Apolochus cresti, Morales-Nunez, Andres G. & Chigbu, Paulinus, 2016

Morales-Nunez, Andres G. & Chigbu, Paulinus, 2016, A new species of Apolochus (Crustacea, Amphipoda, Gammaridea, Amphilochidae) in Maryland coastal bays, USA with notes on its abundance and distribution, ZooKeys 571, pp. 81-104 : 85-97

Taxon classification Animalia Amphipoda Amphilochidae

Apolochus cresti sp. n. Figs 2, 3, 4, 5, 6, 7, 8; 9H, V, Z, B– 9, 1−C-1

Material examined.

Holotype: ovigerous ♀ (USNM 1254651), 3.4 mm, station 10 (38°14.504'N; 75°09.306'W), Isle of Wight Bay, USA, 1.8 m, 17.5 °C, 30.7 PSU, 16 May 2012, coastal lagoon, coll. A.G. Morales-Núñez. Paratypes: 4 ♀♀ (USNM 1254652), 4 ♂♂ (USNM 1254653); 4 ♀♀ and 4 ♂♂ (GCRL 06537), same collection data as for holotype. Additional specimens from the type locality are in the collection of the authors.

Additional material.

587 specimens (558 undetermined, 11 non-ovigerous ♀♀, 1 ovigerous ♀, and 17 ♂♂), station 10 (38°14.504'N; 75°09.306'W), Isle of Wight Bay, 1.8 m, 17.5 °C, 30.7 PSU, 15 March 2012, coll. A.G. Morales-Núñez. − 327 specimens (313 undetermined and 14 ♂♂), station 12 (38°25.778'N; 75°05.956'W), Assawoman Bay, 1.7 m, 17.2 °C, 29.8 PSU, 15 March 2012, coll. A.G. Morales-Núñez. − 2 specimens (undetermined), station 1 (38°03.143'N; 75°16.114'W), Chincoteague Bay, 2.1 m, 17.8 °C, 33.3 PSU, 17 April 2012, coll. A.G. Morales-Núñez. − 1 specimen (ovigerous ♀), station 10 (38°14.504'N; 75°09.306'W), Isle of Wight Bay, 1.8 m, 17.5 °C, 30.7 PSU, 17 April 2012, coll. A.G. Morales-Núñez. − 15 specimens (6 undetermined and 9 ovigerous ♀♀), station 12 (38°25.778'N; 75°05.956'W), Assawoman Bay, 1.7 m, 17.2 °C, 29.8 PSU, 15 March 2012, coll. A.G. Morales-Núñez. − 8 specimens (2 undetermined, 1 non-ovigerous ♀, and 5 ovigerous ♀), station 13 (38°26.240'N; 75°04.651'W), Assawoman Bay, 2.1 m, 17.3 °C, 29.5 PSU, 17 April 2012, coll. A.G. Morales-Núñez. − 3 specimens (undetermined), station 7 (38°14.504'N; 75°09.306'W), Sinepuxent Bay, 1.9 m, 17.5 °C, 32.9 PSU, 21 May 2012, coll. A.G. Morales-Núñez. − 632 specimens (502 undetermined, 22 non-ovigerous ♀♀, 83 ovigerous ♀, and 25 ♂♂), station 10 (38°14.504'N; 75°09.306'W), Isle of Wight Bay, 1.8 m, 17.5 °C, 30.7 PSU, 21 May 2012, coll. A.G. Morales-Núñez. − 1 specimen (undetermined), station 12 (38°25.778'N; 75°05.956'W), Assawoman Bay, 1.7 m, 21 May 2012, coll. A.G. Morales-Núñez. − 552 specimens (517 undetermined, 28 ovigerous ♀, and 7 ♂♂), station 10 (38°14.504'N; 75°09.306'W), Isle of Wight Bay, 1.8 m, 17.5 °C, 30.7 PSU, 25 October 2012, coll. A.G. Morales- Núñez. − 9 specimens (5 undetermined and 4 ovigerous ♀), station 13 (38°26.240'N; 75°04.651'W), Assawoman Bay, 2.1 m, 17.3 °C, 29.5 PSU, 25 October 2012, coll. A.G. Morales-Núñez.

Diagnosis.

