Palaemonella shirakawai Okuno 2017, sp. nov.
Creators: name: Okuno, Junji
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Palaemonidae
Palaemonella
Palaemonella shirakawai

description: Palaemonella shirakawai sp. nov.
Figs. 1–4
Palaemonella lata.— Debelius, 1999: 192, unnumbered fig. in colour. Not Palaemonella lata Kemp, 1922. Palaemonella aliska.— Kuiter & Debelius, 2009: 101, unnumbered figs. in colour; Humann & DeLoach, 2010: 130, unnumbered fig. in colour. Not Palaemonella aliska Marin, 2008.
Palaemonella aff. aliska.— Minemizu, 2013: 42, unnumbered figs. in colour. Not Palaemonella aliska Marin, 2008.
Material examined. Holotype. CMNH-ZC 0 2525, ovigerous female, CL 5.5 mm, off Touma Beach, Zamami-jima Islet, Kerama Group, Ryukyu Islands, Japan, 26°13’51”N, 127°19’41.7”E, 16 m, 23 October 2011.
Host. An unidentified fish belonging to Opistognathidae.
Diagnosis. A medium sized palaemonid shrimp with subcylindrical body. Carapace without supraorbital tooth, postorbital ridge obsolete, hepatic tooth located on normal for genus. Rostrum slender, straight, distinctly shorter than postorbital carapace length, dorsally with 3 postrostral teeth, with 2 of them posterior to level of hepatic tooth, ventrally with a single subapical tooth. Antennal scaphocerite elongate, bearing distolateral tooth reaching level of truncate distal margin of lamella. Second pereiopod with ischium and merus unarmed, carpus distinctly longer than chela, distomesial margin of carpus unarmed, fingers distinctly shorter than palm. Ambulatory pereiopods with propodi not subdivided, dactyli slender.
Description. Carapace (Fig. 1, 2 A) smooth, glabrous, supraorbital tooth absent; orbit feebly developed, postorbital ridge obsolete, inferior orbital angle strongly produced, angular; antennal tooth well developed, slender, submarginal, arising slightly ventral to orbital angle, overreaching distal margin of inferior orbital angle; hepatic tooth small, situated on normal position, arising ventral to level of antennal tooth; pterygostomial angle obsolete. Rostrum (Fig. 2 B) straight, horizontal, reaching distal margin of intermediate segment of antennular peduncle, 0.6 times as long as carapace length; dorsal carina well developed, reaching midlength of carapace, armed with 7 low, acute teeth, including 4 on rostrum proper, anterior-most tooth minute, subequal to apex, thus, tip of rostrum visible as bifid (Fig. 2 C), 3 postrostral teeth present, 2 of them posterior to level of hepatic tooth (posterior-most tooth damaged); ventral carina obsolete, armed with a single minute subapical tooth.
Fourth thoracic sternite (Fig. 2 D) with finger-like median process; fifth sternite (Fig. 2 D) with pair of semiquadrate lobes posteriorly; sixth to eighth sternites unarmed.
Pleonites (Fig. 1) smooth, covers glabrous; first to fourth pleura broad, with margins rounded, fifth pleuron posteriorly produced, angular (Fig. 2 E); sixth pleonite (Fig. 2 E) about half length of carapace, posterolateral process acute, posteroventral margin produced, angular. Telson (Fig. 2 F) slightly tapering posteriorly, posterior margin (Fig. 2 G) convex, rounded, with 3 pairs of spines (lateral and intermediate spines simple, intermediate spines longest, submedian spines plumose); 2 pairs of subequal dorsolateral spines at 0.4 and 0.7 of telson length respectively.
Ophthalmic somite without interocular process. Eye (Fig. 2 A) with large, globular cornea, accessory pigment spot obscure; stalk short, subequal to maximum corneal diameter in length.
Antennular peduncle (Fig. 3 A, B) with proximal segment slightly longer than distal two segments combined; distolateral margin roundly produced, reaching level of proximal third of intermediate segment, with row of long setae, lateral margin almost straight, terminating distally in acute tooth falling slightly short of level of midlength of intermediate segment; ventromesial margin armed with small acute tooth; stylocerite slender, acute, reaching level of proximal third of proximal segment, with sparse setae laterally; statocyst well developed, oblong; intermediate segment slender, feebly lobed laterally, distal and mesial margin furnished with sparse long setae; distal segment subequal to intermediate segment in length, slender, non-setose. Upper flagellum (Fig. 3 A) long, slender, somewhat compressed dorsoventrally, biramous, proximal 16 segments fused, shorter free ramus consisting of 5 segments; about 10 groups of long aesthetascs present; lower flagellum considerably more slender than upper flagellum.
Antenna (Fig. 3 C) with stout basicerite armed ventrolaterally with acute tooth; carpocerite stout, reaching proximal two fifths of scaphocerite; scaphocerite elongate, overreaching distal margin of antennular peduncle, lateral and mesial margins subparallel, 4.4 times as long as maximum width, lateral margin concave, terminating in strong acute tooth reaching level of truncate distal margin of lamella.
