Spongicola teres, Komai, 2015

Komai, Tomoyuki, 2015, A New Species of the Stenopodidean Shrimp Genus Spongicola (Crustacea: Decapoda: Spongicolidae) from French Polynesia, South Pacific, Species Diversity 20 (1), pp. 29-36 : 29-35

Spongicola teres sp. nov.

( Figs 1 –4 )

Material examined. Holotype: male (cl 5.2 mm), TARASOC, stn DW 3440, between Raiatea and Tahaa, Society Islands, French Polynesia, 16°40′S, 151°25′W, 650– 800 m, 16 October 2009, MNHN-IU-2011–5119.

Diagnosis. Male. Rostrum with dorsal margin slightly sloping down toward distal end, bearing tiny teeth or denticles; rostral ridge extending onto anterior part of gastric region of carapace; ventral and ventrolateral margins unarmed. Carapace without postrostral submedian teeth; hepatic and anterolateral teeth greatly reduced, expressed as rudimentary tubercles; branchial region smooth, unarmed. Telson with pair of posterolateral teeth, but without posteromedian tooth. First pereopod with well-developed grooming apparatus. Third pereopod with chela massive (palm 1.2 times as long as high), strongly compressed laterally, sharply carinate on dorsal margin, and slightly serrate in distal half; merus without prominent tooth on lateral face, ventromesial margin with row of tiny tubercles; ischium with strong dorsodistal tooth. Uropodal endopod with slightly serrate lateral margin.

Description. Rostrum ( Figs 1 , 2 A–C) 0.4 of carapace length, directed forward, slightly overreaching first segment of antennular peduncle; dorsal margin slightly sloping down toward distal end, armed with 7 tiny teeth or denticles in total (distalmost tooth and posterior 3 teeth rudimentary, posteriormost one located slightly posterior to rostral base) and sparse short setae; ventral margin unarmed; ventrolateral carina sharp, unarmed, merging into orbital margin. Carapace ( Figs 1 , 2A, B ) subcylindrical, surface glabrous; postrostral median ridge low, extending to anterior 0.2 length of carapace; dorsal outline in lateral view faintly sinuous; cervical groove absent; postrostral submedian teeth absent; antennal tooth small, acuminate; suborbital lobe not differentiated; hepatic tooth reduced to obsolete tubercle; 2 (right) or 3 (left) microscopic anterolateral tubercles present; anterolateral margin with some microscopic denticles ( Fig. 2D ); pterygostomial angle produced, rounded.

Sixth thoracic sternite ( Fig. 2E ) with elongate, spiniform median lobes contiguous with each other. Seventh sternite ( Fig. 2E ) with anterior lobes acutely triangular, separated by moderately wide, V-shaped median notch; margins of lobes smooth, not denticulate or spinulose. Eighth sternite ( Fig. 2E ) with anterolateral lobes subtriangular with acute apex, directed anterolaterally, smaller than those on seventh sternite.

Pleon ( Figs 1 , 2F ) slightly depressed dorsoventrally. First pleomere with distinct transverse carina delimited anteriorly by deep transverse groove, its margin partially overhanging deeply depressed anterior section; pleuron with small acute tooth at anteroventral angle, ventral margin evenly rounded; ventrolateral process of sternite prominent, spiniform. Second pleomere with faint transverse groove on tergum slightly anterior to midlength. Second to fourth pleura each with blunt point ventrally, and faintly denticulate margin. Pleuron of fifth pleomere with blunt point ventrally. Sixth somite widened posteriorly; tergum including posterodorsal margin unarmed; pleuron subtriangular with rounded posterolateral margin, unarmed. Sternites of first to fourth pleomeres each with short, blade-shaped median tooth, that of fifth pleomere with strong, dagger-like median tooth directed posteriorly. Telson ( Fig. 2G ) 1.6 times as long as broad, nearly oblong, slightly narrowing from anterior 0.3 length to rounded, unarmed posterior margin; dorsal surface with 4 pairs of small teeth on obtuse dorsolateral ridges, 1 additional denticle present on right side anterior to first tooth; lateral margins each with 1 conspicuous tooth slightly posterior to midlength and 1 additional denticle on right side only near posterolateral angle, anterior part forming shallow concavity; each posterolateral angle with 1 small tooth.

Eyestalk ( Fig. 2A, B ) moderately large, not covering antennal scale in dorsal view, somewhat inflated, armed with 2 denticles anteromesially, otherwise unarmed; cornea darkly pigmented, semi-globular, narrower than eyestalk.

