Alvinocaris alexander Ahyong, 2009
Description: Body is robust. The integument is thin and soft, with a smooth surface. The rostrum is directed downward or forward, and is straight and reaches beyond the antennular peduncle segment 1, but not to the midlength of segment 2; the rostrum measures 0.25-0.35 times the postorbital carapace length. The dorsal margin has 9-16 teeth (6-10 teeth on the rostrum proper, with 3-6 postorbital). 1 ventral tooth. The posteriormost tooth arises from the anterior 0.17-0.27 of the postorbital carapace length. The ventral margin has a small subdistal tooth. The lateral carina is sharp. The carapace is 0.65-0.70 times as wide as it is long. The postrostral median ridge is moderately high, extending to the posterior two-thirds or three-quaters of the carapace, sloping anteriorly to the rostrum, with a dorsal angle of up to 145°. A pterygostomial tooth is strongly produced anteriorly, well beyond the apex of the antennal tooth. The post-antennal groove is indistinct, and the branchial region is uninflated. Thoracic sternite 8 has a directed median projection between the P5 coxae, which is spinform in males and short and blunt in females.
The abdomen is rounded dorsally. Pleura 1-3 are broadly rounded. Pleuron 4 is posterolaterally rounded or bluntly angular, the posterior margin unarmed or with 4 or 5 small spinules. Pleuron 5 usually has a posterolateral spine and 1-7 small spinules on the posterior margin. The length of abdominal somite 6 is 1.49-1.53 times its height. Abdominal sternites 1-3 in males aech ahve a pair of transverse spines. Sternite 4 has a slender spine, whilst sternite 5 has a large prominent spine. Sterna 1-3 of females are unarmed. Sternites 4 & 5 of juvenile females have a low spine and prominent spine respectively. In mature females sternite 4 is unarmed, whilst sternite 5 has a blunt angular prominence.
The telson length is 2.22-2.54 times the anterior width and 3.21-4.27 times the posterior width. There are 6-8 dorsolateral spines on either side. The posterior margin is convex, with or without a small median point. There are two pairs of posterolateral spines and 11-22 plumose setae that are all longer than the mesial pair of lateral spines.
The eyes are fused mesially, with an unfaceted cornea. They are oval with a small anterodorsal tubercle.
The antennular peduncle reaches or slightly overreaches the distal margin of the antennal scale. Segment 1 has a strong distolateral tooth, which does not reach the midlength of segment 2. The stylocerite is harp, overreaching the apex of the distolateral spine but not does not reach the midlength of segment 2. Segment 2 is stout, 1.25-1.31 times as long as it is wide, with a strong distomesial tooth. The lateral flagellum are about as long as the postorbital carapace length. The mesial flagellum are slightly longer than the lateral flagellum.
The antennal basicerite has a strong ventrolateral and small ventral tooth. The antennal scale is 0.39-0.45 times the postorbital carapace length, and 1.50-1.75 times as long as it is wide in adults, 1.79-1.92 in juveniles. The lateral margin is straight or slightly convex. The distolateral tooth is directed anteriorly, falling short of the broadly rounded distal margin of the blade.
Maxilliped 3 has 4 segments. The ultimate segment (dactylus = propodus) is almost twice the length of the penultimate segment (carpus) and is trigonal in cross section. The distal margin is truncate, with 2 or 3 spines. The mesial surface has multiple, obliquely transverse rows of stiff setae. The antepenultimate segment (fused merus, ischium and basis) is flattened dorsoventrally and is marginally setose. The ventrolateral distal angle has 1 or 2 slender spines. The coxa is stout, whilst the epipod is directly laterally and is bilobed.
Pereopod 1 has fingers curved ventromesially. The outer surface of both fingers are convex, whilst the inner surface is concave with occlusal margins lined with fine, closely set pectinations. The palm is stout with a length subequal to its height, and one-third the dactylus length in females. In males, the palm length is about 1.5 times the height and is as long as the dactylus. The carpus is cupped distally to recieve the palm. The dorsodistal margin has a blunt angle in femalesa and an acute angle in males. The ventral surface has a diagonal ridge terminating in a ventrolaterally directed spine with a sharp tooth. The ventromesial surface of the ridge has a dense patch of grooming setae and a small movable spine proximally. The merus and ischium are unarmed and obliquely articulated.
Pereopod 2 is shorter and more slender than pereopod 1, but does not overreach the distal margin of the antennal scale. The fingers are as long as the palm, each terminating in small corneous unguis that cross each other when closed The cutting edges are without a gape and are pectinate with a single row of minute corneous teeth. The carpus is slightly longer than the chela. The merus and ischium are obliquely articulated in a lateral view. The ischium has one ventrolateral spine.
Pereopods 3-5 are similar in structure, increasingly slightly in length posteriorly. They are sparsely setose. The dactylus have a single row of 5-7 corneous spines on the flexor margin. The combined dactylus-propodus-carpus length is longer than the merus-ischium length. The propodi have slender spinules that are arranged in two rows on the ventral surface. The merus of pereopod 3has 0-3 movable spines ventrolaterally (usually 2), whilst the merus of pereopod 4 has 1 or 2 . The merus of pereopod 5 is umarmed. The ischium has 0-2 minute ventrolateral spines on pereopod 3, whilst the ishium is unarmed on pereopods 4-5.
The appendix masculina is robust and slightly shorter than the appendix interna, with a mesial margi that has about 7 long setae.
The uropod rami are subequal in length, and when folded extend posteriorly beyond the telson apex. The exopod has a small movable spine mesial to a smaller distolateral tooth and sinuous diaeresis.
Ecology and Distribution
Rumble V seamount (36°08.27-07.96S, 178°11.74-11.70 E at 485-415 m depth and other locations) and Brothers Caldera, southern Kermadec Ridge, New Zealand (34°52.89-52.87' S, 179°03.76-03.21' E at 1,346-1,196 m depth) (Ahyong, 2009)