Spongicola depressus, Saito & Komai, 2008

Saito, Tomomi & Komai, Tomoyuki, 2008, A review of species of the genera Spongicola de Haan, 1844 and Paraspongicola de Saint Laurent & Cleva, 1981 (Crustacea, Decapoda, Stenopodidea, Spongicolidae), Zoosystema 30 (1), pp. 87-147 : 103-107

Spongicola depressus n. sp.

( Figs 8-10 )

TYPE MATERIAL. — Holotype: MUSORSTOM 6, stn?, Loyalty Islands, ovig. ♀ 4.7 mm (MNHN-Na 16293).

ETYMOLOGY. — The specific name depressus refers to the depressed body form, one of the characteristics of the new species.

DISTRIBUTION. — Loyalty Islands, depth unknown ( Fig. 37 ; Table 6).

HOST. — Pheronema sp. ( Table 7).

DESCRIPTION OF FEMALE HOLOTYPE

Rostrum ( Fig. 9A, B ) 0.23 of carapace length, slightly upturned, reaching distal margin of first segment of antennular peduncle; dorsal margin slightly concave, armed with 2 teeth in proximal 0.3, unarmed postorbitally; ventral margin with 1 subdistal tooth; ventrolateral ridge sharp, with 2 (left) or 3 (right) small teeth around midlength. Carapace ( Fig. 9A, B ) without postrostral median ridge; postrostral submedian and anterolateral spines absent; antennal spine small, acute; hepatic region with 1 tiny tubercle; anterolateral margin minutely denticulate; pterygostomial angle relatively weakly produced, exceeding antennal spine; branchial region smooth; cervical groove rudimentary.

Sixth thoracic sternite ( Fig. 9C ) with moderately narrow lobes, each terminating in obliquely truncated tip, lateral margins faintly sinuous. Seventh sternite with broadly rounded lobes, each bearing 1 tiny denticle at anteromesial angle. Eighth sternite with triangular plates, each terminating bluntly.

Pleon ( Fig. 8 ) strongly depressed dorsoventrally. First somite with relatively low transverse carina, its margin not overhanging depressed anterior section; anteroventral projection very small; posterolateral margin smooth. Second somite without conspicuous transverse carina. Pleura of first to fifth somites unarmed. Sixth somite ( Fig.9D ) widened posteriorly, lacking lateral spines. Telson ( Fig. 9D ) broadly triangular, 1.4 times longer than broad; dorsal surface without proximal spines; dorsolateral carinae each bearing 3 spines; lateral margins each with subproximal concavity, and armed with row of 3 spines; posterolateral angles not delimited, unarmed; posterior margin convex, with posteromedian spine.

Cornea ( Fig. 9A, B ) relatively small, distinctly narrower than eyestalk, darkly pigmented; base of cornea not constricted; eyestalk widened basally, armed with 2 spines dorsally and 1 similar spine mesially. Antennular peduncle ( Fig. 9A, B ) reaching tip of antennal scale, all segments unarmed; first segment 3.0 times longer than second segment; stylocerite blunt, straight.Antennal basicerite ( Fig. 9A, B ) stout, with small distolateral spine and with 1 additional small denticle on ventrolateral margin; antennal scale small, 0.2 of carapace length, subsemicircular, 2.2 times longer than wide; lateral margin slightly concave, armed with 4 teeth including distolateral tooth, dorsal surface with 2 distinct longitudinal carinae; carpocerite short, reaching second segment of antennular peduncle, unarmed.

Third maxilliped ( Fig. 10A ) overreaching antennal scale by length of dactylus and propodus; dactylus 0.7 of carpal length; propodus subequal in length to carpus; carpus 0.7 of meral length; merus about 0.8 of ischial length; ischium with 4 spinules on dorsolateral margin, unarmed on ventral margin. Exopod rudimentary.