Antennular peduncle ( Figs 1 , 2A, B ) distinctly overreaching midlength of antennal scale, but not reaching to distal end of latter. First segment with distolateral margin produced into small, rounded lobe, ventromesial margin unarmed; stylocerite very small, acuminate, concealed by eyestalk in dorsal view. Second segment less than halflength of first segment, with distolateral margin produced into small, triangular tooth. Third segment shorter than second segment. Outer antennular flagellum subequal in length to carapace, thickened aesthetasc-bearing portion occupying about two-thirds length of entire flagellum, each article with some setae (these 1.0–2.0 times length of article) on distal margin; inner flagellum subequal in length to outer flagellum, each article also with short to long setae on distal margin.

Antenna ( Fig. 2A, B ) short. Basicerite stout; distolateral margin without conspicuous teeth; mesial face with prominent, roundly subrectangular process contiguous with stylocerite on antennular peduncle. Carpocerite (fifth segment) stout, cylindrical, reaching to midlength of antennal scale. Antennal scale subsemicircular, 1.8 times as long as wide; distal lamella rounded; lateral margin slightly concave, serrate with 4 minute teeth in distal half, terminating in small, triangular tooth. Antennal flagellum distinctly longer than carapace, each article with some setae on distal margin, these setae becoming longer toward distal end.

Mouthparts not dissected, but seeming typical for genus (cf. Saito and Komai 2008). Second maxilliped with well-developed, flagellum-like exopod.

Third maxilliped ( Fig. 3A ) overreaching distal margin of antennal scale by length of dactylus and half of propodus. Dactylus slightly shorter than propodus, with blunt tip. Propodus subequal in length to carpus; mesial face with distinct concavity in distal half, filled by minute setae forming transverse tracts and bordered proximally by long, stiff setae ( Fig. 3B ; this structure representing a grooming apparatus). Dactylus and propodus with row of long, stiff outward-directed setae on both ventrolateral and ventromesial margins. Carpus broader than propodus, slightly shorter than merus, ventrodistal margin not produced but forming rounded angle. Merus somewhat twisted, distinctly shorter than ischium, unarmed on distal margin; ventrolateral margin with row of short, stiff setae. Ischium with 1 denticle at ventrolateral distal angle; dorsolateral margin unarmed; ventral margin with row of short, stiff setae increasing in length distally. Exopod rudimentary, bud-like, flexible.

First pereopod ( Fig. 3C, D ) with mero-carpal joint reaching to midlength of antennal scale. Dactylus 0.6 times length of palm; palm subcylindrical. Carpus longest, 1.6 times as long as chela. Grooming apparatus consisting of suboval patch of very short, dense setae on ventromesial face of palm and 3 long, plumose setae arranged in short, obliquely longitudinal row on ventrodistal part of carpus ( Fig. 3E ). Merus about 0.8 times length of carpus. Ischium distinctly shorter than merus.

Second pereopod ( Fig. 3F ) about 1.6 times as long as first pereopod, without grooming apparatus. Dactylus 0.6 times length of palm. Palm subcylindrical, 6.7 times as long as wide. Carpus 1.7 times as long as chela. Merus 0.6 times length of carpus. Ischium about 0.6 times length of merus.

Right third pereopod ( Fig. 4 A–C) with its mero-carpal joint reaching to distal end of antennal scale. Chela massive, strongly compressed laterally, about 1.7 times as long as carapace. Dactylus 0.7 times length of palm, slightly curving, terminating in acute tip crossing tip of fixed finger; dorsal margin bluntly carinate, with row of 4 small tubercles in proximal half; lateral and mesial faces glabrous; cutting edge with prominent triangular tooth slightly proximal to midlength and deep proximal concavity accommodating tooth on fixed finger. Fixed finger subtriangular, terminating in strongly curved tip; ventral margin strongly sinuous, with row of 7 small tubercles in proximal 0.6; lateral and mesial faces with a few tufts of setae; cutting edge bearing prominent, roundly triangular proximal tooth and much smaller subacute tooth separated from former by deep, V-shaped notch; distal 0.6 of cutting edge faintly sinuous, sharply edged. Palm about 1.2 times as long as high; dorsal margin sharply carinate, slightly serrate (serration becoming faint proximally); lateral surface gently convex, almost glabrous, without armature; mesial face also gently convex, with some minute granules distally, otherwise smooth, glabrous; ventral margin slightly convex, sharply carinate, faintly serrate (serration becoming distinct distally). Carpus cup-like, dorsomesial distal angle produced into prominent subtriangular lobe with blunt tip; lateral and mesial faces unarmed; ventrodistal margin divided into 2 lobes by deep, V-shaped notch. Merus unarmed on rounded dorsal surface; lateral face also unarmed; ventrolateral margin not clearly delimited, but with row of very low, small protuberances ( Fig. 4D ); ventromesial margin bluntly carinate, with row of tiny denticles. Ischium with large dorsodistal tooth, and row of 3 tiny denticles on slightly concave dorsal margin; ventral margin with row of minute denticles ( Fig. 4E ).