Epistome with low, rounded submedian prominences.
Mandible (Fig. 3 D, E) robust, with slender, 2-segmented palp, these segments subequal in length, distally with sparse long setae; molar process obliquely truncated distally, with large, blunt teeth; incisor process stout, tapering distally, with 3 acute distal teeth. Maxillule (Fig. 3 F) with strongly bilobed palp, lower lobe with small distal protuberance; upper lacinia narrow, curved, distal margin truncated, with 7 stout spines and sparse spiniform setae; lower lacinia tapering distally, with some serrulate setae distally. Maxilla (Fig. 3 G) with short, stout palp tapering distally; distal endite well developed, narrow, deeply bilobed, distal lobe slightly broader than proximal lobe, with simple setae distally; proximal endite obsolete, mesial margin feebly sinuous; scaphognathite well developed, posterior lobe short, distal half of anterior lobe narrow. First maxilliped (Fig. 3 H) with short simple palp distally narrow, without setae; distal endite subquadrate distally, with mesial margin bearing 2 rows of dense setae, subquadrate distally; proximal endite small, rounded, separated from distal endite by distinct notch; caridean lobe small; epipod large, feebly bilobed, anteriorly pointed, falling shightly short of distal margin of caridean lobe; exopod with well-developed flagellum distally with numerous long setae. Second maxilliped (Fig. 3 I) with normal endopod; coxa inflated mesially, epipod angular, with unilamellar podobranch, shaft stout; ischium and basis completely fused; merus stout, obliquely articulated with ischiobasis; carpus with distinct ventromesial process; propodus with anterior margin broadly rounded, falling short of level of mesial dactylar margin, with slender spines; dactylus broad, mesial margin with numerous setae; exopod with well developed flagellum, distally with numerous slender setae. Third maxilliped (Fig. 3 J) with endopod slender, reaching level of distal fourth of scaphocerite; coxal plate oval, multilamellar arthrobranch present; ischiomerus and basis demarcated, external margin armed with row of small spines distally, mesial margin furnished with long sparse setae; penultimate segment 1.3 times as long as ultimate segment, mesially with long dense setae; ultimate segment tapering distally, external surface with 7 transverse rows of short dense setae; exopod with well developed flagellum, distally with numerous long setae.
Branchial formula as in Table below.
Maxillipeds Pereiopods
I II III I II III IV V Pleurobranchs — — — 1 1 1 1 1 Arthrobranchs — — 1 — — — — — Podobranchs — 1 — — — — — — Epipods 1 1 — — — — — — Exopods 1 1 1 — — — — —
First pereiopod (Fig. 4 A) moderately slender, overreaching distal margin of scaphocerite by lengths of carpus and chela. Coxa with ventral margin sparsely setose, without medial process. Ischium and merus furnished with long sparse setae ventrally, merus 1.7 times as long as ischium. Carpus considerably elongate, 1.8 times as long as ischium, 1.2 times as long as merus, 1.8 times as long as chela, with longitudinal row of serrulate grooming setae distally. Chela (Fig. 4 B) about half of carapace length; palm subcylindrical, slightly compressed, slightly shorter than fingers, with 7 transverse rows of short serrulate grooming setae proximoventrally; dactylus slender, terminating in small, hooked tip, cutting edge situated laterally, edentate, with sparse short setae; fixed finger terminating in small, hooked tip, cutting edge situated laterally, edentate, with sparse short setae, ventral surface with 5 transverse rows of short setae.
Second pereiopods (Fig. 4 C) well developed, similar in size and form, considerably elongate, overreaching distal margin of scaphocerite by lengths of distal two fifths of merus, carpus and chela. Ischium and merus slender, unarmed, furnished with long sparse setae ventrally, merus 1.3 times as long as ischium. Carpus long, without distal lobe (Fig. 4 D), furnished uniformly with short sparse setae, 2.3 times as long as ischium, 1.7 times as long as merus, slightly longer than length of chela. Chela slightly bowed, 1.7 times as long as carapace length; palm 1.7 times as long as dactylus, slightly compressed; dactylus (Fig. 4 E) terminating in hooked, acutely pointed unguis, cutting edge situated laterally, armed proximally with 3 large subtriangular teeth, remaining part unarmed, sharply edged, sparsely with equidistant short setae; fixed finger (Fig. 4 E) generally similar to dactylus, cutting edge armed proximally with 2 large subtriangular teeth opposite to notch among proximal teeth of dactylar cutting edge.
Third pereiopod (Fig. 4 F) slender, overreaching distal margin of scaphocerite by lengths of distal three fourths of carpus, propodus and dactylus. Merus 1.3 times as long as carpus, unarmed. Carpus elongate, unarmed. Propodus (Fig. 4 G) 1.2 times as long as carpus, with 2 distoventral spines and 8 single spines along ventral surface, dorsal surface with few short setae. Dactylus (Fig. 4 H) simple, compressed, feebly sinuous, unguis clearly demarcated. Fourth pereiopod similar to third, overreaching distal margin of scaphocerite by lengths of distal fourth of carpus, propodus and dactylus. Fifth pereiopod overreaching distal margin of scaphocerite by lengths of propodus and dactylus, with propodus (Fig. 4 I) bearing 1 spine and tufts of setae distoventrally (Fig. 4 J), spaced set of 7 spines posterior to distoventral spine.