Female: Antenna 1 and 2 sub-equal in length; accessory flagellum uniarticulate, small (hard to see without higher magnification). Mandibular molar with row of spinules/setae running up the margin of the molar column, with three marginal spines on triturating surface. Mandible palp article 3 longer than two proximal articles. Gnathopod 2 carpus with elongated lobe reaching along posterior margin of propodus to palmar angle; propodus without sub-marginal spines on antero-lateral surface.

Etymology.

Named in honour of NSF - Centers of Research Excellence in Science and Technology (CREST), in recognition of its support to promote the development of new knowledge.

Type locality.

Isle of Wight Bay (38°14.504'N; 75°09.306'W), Maryland Coastal Bays, United States of America.

Distribution.

Maryland Coastal Bays, Mid-Atlantic region, USA, at depths ranging from 1.7 to 2.1 m.

Description.

Ovigerous female (eight eggs).Body (Fig. 2): Length 3.4 mm.

Head (Fig. 2): approximately 15% TL, slightly shorter than pereonites 1−3 combined; lateral cephalic lobe rounded; rostrum strong, downturned. Eyes circular with black center bordered by numerous opaque ommatidia.

Antenna 1 (Fig. 3A−D): sub-equal to antenna 2, slightly shorter than head and pereonites 1−3 combined, peduncle shorter than head. Peduncle article 1 length approximately 1.3 times as long as wide, with four plumose setae (Fig. 3B) on dorso-distal margin, with five (two plumose and three cuspidate (Fig. 3C) setae on ventro-distal margin. Peduncle article 2 length approximately 1.4 times as long as wide, with four (one plumose and three cuspidate) setae on dorso-distal margin; with a cluster of four cuspidate setae on mid-ventral margin, and six (one plumose and five cuspidate) setae disto-ventrally. Peduncle article 3 length approximately 2.2 times as long as wide, with cuspidate seta on dorso-distal margin; with three cuspidate setae on ventro-distal margin. Flagellum with 6 to 8 articles, longer than peduncle, ventro-distal margin of each article with 3 to 4 cuspidate setae, first seven articles bearing two aesthetascs, article 8 with four simple setae of varying lengths apically. Accessory flagellum uniarticulate, small (difficult to see in low magnification), with two apical simple setae, length approximately ⅛ that of peduncle article 3 (Fig. 3D).

Antenna 2 (Fig. 3E): sub-equal to antenna 1, peduncle slightly longer than head. Peduncle article 4 length approximately 1.7 times as long as wide, with two clusters (middle and distal) of cuspidate setae of varying lengths on dorsal and ventral margins. Peduncle article 5 length approximately 3.5 times as long as wide, with two clusters (middle and distal) of cuspidate setae of varying lengths on dorsal and ventral margins. Flagellum with seven articles, shorter than peduncle; first six articles with 2 to 5 cuspidate setae each, article 7 with three simple setae of sub-equal length apically.

Mouthparts: Upper lip (Fig. 3F): bilobed, densely pubescent apically.

Mandibles (Fig. 3 G–J): molar broadly conical, with row of spinules/setae running up margin of molar column, with three marginal spines on triturating surface (Fig. 3G−I). Left mandible, densely setose, spine row with 11 to 13 accessory blades; blades increasing in width distally; lacinia mobilis with six teeth, incisor process dentate. Right mandible, densely setose, spine row with 10 accessory blades, incisor process dentate. Palp: with three articles; article 1 asetose, length less than half of article 2; article 2 asetose, length more than twice of length of article 1; article 3 longest, lanceolate, twice length of article 2, with dense row of longitudinal fine comb setae on medial surface (Fig. 3J).

Lower lip (Fig. 3K): bilobed, outer lobe densely setose, with apical gap, distal inner margin with serrate lobe, outer margin with tubercle.

Maxilla 1 (Fig. 4A−C): inner plate rounded, with apical plumose seta and row of simple setae on distal margin (Fig. 4A); outer plate with oblique distal margin bearing eleven robust spines (eight simple and three serrate (Fig. 4B), with five long slender setae on inner margin, outer margin densely setose (Fig. 4A). Palp (Fig. 4C): with two articles; article 1 asetose; article 2 length twice that of article 1, with two serrate (Fig. 4B) and two simple spines distally, mid-proximal inner margin and mid-distal outer margin with setae of different sizes.