Left third pereopod missing.

Fourth pereopod ( Fig. 3G, H ) relatively long and slender, with its mero-carpal joint falling slightly short of pterygostomial margin of carapace. Dactylus 0.4 times length of propodus, 3.8 times as long as high, biunguiculate (dorsal unguis distinctly longer than ventral unguis, both clearly demarcated basally). Propodus not subdivided, 0.4 times length of carpus, with 2 slender spinules on ventrodistal margin followed by row of 12 slender spinules; sparse long setae present on both dorsal and ventral margins. Among segments, carpus longest, subdivided into 2 greatly unequal articles (articulation at about distal 0.3), unarmed. Merus subequal in length to carpus. Ischium distinctly shorter than merus.

Fifth pereopod ( Fig. 3I ) similar to fourth pereopod.

Gill/exopod formula typical for genus (cf. Saito and Komai 2008: table 1). Gills trichobranchiate, but filaments rather few, stout. In particular, arthrobranchs on third maxilliped and first pereopod small, consisting of stout rachis and few filaments. Epipods moderately to strongly arcuate, increasing in size posteriorly.

Protopods of endopods unarmed on ventrolateral margins.

Uropod ( Fig. 2G ) with protopod unarmed on posterolateral margin, dorsal surface with small but prominent tubercle near junction with endopod. Exopod with serration of 7 (left) or 9 (right) tiny teeth, these teeth becoming more distinct posteriorly on posterior 0.6 of lateral margin, including subacute posterolateral tooth; dorsal surface with 2 blunt longitudinal ridges (mesial ridge concealed by endopod in Fig. 2G ). Endopod with weak serration consisting of microscopic denticles and 2 or 3 tiny posterior teeth; dorsal surface with 1 blunt longitudinal ridge lateral to midline.

Distribution. Known only from the type locality, between Raiatea and Tahaa, Society Islands, French Polynesia, 650– 800 m.

Host. No information on the host was available.

Etymology. From the Latin “ teres ” (= smooth, or polished), in reference to the reduced armature on the carapace of the new species.

Remarks. The present new species is assigned to Spongicola because of the rudimentary exopod on the third maxilliped and the strongly compressed palm of the third pereopod with sharply carinate and slightly serrate dorsal and ventral margins. However, the development of the exopod of the third maxilliped is known to be variable among species presently assigned to Microprosthema ( Saito and Anker 2014) . As pointed out by Saito and Takeda (2003), reappraisal of the genera within Spongicolidae is necessary.

Spongicola teres sp. nov. appears closest to S. depressus , known only by the female holotype from the Loyalty Islands, New Caledonia, and S. levigatus , widely distributed in the western Pacific ( Saito and Komai 2008). These three species share the following characteristics: (1) the armature of the carapace shows a strong tendency toward reduction with, for example, no postrostral submedian teeth and the hepatic and anterolateral teeth reduced to minute or microscopic tubercles or completely absent; and (2) the merus of the third pereopod is devoid of conspicuous teeth on the lateral face. Generally in spongicolids, sexual dimorphism affects the shape of the pleon, the relative sizes of the chelae of the second and third pereopods, and the strength of the armature of the third pereopod, so assessment of differentiating features requires careful consideration. The male of S. levigatus has been described, but not that of S. depressus . Spongicola teres is distinguished from S. levigatus by the following characters displayed by the male ( Saito and Komai 2008): (1) the rostral ridge extends to the anterior part of the gastric region in S. teres but is restricted to the rostrum proper in S. levigatus ; (2) the eyestalks are relatively smaller in S. teres (not covering the proximal half of the antennal scale) than in S. levigatus (covering the proximal half of the antennal scale in dorsal view); (3) the first pereopod is provided with a well-developed grooming apparatus, consisting of a small, oval patch of minute setae on the palm and a few long, feathered setae on the distal part of the carpus, whereas in S. levigatus such a grooming apparatus is not developed; (4) the dorsal margin of the palm of the third pereopod is sharply carinate in S. teres , but non-carinate in S. levigatus .