Uropod (Fig. 2 F) with protopodite posterolaterally produced; exopod broad, overreaching posterior margin of telson, broadly rounded distally, lateral margin nearly straight, terminating in small acute tooth, with larger mobile spine just mesial to distolateral tooth; endopod oval, falling slightly short of posterior margin of exopod.
Colour in life. Carapace and rostrum whitish transparent, lateral surface of carapace covered sparsely with some yellow spots. Pleonites with some yellow spots sparsely, midline of sternites brownish purpule, visible as longitudinal stripe in dorsal view; telson proximally brownish purple, distally colorless. Eyestalk with longitudinal brownish purple stripe, cornea silver. Antennular peduncle and upper flagellum brownish purple. Scaphocerite and antennal flagellum colorless. Ultimate segment of third maxilliped brownish purple, penultimate and antepenultimate segments colorless, both with yellow distal patches. First pereiopod brownish purple, distal part of merus colorless. Second pereiopod uniformly brownish purple. Ambulatory pereiopods with ischial-meral joint yellow; meri generally brownish purple, distal part white; proximal two thirds of carpi brownish purple, distal third white; propodi white, with scattered brownish purple chromatophores. (From the underwater photograph taken before capturing the holotype).
Distribution. Known from the Ryukyu Islands, southern Japan (present study), Philippines (Minemizu 2013), Thailand (Debelius 1999), and Indonesia (Kuiter & Debelius 2009).
Etymology. Named for Mr. Naoki Shirakawa, the collector of the holotype.
Common name. Agito-kakure-ebi (new standard Japanese name).
Remarks. Among the known species of Palaemonella, the present new species appears closest to P. aliska living inside of the holes burrowed by snapping shrimp Alpheus cf. bellulus Miya & Miyake, 1969 in the mangrove littoral zone of Nhatrang Bay, Vietnam (Marin 2008), but presumably more widespread. In the original description, Marin (2008) indicated that the opistognathid-associated shrimp reported as P. lata by Debelius (1999) is possibly also with P. aliska, but herein referred to the new species. Morphologically, the present new species and P. aliska share the post-rostral carina extending to the midpoint of the carapace and armed with teeth posterior to level of the hepatic tooth (Fig. 2 A), and the unarmed ishium, merus and carpus of the second pereiopod. Palaemonella shirakawai sp. nov. is, however, readily distinguishable from P. aliska on account of the following morphological characters: (1) a single, minute subterminal tooth is present on the ventral margin of the rostrum in P. shirakawai sp. nov. (Fig. 2 B, C), instead of 2–3 acuminate rostral ventral teeth in P. aliska (Marin 2008: Fig. 2 a, b); (2) the posterior margin of the telson is rounded in P. shirakawai sp. nov. (Fig. 2 G), whereas its midpoint is distinctly protruding in P. aliska (Marin 2008: Fig. 5f); (3) Palaemonella shirakawai sp. nov. has an elongate antennal scaphocerite with the subparallel lateral and mesial margins, its length is 4.4 times as long as the maximum width, and the distolateral tooth reaching the level of the truncate distal margin of lamella (Fig. 3 C), in contrast in P.
aliska, the scaphocerite is relatively shorter, being about 3 times as long as the maximum width, and the distolateral tooth overreaches the rounded distal margin of lamella (Marin 2008: Fig. 2 f); (4) the epipod of the first maxilliped of P. shirakawai sp. nov. is long, with the anterior margin falling slightly short of the distal margin of the caridean lobe (Fig. 3 H), whereas the epipod in P. aliska is short, and its anterior margin slightly overreaches level of the distal margin of the proximal endite (Marin 2008: Fig. 3 e); and (5) the carpus of second pereiopod furnished with dense setae in P. shirakawai sp. nov. (Fig. 4 C), while the carpus is smooth in P. aliska (Marin 2008: Fig. 4 e).
As an associate in holes constructed by partner fishes (see Colin 1973), ecology of both species is somewhat similar. However, the present study and previous records in the popular guidebooks (Debelius 1999; Kuiter & Debelius 2009; Humann & DeLoach 2010; Minemizu 2013) suggest that P. shirawakai sp. nov. is perhaps an obligatory associate of jawfishes rather than gobies.
description: Published as part of Okuno, Junji, 2017, Palaemonella shirakawai, a new species of shrimp (Crustacea: Decapoda: Palaemonidae), associated with burrow dwelling opistognathid fish from the Ryukyu Islands, Japan, pp. 521-528 in Zootaxa 4299 (4) on pages 522-528, DOI: 10.11646/zootaxa.4299.4.3, http://zenodo.org/record/837065