Maxilla 2 (Fig. 4D−E): inner plate densely setose, with five serrate (Fig. 4E) terminal setae of varying length, outer margin with row of simple setae; outer plate longer than inner, with four serrate terminal setae, outer margin with row of simple setae.

Maxilliped (Fig. 4F−K): inner plate densely setose, with two sub-distal tooth-like modified setae (Fig. 4J); outer plate setose distally, with four short bifurcate (Fig. 4G) setae proximally, a serrate inner distal margin, two small marginal spines, one well-developed serrate spine (Fig. 4I) and a small seta terminally (Fig. 4F−J). Palp (Fig. 4J−K): with four articles; article 1 longest; inner and outer margin with two to three medium bifurcate setae (Fig. 4H); article 2, approximately two-thirds length of article 1, with seven bifurcate setae on inner distal margin, two bifurcate setae on outer distal margin; article 3 slightly longer than article 2, with six (three medium bifurcate setae and three long bifurcate (Fig. 4K)) setae on inner distal margin, with three denticles distally, with three (one central and two distal) bifurcate setae on outer margin; dactylus shorter than article 3, without unguis, lanceolate, with dense longitudinal row of fine comb setae.

Pereon (Fig. 2): approximately 42% TL, pereonites 1−7 deeper than wide; pereonite 7 longest and widest.

Gnathopod 1: Lateral view (Figs 3, 5A−D): subchelate; coxal plate short, sub-oval, partially hidden by coxa 2 (Fig. 3), with one marginal seta. Basis approximately 4.5 times as long as wide, anterior margin with three proximal bifurcate setae, two distal simple setae (Fig. 5B); postero-distal margin with one bifurcate seta. Ischium wider than long, with two setae of unequal length on postero-distal margin, longest seta bifurcate. Merus approximately 3.3 times as long as wide, posterior margin with two long serrate setae (Fig. 5C) centrally, three long serrate setae distally. Carpus with lobe reaching ⅔ length of posterior margin of propodus, anterior margin of lobe with row of serrate setae. Propodus slightly expanding distally, palm convex, nearly transverse, serrate, lined with seven [6 to 9] slender bifurcate spines, corner defined by one stout bifurcate spine, anterior margin with three serrate setae, one near mid-margin and two sub-distal, with one serrate seta distally. Dactylus slightly more than ⅔ length of propodus, slightly exceeding palmar angle, proximal ⅔ of posterior margin serrate. Medial view (Fig. 5E): basis with seven bifurcate setae lining anterior and antero-medial margin. Propodus with three serrate setae on inner surface of palm. Dactylus with small seta inserted at distal end of posterior serrate margin.

Gnathopod 2: Lateral view (Figs 3, 6A−B): sub-chelate; coxal plate sub-rectangular, ventral margin convex, with short marginal setae. Basis approximately 4.8 times as long as wide, anterior margin with four short setae, two proximal, one central, and one distal; posterior margin lined with eleven small setae, one seta distally. Ischium wider than long, with one small seta on postero-distal margin. Merus approximately 4.7 times as long as wide, posterior margin with two setae, one central and one distal. Car pus with elongated lobe reaching along posterior margin of propodus to palmar angle, lateral surface with two small spines and one seta, with two bifurcate setae distally. Propodus slightly expanding distally, palm convex, nearly transverse, serrate, lined with 13 [11 to 14] slender bifurcate spines, corner defined by two stout spines, anterior margin with small spine in distal ⅓, without sub-marginal spines on antero-lateral surface. Dactylus slightly more than ⅔ length of propodus, not quite reaching palmar angle, proximal ⅔ of posterior margin serrate. Medial view (Fig. 6C): basis, anterior margin with two spines sub-distally. Merus with three serrate setae on anterior distal margin. Dactylus with small seta inserted at distal end of posterior serrate margin.