Although no information on the male is available for S. depressus , the following characters are of possible significance for species differentiation ( Saito and Komai 2008): (1) the rostral ridge extends onto the anterior part of the gastric region in S. teres , rather than being restricted to the rostrum proper as in S. depressus ; (2) the telson is armed with a pair of posterolateral teeth but lacks a posteromedian tooth in S. teres , but in S. depressus it is armed with a tiny posteromedian tooth and no posterolateral teeth; (3) the ischium of the third maxilliped is unarmed on the dorsolateral margin in S. teres , but is armed with four denticles in S. depressus ; (4) the palm of the first pereopod is provided with a setal patch consisting of minute, dense setae in S. teres , whereas in S. depressus this patch consists of several long setae; (5) the palm is strongly compressed laterally with sparse setae on the dorsal margin in S. teres , but subcylindrical with a row of numerous short setae on the dorsal margin in S. depressus .

Despite the extensive revisionary study by Saito and Komai (2008), no species of Spongicola has been recorded from French Polynesia, and the present new species represents the first record of the genus from that area. The total number of the species of the genus is raised to eight.

The identification key to the species of Spongicola proposed by Saito and Komai (2008) is emended here to include the present new species.

Key to the species of Spongicola

1. Lateral margin of uropodal endopod unarmed............... ........................................................................ S. parvispinus

– Lateral margin of uropodal endopod serrate................. 2

2. Carapace without postrostral submedian and anterolateral teeth ............................................................................. 3

– Carapace with postrostral submedian and anterolateral teeth..................................................................................... 5

3. Rostral ridge extending onto gastric region of carapace ...................................................................... S. teres sp. nov.

– Rostral ridge restricted to rostrum proper..................... 4

4. Carapace with small tubercle on hepatic region; first pereopod with grooming apparatus; dorsal margin of palm of third pereopod sharply carinate, with row of setae ................................................................... S. depressus

– Carapace unarmed on hepatic region; first pereopod without grooming apparatus; dorsal margin of palm of third pereopod not carinate, without row of setae.......... ............................................................................. S. levigatus

5. Carapace with scattered denticles in branchial region; merus of third pereopod unarmed or armed with row of small teeth or denticles on lateral margin......... S. goyi

– Carapace unarmed in branchial region; merus of third pereopod armed with 1 large tooth on lateral margin.... .............................................................................................. 6

6. First pereopod with well developed grooming apparatus; second pereopod naked, with carpus subequal in length to merus ......................................... S. andamanicus

– First pereopod with rudimentary grooming apparatus; second pereopod with numerous setae, with carpus longer than merus.............................................................. 7

7. Cornea of eye darkly pigmented; second pereopod 1.2–2.1 times longer than carapace in females, 1.5–2.2 times in males.................................................... S. venustus

– Cornea of eye opaque; second pereopod 2.1–2.2 times longer than carapace in females, 2.4–2.6 times in males .............................................................................. S. robustus

Figures

Fig. 1. Spongicola teres sp. nov., holotype, male (cl 5.2mm), MNHN-IU-2011-5119, entire animal in lateral view. Scale bar: 2mm.

Fig. 2. Spongicola teres sp. nov., holotype, male, MNHN-IU-2011-5119. A, anterior part of carapace and cephalic appendages, lateral view; B, same, dorsal view (marginal setae on left antennal scale omitted); C, rostrum, lateral view; D, anterolateral margin of carapace, lateral view; E, sixth to eighth thoracic sternites, ventral view; F, left pleura of first to fifth pleomeres, lateral view; G, telson and right uropod, dorsal view (marginal setae on uropodal rami omitted); H, left antennal scale, dorsal view (setae omitted). Scale bars: 1mm for A, B, E, F, G; 0.5mm for C, D, H.

Fig. 3. Spongicola teres sp. nov., holotype, male, MNHN-IU-2011-5119. A, right third maxilliped, lateral view; B, same, dactylus and propodus, mesial view; C, right first pereopod, lateral view; D, same, chela; E, same, chela and distal part of carpus, showing grooming apparatus (dactylus hidden by fixed finger); F, left second pereopod, lateral view; G, right fourth pereopod, lateral view; H, same, dactylus and propodus, lateral view; I, right fifth pereopod, lateral view. Scale bars: 1mm for A, C, D, F, G, I; 0.5mm for B, E, H.

Fig. 4. Spongicola teres sp. nov., holotype, male, MNHN-IU-2011-5119. A, right third pereopod, lateral view; B, same, chela and carpus, mesial view; C, same, merus, mesial view; D, same, merus, dorsolateral view, showing obtuse protuberances on lateral surface; E, same, close up of ventral margin of ischium, mesial view. Scale bars: 2mm for A–C; 1mm for D; 0.5mm for E.