First pereopod ( Fig. 10B, C ) with rudimentary grooming apparatus; dactylus 0.3 of chela length; carpus slender, 2.0 of chela length; merus 0.8 of carpal length; ischium 0.7 of meral length. Second pereopod ( Fig. 10D ) generally similar to first pereopod, but distinctly longer, about 2.3 times longer than carapace; dactylus 0.4 of chela length; carpus slender and longest, 1.9 of chela length; merus 0.7 of carpal length; ischium 0.6 of meral length. Third pereopod ( Fig. 10E ) with chela about 1.1 of carapace length; dactylus 0.6 of chela length, smooth on dorsal margin; fixed finger with row of tiny denticles extending onto distal 0.6 of palm; palm subcylindrical, about 1.6 times longer than wide, dorsal margin carinate with row of short setae, ventral margin with sparse setae; carpus broadened distally, 1.7 times longer than wide, 0.4 of chela length, unarmed; merus 1.5 of carpal length, unarmed; ischium 0.7 of meral length, with weak spine on dorsodistal angle, ventral margin unarmed. Fourth pereopod ( Fig. 10F, G ) relatively short, moderately slender; dactylus ( Fig. 10G ) 0.4 of propodal length, moderately broad, 2.9 times longer than wide, clearly biunguiculate; propodus 0.4 of carpal length; carpus longest, about 2.3 of propodal length, armed with 2 small spines on ventrodistal angle; merus 0.8 of carpal length; ischium 0.6 of meral length. Fifth pereopod similar to fourth.

Exopod of uropod ( Fig. 9D ) with 13 teeth on lateral margin, dorsal surface with 2 smooth longitudinal carinae; endopod with 7 teeth on lateral margin.

Eggs counting 50, diameter about 0.8 mm ( Table 5).

REMARKS

Spongicola depressus n. sp. is most similar to S.levigatus in the relatively short rostrum, generally reduced armament on the carapace and the rudimentary grooming apparatus on the first pereopod, but it is distinctive in the genus by the strongly depressed pleon and weak armature of the body and of the third pereopod.

The characters differentiating S. depressus n. sp. and S. levigatus include the development of the hepatic spine on the carapace, and the structure and armament of the third pereopod. In S. depressus n. sp., the carapace possesses small tubercle on the hepatic region, possibly representing a rudimentary hepatic spine, whereas there is no trace of hepatic spine in S. levigatus . The palm of the third pereopod is carinate but unarmed on the dorsal margin in S. depressus n. sp., whereas the dorsal margin of the palm is armed with row of small teeth in S. levigatus . The merus of the third pereopod is unarmed in S. depressus n. sp., but armed with spines in S. levigatus .

Review of Spongicola and Paraspongicola ( Crustacea, Decapoda )

Figures

FIG. 8. — Spongicola depressus n. sp., holotype ovig. ♀ 4.7 mm, Loyalty Islands (MUSORSTOM 6, stn?) (MNHN-Na 16293), entire animal in lateral view (pereopods all detached; setae on pleonal appendages and telson partially omitted). Scale bar: 1 mm.

FIG. 9. — Spongicola depressus n. sp., holotype ovig.♀ 4.7 mm, Loyalty Islands (MUSORSTOM 6, stn?) (MNHN-Na 16293):A, anterior part of carapace and cephalic appendages,lateral view;B, same,dorsal view (right eye and antennae omitted);C, thoracic prominences on sixth to eighth somites, ventral view; D, sixth pleonal somite,telson and left uropods, dorsal view (right uropod and marginal setae omitted). Scale bar: 1 mm.

FIG. 10. — Spongicola depressus n. sp., holotype ovig. ♀ 4.7 mm, Loyalty Islands (MUSORSTOM 6, stn?) (MNHN-Na 16293), thoracic appendages: A, right third maxilliped, lateral view;B, left first pereopod, lateral view;C, same, chela and carpus, ventral view; D, right second pereopod, lateral view; E, right third pereopod, lateral view; F, left fourth pereopod, lateral view; G, same, dactylus and distal part of propodus, lateral view. Scale bars: A, B, D-F, 1 mm; C, G, 0.5 mm.

FIG. 37. — Geographic ranges of Spongicola andamanicus Alcock, 1901 (■), S. depressus n. sp (△) and S. goyi n. sp. (○).