Pereopod 3 (Figs 2, 7A−D): coxal plate sub-rectangular, longer than wide, ventral margin convex, with short marginal setae (Fig. 2). Basis approximately 4.5 times as long as wide, anterior margin lined with setae of varying lengths, anterodistal margin with four setae of unequal lengths; posterior margin lined with setae of varying lengths, postero-distal margin with one small seta and one cuspidate seta (Fig. 7B). Ischium sub-quadrate, posterior margin with two cuspidate setae, one central and one distal. Merus twice as long as wide, anterior margin with four setae, with three setae of unequal lengths distally; posterior margin with four clusters of two cuspidate setae and one longer cuspidate seta distally. Carpus approximately 3.7 times as long as wide, antero-distal margin with three cuspidate setae (Fig. 7C); posterior margin with two clusters of two cuspidate setae of varying lengths and four cuspidate setae distally. Propodus approximately 5.0 times as long as wide, anterior margin with three clusters of two setae and two simple setae distally; posterior margin with three clusters of two cuspidate setae and two cuspidate setae distally. Dactylus slightly more than 1/2 length of propodus, with plumose seta (Fig. 7D) on antero-proximal margin; with two small setae on each side distally.

Pereopod 4 (Figs 2, 7E): coxal plate larger than that of coxa 3, quadrate ventral margin straight, with short marginal setae, posterior margin excavate proximally; otherwise as pereopod 3.

Pereopod 5 (Figs 2, 7F): longer than pereopod 4, coxal plate wider than long, with rounded posterior lobe. Basis expanded, with two longitudinal ridges, anterior margin lined with setae, with cuspidate seta distally, anterior ridge lined with setae. Ischium wider than long, anterior margin lined with three cuspidate setae. Merus approximately 2.9 times as long as wide, posterior margin with two setae, cluster of three setae of unequal length, and four setae distally; anterior margin with one seta, three clusters of two cuspidate setae, with four cuspidate setae distally. Carpus approximately 4.0 times as long as wide, posterior margin with cluster of two setae, with five setae distally; anterior margin with two clusters of two cuspidate setae, with three cuspidate setae distally (Fig. 2). Propodus approximately about 6.2 times as long as wide, posterior margin with four clusters of two setae, with two simple setae distally; anterior margin with three clusters of two cuspidate setae, with two cuspidate setae distally (Fig. 2). Dactylus approximately half length of propodus (Fig. 2A).

Pereopod 6 (Figs 2, 7G): similar to pereopod 5 except coxal plate smaller than that of pereopod 5. Basis, merus, and propodus slightly longer and more setose.

Pereopod 7 (Figs 2, 7H): similar to pereopod 6 except coxal plate small and narrowly oval. Basis posterior lobe more expanded. Slightly longer and more setose than pereopod 6.

Pleon (Fig. 2): approximately 28% TL, pleonites 1−3 dorsally smooth; Epimeron 1 (Fig. 2): ventral margin with three spines, postero-ventral corner of plate slightly produced. Epimeron 2 (Fig. 2): ventral margin with five spines, postero-ventral corner of plate slightly produced. Epimeron 3 (Fig. 2): ventral margin with four spines, postero-ventral corner of plate sub-quadrate. Pleopods 1−3 (Fig. 2): rami sub-equal in length.

Urosome (Fig. 2): approximately 15% TL, urosomites 1−3 dorsally smooth (Fig. 2); Urosomite 1 longest (Fig. 2); Urosomite 2 shortest (Fig. 2).

Uropod 1 (Figs 2, 7I−K): extending beyond peduncle of uropod 3; peduncle longer than rami, inner margin with six cuspidate setae with accessory seta (Fig. 7J), outer margin with 12 [10 to 12] setae cuspidate setae with accessory seta; inner ramus with four inner and four outer robust (Fig. 7K) marginal setae; outer ramus slightly shorter than inner ramus, with two inner and six [4 to 6] outer robust marginal setae; opposing margins of rami setulose (not shown).

Uropod 2 (Figs 2, 7L): peduncle shorter than peduncles of uropods 1 and 3, inner margin with one distal cuspidate seta with accessory seta, outer margin with seven to eight cuspidate setae with accessory seta; inner ramus with four to five inner and four outer robust marginal setae; outer ramus approximately ⅔ as long as inner ramus, inner margin without setae, outer margin with two to three robust setae; opposing margins of rami setulose (not shown).

Uropod 3 (Figs 2, 7M): peduncle elongate, shorter than that of uropod 1, inner margin with four cuspidate setae with accessory seta, outer margin with eight cuspidate setae with accessory seta; inner ramus slightly longer than outer ramus, with four inner and two outer robust marginal setae; outer ramus with one inner and four outer robust marginal setae; opposing margins of rami setulose (not shown).

