as propodi ( Fig. 2 A). Females with endopod of second pleopod about 0.25 times as long as exopod ( Fig. 2 E); endopods and protopods of pleopods without lateral lobe or distoventral projection ( Fig. 2 E, F). Male second pleopod with appendix masculina ( Fig. 2 B, C, D) well developed, but shorter than endopod.

Variations. In the 23 specimens examined, the number of dorsal spines on the carapace (ranging from 7–11) is as follows: eight specimens with seven spines, seven each with eight or nine spines, and one with eleven spines. In 21 specimens with the telson intact, the number of posterior spines (ranging from 3–6) is: one specimen with three spines, five with four spines, four with five spines, and 11 with six spines. No sign of missing spines were observed in specimens with an odd number of posterior spines.

Etymology. From the Latin “ incisum ” (incision), a noun in apposition referring to the deep lateral notch in the sixth abdominal somite.

Remarks. Of the seven previously known species of Prionocrangon , three ( P. paucispina , P. p e c t i n a t a, and P. demani ) feature triangular eyestalks and are therefore easy to separate from the new species. Eyestalks of the other four species ( P. curvicaulis , P. f o r m o s a, P. dofleini , and P. ommatosteres ) have bluntly cylindrical or villiform extremities, as in P. i n c i s u m sp. nov. In P. i n c i s u m sp. nov. the dactyli of the fourth and fifth pereopods are short, 0.40–0.50 times as long as propodi, while in P. curvicaulis and P. fo r m o s a the dactyli are much longer (0.70–0.74 times as long as propodi). The scaphocerite of P. f o r m o s a is also proportionally much wider than in P. i n c i s u m sp. nov., and the stylocerite is triangular-shaped in P. curvicaulis , whilst it is oval-shaped in P. i n c i s u m sp. nov. The absence of a dorsal carina on the fourth and fifth abdominal somite separates P. i n c i s u m sp. nov. from P. dofleini (a low carina on fifth and fourth somite present); in the later species, there are 3 or 4 carapace dorsal spines beyond the carapace mid-length versus only 1 or 2 in P. in c is u m sp. nov. . The absence of a proximolateral lobe on the female endopods of pleopods also separates P. i n c i s u m sp. nov. from P. ommatosteres (proximolateral lobe present). Prionocrangon incisum sp. nov. is also distinct from all seven species known to date given the deeply notched sixth abdominal segment (in lateral view), a feature unique within the genus. Indeed, in other species the posteroventral angle of the sixth somite is either acute or provided with a small, sharp spine (P. o m m a t o s t e re s, P. p e c t i - nata, P. curvicaulis , P. f o r m o s a, and P. demani ), or forming a shallow, angular notch (P. d o f l e i n i).

The series of specimens (23 in total) of P.i n c i s u m sp. nov. collected during the TALUD XIV cruise is one of the most numerous samples for any species of this genus. Two of the three ovigerous females are partly spent. The third bears 11 large eggs, about 1.50 mm × 2.10 mm. First post-embryonic stage and broken eggs were found among the pleopods of partly spent females. All larvae examined are similar to first larvae described for Notocrangon antarcticus ( Pfeffer, 1887) , a deep-water species with abbreviated development ( Gurney 1939).

The material examined here was collected in four stations at 380–1165 m depth on muddy bottoms. Epibenthic dissolved oxygen concentrations and temperature were 1.20–1.56 ml O2/l and 11.2–11.4 °C, respectively. We agree with Yaldwyn’s (1960) opinion that species of Prionocrangon have a burrowing habit. Fresh specimens of P. incisum sp. nov. were covered with dispersed, very small clumps of black mud that remained stuck to the body, even after these were gently rinsed, thus indicating that this species probably digs into the sediment. The long, setose head appendages might be used to facilitate respiration.

Figures

FIGURE 1. Prionocrangon incisum sp. nov. Holotype female, CL 8.31 mm (A – C, E, G – J) (EMU- 8926), paratype female, CL 8.70 mm (D) (EMU- 8927), paratype female, CL 6.04 mm (F) (EMU- 8929). A, entire animal, lateral; B, anterior part of carapace, lateral; C, carapace, stylocerite, antennules and antennae, dorsal; D, dorsal margin of carapace, lateral; E, eyes, dorsal; F, eyes, lateral; G, sixth abdominal somite, lateral; H, posteroventral margin of sixth abdominal somite, lateral, enlarged; I, chela and carpus of left first pereopod, ventral; J, same, external. Scale bars: A – C, D, 5 mm; B, J, 2 mm; E – G, I, 1 mm.

FIGURE 2. Prionocrangon incisum sp. nov. Holotype female, CL 8.31 mm (A, E, F, G – I) (EMU- 8926), male paratype, CL 8.38 mm (B-D) (EMU- 8930). A, dactyl and propodus of right fourth pereopod, lateral; B, left second pleopod, ventral; C, endopod and appendix masculina of second pleopod, mesial; D, endopod and appendix masculina of second pleopod, external; E, left second pleopod, ventral; F, left second pleopod, mesial; G, telson, dorsal; H, right stylocerite, lateral; I, right stylocerite, dorsal. Scale bars: B – F, H, I, 0.5 mm; A, G, 1 mm.