Telson (Fig. 7N): sub-triangular, longer than wide, apex rounded.

Adult male.

Body (Fig. 8): Length 2.6 mm, smaller than female; similar to female except for eyes being larger and not completely rounded. Eyes may be darker than those of female (noticed in all males that were found in March 2012). Antenna 1−2 longer than those of female; antenna 1, aesthetascs of flagellum longer and more numerous than those of female.

Habitat.

Marine epibenthic, in coastal shallow waters (≤ 2.1 m); Apolochus cresti sp. n. was associated with a mixture of macroalgae (e.g., Agardhiella sp., Gracilaria sp., Ceramium sp., and Cladophora sp.).

Remarks.

Of the eight described species in the genus, Apolochus cresti sp. n. can be easily distinguished from Apolochus barnardi , Apolochus casahoya , the N-E Atlantic Apolochus neapolitanus complex ( Hoover and Bousfield 2001), Apolochus delacaya , Apolochus picadurus , and Apolochus pillai by having the antenna 1 sub-equal to antenna 2 (antenna 1 is shorter than antenna 2 in the other species). However, Apolochus cresti , Apolochus litoralis , Apolochus neapolitanus from the Mediterranean and Apolochus staudei also have antenna 1 sub-equal to antenna 2. Apolochus cresti is distinct from Apolochus litoralis by (1) the size of the carpal lobe of gnathopod 2 (elongated lobe reaching along posterior margin of propodus in Apolochus cresti vs short lobe reaching halfway along posterior margin of propodus in Apolochus litoralis ), (2) mandible palp article 3 longer than articles 1−2 combined (shorter in Apolochus litoralis ), and (3) form of the telson (sub-triangular in Apolochus cresti vs triangular in Apolochus litoralis ). The new species differs from Apolochus staudei by (1) the size of the accessory flagellum (smaller in Apolochus cresti ), (2) size and shape of the molar process (bigger and not broadly triangular in Apolochus cresti ), (3) the number of accessory blades in the spine row of mandible (10−11 vs 15−17, respectively), and (4) the form of the telson (sub-triangular vs narrowly triangular, respectively).

Apolochus cresti appears to be most closely related to Apolochus neapolitanus (Della Valle, 1893), as figured by Krapp-Schickel (1982) from the Mediterranean, but it can be distinguished by (1) shape of the lateral cephalic lobe (rounded vs truncated, respectively), (2) shape of the molar process (relative strong, with row of spinules/setae running up the margin of the molar column, with three marginal spines on triturating surface in Apolochus cresti vs. rounded and rather feeble, lacking marginal setae on column and spines on triturating surface in Apolochus neapolitanus ), (3) proportion of mandible palp article 3 (longer than previous two articles combined in Apolochus cresti vs. shorter than previous two articles combined in Apolochus neapolitanus ), and (4) gnathopod 2, carpal lobe (just reaching corner of palm in Apolochus cresti vs. slightly passing corner of palm in Apolochus neapolitanus ).

Apolochus cresti sp. n. is the fourth species of the genus to be described from the western Atlantic, after Apolochus casahoya from Gulf of Mexico, Apolochus delacaya from the Gulf of Mexico and Florida Keys, and Apolochus pillai from the Florida Keys. Apolochus cresti differs from Apolochus casahoya and Apolochus delacaya by not having antero-lateral spines on the propodus of gnathopod 2 ( Apolochus casahoya has two spines and Apolochus delacaya has four spines). Finally, it is distinct from Apolochus pillai in having a long carpal lobe of gnathopod 2, reaching the corner of the palm on the propodus; the carpal lobe is short, not reaching the corner of the palm in latter species. Apolochus cresti also differs from Apolochus sp. A., which was reported from Florida waters ( LeCroy 2002), by having a mandible molar process with a row of spinules/setae running up the margin of the molar column and three marginal spines on the triturating surface versus a mandible molar process with no setae on the margin of the column and a single large apical spine (triturating surface lacking).

The fact that illustrations of Apolochus neapolitanus reported around the world are not similar, suggests that it is a complex of cryptic species, or that members of the species have been misidentified due to their small size, fragile body, and difficulty in accessing the mouth parts, which exhibit the most important characters used for taxonomic identification in this group. The following key may be used to further distinguish between the females of known Apolochus species.